Resistance levels to the cassava green mite, Mononychellus tanajoa, in cassava germplasm (Manihot esculenta)
AbstractThe cassava green mite (CGM), Mononychellus tanajoa (Acari: Tetranychidae), is one of the main pests of cassava, causing direct damage by sucking the plant’s sap. Although the mite has a wide distribution in Latin America and Africa and a high potential to expand to Asia, limited information is available on M. tanajoa biology and life history parameters on its primary host. In this study, we quantified the levels of resistance of 10 cassava genotypes (i.e., NAT-31, ALT-12, ALT-6, COL-1505, ECU-72, ECU-160, PER-182, PER-335, 60444, CMC-40) based on the mite’s oviposition preference and development time in no-choice and choice bioassays. The genotype NAT-31 significantly differed from other genotypes for M. tanajoa development time and oviposition rate: each stage of the CGM life cycle appeared to be delayed in NAT-31, suggesting that NAT-31 resistance is mediated through a general reduction of CGM fitness on this genotype. Resistance in the remaining genotypes was variable in comparison to a susceptible (control) genotype. ECU-72, a parental line of NAT-31, present a difference related to oviposition preference, development time and sex ratio. These parameters allow the identification of different levels of resistance (antixenotic and antibiosis) when compared to the susceptible genotype. CGM displayed significantly different oviposition preference from the susceptible genotypes. Identification and characterization of resistance to CGM in cassava germplasm might be key to further advance knowledge about natural resistance mechanisms and develop strategies to introgress resistance to CGM in farmer- and industry-preferred cassava varieties.
