RESUMO
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 (ï¾1.25 kb) and secA (ï¾600 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 (ï¾1.25 kb and ï¾600 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.
RESUMO
The present investigation was focussed on regeneration, evaluation and screening of somaclones for yellow leaf disease (YLD) resistance using in vitro mutagenesis from a popular susceptible sugarcane variety Co86032 using four chemical mutagens at three levels of concentration (sodium azide (SA) at 0.5 mg L-1, 1.0 mg L-1, 1.5 mg L-1; sodium nitrite (SN) at 3 mg L-1, 5 mg L-1, 7 mg L-1; ethyl methane sulphonate (EMS) at 0.6 µ ML-1, 0.8 µML-1, 1.0 µ ML-1 and 2,4 D at 4 mg L-1, 5 mg L-1, 6 mg L-1). A total of 1138 tissue culture seedlings obtained were evaluated for virus resistance both in natural field conditions and in controlled greenhouse condition after aphid vector transmission and presence or absence of virus was observed by visual screening and reverse transcription-polymerase chain reaction method. Four out of 207 asymptomatic plants (16T22, 16T23, 16T29 and 16T31) were devoid of virus coat protein band and were considered to be YLD resistant. The obtained resistance somaclones showed inferior yield traits so they have to be exploited as parents in hybridization programmes with commercial varieties to impart YLD resistance ultimately yielding agronomically superior YLD-resistant varieties in sugarcane.
Assuntos
Resistência à Doença/genética , Luteoviridae/patogenicidade , Doenças das Plantas/genética , Imunidade Vegetal/genética , Saccharum/genética , Animais , Afídeos/virologia , Proteínas do Capsídeo/genética , Proteínas do Capsídeo/metabolismo , Células Clonais , Resistência à Doença/efeitos dos fármacos , Metanossulfonato de Etila/farmacologia , Expressão Gênica , Insetos Vetores/virologia , Luteoviridae/genética , Luteoviridae/crescimento & desenvolvimento , Mutagênese , Mutagênicos/farmacologia , Fenótipo , Doenças das Plantas/imunologia , Doenças das Plantas/prevenção & controle , Doenças das Plantas/virologia , Imunidade Vegetal/efeitos dos fármacos , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/imunologia , Folhas de Planta/virologia , Técnicas de Embriogênese Somática de Plantas , Regeneração/genética , Regeneração/imunologia , Saccharum/efeitos dos fármacos , Saccharum/imunologia , Saccharum/virologia , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/imunologia , Plântula/virologia , Azida Sódica/farmacologia , Nitrito de Sódio/farmacologiaRESUMO
Methyleugenol is naturally occurring substance in oils and fruits and in various foods as flavoring agent. Effect of this methyleugenol in inhibiting A. flavus colonization and aflatoxin production on peanut pods and kernels has been studied. Spray of methyleugenol (0.5%) on peanut pods and kernels checked the colonization of A. flavus and aflatoxin synthesis. This chemical can be used as both prophylactic or post infection spray on peanut pods before storage. It is the first report on the inhibition of A. flavus by methyleugenol on peanut.
