First report of a 16SrII‐V phytoplasma associated with peanut phyllody in India

Abstract

Peanut (Arachis hypogaea, Fabaceae), also known as groundnut, is an important oilseed and food legume crop cultivated in a wide range of climatic conditions across the globe. India is the second largest producer of peanut in the world after China (Food and Agriculture Organization of the United Nations, 2022). Peanut plants exhibiting phyllody, little leaf, excessive shoot proliferation, negative geotropism of pegs with absence of pod formation were observed in February 2021 in Pune, Maharashtra, India (Figures 1, 2). The diseased plants could be easily identified in the field due to their distinct appearance, suggestive of the presence of phytoplasma. Eight peanut fields were surveyed and the overall average disease incidence was four percent. Ten diseased and four asymptomatic plants were sampled to identify and characterise the associated phytoplasma. DNA was extracted from leaf petioles (100 mg) using DNeasy® Plant Mini Kit (Qiagen, Germany). The extracted DNA was subjected to PCR using P1/P7 universal primers (Deng & Hiruki, 1991; Schneider et al., 1995). Products from the first round PCR were used in nested PCR with R16F2n/R2 primers (Gundersen & Lee, 1996). Amplicons of the expected size, c. 1.8 kb and 1.2 kb were obtained in all diseased samples in PCR and nested PCR assay, respectively. No amplification was recorded in asymptomatic samples. The sequences of the nested PCR products were identical to each other and the sequence was deposited in GenBank (Accession No. ON139214). A BLASTn search showed more than 99% sequence identity with phytoplasma sequences including peanut witches’-broom (JN681274; L33765), Desmodium ovalifolium witches’-broom (MK956144), soybean witches’-broom (MW115943) and cowpea phyllody (MZ831318). The peanut phyllody phytoplasma sequence clustered with selected sequences belonging to the 16SrII phytoplasma group following phylogenetic analysis using the neighbour-joining method (MEGA X program) (Figure 3). Virtual RFLP using iPhyClassifier (https://plantpathology.ba.ars.usda.gov/) demonstrated that the peanut phyllody phytoplasma is affiliated to group 16SrII, subgroup V. Phytoplasmas belonging to subgroup 16SrII-V have been recently reported to infect legumes such as mungbean and soybean in Taiwan (Chen et al., 2021; Wang et al., 2021). To our knowledge, this the first report of a 16SrII-V phytoplasma associated with phyllody in peanut as well as the first report of the occurrence of a 16SrII-V phytoplasma in India. The finding is of epidemiological importance as the phytoplasma infection reduces pod formation leading to yield and economic losses for farmers. Moreover, infected peanut plants could serve as natural reservoirs of the phytoplasma aiding its spread to other legume, vegetable and flower crops cultivated in the vicinity. The authors thank the Director, ICAR-IARI, New Delhi and Head, ICAR-IARI, RS, Pune for providing lab facilities.