Host Range Studies of Alternaria Species on Sunflower and Efficacy Studies of Fungicides Against A. Alternata Under Both in-Vitro and in-Vivo Conditions

Alternaria blight is the major profound disease of sunflowers induced by divergent species of Alternaria. Among numerous species of phytopathogenic fungi the genus Alternaria Nees ex Fr. is distributed extensively throughout the world. It is extremely virulent in infection in all economically important plants, including grains, pulses, oilseeds, spices, vegetables, and ornamentals. Current studies aim to explore the widened host range of Alternaria species, influenced by strain variability and environmental factors, leading to yield losses and compromised crop quality. Additionally, these studies conducted to understand expanded host range of sunflower Alternaria species on various crops and weeds within the Asteraceae family. The host range study of Alternaria spp. recovered from sunflowers belonged to six Alternaria species collected from different commercial sunflower growing regions of Karnataka. A. alternata, A. tenuissima, and A. helianthi exhibit a broad host range, infecting various plants of the Asteraceae family, including African marigold, safflower, China aster, and Parthenium. Conversely, A. gossypina, A. burnsii, and A. solani specifically infect sunflowers and do not affect other host species. The results of the host range test indicate that Alternaria spp. infecting sunflower can demonstrate pathogenicity towards other hosts as well, especially under favorable conditions. In vitro testing of novel fungicide compounds against the pathogen revealed that Fluopyram 17.7% + Tebuconazole 17.7% 400 SC, applied at concentrations of 100, 250, 500, 750, and 1000 ppm, effectively prohibited the mycelial growth of the pathogen. Conversely, the most favorable outcomes in the field were observed with seed treatment using Fluxapyroxad FS at 1.5 g/kg seed, resulting in the minimal disease severity (7.36% PDI) and highest seed yield (2153 Kg/ha). This was followed by a foliar spray application of Fluopyram 17.7% + Tebuconazole 17.7% 400 SC at 1 ml/L upon disease onset.