Leaf Sheath Rot of Welsh Onion Caused by Rhizoctonia spp. in Iwate Prefecture and Its Pathogens

Abstract

In the summer of 2019 and 2020, leaf sheath rot and concomitant outer leaf death symptoms were found on four commercial Welsh onion fields in Iwate, Japan. Nine isolates obtained from diseased plants were identified as Rhizoctonia solani anastomosis group (AG)-1 IB, AG-4 HG-I, AG-4 HG-II, AG-4 hybrid subgroup between HG-I and HG-II, AG-5, binucleate Rhizoctonia AG-A, and Waitea circinata var. zeae (Asexual morph: Rhizoctonia zeae), based on cultural morphology, temperature-dependent growth characteristics, hyphal anastomosis reaction, and genome analysis using specific PCR, and rDNA-ITS sequences. In pathogenicity tests on Welsh onion seedlings, isolates of binucleate Rhizoctonia AG-A and W. circinata var. zeae were less virulent than R. solani AG-1 and AG-4 isolates. To the best of our knowledge, this is the first report of leaf sheath rot on Welsh onion caused by binucleate Rhizoctonia AG-A and W. circinata var. zeae.