Top-cross vs. poly-cross as alternative to test-cross for estimating the general combining ability in potato

Test-crosses for estimating combining ability in potato although useful are difficult to make being labour intensive and time consuming, and due to the problem of sterility. The objective of the present study was to test methods for estimating general combining ability (GCA) of parents based on fewer matings. The GCA of 12 females estimated based on matings with specific single testers (top-cross) and three types of bulk pollen (poly-cross) were compared with those estimated by 72 (12 x 6) test-crosses, using common testers in three types of matings. The study was conducted for 2 years at each of the two locations representing short-days subtropical conditions in plains and long-days temperate conditions in hills of India. Analysis of variance of test-crosses showed that both general and specific combining ability effects were important for tuber yield, late blight resistance as well as general impression, the characters studied. Correlation coefficients among three types of matings showed that bulk pollen matings had poor effectiveness in predicting the GCA of the females, whereas matings with selected individual testers resulted in GCA estimates similar to those based on six testers. Thus use of top-cross involving selected tester could substantially reduce the number of matings required for estimating the GCA. Among the six testers used, the tester CFK69.1 could estimate the GCA of the females with reasonably high accuracy both for tuber yield and general impression, and 'Tobique' for reaction to late blight.