HOST RESISTANCE TO THE LEAFHOPPER, AMRASCA DEVASTANS (DISTANT) IN COTTON, GOSSYPIUM SPP.
Mar 13, 2017

Crop Protection WCRC Croprotection-Asia WCRC1
Abstract                                                                         Back to Table of contents

The cotton leafhopper, Amrasca (Empoasca) devastans (Distant) is a key pest on Upland cotton in India and an upsurge of the pest has been noticed in recent years.  The nymphs and adults desap the leaves resulting in hopperburn, drying and shedding of leaves, reduction in plant stand and loss in yield.  The management of this pest is made difficult by the development of resistance to insecticides and resurgence caused by indiscriminate applications of synthetic insecticides.  Among cultivated cottons, Gossypium arboreum and G. herbaceum are resistant to the leafhopper.  Resistance from these species were transferred to G. hirsutum cottons.  Among wild cottons, G. tomentosum, G. armourianum and G. raimondii are resistant to the leafhopper.

Morphology of cotton plays an important role in imparting resistance to leafhopper.  Hairiness of leaf, toughness of leaf veins, thickness of leaf lamina, length and angle of insertion of leaf hair are associated with resistance.  Non-preference for oviposition is because of high concentrations of allomones like tannins and free gossypol.  Non-reducing sugars, tannins, free gossypol and silica are key factors that influence the antixenosis mechanism.  Anti-nutritional factors like total phenols and epicuticular waxes exert significant adverse effects on leafhopper survival and oviposition.  In G. hirsutum, G. tomentosum and G. arboreum varieties, hairiness and leafhopper resistance are governed by a dominant gene.  The available resistance needs to be exploited both by conventional methods and new innovative techniques.  Cumulative resistance derived from diverse gene pools will be more lasting and there is need to identify new genes that govern the resistance.

Conclusions

For cotton farmers, use of leafhopper resistant varieties is economically cheap and reduces the need to use high cost inputs like insecticides. Given the problems associated with reliance on pesticides, the selection of insect resistant varieties is more pressing than ever before.  Even partial resistance may be useful as it may enhance the effect of natural enemies and possibly reduce the need for other control tactics.  Concerted efforts are essential to breed newer varieties as the present day cultivars are of narrow genetic base which would make them vulnerable to other pests and development of biotypes of leafhopper. Cumulative resistance, derived from diverse gene pools will be more lasting and research attempts should be directed in this line. For continued success of host resistance, research programmes should be directed to identify new gene(s) that impart resistance. Chemical ecology which encompasses the role of varieties that influence the host plant-insect interactions should be directed to identify the role of phytochemicals vis-a-vis host selection by leafhopper. Biotechnology, through the use of genetically engineered transgenic plants offers greatest scope and is one of the virgin areas of research with a lot of potential.

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