First report on clover proliferation phytoplasma related strain associated with Matthiola incana floral virescence in Uttar Pradesh, India.

Abstract

Matthiola incana R. Br. (Fam: Brassicaceae) is an ornamental, commonly known as hoary stock has an extremely fragrant flowers, which blooms in dense clusters in a large variety of colors. During a survey of flower nurseries in March 2019 at Indian Institute of Sugarcane Research campus, Lucknow, floral virescence (MiV) symptoms (Fig. 1 A, B) were observed in M. incana pots with an incidence of over 40%. Leaf yellows symptoms were also observed on a weed Acalypha indica (AiLY) in Matthiola nursery (Fig. 1 C). Nested PCR assays were carried out to detect and identify the possible association of phytoplasmas with MiV and AiLY symptoms. Three each of symptomatic MiV and AiLY samples and two non-symptomatic samples were collected and processed for DNA extraction from the leaf midrib by CTAB method. Hishimonus phycitis (HP) (Hemiptera: Cicadellidae) leafhopper feeding on MiV symptomatic plants was also collected and DNA was extracted. The DNA of 8 symptomatic and 4 non-symptomatic plants and from the 10 leafhopper was used as a template for PCR assays. Phytoplasma specific 16Sr RNA gene specific primers (P1/P7 and 3Far/3Rev; Schneider et al. 1995; Manimekalai et al. 2010) and multilocus genes' specific primer pairs for secA (SecAfor1/SecArev3;SecAfo5r/SecARev2; Bekele et al. 2011), secY (SecYF1(VI)/SecYR1(VI);SecYF2(VI)/SecYR1(VI); Lee et al. 2010) and rp genes (rpFIC/rp(I)R1A; rp(VI)F2/ rp(VI)R2; Martini et al. 2007) were employed as previously described. Amplified products of ~1.3kb, ~600bp, ~1.7kb and ~1.0kb of 16S rRNA, secA, secY and rp genes of phytoplasma were consistently amplified in all the MiV and AiLY samples and in the HP leafhopper. No amplifications were achieved in any of the asymptomatic plant samples. Amplified products of all the four genes of MiV, AiLY and HP isolates were purified, sequenced and submitted in GenBank. Sequence comparison and phylogeny analysis of the sequences of the four genes of MiV, AiLY and HP isolates revealed 99% - 100% sequence identity and clustering with clover proliferation phytoplasma related strains (16SrVI group)(Fig.2 A,B,C and D). The virtual RFLP analysis of 17 restriction endonucleases corresponding to the 16S rDNA sequence of MiV, AiLY and HP phytoplasma strains by pDraw program, assigned them into a novel phytoplasma subgroup strain under 16SrVI group, since its HpaII restriction profile was different to earlier classified 16SrVI subgroups but was very close to16SrVI-E subgroup (GenBank acc. no. AY270156) (Fig 3). Earlier, peanut witches' broom (16SrII-A) phytoplasma was identified associated with M. incana from Italy (Davino et al. 2007). However, the association of clover proliferation phytoplasma (16SrVI) related strain associated with virescence symptom of M. incana is the first report in world. The weed (A. indica) and HP leafhopper were also reported as additional hosts of 16SrVI subgroup related new strain in India, which needs further investigation. The report of a new host and new subgroup of clover proliferation phytoplasma related strain in India is having an epidemiological significance and warrants attention.