Vol. 12, Issue 8 (2023)

Author(s):
Jayamurugan C, Rajeswari E, Harish S, Subramanian A and Sharmila Rahale C

Abstract:
Cotton is a natural fibre and a key cash crop farmed in over 50 nations worldwide. Alternaria Leaf Blight (ALB) incited by the Alternaria spp is the most serious disease which inflicts yield loss up to 37 percent. Roving survey was done to evaluate the status of ALB in nine different cotton growing areas in Tamil Nadu between2020 to 2022. The mean district incidence of ALB incidence in surveyed districts ranged from 6.60 to 12.71 PDI (Percent Disease Index). Dindigul district had the highest average district incidence (12.71 PDI), while Trichy district had the lowest average incidence (6.60 PDI). A total of 10 isolates were isolated from the ALB infected cotton field and morphological characterization was done. The colonies of these isolates showed light to dark brown colour with concentric zone. The conidia colour varied from pale to dark brown colour and the size ranged from 26.33-38.19μm to 8.12-14.12 μm with transverse (1-6) and longitudinal septa (1-3).The isolate CA3 was proved to be the most virulent as it was found to produce the highest lesion of 3.7 cm (size) within 6 days in detached leaf assay. The molecular characterization of isolates were done by PCR amplification of ITS region by using universal primers and all the isolates were amplified at 560 bp. Morphological and molecular characterization confirmed all the isolate as Alternaria spp . Sequencing and blast analysis confirmed the isolate CA3 as A. alternata.