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Open Access
Management of foot rot of black pepper (piper nigrum L.) with va mycorrhiza and antagonists
(Department of Plant Pathology, College of Agriculture, Vellayani, 1998) Christin Robert, P; KAU; Sivaprasad, P
Extensive investigation was carried out to develop a native microbial inoculant based technology involving Arbuscular Mycorrhizal Fungi (AMF) and fungal antagonists for the foot rot disease management and growth improvement of black pepper in the nursery and field. Phytophthora capsici Leonian emend A. Alizadeh and P.H. Tsao, the foot rot pathogen isolated from Peringammala, Thiruvananthapuram district was found most virulent isolate. Seven native AMF cultures and fifty fungal antagonists were isolated from Kerala soils. AMF isolates were screened in the green house for plant growth improvement and disease tolerance in comparison with identified species-Glomus fasciculatum, G.clarum and Gigaspora margarita. Of the ten AMF tested isolates Is - 6, Pi - 11, Pi - 9, G. fasciculatum and Gigaspora margarita were very effective in stimulating growth and nutrient (P, K, Ca, Mg, Cu, Fe, Mn and Zn) uptake of black pepper. Regarding the ability of AMF in reducing the foot rot incidence, Glomus fasciculatum recorded the lowest plant mortality and root rot index (53.35% and 62.50%) followed by Is - 6 (60.00% and 64.77%) and Pi - 11 (60.64% and 68.18%) as against 100 per cent mortality and 98.60 per cent root rot index noticed in control. The above five cultures were subjected for further studies. Characterisation of AMF associated with different genotypes of black pepper grown in various soil types indicated the definite influence of soil type on AMF colonization. Sandy soil (oxyaquic quartpsamment) harboured maximum root colonization while forest soil (haplic argiustoll) had the lowest. Species of Glomus particularly G. fasciculatum was the predominant AMF associated with black pepper irrespective of soil type. As an exception Acaulospora and Gigaspora species were frequently noticed in sandy soils. Based on the ability of the fungal antagonists to suppress P. capsici in vitro either through mycoparasitism, antibiosis or soil fungistasis, 24 isolates were selected for green house studies. In the further testing isolates A1, A13, A21, A22and A35 significantly reduced the foot rot infection and increased the plant growth. They showed better population build up in the soil and suppressed the P. capsici population considerably. These native antagonists were further tested in combination with selected AMF in the green house and field. Under green house condition, combination of G. fasciculatum x A1 or A21 showed significant influence on growth stimulation, while Is - 6 x A22 recorded lowest mortality of 32.90 per cent due to foot rot incidence as against 97 per cent in control. The dual inoculation of Is - 6 x A21 and Pi - 11 x A1 was highly effective in plant growth stimulation and disease suppression. Both the combination recorded less than 60 per cent infection and mortality due to the disease, while control showed 95.66 per cent infection and plant mortality. Bordeaux mixture and copper oxychloride recorded 66.67 and 59.68 per cent mortality respectively. AMF colonization and multiplication of antagonists were also favoured by dual inoculation. The potential AMF isolates Is - 6 and Pi - 11 were identified as species of Glomus while, the antagonistic isolates A1, A13, A21, A22, and A35 were confirmed as aspergillus fumigatus Fres., Fusarium oxysporum Schlecht. Ex Fr. Aspergillus sydowii (Bain. & Sart.) Thom. & Church, Trichoderma viride Pers. Ex Gray. And Gliomastix murorum (Corda) Hughes respectively. A technique for AMF inoculation to established pepper vines was developed using ‘carrier plants’. Raising sorghum with AMF inoculation around the pepper vines was found effective to achieve intense colonization in pepper roots by the introduced AMF in the field. This technique developed for the pepper vines may be tried for extending to other perennial crops for AMF inoculation. Promising AMF cultures Pi - 11, Is - 6, G. fasciculatum and antagonists Aspergillus fumigatus, A. sydowii, Trichoderma viride were further tested on eight year old established pepper vines following ‘carrier plant’ based AMF inoculation and cowdung - neem cake based antagonist inoculation. The treatment Pi - 11 x A. Sydowii was most effective with no symptom development, followed by Is- 6 x T. Viride or A. sydowii with disease score of 2.0 as against 7.0 recorded for control. The disease score for bordeaux mixture and copper oxychloride application was 3.5 and 3 respectively. Neem cake-cowdung food base was highly favourable for multiplication and activity of fungal antagonists. The amino acids, total sugar and reducing sugar and total phenols and orthodihydroxy phenol content and activity of cellulose and chitinase were influenced by AMF colonization particularly by Is - 6 and Pi - 11. The positive change could be related with the relative disease tolerance recorded for various AMF isolates. The development of native AMF and antagonists through extensive testing in the green house and field and also the technology of AMF inoculation for established pepper vines are the first record of work.
Open Access
Development of acid tolerant strains of Bradyrhizobium sp. suitable for certain pulse crops of Kerala
(Department of Plant Pathology, College of Agriculture, Vellayani, 1998) Meena Kumari, K S; KAU; Sasikumar Nair
The present investigation on "Development of acid tolerant strains of Bradyrhizobium sp. suitable for certain pulse crops of Kerala" was conducted at College of Agriculture, Vellayani, Trivandrum during 1993-96. The initial isolation of acid tolerant strains of Bradyrhizobium suitable for cowpea, blackgram and green gram was done from seven different locations in Kerala. These locations were broadly grouped into category A and B. The root nodulation and plant dry weight were uniformly higher in category A locations compared to category B locations in all the three crops. In all, 43 native isolates of Bradyrhizobium were obtained including 17 from cowpea, 13 each from blackgram and greengram. The native isolates of Bradyrhizobium obtained were screened as per the Bureau of Indian Standard specification. The screening trial was done both under unamended and amended soil conditions. Thus in unamended soil, the isolates KA-G- C-4, VE-G-B-2 and PA-G-G-5 for cowpea, blackgram and green gram respectively were selected based on plant dry weight and in amended soil, the isolates KA-F-C-7, KA-F-B-6 and PI-G-G-8 for cowpea, blackgram and greengram respectively were selected for further studies. The colony characteristics of the selected isolates were typical of Bradyrhizobium forming white translucent glistening and elevated colonies with entire margin on YEMA with congored. All •the six isolates were gram negative and fast growers attaining satisfactory growth on YEMA within three days. The carbohydrate utilization pattern showed that arabinose, a pentose sugar was the most preferred carbon source for the native isolates. At the sametime, the growth of - the exotic isolates were maximum in glucose. The ability to tolerate low levels of acidic pH upto 4.5 was more for the native isolates. The growth of both these isolates gradually improved and attained a peak level at pH 7.5. The in vitro tolerance to Fe and Al were almost identical for both the native and exotic isolates. In general, the growth was progressively inhibited with an increase in the concentration of these elements from 50 to 250 ppm. The antibiotic resistant markers for ampicillin, streptomycin and kanamycin were same for both the native and exotic isolates. The growth of these isolates were not inhibited at concentrations upto 1000 ppm of ampicillin, 250 ppm of streptomycin and 50 ppm of kanamycin. In the serological characterisation it was observed that one of the heterologous antigens (PI-G-G-8) for green gram showed positive agglutination with that of the cowpea isolate, KA-F-C-7. The effect of application of FYM, liming or pelleting on root nodulation and plant growth characters in cowpea, blackgram and greengram was studied. Significant increases in nodule number, nodule dry weight and plant dry weight were obtained in the treatment combination of Bradyrhizobium inoculation along with FYM and lime application in all the three crops. An almost similar result was also obtained when liming was substituted with calcium carbonate pelleting. The efficacy of the selected isolates of cowpea, blackgram and green gram were tested under field conditions at two locations namely College of Agriculture, Vellayani and Rice Research Station, Kayamkulam during identical cropping season for two years. The seed treatment effects of the two selected Bradyrhizobium isolates for cowpea (KA-G-C-4 and KA-F-C-7), blackgram (VE-G-B-2 and KA-F-B-6), greengram (PA-G-G-5 and PI-G-G-8.) were evaluated with and without POP recommendations along with appropriate cont~ol treatments. In general, the root nodulation, plant growth and yield were significantly improved in all the three crops where Bradyrhizobium inoculation was practised along with the POP recommendation for each crop. Thus at Vellayani, the nodule number, nodule dry weight, leaf area, plant dry weight and yield in cowpea were maximum in the treatment combination of POP+KA-F-C-7. A similar response was also obtained with POP+KA- G-C-4 treatment. At Rice Research Station, Kayamkulam also, the yield increase was maximum in the treatment combinations of POP+KA- F-C-7 and POP+KA-G-C-4. In blackgram and greengram also the treatment effects were more or less similar to that of cowpea. In the last part of the present investigation, the influence of the POP recommendations on plant and soil nutrient status was studied. The nitrogen content of plants was significantly higher in . Bradyrhizobium inoculated plants in cowpea and blackgram at both the locations. In greengram, at Vellayani there were no significant differences between treatments in the NPK content of plants. At Rice Research Station, Kayamkulam, also significant increases in nitrogen content of plants were obtained due to Bradyrhizobium inoculation. Unlike the nitrogen content a uniform treatment effect was not observed in the P and K content of plants. In the studies on soil nutrient status, it was observed that in general the availability of P, K, Ca and Mg were increased in the treatment combinations where POP recommendation was practised along with Bradyrhizobium inoculation. However, there was no significant difference between treatments in soil pH, organic carbon, Fe and Al content of different soil samples.
Open Access
Purification and serology of banana bunchy top virus
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1998) Estelitta, S; KAU; Sukumara Varma, A
Banana is one of the major fruit crop in Kerala and is often affected by the bunchytop disease caused by banana bunchytop virus. The disease is easily spread through infected suckers, which are used as the planting materials. Secondary spread is also seen through banana aphid, Pentalonia nigronervosa. Though field level quarantine measures may check the spread of the disease, rapid and convenient methods for the detection and identification of the virus in the suckers as well as in micropropagated plants have not been developed. In this background a study was designed and carried out to purify the BBTV, to produce antisera for developing a serological technique for the pre-symptomatic detection of virus in the planting materials of banana. Studies were also conducted to identify the type of nucleic acid of the virus and its morphology by direct electron microscopy. The study revealed that the disease incidence was maximum during August-November. The virus was not mechanically transmitted and tissue culture plants were the most susceptible planting materials for aphid transmission. Basic studies of virus-vector relationship were also conducted and the adult aphids were found to be effective vectors. In purification studies, among the different portions of banana plants used, the midribs of younger leaves yielded high concentration of the virus. Tissue culture plants yielded more virus concentration than other planting materials. Electron microscopy of the purified BBTV preparation revealed isometric particles of 18-22 nm size. Nucleic acids extracted from both healthy and infected samples were compared. The bands obtained were sensitive to DNase 1 and SI nuclease but not to RNase A, confirming the nucleic acid BBTV as ssDNA. SDS-PAGE analysis of BBTV coat protein revealed that it contained a major protein component of Mr 21000 with Rf value between that of β lactoglobulin (Mr 18400) and α chymotrypsinogen (Mr 25700). Antiserum of BBTV was produced in the rabbit and used for detection of virus specific antigens in different parts of the plant (midrib, petiole, leafsheath and rhizome) by chloroplast agglutination, agar gel diffusion, tube precipitation and ELISA. Among these methods ELISA was found to be highly sensitive for identification of the virus.
Open Access
Interaction between VA mycorrhiza and bradyrhizobium in cowpea
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1999) Beena, S; KAU; Rajendran Pillai, M V
An investigation . I. on Interaction between VA mycorrhiza and Bradyrhizobium in cowpea was carried out at the College of Horticulture, Vellanikkara during the period 1994-97. The main objectives of the study were to explore the beneficial effects of dual. inoculation of VA mycorrhiza and Bradyrhizobium in enhancing the uptake of nitrogen and phosphorus and to evolve specific recommendation on the use of these inoculants together in reducing the use of nitrogenous and phosphatic fertilizers. The results of this investigation revealed the following conclusions. The survey on the natural occurrence of VAM in cowpea showed a fairly good VAM colonisation in all the plant samples collected from the five locations. VAM colonisation was found more in lateral roots than in tap root. The VAM colonisation and spore count were more during rainy season compared to summer. The predominant spores present in all the survey locations were identical to that of Glomus sp. After the screening of V AM, the local isolate from farmer's field at Nadathara was selected for further studies based on its performance. Observation of cowpea plants at 10 days after sowing showed the presence of nodules and VAM colonisation in the roots of inoculated plants. Both the nodulation and VAM colonisation were found to reach a peak at 40th day after sowing. Dual inoculation was found to have a synergistic effect in nodulation and VAM colonisation. Light microscopy of VAM infected roots showed both 'H' and 'V' shaped branching of hyphae, arbuscules and vesicles of VAM fungus. : j Electron microscopy revealed two types of fungal penetrations into the roots. It also showed the terminal attachment of oval shaped vesicles and highly branched arbuscules with short twisted branches with bulged tips in the root cortex. Electron microscopic study of nodules revealed that the nodule surface was free of V AM hypha, but the inner tissues of nodules had the hyphal presence. The pot culture experiment recorded synergistic effect in dual inoculation with VAM and Bradyrhizobium in enhancing five biometric characters, viz. number of leaves, fresh and dry weights of plant, number of nodules and fresh weight of nodules. : i Among the inoculant-fertilizer interactions, eventhough all observations except fresh weight of plant recorded non significance between treatments, those in I which VAM was a partner, recorded the maximum values for all the observations except root length. Dual inoculation with VAM and Bradyrhizobium improved the level of six nutrients, viz. nitrogen, phosphorus, magnesium, calcium, zinc and manganese in cowpea. The result of interaction with microsymbionts and fertilizer levels recorded inconsistent values. Treatment with VAM + B + 1/4 N + P + K recorded maximum nitrogen, VAM + ½ N + P + K and N + ½ P + K alone recorded maximum phosphorus and dual inoculation along with ½ N+P+K recorded maximum magnesium and calcium content of plant. Inoculation of VAM + Bradyrhizobium along with ½ N + P + K ranked top III increasing the soil nitrogen to the maximum. There were no significant differences among treatments and its combinations in influencing the phosphorus J status of soil. The application of either VAM or Bradyrhizobium or its combinations reduced the potassium content of soil. The results of the field experiment revealed that the treatment T 10 (VAM+B+ ½ N+ ½ P+K) out perform other treatments in five characters, viz. plant height, fresh and dry weights of plant, nodule number and fresh weight of nodules at 50 per cent flowering. At harvest this treatment recorded the maximum values in fresh and dry weights of plant, nodule number and fresh and dry weights of nodules. Treatment T 10 increased nodulation to 180 per cent over Bradyrhizobium inoculation alone. Bradyrhizobium+ ½ N+P+K was found to be the best treatment in improving the nitrogen content of plant, whereas VAM+B+ ½ N+ ½ P+K was the best for improving the phosphorus, potassium, magnesium and zinc content of plant. Another finding was that the different treatments involving microsymbionts and different fertilizer doses were not able to influence the nitrogen, phosphorus and potassium content of soil to a significant level. The percentage of V AM colonisation was not significantly affected by dual inoculation and also by the application of different levels of fertilizers. Dual inoculation had no influence on the spore count of V AM. 'The high level of phosphorus in soil had some negative influence on the spore count. Treatment B+ ½ N+ P+K was the best in increasing the yield to the maximum, which was on par with T 10. The overall results showed that T10 (VAM+B+ ½ N+ ½ P+K) where dual inoculation was done and nitrogen and phosphorus fertilizers were reduced to half of the recommended dose, was the best treatment in improving the biometric characters and nutrient status and yield of cowpea. Thus a judicious treatment would be VAM+B+ ½ N+ ½ P+K to get the best performance of cowpea. The percentage of V AM colonisation recorded a significant positive correlation with nodule number and fresh and dry weights of nodule. There was a significant positive correlation between nodule number and plant dry weight and also with yield. The percentage of VAM colonisation had a significant positive correlation with calcium content and significant negative correlation with manganese content of plant.
Open Access
Biochemical and biological bases of resistance in solanaceous vegetables against bacterial wilt incited by Ralstonia solanacearum (Smith) yabuuchi etal
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1998) Sheela Paul, T; KAU; James Mathew
An investigation on biochemical, biological and nutritional bases of resistance in solanaceous vegetables against bacterial wi1t incited by Ralstonia solanacearum (Smith) Yabuuchi et al., has been attempted. The pathogen R. solanacearumwas isolated from respecti ve hosts and characterised by various morphological, cultural, biochemical and physiological tests upto biovar level. The three isolates were cross inoculable, and were sensitive to AmDistryn and Streptocycline. Based on these studies the tomato and chilli isolates were identified as Ralstonia solanacearum race I biovar III and that from brinjal as R. solanacearum race I biovar V. The study on toxigenic property of the bacterial isolates revealed that the toxic metabolites were not host specific. Out of the 43 varieties / lines screened , 12 varieties / lines were selected, one each from resistant, moderately resistant, moderately susceptible and susceptible categories. The varieties / lines selected were LE 79-5, BT-IO, LE 470 and Pusa Ruby for tomato; Swetha, Composite-2, BB-7 and Pusa Purple Long for brinjal and Ujwala, Manjari, Jwalasakhi and Pusa Jwala for chilli. The studies on biochemical, biological and nutritional factors in tomato, brinjal and chilli showed considerable variation between crops, between varieties/ lines, and between plant parts. However the root being the primary foci of infection by R. solanacearum the biochemical reactions in root is considered more important than other plant parts. Among the biochemical factors, the OD phenol and specific activity increased due to infection and the content was higher in the resistant genotype (LE 79-5) both under heal thy and diseased condition in tomato. In brinj al, the polyphenol oxidase activity, specific activity and peroxidase activity increased due to infection and were higher in resistant genotype (Swetha) both under healthy and diseased condition. In chilli, total phenol and OD phenol, increased due to infection and were higher in resistant plants (Ujwala) under healthy and diseased condi tions. The soluble sugar content and specific activity were also higher in resistant plants both under healthy and diseased condition even though a decrease was observed due to infection . In tomato, the resistant genotype showed a higher content of OD phenol, polyphenol oxidase activity, specific activity and alkaloids under healthy condition; and total phenol, OD phenol, soluble protein, specific activity and peroxidase activity under diseased condition. In brinjal, the resistant genotype recorded higher content of total phenol, OD phenol, soluble sugars, amino acids, soluble protein, polyphenol oxidase activity, specific activity and peroxidase activity under healthy condition; and polyphenol oxidase activity, specific activity and peroxidase activity under diseased condition. In chilli, the resistant genotype recorded higher total phenol, OD phenol, soluble sugars and specific acti vi ty under heal thy condition; and total phenol, OD phenol, soluble sugars, specific activity and peroxidase activity under diseased condition. Among the biological factors, the total microflora (fungi and actinomycetes), Pseudomonads and parasitic nematodes increased due to infection in resistant genotype whereas beneficial microbes recorded a decrease in population in resistant genotype by infection. In tomato the resistant genotype recorded higher nematode population under heal thy condi tion and higher total microflora, virulent Ralstonia and avirulent Pseudomonas under diseased condition. In brinjal the resistant genotype recorded higher population of fungi, avirulent Pseudomonas, mycorrhiza and saprophytic nematodes under heal thy condition, and fungi, virulent Ralstonia, avirulent Pseudomonas and nematodes under diseased condition. In chilli, the resistant genotype recorded higher populations of avirulent Pseudomonas, mycorrhiza and nematodes under heal thy condition and fungi, avirulent Pseudomonas and mycorrhiza under diseased condition. Among the nutritional factors, in tomato the resistant genotype recorded higher content of potassium and calcium under heal thy condition and iron, zinc and manganese under diseased condition. In brinjal the resistant genotype recorded higher content of nitrogen, calcium, magnesium and zinc under heal thy condition; and potassium, magnesium, iron and zinc under diseased condition. In chilli, the resistant genotype recorded higher content of phosphorus, calcium and iron under heal thy condition; and nitrogen, potassium magnesium and zinc under diseased condition. Thus the study revealed that it was not possible to arrive at common bases for resistance to bacterial wilt in tomato, brinjal and chilli taken together. However it was possible to outline the important parameters that conditions resistance in individual crops.

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