Disease incidence and distribution in surveyed fields of yellow shoot/ dieback disease of papaya (Papaya carica L.) caused by Candidatus Phytoplasma solani

Abstract

Phytoplasma, the pathogen of yellow shoot/ dieback disease of papaya in Thailand was idientified as Candidatus Phytoplasma solani which showed similarity of 16SrRNA gene sequnce to Ca. Phytoplasma solani reference strain (GenBank accession: AF248959) 99.5%. Results of in silico RFLP analysis showed that phytoplasma was classified into subgroup 16SrXII-A. Restriction fractments of AluI, TaqI, BstUI, and BfaI showed distinct finger printings from other subgroups. Classification by phylogenetic tree analysis of 16S-23S rRNA gene and secY gene sequences which classified into that same group with Ca. Phytoplasma solani. Papaya plants about 1 year old were serveyed in two different fields from April to September, 2020 in Khamphaeng Saen district, Nakhon Pathom province. Disease indexs and mortalrity rates within the same field were significantly increased (P < 0.01) in both fields when analysis of variances and comparison of means were peformed by Tukey’s Honestly Significant Different (HSD) test. Disease indexs in filed 1 from April to September, 2020 were 27.64, 30.65, 31.1, 38.57, 41.46 and 48.74, respectively, and in field 2 were 13.23, 14.29, 15.21, 18.52, 19.58 and 23.81, respectively. Mortality rates in field 1 were 2.51, 5.53, 26.13, 29.15, 30.15 and 31.16 respectively and in field 2 were 0.00, 1.59, 12.70, 14.82, 14.82 and 17.99, respectively.