Inheritance and breeding strategies for phosphorus efficiency in tropical maize (Zea mays L.).

Information available from full cycle maize trials regarding the inheritance of phosphorus (P) efficien- cy in tropical maize is limited. This type of information is essential to establish selection strategies for these charac- teristics. The objective of this study was to investigate the inheritance and relationships between characteristics relat- ed to phosphorus efficiency in tropical maize. Six tropical maize lines with contrasting P efficiency and seven F1 crosses derived from these lines were used in this study. The parental lines, the F1's, F2's, BC1P1, BC1P2, BC2P1 and BC2P2 from each of the seven crosses were evaluated in three low P and two high P environments. Efficiency traits evaluated were: grain yield (GY), stover yield, (SY), grain P concentration (GPC), stover P concentration (SPC), P acquisition efficiency (PAE), P internal utilization efficien- cy (PUTIL), P harvest index (PHI) and the quotient of P utilization (QUTIL). Anther silk interval (ASI), which has been related to drought tolerance, was also determined. For each trait, the following parameters were estimated: mean effect (m), additive effects (a), dominant effects (d) and epistatic digenic effects (aa, ad, dd). A 47% mean yield reduction was observed at the low P level compared with the high P level in the soil. Dominance effects and epistatic effects (when detected) were more important than additive effects for the majority of the traits studied. A low correlation for PAE was observed between low and high P environments, suggesting that different mecha- nisms of soil P acquisition occur in low and high P envi- ronments. For the PUTIL a high correlation was observed between low and high P environments, suggesting that similar plant internal mechanisms occur in both soil P lev- els. A medium and negative correlation was observed be- tween ASI and GY at low P environments. Our results suggest that the selection criteria adequate to select for P efficiency include GY under low P environments to deter- mine PAE under low P soils, and grain P concentration under high P environments to determine PUTIL.