Screening for resistance against the green spider mite [Mononychellus tanajoa]
1981
Leuschner, K. (International Institute of Tropical Agriculture, Ibadan (Nigeria))
After a brief introduction on the history, symptoms, yield loss, biology, and behaviour of the green spider mite, the paper outlines the methods for screening cassava varieties for resistance to the pest. In Tanzania and Zanzibar, resistant clones have been identified from local and IITA germ plasm. In Nigeria, at present all available germ plasm and the 1980 seedlings have been evaluated for resistance. For this a scoring system ranging from 1 to 5 has been developed, 1 being highly resistant and 5 highly susceptible; 27 clones from the germ plasm have been identified as less susceptible. At present, these clones are being tested more intensively. The testing program includes: (a) Monitoring the mite population on each clone for 12 months; (b) Monitoring plant growth because the vigorously growing clones seem to withstand green spider mite effectively; (c) Identifying the mechanisms of resistance, such as pubescence (shaved and unshaved leaves are compared in terms of mite population development); and (d) Monitoring reproduction of the female insects (number of eggs, egg and nymph mortality, and length of time needed for each development stage)
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