Background: The YMD is one of the serious viral diseases in blackgram and is being transmitted by whitefly (Bemisia tabaci). The development of YMV resistant blackgram varieties is one of the important aspects for sustainable blackgram production. Marker assisted selection and genetic transformation could be utilized in developing YMV resistant blackgram genotypes.
Methods: We attempted to map the QTLs governing YMV resistance in blackgram employing parents i.e., PBG32 (susceptible) and PU31 (resistant). Parental polymorphic studies were conducted using 147 SSR markers and genotyping and phenotyping data were used for QTL mapping. The markers, CEDG097 and CEDG172 that flanked to qYMV1 QTL were validated in 25 blackgram genotypes.
Result: SSR markers showed 16% polymorphism between the parents. By using F2 genotypic data, genetic linkage map was constructed and total genetic map length observed was 335.47 cm. Single QTL (qYMV1) for YMV tolerance was detected and located between markers CEDG097 and CEDG172 with LOD score value of 2.76. The PVE by qYMV1 is 13.10% and the QTL is tightly linked (0 cM) to the left flanking marker CEDG97, which denotes a major QTL. Genotyping of the 25 known blackgram genotypes employing CEDG097 and CEDG172 markers, CEDG097 showed 91% linkage in known resistant and susceptible varieties to the YMV disease reaction and CEDG172 exhibited 74% linkage in known varieties to the YMV disease reaction. The resistance alleles (PU31 allele) of both markers i.e. CEDG097 and CEDG172 were recorded in VBN7, LBG922, LBG933 and TBG130-1 hence, these genotypes can be considered as potent YMV resistant varieties and also can be used as donor parents in resistance breeding programmes.
Pearl millet [Pennisetum glaucum (L).R.Br.] also known as bajra, is one of the oldest millets and is cultivated in dry regions of arid and semi-arid tropics where no other cereal can be successfully grown. Pearl millet cultivation in India accounts for about two-thirds of millet production and is the fourth most cultivated food crop after rice, wheat and maize in India (Reddy et al. 2021a). In February 2021, the typical symptoms of stunting, phyllody and little leaf were observed after 25-30 days after sowing pearl millet seeds at Agricultural Research Station in Perumallapalle, Tirupati, India (Fig.1 A-C). The disease incidence was recorded up to 20% in the sampling regions. Total DNA was extracted from two symptomatic and two asymptomatic plant samples using CTAB DNA extraction method (Murray and Thompson, 1980). The extracted DNA was amplified in direct PCR and nested PCR assay using phytoplasma 16S rRNA universal primer pairs P1/P7 and R16F2n/R16R2 (Gundersen and Lee.1996) and secA gene with secAfor1/SecArev3 and SecAfor2/SecArev3 primer pairs (Hodgetts et al. 2008). 16SrRNA (1.25 kb) and secA (600 bp) gene amplicons were obtained from two symptomatic samples by nested PCR. No amplicons were produced with DNA from healthy leaf samples. Nested PCR amplified products (1.25 kb and 600 bp) from the symptomatic samples corresponding to the F2nR2 region of 16S rRNA and secA were directly sequenced at automated DNA sequencing facility (Eurofin Genomics India Pvt., Ltd Bangalore) and sequence data was deposited to NCBI GenBank with accession number ON005559 and ON067810. BLAST analysis revealed that pearl millet phytoplasma strain shared 100% sequence identity in 16Sr RNA and secA genes to ‘Canditatus Phytoplasma aurantifolia’ related strains (Acc. Nos. OM616883 and MT952965) from India. The subgroup was identified as 16SrII-D using the iPhyClassifier based on the virtual RFLP pattern derived from the query 16S rDNA F2nR2 fragment (Zhao et al. 2009). The virtual RFLP pattern is similar to the reference pattern of 16SrII-D (Y10096) with similarity coefficient 1.00. Phylogenetic analysis of 16S rRNA and secA gene sequences using MEGA version 7.0 revealed that the pearl millet phytoplasma strain clustered with ‘Ca. P. aurantifolia’ isolates of 16SrII-D subgroup. (Fig.1D-E) Earlier, one of 16SrI-B-phytoplasma strain (HM 134245) associated with green ear disease of pearl millet was reported in North India (Kumar et al. 2010). In this study, we reported the association of 16SrII-D subgroup phytoplasma with little leaves and witches’-broom disease of pearl millet in South India. Phytoplasmas belonging to the 16SrII-D subgroup have a wide range of hosts, including the agricultural and horticultural crops (Reddy et al., 2021b). Hence, this is the first report of ‘Ca. P aurantifolia’ infection in bajra in South India. The increase in the spread of 16SrII-D sub group phytoplasma diseases and the expansion of the host range strongly suggest further studies on the epidemiology of the dynamic dissemination of this disease in India.
16SrII-D group Martynia annua (Martyniaceae) is a small, herbaceous annual plant distributed across India. It is used for the treatment of epilepsy, tuberculosis, sore throats and wounds (Kaushik et al., 2021). In August 2021, symptoms of witches' broom and little leaf were observed in M. annua in the Anantapur forest area, Andhra Pradesh. India. Leaves were collected from two diseased and two symptomless plants (Figures 1 and 2). Total DNA was extracted from 100 mg of leaf F I G U R E 1 Martynia annua plant showing witches' broom and little leaf symptoms This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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