Genetic analysis in tropical maize for phosphorus utilization in phosphorus-limited soil

Abstract

Maize is one of the most important economic crops on the African continent. However, its production is constrained by both abiotic and biotic factors. Phosphorus (P) deficiency is one of the major abiotic constraints in maize production. It was for this reason the study was undertaken whose objectives were to: 1) evaluate genotypes which are efficient at utilizing phosphorus in P-limited soil, 2) investigate the type of the of gene action associated with traits linked to utilization of phosphorus in P-limited soils and 3) map quantitative trait loci (QTL) associated with phosphorus utilization in P-limited soil. Thirteen inbred lines (8 females and 5 males) previously screened for phosphorus utilization were obtained from CIMMYT, Zimbabwe through the maize team at Golden Valley Research Trust (GART) in Chisamba District, Zambia. To evaluate genotypes efficiency to phosphorus utilization and determining the type of gene action, eight (8) females and five (5) with varying reactions to P utilization were mated in an 8 x 5 North Carolina Design (NCD II). Forty (40) progenies were evaluated in the screen house using Completely Randomized Design (CRD) with three replications and two treatments (0 kg P and 60 kg P). The shoot biomass, root biomass, plant biomass and plant height were determined after the plants were harvested and dried at 80 oC for 72 hrs. Five crosses were observed to be highly efficient at utilizing phosphorus in P limited soils. Specific combining ability (SCA) effects were found to be highly significant different from zero (P = 0.001) for all measured parameters. Analysis of general combining ability (GCA) effects revealed that only the root biomass was significantly different from zero (P = 0.05). The Baker‘s ratio for Plant height, Shoot biomass, Root biomass and Plant biomass was found to be 0.12, 0.15, 0.49 and 0.28 respectively. This implied that non additive gene action conditioned plant height, shoot biomass and plant biomass responses in P-limiting soils. On the other hand, Baker‘s ratio for shoot biomass was 0.49 implying that additive and non-additive gene action conditioned this trait response in P-limited soils.

Inclusive composite interval mapping (ICIM) analysis identified seven QTLs related to phosphorus utilization on chromosome 5. All the mapped QTLs were more than 5 cM from the nearest molecular marker utilized in the study. Therefore, there is need to utilize the maize genomic map to identify and test several markers near the mapped QTL, in order to locate more reliable molecular markers for marker assisted selection (MAS).