RESISTANCE TO BIRD CHERRY-OAT APHID (RHOPALOSIPHUM-PADI L) IN WINTER-WHEAT VARIETIES

In Hungary the bird cherry-oat aphid (Rhopalosipkum padi L.) is the mo st frequent aphid species in winter wheat (Triticum aestivum L.). Esti mations of infestation by R. padi as well as measurements of grain yie ld and thousand-kernel mass were carried out in 26 winter wheat genoty pes in conditions of naturally infested and not infested (protected) c ontrol plots. The experiment was performed in isolated conditions in t wo field cages covered by nets. The aphids overwintered on wheat and g ot into cage, extremely quickly multiplied, therefore there was no nee d to apply any artificial aphid infestation. Highly significant differ ences were demonstrated among genotypes in infestation severity of R. padi as well as in losses of grain yield and thousand-kernel mass. The most resistant variety 'GK Zombor' had 25% infestation, and the most susceptible one 'GK Lili' had 79.2%. The reduction of grain yield of t he most tolerant genotypes ('GK Korany','Downy','Mv 4','Jubilejnaja 50 ', 'Mv 8', 'GK Kincso' and 'GK Zombor') was 26-33%, and that of thousa nd-kernel mass was 23-30%. The most sensitive genotypes ('GK Lili', 'G K Orzse', 'GK Koppany' and 'Mv 13') suffered 58-63% losses in yield, a nd 40-50% in thousand-kernel mass. A close correlation was found betwe en infestation of R. padi in different wheat genotypes and losses of g rain yield (r = 0.7572, P < 0.001). Also there were tolerance differen ces among genotypes even within the same level of infestation. The red uctions of thousand-kernel mass correlated very closely with the reduc tions of grain yield (r = 0.9212, P < 0.001), that makes screening pos sible by reductions of thousand-kernel mass. These results have found application in breeding. The leaf pubescence of the varieties studied did not generally influence the infestation by R. padi.