Molecular characterization of phytoplasma strains associated with brinjal little leaf and screening of cultivated and wild relatives of eggplant cultivars for disease resistance

Brinjal little leaf (BLL) is one of the most important and widespread disease of eggplant associated with a phytoplasma in India. It severely infects eggplant cultivation in India and causes serious economic losses. Severe incidence (8 to 30%) of the disease was recorded in three districts of Uttar Pradesh (Varanasi, Mirzapur and Jaunpur) state of India during 2015 and 2016. A total of 58 symptomatic BLL leaf samples were collected from the surveyed fields and processed for nested PCR assays using phytoplasma-specific primer pairs (P1/P7, R16F2n/R16R2). Pair wise sequence identity and phylogeny analysis of 16S rRNA gene sequences of BLL isolates in the study confirmed association of Ca. P. trifoli (16SrVI group) with the BLL symptomatic samples. Association of similar strain of phytoplasma was identified in Hishimonus phycitis collected in brinjal fields at all the locations, utilizing a similar set of primers pairs as described above. The population of H. phycitis was positively correlated with the incidence of BLL disease in the fields. The phytoplasma indexing of 55 eggplants varieties and 17 wild Solanum species through PCR assays revealed that one eggplant cultivated variety (Uttara) and 17 wild Solanum species were found immune, one resistant (Pusa Ankur) and 12 eggplant varieties/lines were found moderately resistant to BLL. However, all the 17 wild Solanum species were recorded free from phytoplasmas in PCR assays. Further, biochemical analysis of the resistant eggplant varieties showed higher peroxidase and polyphenol oxidase enzymatic activities along with the increased total phenols content. These resistant varieties identified in the present study can be utilized as pre-breeding materials to breed and develop eggplant resistance to BLL phytoplasma disease.