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Open Access
Mitigation of solar ultraviolet-B radiation induced photoinhibition in photochemistry and photosynthesis of rice (Oryza sativa L.)
(Department of Plant Physiology, College of Horticulture, Vellanikkara, 2016) Shafeeqa, T.; KAU; Nandini, K
Sun light contains ultraviolet (UV) radiation which is separated in to UV-C (100-280nm),UV-B (280-320 nm) and UV-A (320-400nm). Evidences from data collected from both satellite and field experiments indicated an increase in UV-B radiation reaching on the earth surface, due to decrease in ozone layer. Hence, UV-B has become more challenging nowadays causing threat to agriculture production in tropics. UV-B exclusion and enhancement studies conducted in the Department of Plant Physiology, College of Horticulture, Vellanikkara have revealed a decline in rice yield due to UV-B radiation in rice varieties Jyothi and Uma (Wagh, 2015). The present study entitled “Mitigation of solar ultraviolet-B radiation induced photoinhibition in photochemistry and photosynthesis of rice (Oryza sativa L.)” was conducted during 2014-2016 in the Department of Plant Physiology, College of Horticulture, Vellanikkara with the objective to understand the photo protective potential of ecofriendly stress mitigating chemicals on photoinhibition and photosynthesis of rice (Oryza sativa L.) under solar ultraviolet- B radiation. The pot culture experiment was conducted during November 2015 to March 2016 with rice variety Uma under two growing conditions viz. open condition- where the crop exposed to 100% solar radiation and polyhouse condition- which transmit 20% reduced full spectrum solar radiation including UV-B. Three ameliorative chemical treatments with two concentrations such as glycine betaine (10ppm and 20ppm), ascorbic acid (50ppm and 100 ppm) and combination fungicide 25WG trifloxystrobin + 50 WG tebuconazole (Nativo 75 WG- 50ppm and 70ppm) were given as foliar application at 30th and 60th DAT and observations were taken 15 days after each chemical spraying. The experiment was laid out as completely randomized design (CRD). The UV-B and Photosyntheticaly Active Radiation (PAR) in both conditions were monitored regularly throughout the crop period. The data on UV-B and PAR revealed significantly higher UV-B (2.18 Wm-2) and PAR (1786 μmolm-2s-1) during March-2016 under ambient condition. All growth phenophases were delayed under 100% solar radiation. Combination fungicide 25 WG trifloxystrobin+50WG tebuconazole 70ppm enhanced grain filling period under both the growing condition compared to other chemical treatments; the ultimate realization being a relatively good yield. Gas exchange parameters like photosynthetic rate, stomatal conductance and transpiration rate decreased during reproductive phase under 100% solar radiation, where the crop experienced high UV-B radiation. Among chemicals, 25 WG trifloxystrobin+50WG tebuconazole 70ppm enhanced the above parameters by alleviating the photoinhibition in photosynthesis and PSII activities. Photochemical efficiency as indicated by high Fv/Fm ratios was enhanced by foliar application of 25 WG trifloxystrobin+50WG tebuconazole 70ppm. High chlorophyll content, catalase activity and xanthophyll content were observed under reduced UV-B condition. Among chemical treatments significantly higher chlorophyll content was recorded for the rice plants treated with 25 WG trifloxystrobin+50WG tebuconazole 70ppm and this might be the reason for the increased photosynthetic rate in plants due to its application. The maximum yield contributed by 25 WG trifloxystrobin+50WG tebuconazole 70ppm may be due to the enhancement in thousand grain weight and number of spikelet per panicle, more photosynthetic rate and less fluorescence emission / increased photochemical efficiency of PS II, more chlorophyll content, catalase activity and reduction in the synthesis of secondary metabolites like flavanoid and xanthophylls. The ameliorative effect of this chemical has to be explored under field level for better results and recommendation to farmers for raising 3rd crop during puncha season.
Open Access
Biochemical and molecular studies on post-harvest physiological deterioration of cassava (Manihot esculenta crantz)
(Department of plant physiology, College of agriculture,Vellayani, 2015) Saravanan, R; KAU; Roy Stephen
The project entitled “Biochemical and molecular studies on post-harvest physiological deterioration of cassava (Manihot esculenta Crantz)” was conducted at the Dept of Plant Physiology, College of Agriculture, Vellayani and at ICAR-CTCRI, Thiruvananthapuram during 2013 to 2015. The main objective of the work was to analyse the physiological biochemical and molecular mechanisms associated with post harvest physiological deterioration (PPD) and develop methods to delay the PPD in cassava. The initial screening of the cassava genotypes for their performance of PPD was done with 61 different genotypes including some released varieties. Significant differences were observed for PPD development and shelf-life of harvested roots. Cassava genotypes such as IMS2-8, 9S-172, 11S-53, IRS 2-10 and 9S-286 started showing the visible discolouration in the parenchyma tissue earlier (less than 3 days of storage). Genotypes such as 9S-7, 9S-98, 11S-31, 11S-86, 11S-14, CE63-3, CI43-2, CR43-2, CR54-A5, CR59-8R, Sree Athulya and Kalpaka showed low PPD scores and better shelf-life. Tissue imprinting for peroxidase enzyme showed that there was a remarkable increase in peroxidase activity in the root tissues with increasing PPD symptoms. There was no correlation between the root morphological traits and PPD severity. Carotene and starch content of root did not influence the PPD in the genotypes studied. Chemotypic profile of roots with PPD symptoms was used to classify the genotypes based on PPD. To develop an objective screening tool, Near Infrared Spectroscopy (NIRS) was utilized to analyse root samples for PPD. Principal component analysis (PCA) and chemometric tools clearly grouped the different PPD category in root tissues. Various stains such as saffranin, aniline blue, erythrocin, fast green and phloroglucinol stained the tissue specifically at vascular tissues and other cell components and were not suitable for detecting PPD. Storage techniques such as storing the harvested roots in de-aerated bags, wax coating and burying the roots under the soil were employed with selected cassava varieties like Sree Athulya, Sree Jaya, Vellayani Hrashwa, Kalpaka and Sree Padmanabha to delay PPD. Wax coating was suitable to reduce PPD for few weeks. Effect of different storage temperature on PPD was studied for five cassava varieties. Root respiratory flux was higher in roots stored at ambient conditions compared to high (40o C) or low temperature (4o C) storage. There were significant positive correlation between root respiratory flux at 3 and 9 days of storage to the CAT and POX activities studied in different cassava varieties. Roots were treated with various food preservatives at two different concentrations (0.5 and 1%). There was a weak, but significant reduction in symptom development in butylated hydroxy touline – (BHT, at 0.5 and 1% level) treated roots compared to other treatments. Nearly three folds increase in total phenol content was noticed in BHT and butylated hydroxy anisole (BHA) treated roots. The plant hormones related to wound response such as Salicylic acid and jasmonic acid were used to study the PPD response in roots under storage. The roots did not show marked influence to hormone application. Significant genetic variation was observed for PPD. The low PPD type genotypes such as 9S-7, 9S-98, 11S-31, 11S-86, 11S-14, CE63-3, CI43-2, CR43-2, CR54-A5, Sree Athulya and Kalpaka can be utilized for breeding programmes. High temperature storage of cassava at 40 oC resulted in reduced respiratory rate and increased antioxidant scavenging enzyme activity and also reduced the PPD. Differentiation of cassava roots at the metabolites level corresponding to visual symptoms and chemotypic profile of PPD and NIR spectroscopy offer a rapid screening tools. Among the different storage treatments, wax coating with antiseptic pre-treatment is most suitable and economical for increasing shelf-life of roots. Food preservatives like BHT and BHA have a significant, albeit marginal influence on PPD symptom development in cassava.
Open Access
Spectral management for improving hotosynthetic efficiency in polyhouse cultivation of vegetables
(Department of Plant Physiology, College of Agriculture, Vellayani, 2016) Anjana, J Madhu; KAU; Roy Stephen
Plant growth is influenced by both the quality and intensity of light. The transmittance of light by different shade nets are unique. Hence the spectral quality of light vary under each coloured net. Different wave length of light influence specific physiological process. In this context, the study entitled “Spectral management for improving photosynthetic efficiency in polyhouse cultivation of vegetables” was conducted at the Dept of Plant Physiology, College of Agriculture, Vellayani and at Pothencode, Thiruvananthapuram during 2014- 2016. The main objective was to study the morphological and physiological responses of vegetables, viz. tomato, salad cucumber, capsicum and yard long bean exposed to spectral modification through different colored shade nets. A survey was conducted in 20 polyhouse units in Thiruvananthapuram district to know the adoption of shade nets by the farmers practicing polyhouse cultivation. The experiment was done in a polyhouse of dimension 500m2, which was divided into five parts on an east-west direction roofed with two photoselective and two neutral shade nets of four different optical properties and one part without any shade net. The light interception by shade nets were analysed using spectro radiometer at University of Agricultural Science, Bangalore. The green net reduced 59.9%, white net reduced 55.14% and red net reduced 41.05% of red light compared to open. Four different crops, viz. salad cucumber, yardlong bean, capsicum and tomato were grown under these shade nets. Weather parameters such as Photosynthetically Active Radiation (PAR), global radiation and temperature were recorded but didnot show much variation. The pollen viability was not altered by spectral variation. Earliness to flowering, fruiting and fruit maturity was observed in open condition for salad cucumber and capsicum. The number of leaves at first flowering was higher in white net for salad cucumber and yardlong bean while it was higher in red net for capsicum and tomato. Specific Leaf Area was significantly higher under red net for salad cucumber (979.52cm2g-1), capsicum (564.21cm2g-1) and tomato (631.18 cm2g-1). The same trend was followed in case of photosynthetic rate also. The internode elongation was found to be minimum in open condition for all the four crops. The leaf anatomy of salad cucumber grown under white net showed higher vascular thickness. Setting percentage was higher in white and green shade nets for salad cucumber (85.40%) and yardlong bean (89.35%) respectively where as red net was suitable for capsicum (80.99%) and tomato (81.80%). Higher shoot weight and root weight were observed under white shade net for tomato. Root shoot ratio and total dry matter content was higher in capsicum grown under red shade net. Transpiration rate of yardlong bean and tomato plants grown under green shade net was higher while higher transpiration rate of salad cucumber and capsicum was observed under white shade net. The pigment composition of salad cucumber was higher under black shade net. Abaxial stomatal frequency in all the four crops was higher in open condition. Total soluble protein content of tomato and salad cucumber at flowering stage was higher under red shade net. Higher carbohydrate content was observed under open condition in case of yardlong bean, capsicum and tomato. Phenol content increased in tomato plant grown under white shade net. There was no significant variation in IAA. Higher crude protein was observed in yardlong bean grown under white shade net while the crude fibre was higher under open condition. Ascorbic acid was higher in capsicum grown under open condition while for tomato it was under white shade net. Spectral modifications through shade nets altered morphological and physiological responses of salad cucumber, yardlong bean, capsicum and tomato. Varietal suitability was observed in different shade nets. Photosynthetic efficiency was also influenced by shade nets and reflected in the yield of selected crops. Red net was suitable for capsicum and tomato while white net was ideal for salald cucumber and green for yardlong bean.
Open Access
Nutrio-physiological and molecular analyses and carbon dioxide enrichment studies of coconut palms (Cocos nucifera L.) with foliar yellowing
(Department of Plant Physiology, College of Agriculture, Vellayani, 2017) Deepa, S; KAU; Manju, R V
A study entitled “Nutrio-physiological and molecular analyses and carbon dioxide enrichment studies of coconut palms (Cocos nucifera L.) with foliar yellowing” was carried out with the objective to analyze the nutrio - physiological changes occurring in the palms affected with foliar yellowing and to assess the impact of enhanced carbon dioxide on phytoplasmal response. In this study, palms showing mid whorl yellowing (MWY), root (wilt) affected palms (RW) and healthy palms were selected from two different locations viz the Instructional Farm, College of Agriculture, Vellayani (location 1) and Venganoor region (location 2) in the Thiruvananthapuram district. Coconut seedlings showing yellowing were selected from the Instructional Farm, College of Agriculture, Vellayani to study the effect of enhanced carbon dioxide on phytoplasmal response. Catharanthus and brinjal plants with ‘little leaf symptom’ maintained at the Department of Plant Pathology were utilised for grafting into healthy catharanthus and brinjal plants and these were also taken for studying the phytoplasmal response under elevated carbon dioxide condition. Physiological and biochemical analyses revealed significant variations in all the parameters studied. Palms with mid whorl yellowing (MWY) showed a significant reduction in the chlorophyll a, b and total chlorophyll contents, relative water content, membrane integrity and phenol content compared to the healthy palms. An increase in the protein (88%), carbohydrate (25.14%), reducing sugar (28%) and starch content (28.33%) was noted in palms with MWY. In the case of antioxidant enzymes there was build up of polyphenol oxidase (145.38%) and peroxidase activities in palms with MWY compared to the healthy palms. A similar trend was observed in almost all cases of RW affected palms. Nutrient analyses revealed significant alterations in the nutrient content of the selected palms. Significant reduction in the nitrogen (47.74%), magnesium (22.72%) and zinc content (24.19%) was observed in palms with yellowing compared to the healthy palms. Accumulation of elements like potassium (37.96%) calcium (40.79%), iron (54%) and copper (35.75%) was observed in palms with mid whorl yellowing compared to the healthy palms. These variations in the nutrient levels can have an influence on symptom development in coconut palms. The results on the soil nutrient analyses did not show any particular role in development of yellowing symptoms. Phytoplasma cells were detected in the phloem tissues of both mid whorl yellowing and root wilt affected palms under Scanning Electron Microscopy (SEM) study. Morphological and anatomical analyses of fresh roots indicated browning and necrosis of roots and vascular disintegration in MWY and RW affected palms. The presence of phytoplasma in the selected samples were checked by nested PCR analysis using phytoplasma specific universal primers-P1/P7- R16F2n/ R16R2, Phytoplasma 16S rDNA specific semi nested primers 1F7/7R3 - 1F7/7R2 and by real time PCR technique using real time primers QPF2/R2. Semi- nested PCR yielded an amplicon of 493 bp in all the MWY and RW palms in both the locations. Real time PCR yielded an amplicon of 140 bp in the RW palms, 3 MWY palms in location 1. Nested PCR with phytoplasma specific universal primer pairs P1/P7-R16F2n/ R16R2 yielded an amplicon of 1.2 kb in MWY palm and RW palm. Sequence analysis of the mid whorl yellowing phytoplasma revealed 89% similarity to the root wilt phytoplasma. In experiment II, nested PCR with universal primer pairs showed no amplification in the coconut seedlings and hence only catharanthus and brinjal grafts with phytoplasmal infection were kept in Open Top Chamber (OTC) with 500 ppm Carbon dioxide concentration for a period of one month. After the exposure period, the plants kept in OTC showed an increased rate of growth and development with phytoplasmal symptoms. Physiological and biochemical analyses showed a significant increase in the reducing sugar content (63%), protein content (147%) and PAL activity (32%) and significant reduction in the phenol content (37%), and polyphenol oxidase activity (62%) in the infected plants kept in OTC compared to the infected plants kept in open condition. Molecular analyses of the infected samples using real time PCR kept in OTC and open condition with the DNA samples isolated at the 15th and 30th day of exposure was done. No significant variation was observed in the phytoplasmal load after elevated carbon dioxide exposure. The role of phytoplasma in causing MWY was established by molecular and anatomical studies. Sequencing of the PCR product revealed that MWY phytoplasma can be a variant of root (wilt) phytoplasma. The present study indicated that the overall health status of the palms with MWY was highly deteriorated. Significant variation in the nutrient profile was noted which emphasise the need for proper nutrient management. Semi- nested PCR was found to be more accurate and specific in phytoplasmal detection which can be utilised for phytoplasmal indexing and mother palm and disease free seedling selection. Elevated carbon dioxide showed an improved growth and development and activated defense response to phytoplasma in the infected plants but the CO2 induced modifications in phytoplasmal load was not detected. The results indicated a better tolerance strategy to environmental conditions. phytoplasma under changing
Open Access
Carbon dioxide enrichment mediated plant-microbe interaction in cowpea (Vignaunguiculata L.) under water stress
(Department of Plant Physiology, College of Agriculture, Vellayani, 2016) Athibha, P B; KAU; Manju, R V
The level of CO2 in the atmosphere is rising at an unprecedented rate. According to NOAA (National Oceanographic and Atmospheric Administration) 2014, global concentration of CO2 has reached 400 ppm for the first time in recorded history. This rise, along with other trace gases in the atmosphere is widely thought to be a primary factor driving global climate change. Moreover the report of IPCC, 2012 has reconfirmed the increasingly strong evidence of global climate change and projected that the globally averaged temperature of the air would rise by 1.8–6.4°C by the end of the century. Pulses are the main sources of protein and is commonly called poor man’s meat. They are also used as fodder and concentrate for cattle. Pulses are responsible for improving soil fertility by increasing the amount of N2 in the soil. Drought is a recurring problem limiting pulse production in rainfed areas. High frequency of crop failure and yield instability due to biotic and abiotic stresses also contribute to low productivity in pulses. The pulse production scenario is also getting affected by the changing climate and the resulting rise in temperature and decline in rainfall. Under such changing climatic scenario, soil microbes play an important role in the maintenance of physicochemical properties of soil and also in making the soil nutrients available to the plants. In this context, the current programme “Carbondioxide enrichment mediated plant- microbe interaction in cowpea (Vigna unguiculata L.) under water stress ” attempts to study the water stress tolerance character and N2 fixation efficiency of cow pea as influenced by microbial inoculants under elevated CO2 condition. This investigation will help to design improved production technologies with suitable varieties for a changing climatic scenario. Two pot culture experiments were conducted at different carbon dioxide concentrations with three different levels of soil moisture regimes i.e Field capacity, 75% field capacity and 50% field capacity. The cowpea seeds were sown in pots inside OTCs and in open field, one set with microbial seed inoculation and the second set without inoculation. The technology used for subjecting the plants to elevated CO2 environments is the Open Top Chambers (OTC) system. In both set of experiment entire crop period was completed in OTCs. Respective moisture stress levels were imposed during the second month. Experimental plants were maintained for a period of three months. Observations on growth parameters and microbial population studies were done at the end of CO2 exposure period and all the other parameters were taken at monthly intervals. The experiments were laid out in CRD with 18 treatments and three replications. The observations on growth parameters during first month of CO2 exposure on cowpea inoculated with Rhizobium revealed a reduction in specific leaf area by 21.39% under elevated CO2 condition compared to absolute control. Among the physiological and biochemical parameters studied, highest relative water content was recorded under elevated CO2 (4.69%). Carbon dioxide enrichment significantly lowered the stomatal frequency by 28.40 % and transpiration rates by 89.27%. Significant increase in total chlorophyll contents by 50 % was registered under elevated CO2 conditions. Per cent leakage was found significantly lower (38.74%) under CO2 enriched treatment compared to control. Among physiological parameters, a marked rise in phenol content was noticed by 56.68% under elevated CO2. Significant increase in reducing sugars, free amino acid, and ascorbic acid contents by 5.97%, 23.92% and 63.79% was recorded in elevated CO2. Protein content was found decreasing under elevated CO2 by 29.02%. The observations on growth parameters during water stress period in cowpea inoculated with Rhizobium revealed a reduction in specific leaf area by 17.24% under elevated CO2 condition compared to absolute control. Root and shoot dry weights were also found to be higher by 56.08% and 140.77% under elevated CO2 resulting an increase in root shoot ratio by 36.51%. Dry matter production was recorded 116% higher under elevated CO2. Parameters related to nitrogen fixation was recorded lower leaf nitrogen status (17.15% reduction), nitrogen use efficiency (36.46% reduction), and soil nitrogen status (8.79% reduction) under elevated CO2. But the Rhizobial inoculated plants was found to have a positive influence on soil nitrogen status (8.46% increase). Under elevated CO2 tremendous increase in root nodule number plant and nodule dry weight, but Rhizobium doesn't have any significant influence on this parameter. Among the physiological and biochemical parameters studied, highest relative water content was recorded under elevated CO2 (18.57%). Carbon dioxide enrichment significantly lowered the stomatal frequency by 15.53% and transpiration rates by 88.12%. Significant increase in total chlorophyll contents by 13.26 % was registered under elevated CO2 conditions. Per cent leakage was found significantly lower (51.45%) under CO2 enriched treatment compared to control. Among biochemical parameters, significant increase in reducing sugars, free amino acid, phenol, SOD and ascorbic acid contents by 22.63%, 30.65%, 67.56%, 42.12% and 34.06% was recorded in elevated CO2. Protein content was found decreasing under elevated CO2 by 44.92%. Nitrogen fixation efficiency was found to be decreased in terms of reduced leaf nitrogen status under elevated CO2. But nodule number per plant and nodule dry weight were increased. Rhizobial inoculated cowpea plants were observed to have better growth and improved stress tolerance in terms of better leaf water status and membrane integrity under elevated CO2. In the case of cowpea inoculated with P.indica during first month of CO2 exposure, number of leaves (33.30%)was found to be highest under elevated CO2. Lower stomatal frequency (35.78%), transpiration rate (86.89%) and per cent leakage (63.25%) were observed prominently under elevated CO2 compared to open control. Significant increment in reducing sugars by 21.78%, phenol by 77.71%, free amino acid content by 27.42% was recorded under elevated CO2. SOD and ascorbic acid content was found increased by 49.39 % and 8.05 % under elevated CO2 treatment compared with control. Root weight, shoot weight and total dry matter production were found enhanced by 42.39%, 27.27% and 35.31% under elevated CO2 in comparison with control. In the case of water stress also, elevated CO2 was found to have positive influence on growth like number of leaves (57.27%). Significant increment of relative water content (13.933%), total chlorophyll (124.9%), reducing sugar (23.43%), phenol(135.5%) was recorded under elevated CO2 in comparison with control. P. indica inoculated plants under CO2 was found to have better stress tolerance. This was achieved through maintenance membrane integrity and stomatal modifications. There was reduction in stomatal characters like stomatal frequency and stomatal conductance resulting in reduced transpiration and better tissue water status. There were enhanced accumulation and increased activity of antioxidants like ascorbic acid and SOD. This also would have helped the experimental plants in achieving better stress tolerance. The present investigation was carried out with the objective to study the water stress tolerance character and N2 fixation efficiency of cowpea as influenced by microbial inoculants under elevated CO2 condition. Considering all the physiological, biochemical studies conducted, it can be concluded that carbon dioxide enrichment has a positive role on water stress tolerance character of cowpea variety Bhagyalakshmy. There was further enhancement of stress tolerance by both microbial inoculants, Rhizobium sp and P.indica. The underlying tolerance mechanisms were found to be stomatal modifications resulting in reduced transpiration and better tissue water status, activation of antioxidants like ascorbic acid and better maintenance of membrane integrity. Nitrogen fixation efficiency was improved tremendously by elevated CO2 in terms of nodule number per plant and nodule dry weight but leaf nitrogen content and nitrogen use efficiency were reduced by CO2 enrichment. The outcome of the programme reveals the possibility of improving yield potential and stress tolerance under elevated CO2 by integrating photosynthesis and nitrogen use efficiencies with the application of microbial inoculants like P.indica. References
Open Access
Physiological effects of growth stimulants on yield and quality of okra (Abelmoschus esculentus L.)
(Department of Plant Physiology, College of Horticulture, Vellanikkara, 2017) Vishnu, K S; KAU; Sudarsana Rao, G V
Okra or Bhindi (Abelmoschus esculentus L.) is one of the most popular summer vegetable crop grown widely in Kerala. It accounts for 65 % of the fresh vegetables exported from the country. However, the productivity of the crop is low in the state. The low fertility status of the soil due to heavy rains may be a major reason. Currently, for sustainable increase in productivity soil test based nutrient management practices are recommended. Another approach is the use of environment friendly growth stimulants, which have beneficial effects on plants. Hence, the present study was carried out to understand the influence of growth stimulants on growth, yield and quality attributes of okra variety Arka Anamika under standard package of practices (POP) recommended by KAU and also soil test based nutrient management system. The experiment was laid out in Randomized block design with 15 treatments and three replications at Central nursery, College of Horticulture, Vellanikkara. The crop was raised as per standard POP recommendations of KAU and also under soil test based nutrient management system. Experiments consisted of 15 treatments viz., standard POP, KAU (T1) as control, soil test based modified nutrient management (T2), T1 + humic acid spray @ 0.2 % (T3), T1 + potassium silicate spray @ 0.3 % (T4), T1 + cytozyme spray @ 0.2 % (T5), T1 + putrescine spray @ 50 ppm (T6), T2 + humic acid spray @ 0.2 % (T7), T2 + potassium silicate spray @ 0.3 % (T8), T2 + cytozyme spray @ 0.2 % (T9), T2 + putrescine spray @50 ppm (T10), 50 % T1 + humic acid spray @ 0.2 % (T11), 50 % T1 + potassium silicate spray @ 0.3 % (T12), 50 % T1 + cytozyme spray @ 0.2 % (T13), 50 % T1 + putrescine spray @ 50 ppm (T14) and T1 + water spray (T15). Foliar application of growth stimulants was given at 15, 30 and 45 DAS. Morphological, physiological and biochemical parameters were recorded at 25 and 50 DAS and the yield and fruit quality characters were recorded at the time of harvest. The use of growth stimulants such as humic acid, cytozyme and potassium silicate with soil test based nutrient management system improved the morphological parameters like plant height, leaf area, the number of leaves per plant etc. than control. Plants which received potassium silicate, putrescine and humic acid as foliar spray recorded higher total chlorophyll content and IAA content. Comparison of photosynthetic rate, transpiration rate and stomatal conductance of crop at two different growth stages revealed that growth stimulants such as humic acid, cytozyme and potassium silicate along with soil test based nutrient management showed a significant improvement over control. A similar pattern of the effectiveness of growth stimulants was observed in the case of fruit yield and quality characters such as crude fiber content, ascorbic acid content, mucilage content and total protein content. Comparison of POP, soil test based application of fertilizers and 50 per cent POP showed that soil test based nutrient management gave significantly higher yield as compared to the other treatments including control. The response of the stimulants was also higher for soil test based nutrient management treatments. Growth stimulants with soil test based nutrient management applied plots recorded 12 to 23 per cent higher fruit yield over control followed by standard POP with growth stimulants which recorded an improvement of 5 to 9 per cent over control. Reduction in fruit yield of 3 to 6 per cent was recorded with 50 per cent standard POP over control. Among the four growth stimulants used, humic acid performed better followed by cytozyme and potassium silicate. These growth stimulants may have enhanced the nutrient use efficiency of the plants which further improved the photosynthesis, plant growth and development. The result of the present study indicated that growth stimulants can be recommended along with soil test based nutrient management for enhancing crop growth, fruit quality and yield of okra.
Open Access
Identification of microsatellite markers associated with root traits for drought tolerance in rice (Oryza sativa L.)
(Department of Plant Technology, College of Agriculture, Vellayani, 2017) Rejeth, R; KAU; Beena, R
The present investigation entitled “Identification of microsatellite markers associated with root traits for drought tolerance in rice (Oryza sativa L.)” was conducted at Department of Plant Physiology, College of Agriculture, Vellayani during 2016-17. The objective of the study was to validate the role of root traits in rice for drought tolerance and to identify the microsatellite markers associated with root traits for drought tolerance in rice. The extend of variation for water stress indicators, physio-morphological and yield components were assessed by evaluating 35 rice genotypes collected from RARS, Pattambi under water stress and irrigated conditions in the rainout shelter. The rice accessions grown in polythene tubes of 1 meter height were exposed to water stress at panicle initiation stage for a period of 15 days along with irrigated control. The physio-morphological, biochemical and yield components were recorded on completion of stress period. Significant variation was observed for these traits and ten drought tolerant and ten drought susceptible genotypes were selected. The genomic DNA was isolated from these rice genotypes and were pooled into drought tolerant and susceptible bulks. Bulked line analysis was carried out to identify microsatellite markers linked to drought tolerance in rice. The result of the study revealed that physiological parameters such as Relative Water Content (RWC), photosynthetic rate, transpiration rate and stomatal conductance decreased where as proline content and leaf temperature increased significantly in most of the genotypes under water stress condition. Highest leaf rolling (score – 9) was observed in Ptb–7 and Ptb-13 while the genotypes Ptb–29 and Ptb-30 showed no leaf rolling symptoms (score – 1). Among the genotypes, the RWC was recorded to be highest in Ptb–4 while the lowest was recorded in Ptb–13 under water stress condition. The percentage decrease in RWC compared to irrigated control was less in Ptb–15. Membrane stability index was more in Ptb–29 (98.5 %) and Ptb-10 (98.1 %) as compared to other genotypes under water stress condition. Maximum leaf temperature was observed in Ptb–1(31.70C) and minimum in Ptb–7 (27.80C) under water stress condition. Among the genotypes, stomatal conductance was recorded to be highest in Ptb–30 (674 m moles m-2 s-1) while the lowest in Ptb– 20 (92 m moles m-2 s-1). The photosynthetic rate decreased significantly under water stress condition with maximum in Ptb–30 (15.2 μ moles m-2 s-1) and minimum in Ptb–6 (3.4 μ moles m-2 s-1). Under water stress condition, maximum transpiration rate was observed in Ptb–4 (1.4 m moles m-2 s-1) and minimum in Ptb–31 (0.05 m moles m-2 s-1). Proline content increased at 50% flowering stage in water stress condition with maximum accumulation in Ptb–27 and minimum in Ptb–22. At flowering stage highest root length was noticed in Ptb-15 and lowest for Ptb–3 and Ptb-8 under water stress condition. Root volume differed significantly in several genotypes with maximum in Ptb–21 and minimum in Ptb-31. Root dry weight decreased in water stress compared to control in most of the genotypes with highest in Ptb-13 and lowest in Ptb-31. Root shoot ratio was found to be highest in Ptb-29 and Ptb-30 and lowest in Ptb-31. The plant height at maturity was observed to be highest in Ptb-1 and lowest in Ptb-34 under water stress condition. Days to 50% flowering reduced in most of the genotypes under water stress condition compared to irrigated control. Productive tiller number of most of the genotypes significantly reduced in water stress condition with maximum reduction in Ptb-28. Maximum yield under water stress was recorded in Ptb-55 and minimum in Ptb-21. Number of filled grains and unfilled grains were observed as major attributes affected drastically under water stress condition. The spikelet fertility percentage was highest in Ptb-25 and lowest in Ptb-1. Ptb-28 had maximum 1000 grain weight under water stress and minimum was for Ptb-17. Correlation study revealed that grain yield per plant under water stress condition was positively correlated with parameters such as relative water content, membrane stability index, proline content, stomatal conductance, photosynthetic rate, transpiration rate, root length, root shoot ratio, spikelet fertility % and 1000 grain weight where as negatively correlated with leaf temperature, leaf rolling score, root volume, root dry weight, plant height, days to 50% flowering and panicle length. In Bulked Line Analysis, out of the 150 microsatellite primers screened only one marker i.e., RM 474 showed polymorphism between the tolerant and susceptible bulks. The same primer showed similar product size (252bp) among the individual lines which constituted respective bulks. In summary, there was significant variation for physio-morphological and yield components among rice genotypes under water stress condition. Genotypes having higher root length and root shoot ratio were found to be tolerant to drought. The genotypes identified as drought tolerant viz Ptb-29, Ptb-30, Ptb-15, Ptb-1, Ptb-55 etc. can be used in breeding programmes to improve drought tolerance in rice. Microsatellite marker RM 474 which could distinguish drought tolerant and susceptible bulks can be used for marker assisted selection for drought tolerance in rice.
Open Access
Enhancing morpho-physiological vigour of sesame seedlings for improving productivity and weed competitiveness
(Department of Plant Physiology, College of Horticulture, Vellanikkara, 2017) Sreepriya, S; KAU; Girija, T
Sesame is one of the oldest oilseed crops grown in summer rice fallows of Kerala. Weed infestation is a major biotic stress affecting the yield of sesame. Seedling growth of sesame is slow during the first four weeks, making it a poor competitor during this period. Weed suppression during the early stages of crop establishment (10 to 30 DAS) is important for improving the productivity of the crop. The present study was initiated to enhance the early vigour of sesame plants by suitable seed priming treatments and also to assess the effect of early vigour on weed competitiveness and analyse the carry over effect of these treatments on the productivity of the crop. The variation in varietal response to these priming treatments were also studied. A laboratory study was conducted with five popular varieties of sesame viz., Surya, Thilak, Kayamkulam 1, Thilarani and Thilathara, released from Kerala Agricultural University. Ten priming treatments with plant growth regulators (IAA, GA), micronutrients (MnSO4, borax), mixture of MnSO4 and borax with GA (Tank mix), biofertilizers (phosphobacteria, azospirillum, PGPR mix-1) and water were tried. Results on observations showed that seed priming improved the germination and vigour of all the five varieties tested. Among the treatments, priming with micronutrients and hormones gave the best results. Based on the vigour index, five priming treatments were selected for the field trial and the variety Thilak, which gave maximum response to these treatments, was used as the test variety in the field. The experiment was laid out in split plot design at ORARS, Kayamkulam. Weeded and unweeded treatments formed the main plots and five selected treatments along with control (unprimed seeds) were the sub-plot treatments. Observations on morphological characters were studied at 20 days interval and yield characters were recorded at the time of harvest. Physiological and biochemical effects of the priming treatments were studied at vegetative and reproductive stages of the crop. Weed count and weed dry matter were recorded at 10 DAS and at the time of harvest in the unweeded plots. Weed control efficiency of the priming treatments was computed at the time of harvest. The biochemical parameters such as contents of chlorophyll, total soluble protein and GA were higher during the reproductive phase as compared to the vegetative phase. Chlorophyll including chlorophyll a and chlorophyll b, and soluble protein content showed greatest improvement in MnSO4 primed plants. The nitrate reductase enzyme plays a major role in nitrogen metabolism of the plant. In the present study, the nitrate reductase enzyme activity was found to be higher during the reproductive phase of the crop in all the treatments except for control (unprimed seeds) and water priming. The IAA content was also higher in the reproductive phase in all the treatments. Major improvement in IAA content was observed with borax priming. The growth indices such as crop growth rate, relative growth rate, net assimilation rate and leaf area index were improved with priming treatments in both unweeded and weeded plots. Yield and yield attributes such as number of branches, number of capsules and seeds per capsule improved significantly with MnSO4 and tank mix treatments, which contributed to higher yield. The improvement in vigour of sesame plants with seed priming treatments reduced the weed count and weed dry matter production in the unweeded plots as compared to the control (unprimed seeds) due to the higher competitiveness of the primed seeds. The study revealed that seed priming with MnSO4 or Tank mix of GA, borax and MnSO4 can be an effective component in the integrated management of weeds in sesame as it can contribute to 30 per cent control of weed growth.
Open Access
Photosynthetic efficiency and productivity of gynoecious parthenocarpic cucumber in naturally ventilated poly house
(Department of plant physiology, College of horticulture, Vellanikkara, 2015) Gayathri, Rajasekharan; KAU; Nandini, K
Poly house cultivation of vegetables is an emerging approach for production of vegetables in Kerala. The main principle of poly house cultivation is the facilitation of favourable micro-climates, which favour maximum production. The top of poly house is cladded with UV-stabilised plastic sheet which selectively screen the various spectral components of solar radiation and transform direct sunlight into scattered light inside. This type of spectral manipulation is aimed to specifically promote desired physiological processes and to modulate morphological and photosynthetic responses of plants. Hence, basic information on the physiological aspects involved in the photoresponse of crop in poly house is needed to realize maximum yield potential. In this context, a study was undertaken in a farmer’s field at Thannyam to compare the photosynthetic productivity of gynoecious parthenocarpic cucumber in poly house and open condition. High light intensity, Ultra violet (UV) radiation and Photosynthetically Active Radiation (PAR) caused a stressful environment which in turn reduced most of its morphological and biochemical characters in cucumber grown under open condition. However ambient CO2 concentration, which decides the photosynthetic rate was more under polyhouse condition. Poly house cladded with UV stabilized sheet, reduced light intensity, UV-radiation and PAR favoured most of the morphological characters of the crop. The morphological characters like leaf area, Leaf Area Index (LAI), number of leaves, number of nodes and internodal length were significantly high for poly house grown cucumber. The chlorophyll content- Chl a, b and total chlorophyll in leaves was significantly high when grown under poly house. However, the activity of IAA Oxidase (IAAO) observed at 15 and 60 DAS was significantly lower inside the poly house indicating auxin availability for morpho-physiological fuctions. The Gibberelic acid content also increased but significant difference was observed only at 75 DAS in poly house grown crop. Photosynthetic rate of the crop under both conditions when recorded gradually increased from 15 DAS to 45 DAS and thereafter declined. This was significantly high under open condition at 15, 30 and 45 DAS, whereas it was significantly high in poly house only at 60 and 75 DAS. The poly house crop could maintain higher photosynthetic rate even at later growth stages of crop thereby prolonging the crop duration. Transpiration rate was significantly high under open condition at 30 DAS, but significantly higher values were observed in poly house condition at 45 and 75 DAS. The lower photosynthetic rate was due to low influx of CO2 in to mesophyll cells which is evident from low intercellular CO2 concentration in the poly house crop. This is also related to high stomatal resistance inside the poly house at 15 and 30 DAS. The carboxylation efficiency, which relates to photosynthetic rate, was significantly high at 60 and 75 DAS in the poly house crop. The photochemical efficiency of PS II as indicated by Fv/Fm ratio was higher under poly house environment. Canopy temperature depression did not give any significant difference between two conditions. Light absorption coefficient was significantly high in open condition where the LAI was less. The lower values of light absorption coefficient observed inside the poly house may be related to high LAI. There was no significant difference in number of days to flowering and days to first harvest between open and poly house grown crops. But the number of days to last harvest and number of harvests made from poly house grown crop were significantly high when compared to open condition. The yield contributing components such as number of fruits per plant, fruit weight, yield per plant and marketable yield were significantly high for poly house grown crop. Early senescence of the crop was observed under open condition compared to poly house. Retention of more chlorophyll content even at later stages of crop delayed senescence in poly house grown crop. The ascorbic acid content, one of the quality parameter was significantly high in crop grown under open condition. Organoleptic evaluation of fruits revealed that the poly house grown crops maintained significantly high colour, texture and overall acceptability of the fruits. This study suggests that the diffused light and equal distribution of radiation over the crop canopy favoured morphological characters of poly house grown crop. This in turn helped the crop to maintain high photosynthetic rate and carboxylation efficiency even at later stages of the crop which resulted in increased number of harvest in poly house.

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