N. K. Krishna Kumar

Molecular differences in the mitochondrial cytochrome oxidase I (mtCOI) gene and development of a species-specific marker for onion thrips, Thrips tabaci lindeman, and melon thrips, T. palmi Karny (Thysanoptera: Thripidae), vectors of tospoviruses (Bunyaviridae)

A quick and developmental-stage non-limiting method of the identification of vectors of tospoviruses, such as Thrips tabaci and T. palmi, is important in the study of vector transmission, insecticide resistance, biological control, etc. Morphological identification of these thrips vectors is often a stumbling block in the absence of a specialist and limited by polymorphism, sex, stage of development, etc. Molecular identification, on the other hand, is not hampered by the above factors and can easily be followed by a non-specialist with a little training. The mitochondrial cytochrome oxidase I (mtCOI) exhibits reliable inter-species variations as compared to the other markers. In this communication, we present the differences in the mtCOI partial sequence of morphologically identified specimens of T. tabaci and T. palmi collected from onion and watermelon, respectively. Species-specific markers, identified in this study, could successfully determine T. tabaci and T. palmi, which corroborated the morphological identification. Phylogenetic analyses showed that both T. tabaci and T. palmi formed different clades as compared to the other NCBI accessions. The implication of these variations in vector efficiency has to be investigated further. The result of this investigation is useful in the quick identification of T. tabaci and T. palmi, a critical factor in understanding the epidemiology of the tospoviruses, their management and also in quarantine.

One-step DNA fragment assembly for expressing intron-containing hairpin RNA in plants for gene silencing

Double-stranded RNA-mediated RNA interference in plants involves generating a construct expressing intron-containing hairpin RNA (ihpRNA), which usually is a cumbersome, multistep process. Here, we describe a simplified method involving single steps of PCR, restriction, ligation, and transformation for assembling an ihpRNA construct for plant transformation. Our method has several advantages over the currently available ones, viz., wider choice of restriction sites and facility for rapid screening of positive clones, among others. We demonstrate the utility of this approach in assembling the tomato phytoene desaturase gene. This simplified DNA fragment assembly strategy for ihpRNA construction facilitates high-throughput gene silencing in plants.

Studies on the seasonal abundance and control of okra stemfly, Melanagromyza hibisci Spencer (Diptera: Agromyzidae) in India

Incidence of okra stemfly, Melanagromyza hibisci Spencer in India was high (40–60%) in winter months, i.e. during October, November, December and January sowings. Mean maximum and minimum temperature that prevailed 30 days after sowing had significant negative correlation with percentage main stem damage. Carbofuran, phorate, quinalphos and aldicarb, applied at 1 kg per ha reduced damage to main stem at the seedling stage but could not control subsequent damage to petioles. Eurytoma sp., a parasitoid on M. hibisci, had a high density-dependent relationship with its host, and played a significant role in keeping it under control.RésuméL’influence de la mouche okra [Melanagromyza hibisci Spencer] sur les tiges des semailles pendant les mois d’hiver c’est-à-dire en octobre, novembre, décembre et janvier est ‘élevé’ de 40–60% de plantes parasitées. La température moyenne maximale et minimale qui prevant 30 jours après les semilles a montre une corrélation négative significative par rapport au pourcentage des dommages sur la tige centrale carbofuran, quinalphos, phorate et aldicarb répandus à raision d’un kilo/hectare, a réduit les dommages sur la tige centrale de la jeune poussé mais n’a en aucune influence sur ceux des pétioles. Eurytoma sp. un parasite de la mouche M. hibisci, très dépendante de son hôte, à joue un rôle significatif pour le contrôler.

Evaluation of time of insecticidal application on the control of leafhopper, Amrasca biguttula biguttula Ishida (Cicadellidae: Homoptera) and aphid, Aphis gossipii Glover (Aphididae: Homoptera) on okra

Studies on critical time of insecticidal protection in relation to damage by aphid, Aphis gossipii Glover and leafhopper, Amrasca biguttula biguttula Ishida on plant growth and yield of okra revealed that 21–42 days after germination, was the most critical time prior to fruiting. Application of carbofuran at the time of sowing was redundant. Effective plant protection 21–42 days after germination resulted in lowest leafhopper and aphid infestation and subsequently the highest benefit to cost ratio.RésuméDes études sur le temps critique de la protection d’insecticide en relation avec le ravage par des pous et des sauteurs de feuilles sur la croissance et le rendement de la plante en okra a révélé que 21–42 jours après la germination, d’être le plus critique avant la phase fruitière. L’application de carbofuran au temps des semilles était redondant. Dés méthodes effectives de la protection de plante 21–42 joure après la germination avait pour résultat la moindre infestation des sauteure de feuilles et des pour et par la suite le phis haut avantage économique.