Incidence, symptomatology, molecular detection and yield loss assessment of brinjal little leaf disease in Assam, India

A roving survey was conducted in seven major brinjal growing districts of Assam (India) namely Biswanath, Darrang, Golaghat, Jorhat, Nagaon, Sibsagar and Sonitpur during 2018–2020 to study the incidence, symptomatology, molecular detection, predominant leafhoppers in the brinjal fields, and yield loss assessment for the brinjal little leaf disease. Infected plants exhibited symptoms like severe reduction in leaf size, stunted growth, yellowing of leaves, phyllody and witches’ broom. The highest average of disease incidence (23.63%) was recorded in Sibsagar district and the lowest (3.62%) in Darrang district. Among the different varieties grown, the highest disease percentage (25.45%) was observed in the variety Basudha in the Dishangmukh area of Sibsagar district and the lowest (3.33%) in the variety Pusa Hybrid-5 in Kharupetia area of Darrang district. PCR and 16S rRNA gene sequencing analysis confirmed the presence of a phytoplasma enclosed in the clover proliferation group (16SrVI) in brinjal and other plant species. The disease adversely affected both growth and yield of brinjal plants according to the stages of growth at infection time. Early infection had drastic effects as compared to infection at later stages of plant growth. The highest reduction of fruit yield amounting to 94.79% over healthy plants was recorded in the infected plants at 65–70 days after sowing. Among the 4 leafhopper species collected, only Hishimonus phycitis tested positive in PCR analysis. Other than brinjal, symptomatic Datura stramonium and Solanum violaceum present around the symptomatic brinjal fields resulted positive for the same phytoplasma, indicating them as potential reservoir hosts of brinjal little leaf phytoplasma in Assam.