First report of sunn hemp Fusarium wilt caused by Fusarium udum f. sp. crotalariae in Taiwan

Sunn hemp (Crotalaria juncea L.) is cultivated for fiber, green manure and fodder in tropical and subtropical countries. It is commonly used as a green manure and a cover crop in Taiwan. In May 2016, wilting of sunn hemp was observed in six farms in Tainan, southern Taiwan. About 13% of plants were symptomatic on the most affected farm. External symptoms varied with severity, ranging from general yellowing of the lower leaves to wilting of the plant. Discoloration of vascular bundles first appeared at the crown and continued upward on one side of the stem. Often, white to pinkish fungal spore masses formed on the stem surface at a later stage. To cultivate the presumed fungal pathogens, the internal freshly-discolored stem tissues were excised and surface sterilized before plating on potato dextrose agar (PDA). Several individual Fusarium isolates with similar morphological characteristics were obtained from diseased tissues. Single spore isolates (F-1 and F-2) were used for further study. To determine pa...