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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
Physiological aspects of ex vitro establishment of tissue cultured orchid plantlets
(Department Of Plant physiology, College Of Agriculture, Vellayani, 2000) Samasya, K S; KAU; Viji, M M
The present investigation was undertaken to elicit information on the physiological, morphological, biochemical, biometric and anatomical changes during in vitro propagule multiplication and ex vitro establishment in tissue cultured plantlets of orchids. Dendrobium hybrid Sonia 17 was the variety used for the study. The rooting media was supplemented with different levels of sucrose. At the time of planting the plantlets were subjected to triazole treatment. During the process of hardening the plantlets were maintained in hardening chambers with different levels of light and humidity. Among growth parameters the crop growth rate (CGR), net assimilation rate (NAR) and relative growth rate (RGR) were found to be high at 40 gIl of sucrose concentration. The CGR of these plantlets were on par with normal green house grown plantlets. The photosynthetic rate was found to increase and the transpiration rate was found to decrease at 40 gIl of sucrose . concentration. The maximum survival percentage of the in vitro plantlets occur when 40 g11 of sucrose incorporated in the rooting medium. This may be attributed to the influence of the sucrose concentration on morphological characters studied viz. plant height, number of leaves per shoot and number of roots per shoot. With regard to photosynthetic pigments an increase in the content of total chlorophyll, chlorophyll a chlorophyll b and carotenoids occurred in plantlets treated with 40 g/1 of sucrose. Also the protein content and carbohydrate content was maximum at the above sucrose level. The leaf area, root length, total fresh weight and dry weight of the plantIets maintained at 40 gIl of sucrose level were higher than other treatments. These effects ultimately lead to better survival percentage. Triazole treatment of plantIets during planting out helped in better survival percentage. With regard to the growth parameters the effect was distinct towards the later stage of growth. CG~ NAR and RGR were maximum on the triazole treated (5 mgll) plantIets and was comparable to normal green house grown plants. There was marked increase in the photosynthetic rate and decrease in transpiration rate of plantIets treated with 5 mgll of triazole. However the photosynthetic rate of normal green house grown plants were much more than the tissue cultured plantIets. Regarding morphological characters, increasing concentration of triazole had negative influence on plant height. However plant height of normal green house grown plants were distinctively higher than tissue cultured plantIets. With regard to number of leaves per shoot, triazole treatment showed significant effect only after 30 days of planting out, whereas the number of roots per shoot was very much influenced by triazole. The maximum number of roots was produced at 5mgll of triazole treatment and these effects in turn influenced higher survival percentage of plantIets. ------....- ....- ~ - - - ----- Regarding the biochemical aspects total chlorophyll, chlorophyll a, chlorophyll b and carotenoids contents of plantlets treated with triazole (5 mg/l) were higher and found to be on par with that of green house grown normal plants towards the later stage. The protein content was also positively influenced by triazole treatment (5 mgll) and the value was comparable to that of normal plantlets. In the case of carbohydrate content the treatment becomes statistically significant and the normal green house grown plants exhibited distinctively higher value. The plantlets treated with 5 mgll of triazole were found to have higher leaf area, root length, root: shoot ratio, total fresh weight and dry weight than other treatments. However the root shoot ratio and total fresh weight of treated plantlets were on par with the normal green house grown plants towards the later stage viz, 45DAP. The physiological, morphological, biochemical and biometric characters of the plantlets were also found to be influenced by different levels of light intensity and humidity maintained in the hardening chamber. Among the different treatments, plantlets grown at 50 percent light intensity and 70 to 90 percent relative humidity exhibited higher CG~ NAR and RGR. Also these plantlets exhibited a marked increase in photosynthetic rate and decrease in transpiration rate. However CGR and NAR of green house grown normal plants were distinctively higher during the later period. However the normal plants had distinctively higher CG~ RGR and photosynthetic and very less transpiration rate than other treatments. The plantlets grown under 50 percent light intensity and 70 to 90 percent humidity produced maximum plant height, number of leaves and number of roots per shoot. The survival percent of the tissue cultured plantlets in the field condition (green house) was found to be superior under appropriate environment of light and humidity (50 percent light intensity and 70 to 90 percent relative humidity) There was not much significant difference among the treatments of light and humidity in the case of pigment content. However the plantlets grown in the hardening chamber maintained at 50 percent light intensity and 70 to 90 percent of relative humidity recorded maximum value of total chlorophyll, chlorophyll a, chlorophyll b and carotenoids among treatments and the normal green house grown plants exhibited distinctively higher pigment content. The normal plantlets recorded marked increase in protein content and carbohydrate content than the tissue cultured plantlets. In the present study, an environment of 50 percent light intensity and 70 to 90 percent relative humidity was found to be superior and could favour enhanced leaf area, total fresh weight, total dry weight and root length of plantlets which ultimately resulted in better survival percentage. The in vitro plantlets observed to have anatomical characters as compared to the normal green house grown plants and hardened plantlets. The stomata remained open and less number of stomata per unit area of leaf was observed as the in vitro leaves were concerned. Another peculiarity of the in vitro plantlets was the absence of cuticle layer. The mesophyll layers were also found to be less compared to normal plantlets. These anatomical characters were one of the severe limitations of the micropropagated orchid plantlets during ex vitro establishment which ultimately resulted in high rate of field mortality.
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
Influence of host plants and soil moisture stress on the water relations in sandal
(Department of Tree Physiology and Breeding, College of Forestry,Vell, 2006) Dhaniklal, G; KAU; Asokan, P K
The influence of host plants and soil moisture stress on water relations in sandal was investigated in a pot culture experiment at College of Forestry, Kerala Agricultural University, Vellanikkara. Five host plants, Divi divi (Caesalpinia coriaria Jacq.), Casurina (Casuarina equisetifolia J.R & H.G. Forst), Pongamia (Pongamia pinnata (L.) Pierre), Lantana (Lantana camara L.) and Erythrina (Erythrina indica Lamk.) were selected for this study. The results showed that Sandal seedlings with and without host showed similar height increment, except when erythrina was the host. The host plant had no influence on most of the growth parameters of sandal seedlings. The collar diameter of sandal seedlings with and without host was on par during the early seedling stage and by the end of the experimental period it showed a significant difference. There was no significant difference in the number of leaves, leaf area and root length of sandal with different hosts. Haustorial connections were not recorded even after the experimental period. Sandal seedlings with Erythrina indica as host decreased the pre dawn water potential. Water stress decreased the seedling height, collar diameter, number of leaves, leaf area, shoot dry weight and total dry weight of sandal seedlings. Fully irrigating the pots once in three days resulted in better growth of sandal seedlings as compared to irrigation once in six days. Water stress increased the root length and root dry weight. Root length was found to be more for sandal seedlings which were irrigated once in six days compared to that, irrigated once in three days. Water stress decreased leaf area of sandal seedlings. Transpiration rate at 14:00 hrs was found to be more than that of transpiration at 8:00 hrs. Transpiration rate decreased with increase in soil moisture stress. Pre dawn water potential was lower for sandal seedlings irrigated once in six days compared to that irrigated once in three days. As the haustorial connections were not observed even after 270 days after planting it can be concluded that the difference in the seedling growth parameters of sandal with some of the hosts is due to the above and below ground competition for sun light, water and nutrients.
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
Studies on the physiological and biochemical changes in relation to reproductive efficiency in Chickpea (Cicer arietinum L.)
(Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi, 1981) Seshadrinath, S; KAU; Sabra Abbas
The average yield of chickpea in India is as low as 700 kg/ha. One of the major causes for this low yield can be attributed to the low reproductive efficiency. The cause for low reproductive efficiency is mainly due to heavy shedding of reproductive structures. The present investigations were, therefore, initiated with the following objectives: 1) To study the genetic variability and diversity with reference to the flowering behaviour and shedding of flowers during the reproductive stage in order to evaluate the peak periods of flowering, shedding percentage and reproductive efficiency.
Open Access
Physiological and biochemical basis of degeneration in Root (Wilt) affected coconut palm
(Department of Agricultural Botany, College of Agriculture, Vellayani, 1983) Sheela Cherian; KAU; Abraham, A T
Several studies on the physiological and biochemical aspect of the root (wilt) disease have been carried out and conclusions have been drawn. A recent study comprising o f the estimation of protein non protein amino acids and cytokinin from the leaf, root and developing nut o f healthy# apparently healthy and root (wilt) affected coconut palm was carried out in tills, laboratory (unpublished). The chlorophyll content of leaves was also estimated. The present study comprised o f estimation o f gibberellin s and abscissic acid from the leaf# root and nut of healthy apparently healthy and five different intensities of root (wilt) affected coconut palms. The results of the biochemical analysis show that in the root (wilt) affected coconut palms there are alterations or deviations in normal metabolic activities from that o f healthy palms. Earlier work done has shown a reduction in cytokinin content in the root(wilt) affected palm in addition to protein and chlorophyll content. The present study has revealed a deficiency of gibberellins another important growth regulator and an accumulation of the growth inhibitor abscissic acid in the root(wilt) affected palms. The site s of synthesis and / interconversion o f gibberellins are damaged together with the impairment o f the translocation system. Increased respiration lowered CO2 fixation and severe damage o f the shoot system in the later stages are in brief the in tern al and external expressions o f the root (wilt) syndrome. Thus the shoot and root system which are interdependant are unable to function in harmony leading to a failure in their growth and development. An accumulation of ABA along with a reduction in gibberellin level might be the reason for the stunting syndrome seen in root(wilt) affected palms.
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

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