Combining Ability And Heterotic Orientation Of Selected Zambian Maize Inbred Lines Under Low Soil Phosphorus Conditions

Maize (Zea mays L.) production in sub-Saharan Africa (SSA) is limited by low availability of soil phosphorus, affecting 98% of maize fields grown by small scale farmers in Zambia. Therefore, developing and releasing P-efficient maize hybrids is the sustainable way of increasing maize yield in P deficient soils cultivated by small scale farmers. The present study was carried out to assess the mode of gene action and heterotic orientation of selected maize inbred lines to low P soils. Six maize inbred lines were crossed to three inbred testers and the 18 testcrosses were evaluated under low P soil conditions. General combining ability (GCA) effects were significant (p<0.05) for grain yield, phosphorus use efficiency (PUE) and phosphorus utilisation efficiency (PUtE) suggesting that genes with additive effects were controlling the traits. The phosphorus deficiency symptom, days to anthesis and phosphorus uptake were both under significant (P<0.05) GCA and specific combining ability (SCA) effects suggesting the importance of both additive and non-additive gene effects. However, the SCA variance was greater than the GCA variance for all the traits, suggesting the preponderance of non-additive over additive gene action. Stepwise multiple regression showed that PUtE was 9 times more important than PAE for grain yield. Therefore, inbred lines L152, J185 and Mo17 with positive GCA for GY, PAE and PUtE can be used in breeding. The lack of correlation between PAE and PUtE, indicates that simultaneous selection for these traits is possible.