INHERITANCE OF PARTIAL RESISTANCE TO MYZUS-PERSICAE IN LETTUCE

The genetics of partial resistance of lettuce to Myzus persicae was st udied using F-1 and F-2 generations of two crosses between a susceptib le and partially resistant accession (Norden x Batacer and Liba x Nord en) and three crosses in which both parents were partially resistant ( Batavia la Brillante x Batacer, Batacer x Liba and CGN4741 x Batacer). Partial resistance to M. persicae inherited quantitatively, without i mportant dominance effects. Only in the cross Batacer x Liba were sign ificant departures of the F-1 and F-2 from the midparent found, which were probably caused by epistatic effects. Reciprocal F(1)s had simila r resistance levels, indicating the absence of cytoplasmic or other ma ternal effects. Estimates of broad-sense heritability ranged from 0.34 to 0.61. The results indicated that lines with an improved resistance level can be obtained from crosses between partially resistant access ions, preferably by line selection or the application of indirect mark er aided selection.