Genetic Effects for Maize P Efficiency Traits in Acid and Non-acid Soils of Western Kenya

Soil acidity is a major constraint to maize (Zea mays L.) productivity in tropical soils due to toxic levels of aluminium (Al) and phosphorus (P) deficiency. The objectives of this study were to: (i) determine the genetic effects of certain traits associated with phosphorus efficiency in maize (ii) compare the genetic control of maize P efficiency traits in acid and non-acid soils. Six F1 single crosses derived from acid soil tolerant and susceptible lines were used in this study. The parental inbred lines, the F1’s, F2’s, BC1P1, BC1P2, from each of the six crosses were evaluated in two low P acid and two low P non-acid soils in Kenya. Mean genetic effect (m), additive genetic effects (a), dominant genetic effects (d) and epistatic digenic effects (aa, ad, dd) were computed for Shoot dry matter (SDM), Root Length density (RLD), P content (PC), P utilization efficiency (PUE) and P efficiency (PE). For most of the traits, greater variation was accounted for by dominance followed by epistatic and additive genetic effects in both acid and non-acid soils. Means for all the traits studied were significantly higher at high P conditions (36 kgP/ha) in non-acid soils compared to acid soils for all the generations. Both RLD and PE exhibited higher means under non-acid soils compared to acid soils under both P conditions. Mean heritabilities were generally higher in non-acid soils compared to acid soils. There was higher reduction in PE in acid soils (25-50%) compared to non-acid soils (15 to 30%). The magnitude of both additive and non-additive gene effects were always greater in non-acid compared to acid soils pointing to the effects of soil acidity on gene action. The inheritance of major PE traits did not differ in acid and non-acid soils even though soil acidity affected the magnitude of the gene effects.