Abstract:
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) leads to extensive economic
damage to wheat (T riticum aestivum L.) and barley (Hordeum vulgare L.) in Kenya This pest
first appeared in Kenya in 1995. Pesticide control of Russian wheat aphid (RWA) is difficult
because severe infestation makes the leaves to tightly roll protecting the aphid from contact
insecticides, while the use of systemic insecticides is expensive. The most effective method of
RWA control is, therefore, the development of RWA resistant cultivars. Breeding of RWA
resistant cultivars is further complicated due to presence of RWA biotypes. There are at least
eight known biotypes worldwide. Genetic information is necessary to effectively develop adapted
resimnt cultivars. This study was initiated to determine inheritance of resistance of selected
bread wheat culfivars to RWA Inheritance of RWA resistance and allelic relationships among
three sources of resistance was studied in parents, FL F; and backcross populations of wheat
crosses involving three resistant (RWAPC9, RWAPC16 and KM21/RWAPC16) and one
susceptible (Kwale) cultivars at Njoro, Kenya‘ Seedlings were infested at one leaf stage with five
fourth-instar Russian wheat aphids at the base of the plant and were scored for damage on a
visual scale of 1 to 9 afier l4 days of infestation. The segregation data from three crosses between
the resisant and susceptible cultivars indicated that RWA resistance was inherited as monogenic
dominant trait (3R:lS in F2 and lR:lS in backcross). Segregation data (l5R:1S) from crosses
among three resistant cultivars indicated that two non-allelic loci were involved in the expression
of resistance to Russian wheat aphid. No reciprocal difference was detected in any cross studied.
It was recommended that two resistance genes should be transferred through backcross breeding
into locally adapted susceptible cultivars. Pyramiding of two independent resistance genes could
enhance the resistance in the adapted cultivars.
