Research News

Identification and characterization of cardamom vein clearing virus, a novel aphid-transmitted nucleorhabdovirus

The vein clearing (kokke kandu) disease suspected to be caused by an unknown virus is an important production constraint of cardamom in India.In the present study the causal virus was transmitted from infected to healthy cardamom plants through the aphid, Pentalonia caladii. Small RNA (sRNA) and RNA sequencing (RNA-seq) of the aphid-inoculated plant showed several nucleorhabdovirus-like contigs. The sRNA and RNA-seq results were verified through reverse transcription polymerase chain reaction (RTPCR) using total RNA from infected plant and primers designed from the contigs. The cloning and sequencing of RT-PCR products resulted in a sequence of 13,392 bases that showed similarities to nucleorhabdoviruses. The sequenced region contained six open reading frames in the order 3’-N-P-P3-M-G-L-5′ and showed nucleotide sequence identities ranging from 37 to 55% with nucleorhabdoviruses indicating its distinct nature for which we propose the name, cardamom vein clearing virus. A reliable RT-PCR and SYBR Green-based real-time RT-PCR assays were developed for the detection of the virus that will aid in the identification and propagation of virus-free cardamom plants.

Plant morphological traits associated with field resistance to cardamom thrips (Sciothrips cardamomi) in cardamom (Elettaria cardamomum)

Cardamom thrips (Sciothrips cardamomi) is a major insect pest of cardamom(Elettaria cardamomum) causing severe economic losses to the crop in all cardamom producing countries. The present control measures rely heavily on chemical insecticides,which in addition to increased input costs also lead to pesticide residues in the produce and environmental hazards. Although the crop is of high commercialvalue, limited efforts have been made to identify sources of resistance to this major pest. Exploiting sources of resistance along with integrated pest management tactics will help to reduce pesticide usage in this crop promoting sustainable production.The present study aimed at identifying sources of resistance against cardamom thrips and the associated plant morphological traits conferring resistance against the pest. Field screening of 180 cardamom germplasm accessions for 3 years at Appangala, Karnataka, India, resulted in identification of eight accessions resistant to cardamom thrips. Differences in panicle type and the nature of adherence of leaf sheath to the pseudostem explained a significant amount of the variance in resistance and therefore are likely to play a major role in conferring resistance against this pest.Field screening of 180 cardamom germplasm accessions for 3 years at Appangala, Karnataka, India, resulted in identification of eight accessions resistant to cardamom thrips. Differences in panicle type and the nature of adherence of leaf sheath to the pseudostem explained a significant amount of the variance in resistance and therefore are likely to play a major role in conferring resistance against this pest. Multiple regression analysis of the different traits indicated that accessions with prostrate panicles having leaf sheath loosely adhered to the pseudostems were found to have significantly less thrips damage, when compared with other panicle and leaf sheath types. However, persistence of flower bract did not have a significant additive effect on imparting resistance against thrips. Metabolomic analysis of the accessions may provide further insight into the existence of supplementary biochemical mechanisms, if any, in imparting resistance. The identified traits and accessions can be exploited in future breeding programmes
for developing thrips resistant cardamom varieties.

Characterization of Beauveria bassiana associated with allspice auger beetle

The incidence of auger beetle, Sinoxylon anale Lesne (Bostrichidae: Coleoptera), a destructive pest of cosmopolitan occurrence is reported for the first time on allspice trees from Kozhikode, Kerala. The insects bored through the basal region of fresh twigs resulting in dieback symptoms. Morphological characterization and sequencing of a partially amplified fragment of the mitochondrial CO1 gene revealed the insect to be Sinoxylon anale. An entomopathogenic fungus was isolated from infected cadavers of S. anale that was identified as Beauveria bassiana (Bals.-Criv.) Vuill., sensu stricto (s.s) (Ascomycota: Hypocreales) based on morphological and molecular studies. The fungus was virulent against adult beetles and this is the first record of B. bassiana naturally infecting S. anale. The findings were published in the Journal of Invertebrate Pathology

Biocontrol efficacy of Streptomycetes against Sclerotium rolfsii

Sclerotium rolfsii is a soil borne pathogen, which commonly occurs in black pepper nurseries causing root rot. Biocontrol agents viz., Trichoderma harzianum and Streptomycetes spp. were tested against the pathogen under in planta challenge inoculated conditions. The results indicated that IISRBPAct 1 (Streptomyces sp.) was very effective in reducing the number of roots infected by Sclerotium rolfsii. The isolate was found to enhance the growth of plants as evidenced from the plant growth parameters

Sequencing of full-length transcripts in black pepper and small cardamom

Survey of transcriptomes by direct sequencing of fulllength transcripts in the range of 1 to 3 kb was done in black pepper and small cardamom using SMRT Sequencing with PacBio RS II System. Using the PacBio protocol, we obtained 53689 reads of insert (ROIs) with mean read length of 2378 bp in black pepper and 56439 reads of insert with mean read length of 2267 bp in small cardamom. Numbers of polished high-quality isoforms recovered from black pepper and small cardamom transcriptomes were 8,380 and 9,270 respectively. Potential coding regions were also predicted from these sequences.

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