Effect of Aspergillus flavus on groundnut seed quality and its management

Groundnut (Arachis hypogaea L.) is an important oil seed crop in India. It contains oil to an extent of 48 - 51 %. The major problem associated with groundnut is aflatoxin contamination. It is mainly caused by Aspergillus flavus and Aspergillus parasiticus. Groundnut being an oil seed, it contains lesser amount of carbohydrates than cereals but more amount of oil and protein and they break down into simple sugars and amino acids which is essential for germinating seed as an energy source. Several management strategies were adopted to minimize the aflatoxin problem viz., development of resistant varieties, use of biocontrol agents and cultural practices. Keeping this in view, the present findings pertaining to the present investigations were carried out on detection of seed mycoflora, mode of entry of A. flavus into groundnut seed, effect of A. flavus on seed and oil quality and evaluation of bioagents and fungicides in the management of A. flavus of groundnut under glasshouse conditions. A total of seventy two groundnut (72) pod samples comprising farmer samples (36) and market samples (36) from major groundnut growing districts of Telangana state during 2015 - 2016. The seed samples were analysed for seed health by agar plate method as per ISTA (1996). Significant differences in occurrence of total number fungal colonies due to location and source of seed samples were observed. Irrespective of the districts, total per cent occurrence of seed mycoflora was found high in farmer samples (92.4 %) over market samples (45.3 %). Out of four districts, samples of Mahabubnagar district (47.1 % & 26.2 %) followed by Warangal district (43.5 % & 24.6 %) recorded more total number of fungal colonies in farmer and market samples. Irrespective of the samples, occurrence of six fungal flora viz., A. flavus, A. niger, Fusarium sp. Alternaria sp. Macrophomina sp. Penicillium sp. were observed. Among them, A. flavus (43.2 %), A. niger (26.7 %) were found predominant in both farmer and market samples. External seed colonization due to A. flavus in groundnut resistant cv. J 11 and susceptible cv. JL 24 were observed at different days of incubation period indicated that resistant groundnut cv. J 11 inoculated with A. flavus colonized the seeds with severity score of 1, 2, 3, 4 and susceptible cv. JL 24 inoculated with A. flavus colonized the seeds with disease severity score of 2, 3, 4, 4 at 3, 5, 7 and 9 days after incubation period. The mode of entry of pathogen into groundnut seed was studied by Scanning Electron Microscopy. Groundnut seeds of resistant and susceptible cultivars inoculated with A. flavus toxigenic strain, the penetration and establishment of the fungi in case of J 11 was slow compared to JL 24. The present investigation reveals that A. flavus is seed borne in nature and contaminated seeds were important source of inoculum for seed infection and spread of the fungus from one seed to another during storage. The per cent reduction in oil content was high in susceptible groundnut cv. JL 24 (18.3%) as compared to resistant groundnut cv. J 11 (9 %). While the reduction in oil content was less in the untreated seeds of groundnut cv. JL 24 and groundnut cv. J 11 ( 13.7% and 6%). Overall the per cent reduction in the protein content was found high in susceptible groundnut cv. JL 24 (16.3 %) as compared to resistant groundnut cv. J 11 (6.5 %). While the reduction in protein content was less in the untreated seeds of groundnut cvs. JL 24 and J 11 (14.2 % & 5.1 %). The per cent reduction in the unsaturated fatty acids like linoleic and oleic acids were high in susceptible groundnut cv. JL 24 (17.5 % and 16.6 %) as compared to resistant groundnut cv. J 11 (15 % and 14 %). Whereas in the untreated seeds, the per cent reduction in linoleic and oleic acids were found low (11.3 % and 6 %) in cv. J 11 and 13.3 % and 8.2 % in cv. JL 24, respectively. The increase levels of saturated fatty acids viz., palmitic and stearic acids were high in susceptible cv. JL 24 (4.5 % & 4.5 %) as compared to resistant cv. J 11 (3.9 % & 2.93 %). Where as in untreated seeds, the increased levels in palmitic and stearic acids were found low (2.5 & 2 %) in cv. J 11 and 2.9 % and 1.94 % in groundnut cv. JL 24 respectively. The aflatoxin content at 1 to 56 days after incubation increased in groundnut cv. J 11 (2.15 μg/kg - 2861.3 μg/kg) & 63.4 μg/kg - 4077.1 μg/kg in cv. JL 24, respectively. In the untreated seeds there was low level aflatoxin content of 2.15 μg/kg - 14.7 μg/kg in cv. J 11 and 2.15 μg/kg - 21.1 μg/kg in cv. JL 24 were recorded. The efficacy of seed treatments against seed borne A. flavus were evaluated under glasshouse conditions. Groundnut seeds treated with T. harzianum was significantly superior in recording higher seed germination (96 %), plant height (4.75, 12.9 and 14.1 cm) and yield (4.60 g) followed by T. viride (91 %, 4.10, 11.5 and 13.5 cm, 4.20 g) which was on par with P. fluorescens (88.2 %, 3.40, 10.2 and 10.8 cm 4.10 g). The remaining seed treatments were also found effective in improving seed germination, plant height and yield in seeds treated with carbendazim (81 %, 2.77, 8.02 and 9.21 cm, 3.65 g), mancozeb (73.5 %, 2.72, 6.92 and 8.43 cm, 3.37 g) over untreated (65 %, 2.67, 6.62 and 7.37 cm, 29.2) and pathogen treated seeds (54.5 %, 2.57, 5.65, 6.41 cm, 2.55 g) at 15, 30, 45 DAS. Aflatoxins were detected in pathogen treated seeds (1.38 μg/kg) and untreated seeds (0.69 μg/kg) which is below permissible level. While aflatoxin was not observed in the seed treated with T. harzianum, T. viride and P. fluorescens