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Sesame (Sesamum indicum L.), is an important oilseed crop in the tropics and subtropics, referred as “Queen of Oilseeds” owing to its high cooking quality and medicinal value. Sesame production, particularly in India, has been declining since last decade and ‘Leaf blight’ caused by Alternaria spp. is reported to cause yield loss up to 30-40%. Here, we investigated the fungal toxin produced by Alternaria and its pathogenicity. A total of 164 Alternaria strainswere isolated on potato dextrose agar media from the infected sesame leaves showing circular concentric rings with dark brown spots symptoms. All the isolates were screened for cultural and morphological characters. Colour of the fungus was grey to dark brown, formed smooth, raised, fluffy, and regular to irregular margins. Among 164 isolates, 43 isolates were moderately growing and 121 were fast in growth. The DNA of the isolate was amplified with ITS primers and sequence of BLAST results confirmed seven different species of Alternaria of NCBI database. Further, toxigenic potentiality of the isolates was tested with dilutions of culture filtrate (1:1 to 1:5) on sesame leaves. Among 164 isolates, 23 showed toxigenicity, varied from highly toxigenic to least toxigenic. Pathogenicity of the isolates showed that they were highly virulent to less virulent when tested by the detached leaf method. Based on the toxigenicity, the toxin was partially purified and brown coloured paste was recovered. Chemistry of the toxin was confirmed based on the IR, UV, NMR and mass spectra analyses, and it resembled the structure of alternariol mono methyl ether and altenuene which are mycotoxins in nature. Further, bioassay of toxin was carried out at different concentrations (50 to 2000 ppm) on seeds and seedlings of sesame. Maximum inhibition of seed germination of 81.1% was observed at 2000 ppm and the least was 6.67% at 50 ppm. With the increase in the concentration of toxin, the manifestation of the symptom was conspicuous and quick such as marginal, veinal necrosis, drooping and yellowing with lesion formation. From the present study, it is found that the species of Alternaria are responsible for the cause of blight disease symptoms and the toxicity of toxin produced by the pathogen was very high. The Alternaria toxin could inhibit the growth of the plant as well as seed germination rate.

Investigations on biological activities of pod borer, Helicoverpa armigera (Hubner) on 20 promising chickpea genotypes using detached leaf assay method at Agriculture Research Station Kalaburagi, UAS, Raichur, Karnataka was carried out during rabi 2016-17. The results revealed that at vegetative and flowering stage there was significantly lesser larval survival (70 to 76.67 %), larval weight (8.37 to 8.90 mg) and damage rate (3.67 to 4.67 of visual Rating in 1-9 Scale) on resistant check ICCL 86111, HC-1 and DBGV-3104 genotypes where as maximum per cent larval survival (86.67 to 90 %), larval weight (13.60 to 14.10 mg) and damage rate (7.67 to 8.00 of visual Rating in 1-9 Scale) was recorded in susceptible checks (ICC-3137, A-1 and JG-11). During pod formation stage, highest weight gain by larvae was noticed on susceptible check ICC-3137 (409.18 mg), on the contrary lowest weight gain by larvae was found on resistant check ICCL-86111 (275.43 mg) also these genotypes recorded more amount of malic acid and trichomes indicating that biological activity of insect was affected through antibiosis mechanism which is one of the component of resistance to H. armigera in chickpea.

Different temperatures and pH were taken to observe the radial growth and dry mycelial weight of Trichoderma spp. The radial growth of Trichoderma was maximum for all the four species i.e., T. harzianum, T. viride, T. hamatum and T. virens (90, 82, 91.3 and 85mm) at 30oC, where it was minimum in four species at 40oC (30.70, 35, 22.53 and 20 mm), respectively and dry mycelium of T. harzianum (1.05 mg), T. viride (1.83 mg), T. hamatum (2.42 mg) and T. virens (0.82 mg) were maximum at 25oC whereas, the radial growth of four isolates were maximum at pH 6 (90, 88, 92 and 91mm) in T. harzianum, T. viride, T. hamatum and T. virens, respectively. At neutral pH, radial growth of T. harzianum (89 mm), T. viride (91 mm), T. hamatum (89 mm) and T. virens (87 mm) was minimum and dry mycelium weight of T. harzianum (729 mg), T. viride (1639.67 mg), T. hamatum (798 mg) and T. virens (583.67 mg) were maximum at pH 8. It was minimum at pH 4 for T. harzianum (120 mg), T. viride (257 mg), T. hamatum (154 mg) and T. virens (262.67 mg).

Azotobacter strains were isolated by serial dilution method and colonies were viscous, smooth, glistening, and brown to black colour on Jenson's N-free agar. Morphological and biochemical tests showed characteristic features of Azotobacter. Further, molecular analyses revealed the presence of different Azotobacter species viz., A. armeniacus, A. chroococcum, A. salinestris, A. tropicalis and A. vinelandii. The isolates were tested for their ability of nitrogen fixation, indole acetic acid (IAA), gibberllic acid production and phosphate solubilization. Four isolates (GVT-1, GVT-2 KOP-11 and SND-4) were efficient in fixation of highest amount of N2 (29.21 μg NmL(-1) day(-1)), produced IAA (25.50 μg mL(-1)), gibberllic acid (17.25 μg 25 mL(-1)) and formed larger P solubilizing zone (13.4 mm). Some of the Azotobacter strains were produced siderophores, hydrogen cyanide and were positive for ammonia production with respect to antifungal activity of Azotobacter was tested with dual culture method and A. tropicalis inhibited the growth of Fusarium, Aspergillus and Alternaria species. Azotobacter isolates were tested against salt (0-10%), temperature (4-55 degrees C), pH (5.0-10) and insecticide chloropyrifos (0-3%) tolerance study. Among them, A. chroococcum was found tolerant to a maximum of 6% NaCl with a temperature of 35-45 degrees C and to a pH up to 8. All the 4 strains showed effective growth against 3% chloropyrifos concentration. The studies revealed that the Azotobacter strains not only produced plant growth promoting substances but are also tolerant to abiotic stresses such as temperature, pH and insecticides.

The antagonistic potential of forty four isolates of Trichoderma were evaluated in vitro against the most widely occurring soil borne plant pathogens viz., Macrophomina phaseolina, Rhizoctonia solani, Rhizoctonia bataticola and Sclerotium rolfsii to identify the most potential Trichoderma isolate. Maximum growth inhibition of M. phaseolina (81.11 %), R. solani (82.59 %) and S. rolfsii (76.67 %) was recorded by T. hamatum where as T. virens was most aggressive against R. bataticola (68.15 %) in dual culture technique.