Identification of phytoplasmas associated with Bunchy Top disease of papaya in Colima, Mexico

Abstract

Phytoplasmas, rickettsiae and viruses have been detected in papaya plants with Bunchy Top disease (BT). In 2019, papaya plants with BT-like symptoms were observed in agroecosystems of Colima, Mexico. In order to determine the BT-associated phytoplasmas species or subgroups, asymptomatic and symptomatic plants were collected from papaya agroecosystems in four papaya producer municipalities, as well as papaya-associated weeds and insects. Phytoplasma detection and identification was conducted by PCR, sequencing and phylogenetics of translocase subunit SecA (secA) and 16S ribosomal RNA (16Sr) genes, and PCR-RFLPs in vitro and in silico for 16Sr gene. In papaya, phytoplasma groups 16SrI (subgroup AF), 16SrX, and 16SrXIII were identified in 2.08% (4 out of 192) symptomatic samples. The results of RFLPs in silico analysis showing the presence of 16SrX and 16SrXIII (sub)groups. In papaya-associated weeds and insects, phytoplasmas of group 16SrI (subgroups AF and B) were identified in 1.7% (3 out of 174) and 1.1% (2 out of 185) evaluated samples, respectively. Phytoplasma-carrying weeds were Amaranthus palmeri and Echinochloa colona; positive insects were Micrutalis calva and Balclutha mexicana. It is the first time that phytoplasmas 16SrI-AF, 16SrX y 16SrXIII are associated with Bunchy Top disease of papaya in agroecosystems from Colima, Mexico. Phytoplasmas 16SrX y 16SrXIII are first reported in papaya plants at the world level and in Mexico, respectively. Phytoplasma-carrying weeds and insects are new records as natural reservoirs and potential vectors.