Tandemly duplicated genes encoding polygalacturonase inhibitors are associated with bruchid (Callosobruchus chinensis) resistance in moth bean (Vigna aconitifolia)

Bruchids are stored-grain insect pests responsible for serious seed loss in legume crops. A previous study using an F₂ population (F2OA) derived from a cross between wild moth-bean (Vigna aconitifolia [Jacq.] Maréchal) accession TN67 (resistant) and cultivated moth-bean accession ICPMO056 (susceptible) revealed that resistance to the azuki bean weevil (Callosobruchus chinensis L.) in TN67 was regulated by a single gene located in the major quantitative trait locus-qVacBrc2.1. In this study, qVacBrc2.1 was finely mapped and candidate genes in this locus were identified using F2OA and another large F₂ population (F2NB) derived from the cross mentioned previously. In contrast to the previous study, segregation analysis in the F2NB population revealed that resistance against this pest was controlled by two genes. Furthermore, the addition of novel markers to qVacBrc2.1 and reanalysis of the QTL in the F2OA population demonstrated that qVacBrc2.1 constituted two linked QTLs-qVacBrc2.1-A and qVacBrc2.1-B. The presence of qVacBrc2.1-B was verified using the population F2NB. Comparative genomics using three Vigna spp. strongly suggested the presence of two tandemly duplicated genes, VacPGIP1 and VacPGIP2, which encoded polygalacturonase inhibitors (polygalacturonase-inhibiting proteins) as the candidates for conferring resistance, but only VacPGIP1 could be successfully cloned and sequenced. The alignment of VacPGIP1 coding sequences of TN67 and ICPMO056 revealed eight single nucleotide polymorphisms, three of which altered the amino-acid sequence of the predicted domains of polygalacturonase inhibitors in ICPMO056. Overall, these findings indicate that VacPGIP1 and VacPGIP2 regulated C. chinensis resistance in TN67.

Efficacy of Ocimum tenuiflorum essential oil as grain protectant against coleopteran beetle, infesting stored pulses

In the present investigation, essential oil (EO) of Ocimum tenuiflorum and its principal constituent (eugenol) was evaluated for its toxicity and mode of action against Callosobruchus maculatus. Furthermore, fumigant toxicity and germination studies on the application of O. tenuiflorum EO and eugenol against C. maculatus on different pulses was also studied. Fumigant activity studies revealed that EO toxicity was significantly (p < 0.05) influenced by concentration and exposure time. In fumigant toxicity assay without food, O. tenuiflorum EO and eugenol showed LC50 value of 278.6 and 256.5 µL/L air, respectively, at one hour exposure. Further, O. tenuiflorum EO displayed fumigant toxicity via inhibiting acetylcholinesterase activity. Pulses treated with O. tenuiflorum EO showed 70% of C. maculatus mortality at 250 µL/L air concentration after 24 h. Furthermore, these treatments didn't affect the seed viability of the pulses tested. Hence, the application of O. tenuiflorum EO has potential scope as a botanical insecticide.

Bruchid beetle ovipositioning mediated defense responses in black gram pods

BACKGROUND

Black gram [Vigna mungo (L)] seeds are a rich source of digestible protein and dietary fibre, both for human and animal consumption. However, the quality and quantity of the Vigna seeds are severely affected by bruchid beetles during storage. Therefore, analyses of the expression of the bruchid induced transcript dynamics in black gram pods would be helpful to understand the underlying defense mechanism against bruchid oviposition.

RESULTS

We used the RNAseq approach to survey the changes in transcript profile in the developing seeds of a moderately resistant cultivar IC-8219 against bruchid oviposition using a susceptible cultivar T-9 as a control. A total of 96,084,600 and 99,532,488 clean reads were generated from eight (4 each) samples of IC-8219 and T-9 cultivar, respectively. Based on the BLASTX search against the NR database, 32,584 CDSs were generated of which 31,817 CDSs were significantly similar to Vigna radiata, a close relative of Vigna mungo. The IC-8219 cultivar had 630 significantly differentially expressed genes (DEGs) of which 304 and 326 genes up and down-regulated, respectively. However, in the T-9 cultivar, only 168 DEGs were identified of which 142 and 26 genes up and down-regulated, respectively. The expression analyses of 10 DEGs by qPCR confirmed the accuracy of the RNA-Seq data. Gene Ontology and KEGG pathway analyses helped us to better understand the role of these DEGs in oviposition mediated defense response of black gram. In both the cultivars, the most significant transcriptomic changes in response to the oviposition were related to the induction of defense response genes, transcription factors, secondary metabolites, enzyme inhibitors, and signal transduction pathways. It appears that the bruchid ovipositioning mediated defense response in black gram is induced by SA signaling pathways and defense genes such as defensin, genes for secondary metabolites, and enzyme inhibitors could be potential candidates for resistance to bruchids.

CONCLUSION

We generated a transcript profile of immature black gram pods upon bruchid ovipositioning by de novo assembly and studied the underlying defense mechanism of a moderately resistant cultivar.