First report of storage rot in yam (Dioscorea alata L.) caused by Junghuhnia sp. AK15 in Odisha and its in vitro biocontrol strategies

Dioscorea alata L. is well known for its starchy root tubers, which serve as both a staple food and a source of income in many tropical and subtropical regions, including Odisha. In Odisha, yam tubers hold significant importance in traditional Odia cuisine. However, due to the region’s warm and humid climate, post-harvest decay of the tubers is commonly observed during storage. This decay leads to several serious issues, adversely impacting the agricultural economy and threatening the livelihoods of farmers. A fungal pathogen, Junghuhnia sp. AK15 was identified as being associated with post-harvest rot of yam (D. alata) tubers in Odisha. The incidence of infection was recorded at 27% among the collected tubers. The pathogen was found colonizing both injured and apparently healthy tuber surfaces. Although several fungal pathogens have been reported in association with yam storage rots, this is the first record of Junghuhnia sp. infecting D. alata tubers, making it a new host-pathogen association in Odisha. The isolate exhibited robust growth (100%) on both Sabouraud’s dextrose agar and potato dextrose agar media. Under laboratory conditions, artificial inoculation of the pathogen in the healthy tubers caused the rotting of around 11% tubers among all the test tubers, but caused, on average, 48% of damage in each test tuber within 10 days of incubation. The in vitro antifungal efficacy of petroleum ether and methanolic leaf extracts from sixteen selected medicinal plants was assessed against Junghuhnia sp. AK15 is using the poisoned food technique. The plant extracts effectively inhibited fungal growth, with inhibition rates ranging from 18% to 100%, whereas four tested synthetic fungicides exhibited comparatively lower efficacy, ranging from 18.75% to 80%. Among the botanicals tested, the petroleum ether extracts of Alstonia scholaris and Pongamia pinnata, along with the methanolic extracts of Ageratum conyzoides and Averrhoa carambola, were the most effective at 20 mg/mL. The comparative analysis suggests that plant-based formulations may serve as promising biofungicidal alternatives to conventional chemical fungicides.