IDENTIFICATION AND CHARACTERIZATION OF Alternaria alternata (Fr.) KEISSLER INCITING LEAF BLIGHT IN LITTLE MILLET
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Date
2021-02-25
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University of Agricultural Sciences, Bangalore
Abstract
Little millet is one of the hardiest minor millet indigenous to the Indian subcontinent and is mainly grown for food, fodder and feed. However, leaf blight caused by Alternaria alternata is one of the emerging malady in the successful cultivation of little millet. Intensive roving survey unravelled that the severity of leaf blight ranged from 19.49 to 67.33 per cent. The leaf blight pathogen was identified as Alternaria alternata based on morpho-cultural characteristics and molecular profiling with ITS, SSU, Histione-H3, GAPDH, RPB2, Alt a1, endoPG, OPA10-2 and KOG1058 gene/genomic regions. Whole genome sequencing of A. alternata UASB1 isolate using Illumina and Oxford Nanopore ensued genome size of 33. 13 Mb, 12, 388 predicted genes, 10, 266 proteins in which 762 were annotated and 9504 hypothetical proteins and 635 Simple Sequence Repeats (SSRs). Effect of fungal culture filtrate on Vigour Index (V. I) showed drastic reduction compared to water control. Seedling growth was also affected with culture filtrate and the crop leaves exhibited chlorosis, necrosis, drooping with loss of turgidity. Toxin characterization through LCMS revealed that the pathogen produces various toxic compounds like Tenuazonic acid (TeA), Alternariol Monomethyl Ether (AME), Alternariol (AOH), Altenuene (ALT), Altertoxin II, Alterperylenol and Stemphylotoxin III. Host range studies indicated that the pathogen is not host specific and can infect other plant species like kodo millet, wheat and oat. Among the 142 genotypes screened under natural field conditions 46, 38 were found resistant to leaf blight disease at Mandya and Bangalore respectively. Eucalyptus leaf extract recorded highest mean per cent inhibition of mycelial growth (84.82 %) in vitro. Among the bio-agents, highest mycelial radial growth inhibition was noticed with Trichoderma harzianum ThB5 (75.18%) and Bacillus velezensis strain P42 (84.75%) in vitro. Highest mean mycelial growth inhibition of Alternaria alternata was observed in mancozeb 75% WP (78.43%) among the contact fungicides, tebuconazole 50 % WG + trifloxystrobin 25 % WG (95.74 %) combi-product and hexaconazole (100.0%) systemic fungicide in vitro.