Isolation, identification and pathogenicity of two root rot pathogens Fusarium solani in citrus

Root rot is a prevalent soil-borne fungal disease in citrus. Citron C-05 ( Citrus medica ) stands out as a germplasm within Citrus spp. due to its complete resistance to citrus canker and favorable characteristics such as single embryo and easy rooting. However, Citron C-05 was found to be highly susceptible to root rot during cultivation, with the specific pathogens previously unknown. In this study, four candidate fungal species were isolated from Citron C-05 roots. Sequence analysis of ITS, EF-1α , RPB1 , and RPB2 identified two Fusarium solani strains, Rr-2 and Rr-4, as the candidates causing root rot in Citron C-05. Resistance tests showed these two pathogens increased root damage rate from 10.30% to 35.69% in Citron C-05, sour orange ( Citrus aurantium ), sweet orange ( Citrus sinensis ) and pummelo ( Citrus grandis ). F. solani exhibited the weak pathogenicity towards trifoliate orange ( Poncirus trifoliata ). DAB staining revealed none of reddish-brown precipitation in the four susceptible citrus germplasm after infection with F. solani , while trifoliate orange exhibited significant H 2 O 2 accumulation. Trypan blue staining indicated increased cell death in the four susceptible citrus germplasm following infection with these two pathogens but not in trifoliate orange. These findings provide a comprehensive understanding of citrus root rot and support future research on the mechanisms of root rot resistance in citrus.