• Kasi Viswanathan

      Articles written in Proceedings – Animal Sciences

    • Comparative study on varietal resistance to rice green leafhoppersNephoteitix virescens (Distant) andN. nigropictus (St⇘l)

      Kasi Viswanathan M B Kalode

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      Employing three different methods, 108 rice varieties were screened for resistance againstN. virescens andN. nigropictus. In mass screening test, 76 varieties suffered significantly less damage byN. virescens, whileN. nigropictus caused less damage to 72 varieties. Ten varietiesviz. Ptb 2, Ptb 18, Ptb 7, Khama 49/8, Ptb 21, DS 1, ARC 6049, Khama 49/2, ARC 10243 and Jhingasail were greatly detrimental to insect bionomics in the studies using first instar nymphs and newly emerged adults. Adult longevity test could be a good criterion to identify the high degree of resistance in the varieties. From an overall assessment, Ptb 18, Ptb 2 and Ptb 7 were identified as highly resistant to both the species.

    • Host specificity of rice green leafhoppers,Nephotettix virescens (Distant) andN. nigropictus (Stål)

      Kasi Viswanathan M B Kalode

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      Intensive host range studies comprising of 55 common weeds and eight cultivated plant species indicated thatNephotettix virescens could survive and breed only on susceptible rice variety, whileN. nigropictus had a wider host range consisting of rice, sugarcane and five graminaceous weeds.N. virescens preferred rice plant both for settling and egg laying whileN. nigropictus showed greater preference toLeersia hexandra than others. Both species selected the host plants by gustation rather than by vision or olfaction.

    • Nature of resistance in selected rice varieties and population fluctuation of green leafhoppers,Nephotettix virescens (Distant) andNephotettix nigropictus (Stål)

      Kasi Viswanathan M B Kalode

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      In multiple-choice tests with 30-day-old plants of resistant and susceptible varieties, both the species of green leafhoppers,Nephotettix virescens (Distant) andNephotettix nigropictus (Stål) exhibited relative non-preference to highly resistant varieties (Ptb 2, Ptb 7 and Ptb 18) both for settling and oviposition. Even when 100 first instar nymphs were caged on individual 25-day-old plants of highly resistant varieties, the plants suffered very low damage and also induced high mortality of nymphs. Different ages of the plants had no influence on the antibiosis mechanism of resistant varieties. Feeding behaviour studies revealed that both the species made more punctures and excreted less honeydew while feeding on resistant varieties than on susceptible ones. Histological studies indicated no mechanical barrier for feeding in resistant varieties.

      Field investigations indicated that resistant varieties viz Ptb 18, Ptb 2 and Ptb 7 harboured less population of green leafhoppers and had relatively nil or very low incidence of tungro virus disease. An year round survey in the rice ecosystem and marshy habitat whereLeersia hexandra grows in abundance revealed that although both the species coexisted in rice fields,Nephotettix nigropictus alone was present in the marshy habitat.

    • Biochemical aspect of varietal resistance to rice green leafhoppers,Nephotettix virescens (Distant) andNephotettix nigropictus (Stål)

      Kasi Viswanathan M B Kalode

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      Biochemical analysis of 4 rice varieties and a weed showed that the total free amino acid content was greater in the susceptible variety TN 1 than in Ptb 2, Ptb 7 and Ptb 18 which are resistant to both the species of green leafhoppers. However, the weed Leersia hexandra the most suitable host ofNephotettix nigropictus, had the lowest amount of free amino acids. No apparent differences were observed in relation to sucrose, glucose and fructose content in the test varieties. Total phenol content was the highest inLeersia hexandra followed by resistant varieties, while it was the lowest in the susceptible rice variety.

      Bioassay of plant extracts in various organic solvents showed that the chloroform and acetone extracts of the resistant variety Ptb 18 were phagodeterrents to either species of green leafhoppers, while the extract of the susceptible variety with the same solvent was phagostimulant. Of the various chemicals bioassayed, sucrose (5%) among the sugars tested, was found to be highly stimulatory for feeding. Among amino acids, serine, alanine and glutamine were feeding stimulatory in nature. On the other hand, most of the amino acid derivatives, all organic acids and phenolic compounds tested exhibited phagodeterrency.

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