Identification and characterization of the phytoplasma associated with lettuce chlorotic leaf rot disease together with its natural reservoirs and leafhopper vectors in China

Abstract

Lettuce (Lactuca sativa L.) is an important vegetable crop that is produced commercially in many countries. Lettuce chlorotic leaf rot disease (LCLRD) was first reported in China in 2005, and in 2008, a severe outbreak in Yongan county occurred with an incidence of approximately 25%, causing significant economic losses. However, the causal agent, insect vector, and alternative hosts of this disease are still unknown. The results from the phylogenetic tree and virtual RFLP patterns of the 16S F2nR2 region showed that the phytoplasma associated with LCLRD was more related to the 16SrI-B subgroup with 99% nucleotide identity and a similarity coefficient of over 0.97. Only leafhopper Macrosteles striifrons could transmit LCLRD phytoplasma to the healthy lettuce plants under experimental conditions. Six out of 52 plant hosts, which were collected from some of the fields, could harbor phytoplasma, but only the chinaberry tree (Melia azedarach) might serve as an alternative host with a similarity coefficient of 1.0 to LCLRD phytoplasma. The other hosts of the head lettuce, pepper, and sweet potato could also harbor the phytoplasma, which had the same KpnI digestion profiles from leafhopper of Deltocephalinar spp.. Interestingly, the phytoplasmas from wild and longleaf lettuce belonged to the subgroup of 16SXII-A, which was not detected in leafhoppers in this study. Identification and characterization of the LCLRD agent, its insect vector, and alternative host plants are useful for developing strategies to control this phytoplasma-induced disease in lettuce.