K. Vijay Krishna Kumar

Efficacy of Bacillus subtilis MBI 600 Against Sheath Blight Caused by Rhizoctonia solani and on Growth and Yield of Rice

Rice sheath blight disease (ShB), caused by Rhizoctonia solani, gives rise to significant grain yield losses. The present study evaluated the efficacy of Integral®, the commercial liquid formulation of Bacillus subtilis strain MBI 600, against rice ShB and for plant growth promotion. In greenhouse studies, four log concentrations of Integral (from 2.2×106 to 2.2×109 cfu/mL) were used as seed treatment (ST). After 25 d, seedlings were dipped (SD) into Integral prior to transplanting. At 30 d after transplanting (DAT), leaf sheaths were inoculated with immature sclerotia of the pathogen. At 45 DAT, a foliar spray (FS) with Integral was applied to some treatments. The fungicide control was 50% carbendazim at 1.0 g/L, and a nontreated control was also included. Overall, there were 10 treatments, each with five replications. ShB severity was rated at 52 DAT, and seedling height and number of tillers per plant were rated at 60 DAT. In 2009, two field trials evaluated Integral at 2.2×108 and 2.2×109 cfu/mL. Integral was applied as ST, and seedlings were produced in a nursery bed. After 32 d, seedlings were treated with Integral as SD and transplanted into 10 m2 blocks. Foliar sprays were given at 45 and 60 DAT. There were seven treatments, each with eight replications arranged as a factorial randomized complete block design. At 20 DAT, the plots were broadcast inoculated with R. solani produced on rice grains. Seedling height before transplanting, ShB severity at 90 DAT, and grain yield at harvest were recorded. Integral at 2.2×109 cfu/mL provided significant increase of seedling heights over other treatments under greenhouse conditions. The Integral treatments of ST + SD + FS at 2.2×109 cfu/mL significantly suppressed ShB over other treatments. In field studies, Integral provided significant increase of seedling height in nursery, and number of tillers per plant, compared with the control. ShB severity was significantly suppressed with higher concentrations of Integral compared to lower concentrations. Grain yield were the highest at an Integral concentration of 2.2×109 cfu/mL. Overall, Integral significantly reduced ShB severity, enhanced seedling growth, number of tillers per plant and grain yield as ST + SD + FS at the concentration of 2.2×109 cfu/mL under the conditions evaluated.

Characterisation, genetic diversity and antagonistic potential of 2,4-diacetylphloroglucinol producing Pseudomonas fluorescens isolates in groundnut-based cropping systems of Andhra Pradesh, India

This study is focused on isolation and characterisation of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens isolates from different soils of groundnut-based cropping systems in Andhra Pradesh. In our studies, 21 isolates of P. fluorescens were isolated and confirmed through various biochemical tests, of which five were tested positive for 2,4-DAPGproduction with specific primers. Biocontrol potential of these isolates on groundnut stem rot pathogen (Sclerotium rolfsii) was determined through in vitro dual culture assays. The eight isolates were found effective against S. rolfsii (up to 75% inhibition) in dual culture method. All the five 2,4-DAPG-producing Plant Growth-Promoting Rhizobacteria isolates were highly antagonistic to S. rolfsii. Genetic diversity of these P. fluorescens isolates was determined by random amplification of polymorphic DNA analysis. Overall, our results suggest that the prevalence of 2,4-DAPG-producing fluorescent Pseudomonads in different crop rhizospheres of groundnut-based cropping systems.

Potential of Plant Growth-Promoting Rhizobacteria for Sustainable Agriculture

Plants absorb many nutrients and elements from soil. These elements are continuously removed from soil. Therefore, there is a continuous demand for replenishment of these elements, which is usually fulfilled by chemical or biological fertilizers. Biofertilizers have numerous merits over the chemical fertilizers. The fertilizer (NPK) production in India is less than the required amount, and hence biofertilizers are seen as the best alternate source to bridge future gaps. Such an integrated approach will help to sustain soil health and productivity. Hence, the major thrust is being given to nitrogen fixers, phosphate solubilizers, and plant growth-promoting rhizobacteria (PGPR). PGPR are multipotent bioinoculants that promote plant growth, impart resistance to the plant, and provide a pathogen suppressiveness property to the soil and suppress major phytopathogens.

Pathogenic and Molecular Variability of Aspergillus niger Isolates Causing Collar Rot Disease in Groundnut

Pathogenic variability studies of 26 isolates of collar rot pathogen (Aspergillus niger) of groundnut collected from different districts of Telangana and Andhra Pradesh states were conducted under greenhouse conditions by using two groundnut cultivars TMV-2 and JL-24. The mean seedling mortality ranged from 29.7 per cent (MBNRAn-1 (Palkapally)) to 94.4 per cent (ATPAn-1 (Jogannapet)). All the isolates of A. niger showed differential reaction with regard to seedling mortality on JL-24 and TMV-2 cultivars. Similarly genetic relatedness among eight virulent isolates (two isolates from each district) of A. niger from groundnut was assessed by using RAPD analysis. The similarity index values among the A. niger isolates varied from 0.571 (between WGL An-2 and CHT An-3) to 0.229 (between MBNR An-3 and WGL An-2).

Resistance Screening of Groundnut Advanced Breeding Lines against Collar Rot and Stem Rot Pathogens

Forty groundnut advanced breeding lines along with susceptible checks JL-24, J-11 and TMV-2 were used for collar rot (Aspergillus niger) and stem rot (Sclerotium rolfsii) disease screening. Based on the per cent number of plants affected by the collar rot pathogen, the advanced breeding lines were categorized into four groups. The lines present in group I (Resistant) having < 15% incidence, group II (Moderately resistant) having 15.1 to 30%, group III (Susceptible) having 30.1 to 45 % and group IV (Highly susceptible) having > 45% incidence. Similarly among 40 breeding lines only three lines (ICGV86699, ICGV91114 and ICGV 89280) have shown stem rot disease reaction below 3 (up to 25 % plants were symptomatic) and considered to be moderately resistant to stem rot pathogen. The advanced breeding line ICGV99058 has recorded a disease reaction of 5 scale (> 50 % of the plants symptomatic) equal to the susceptible checks which is considered to be highly susceptible to stem rot pathogen.

Endophytes: Role and Functions in Crop Health

Plant-microbe interactions is an important concept, and the significance of these interactions on sustainable agriculture is enormous. These interactions can be neutral, commensal, mutualistic, saprophytic, or harmful. Endophytes are beneficial microbes that reside and establish symbiotic relationships with the plants. These beneficial microbes are of either bacterial, fungal, or actinomycete origin. A wide array of beneficial effects are reported with endophytic associations in plants that include bioremediation, herbivory, induced resistance, plant growth promotion, and pest and disease management. Nomenclature of endophytes is generally according to the plant tissue it harbors, such as endophytes of root, shoot, leaf, seed, etc. Our review presents different bacterial and fungal endophytes in plants and their role in improving crop health. The plant growth-promoting (PGP) activities of these endophytes such as production of growth hormones like indoleacetic acid (IAA), gibberellic acid (GA), and cytokinins and phosphate solubilization in different crops by specific endophytes are discussed in detail. Further, specific antagonistic activities of endophytes like induced systemic resistance; production of salicylic acid, siderophores, HCN, cell wall-degrading enzymes, and antimicrobial metabolites including antibiotics; and direct antagonism against different plant pathogens are thoroughly discussed. The preferences of endophytes to different plant parts; their different niches such as roots, shoots, leaves, and whole plants; and specific antagonistic and PGP activities are elaborated in detail. Other beneficial activities such as herbivory, bioremediation, biodegradation, and biofertilization including nitrogen fixation are also discussed briefly. Finally, we have also discussed the scope and future prospects of endophytes in improving soil and crop health.

Detection of Toxigenic and Atoxigenic Strains of Aspergillus flavus in Telangana and Andhra Pradesh

In groundnut Aspergillus flavus causes aflatoxin contamination which is a qualitative problem occurring at both pre-and post-harvest stages. These aflatoxins have carcinogenic, hepatotoxic, teratogenic and immuno-suppressive effects. The A. flavus strains which produces aflatoxins are called as toxigenic and which do not produce toxins are called as atoxigenic starins. To detect the toxigenic and atoxigenic starins of A. flavus from Telangana and Andhra Pradesh (AP), pod samples were collected from eight selected oil mills/traders’ in Mahaboobnagar, Rangareddy, Nizamabad, Karimnagar (Telangana); and Anantapur (AP) districts. A total of 24 A. flavus cultures were isolated from the collected pod samples. These isolates were identified as toxigenic/atoxigenic using cultural detection methods on Yeast extract sucrose (YES) media and coconut agar medium (CAM). Based on cultural methods, it was confirmed that there were18 toxigenic, five atoxigenic and one false positive/negative strain out of the 24 A. flavus isolates obtained from surveyed oil mills. Atoxigenic strains were obtained from Karimnagar and Nizamabad districts of Telangana.

Prevalence of Aspergillus flavus Infection and Aflatoxin Contamination of Groundnut in Telangana and Andhra Pradesh

Aflatoxin contamination is a qualitative problem in groundnut (Arachis hypogaea L.) occurring at both pre-and post-harvest stages. These aflatoxins are secondary metabolites produced by Aspergillus flavus and A. parasiticus and have carcinogenic, hepatotoxic, teratogenic and immuno-suppressive effects. To evaluate the prevalence of A. flavus infection and aflatoxin contamination in groundnut oil mills/traders’ of Telangana and Andhra Pradesh (AP) pod samples were collected from eight selected oil mills/traders’ in Mahaboobnagar, Rangareddy, Nizamabad, Karimnagar (Telangana); and Anantapur (AP) districts. A total of 24 pod samples were collected (Three samples from the each selected oil mill). Aflatoxin contamination in kernels was estimated by indirect competitive ELISA. In Telangana, kernel infection ranged from 42 (Mahaboobnagar) to 90.7% (Nizamabad). In AP, Tadimarri mandal recorded kernel infection up to 29.3% whereas Tadipatri recorded up to 59.3%. Aflatoxins in kernels from these mills in Telangana were highest in Rangareddy (1205.2 µg kg-1 ) followed by Karimnagar (365.5 µg kg-1 ). Oil mills of Nizamabad and Mahaboobnagar have recorded aflatoxins to a tune of 4.9 and 11.5 µg kg-1 in Telangana. In AP, aflatoxins in pod samples were 2.8 µg kg-1 (Tadipatri) and 6148.4 µg kg-1 (Tadimarri).

Evaluation of fungicides and herbicides against groundnut collar rot pathogen Aspergillus niger under in vitro conditions

Collar rot of groundnut is caused by Aspergillus niger Van Tieghem. It is a soilborne pathogen, usually the occurrence of collar rot disease during the early stages of crop growth and results in high seedling mortality. The collar rot pathogen produces both seed rot (pre-emergence) and seedling blight symptoms (post-emergence). In case of seed rot, black masses of mycelium were seen on the surface of seed. Later, the pathogen causes rotting of seed. Rotten seed do not emerge from the soil. Collar rot affected seedlings show a circular brownish spot on cotyledon region. Later, the discoloured area rapidly disintegrates spreading to the stem and hypocotyl. The affected plants show general wilting, rotting just below the ground level. An experiment was conducted under in vitro conditions to evaluate the fungicides against the collar rot pathogen apart from these fungicides, some herbicides also evaluated to test their non-target effect against collar rot pathogen. A total of six fungicides and eight herbicides were evaluated by using poisoned food technique. Maximum inhibition (100%) of radial growth of A. niger was obtained with tebuconazole at recommended and half recommended dosage and least inhibition was obtained with mancozeb and azoxystrobin. Among herbicides pendimethalin was shown maximum inhibition (100%) against A. niger and least inhibition was observed with herbicide imazythapyr and imazythapyr + imazamox.