Viruses are a major biotic constraint on sweet potato (Ipomoea batatas (L.) Lam) production worldwide. In 2005, 10 to 60% viral disease incidence was observed in sweet potato fields. Symptoms include ring and chlorotic spots, puckering, feathering, vein clearing, and leaf curl with chlorotic specks and pink spots. Cuttings from symptomatic plants were collected from Kerala (two clones), Orrisa (eight clones), and Adrapradesh (three clones) and maintained in an insect-proof glasshouse. Leaves from symptomatic plants were mechanically inoculated to I setosa, I. nil, Nicotiana tabacum, N. benthamiana, Datura stramonium, and Chenapodium quinoa (12 seedlings each). Vein clearing, netting, and leaf distortion were observed in I. setosa and N tabacum 7 days postinoculation, chlorotic spots observed in N. benthamiana, and violet spots and violet margins on leaves observed on I. Nil. No symptoms were observed on D. stramonium and C. quinoa. When scions from the symptomatic sweet potato plants were graft inoculated onto I. setosa, vein clearing, leaf curl, and puckering-like symptoms were observed within 5 days. Mosaic and leaf curling symptoms were also observed on mechanically inoculated N. tabacum. Total nucleic acids isolated from the 33 field-collected sweet potato samples, graft inoculated I. setosa plants, and mechanically inoculated N. tabacum and I. nil plants were used for PCR and reverse transcription (RT)-PCR with geminivirus group specific (2) and potyvirus group specific primers (1). The expected 530-bp and 1.3-kb fragment were generated from the geminivirus and potyvirus primer sets, respectively. Potyvirus alone was detected in 7 of the 33 field-collected plants; geminivirus alone was detected in 7 other plants, while 19 plants contained detectible levels of potyvirus and geminivirus. To further identify the viruses, nested primers specific for the coat protein gene of Sweet potato feathery mottle virus (SPFMV) (CP1S 5′AGT GGG AAG GCA CCA TAC ATA GC 3′, CP1A5′ GCA GAG GAT GTC CTA TTG CAC ACC 3′) (CP2S 5′TCT AGT GAA CGT ACT GAA TTC AAA GA 3′, CP2A 5′ATT GCA CAC CCC TGA TTC CTA AGA 3′) and Sweet potato leaf curl virus (SPLCV) (CP1- 5′ATG ACA GGG CGA ATT CGC GTT TC 3′, CP2- 5′TTA ATT TTT GTG CGA ATC ATA 3′) were designed. I. setosa and N. tabacum were amplified with SPFMV and SPLCV primers and the amplicons of 960 and 764 bp, respectively, obtained were subsequently cloned into pGEM-T Easy vector and sequenced. Nucleotide BLAST analysis revealed that the 960-bp fragment (GenBank Accession No. EF015398.) was 98% identical to two Egyptian isolates of SPFMV (Nos. AJ 515379 and AJ 515378). The nucleotide sequence of the 764-bp products (Nos. EF 151926 and EF15483) from the samples collected from Kerala and Orisa was 95% identical to each other. The sequence identity of EF 15483 with Sweet potato leaf curl Georgia virus (SPLCGV) isolate AF326775. was 91% and identity with China isolate DQ 512731 was 90% The isolate EF 151926 also was 91% identical to the SPLCGV with a high query and alignment score whereas identity with the China isolate was 91% with a low query coverage and alignment score. Phylogenic analysis with MEGA software program also showed the highest sequence similarity with SPLCGV, hence it is concluded that the geminivirus isolate under study is SPLCGV. To our knowledge, this is the first report of identification of SPFMV and SPLCGV occurring on sweet potato in India. Further study is required to understand the consequences of occurrence of these two viruses in India. References: (1) D. Colinet et al. Plant Dis. 28:223 1998. (2) D. D. Deng et al. Ann. Appl. Biol 125:327, 1993.
Yam bean (Pachyrhizus erosus (L.) Urban) is an underutilised tuberous legume crop which has great potential as a food crop. As a root crop, it produces high yields and as a legume, it can produce protein‐rich food. The phenological growth stages of yam bean are first described here using BBCH (Biologische Bundesanstalt, Bundessortenamnt and Chemische Industrie) scale. We have developed a basic and extended numerical BBCH scale for the identification of different phenological growth stages of yam bean. All phenological stages, including germination (stage 0), leaf development (stage 1), formation of side shoots (stage 2), stem elongation (stage 3), tuber formation (stage 4), inflorescence emergence (stage 5), flowering (stage 6), development of pods (stage 7), ripening of pods (stage 8) and senescence (stage 9) are described using the BBCH scale. This BBCH phenological study in yam bean will be helpful for better crop management, crop improvement and characterisation of germplasm. This scale will also be useful for the yield enhancement of this crop as an emerging underutilised tuber crop.
Climate change is an unavoidable phenomenon of natural and anthropogenic origin against which mitigation and adaptation are required to reduce the magnitude of impact and vulnerability, to avoid risk in vegetable farming and to ensure sustainable livelihoods of the agricultural community. Genetic improvement of vegetable crops is an appropriate adaptation strategy to cope with climate change adversities. A combination study of genomics and phenomics provides a clear understanding of the environment's effect on the transformation of a genotype into phenotype. Grafting of a susceptible scion cultivar onto a resistant rootstock is another way of utilising plant biodiversity against climate change. Agronomic practices such as resource conservation technologies, mulching, organic farming, carbon sequestration by cropping systems and agroforestry provide a suite of possible strategies for addressing the impacts of climate change on vegetable production. Protected cultivation and post-harvest technology can be significant practices in facing the challenges of climate change. Weather forecasting models and growth simulation models can be used to predict the possible impact of climate change on vegetable crop production and they also help in framing necessary adaptation measures.
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