First report of Pythium aphanidermatum and Pythium myriotylum causing root rot on chili pepper (Capsicum annuum L.) in Guizhou, China

Chili peppers (Capsicum annuum L.) are popular globally as a vegetable and condiment and are particularly popular in Guizhou, China. Root rot, the most prevalent soil-borne disease affecting chili peppers, is widespread in Guizhou. In 2023, it was observed in 10–20% of six fields, leading to significant economic losses. Eight strains were isolated from rotten roots of ‘Huaxi’ chili samples to support the need for appropriate pathogen control. Four strains were identified as Pythium aphanidermatum (strains: HSLJ-2, HSLJ-4) and Pythium myriotylum (strains: LDLJY-1, LDLJJ-3) through morphological analysis of sporangia, oospores, antheridia, and oogonia; multi-locus phylogenetic analysis of the internal transcribed spacer and mitochondrial cytochrome c oxidase subunit 1 gene regions; followed by pathogenicity testing using inoculated autoclaved wheat seeds. The two Pythium species were thus identified as novel causal agents of chili pepper root rot in Guizhou, China. •Root rot is a widespread soil-borne disease of chili pepper (Capsicum annuum L.) in Guizhou, China.•In 2023, root rot affected 10–20% of six fields in Huishui and Luodian prefectures, resulting in significant economic losses.•Four strains, isolated from rotten roots, were identified as Pythium aphanidermatum and Pythium myriotylum.•These two Pythium species were found to be the novel causal agents of chili pepper root rot in Guizhou.