Inheritance of phosphorus use efficiency and resistance to anthracnose in selected sorghum genotypes grown in the acid soils of Western Kenya

The acid soils of western Kenya where most of the sorghum is grown have very low available phosphorus, at 2-5mg P/kg soil compared to the recommended levels of 10-15mg P/ kg soil required for optimal crop productivity. In these soils, sorghum grain yield is low ( 1.0 t/ha) and has continued to decline due to low P availability in the soil, use of low yielding varieties and anthracnose susceptibility, among other factors. Inorganic phosphorus fertilizer supplementation is not economically viable for the resource constrained farmers in these areas. In addition, only between 10-30% of the applied P is available to the crop while the rest get fixed by clay minerals. The poor plant mineral nutrition in western Kenya is further compounded by the prevalence of foliar diseases notably anthracnose (Colletotrichum sublineolum) which causes yield loss of up to 70% in susceptible cultivars. Since both problems tend to occur together in sorghum growing areas, there is a need to develop cultivars that are not only anthracnose resistant but are also efficient in phosphorus use. At present, such cultivars are not available to farmers in western Kenya. This study sought to determine the mode of gene action governing the inheritance to phosphorus use efficiency (PUE) and resistance to anthracnose to support breeding for multiple stress tolerance in sorghum. Six stable inbred lines (G2, C1, K5e, L6, O2 and P5), contrasting for the two traits were used as parents in this experiment. A six-parent half diallel cross was used to generate F1 seed using the hot emasculation technique. F1s were advanced to F2. Genetic analysis was conducted on F2 progeny for both traits. Recombinant F2 populations plus their parents were screened at Sega, a low P site. For the anthracnose study, screening of recombinant F2 populations plus their parents was done at Kibos; the disease hotspot. Both sites lie in the major sorghum growing region in western Kenya. Standard statistical data analyses were used to determine the mode of gene action governing the inheritance of PUE and resistance to anthracnose disease in sorghum. Both additive and non-additive genetic effects were found to govern the inheritance of PUE with the predominance of non-additive genetic effects over additive effects. In study two, both were found to govern the inheritance of resistance to anthracnose with additive effects largely determining resistance to the disease. This study identified three parental genotypes (G2, C1 and O2) and two crosses (G2xL6 and G2xO2) which combine efficiency in phosphorus use and resistance to anthracnose disease. These should be used in the development of multiple stress tolerant sorghum varieties for farmers to improve sorghum yield in the low P and anthracnose endemic soils of western Kenya and Eastern Uganda.