Evaluation of Sorghum Genotypes for Striga (S. hermonthica) Tolerance

Striga infestation and transmission, and the adverse impact of Striga on crop yield can essentially be diminished through selection of resistant genotypes. The study was carried out to screen sorghum genotypes for Striga hermonthica (Striga) tolerance based on their physiological responses to the parasitic effects of this weed. Seventy-five grain sorghum [Sorghum bicolor (L.) Moench] genotypes were subjected to three levels (0 mg, 2.5 mg and 5 mg/pot) of Striga at Rattary Arnold Research Institute in Zimbabwe. One way analysis of variance results show that there were significant difference among genotypes on plant height, chlorophyll content, leaf number, field weight, grain weight, panicle height for Striga*genotype interaction for all the 75 sorghum genotypes (P<0.001). The correlation matrix show that fresh panicle weight and grain dry weight showed a very high correlation (0.948) at P<0.05. Panicle height and fresh panicle weight are highly correlated (0.736) at P<0.05. Similarly, panicle height and grain dry weight were also highly correlated (0.718) at P<0.05. The heatmap analysis shows that 45%, 31% and 24% of the cultivars exhibited high, medium and low plant heights respectively. Chlorophyll content showed that 80% and 20% of the cultivars showed medium and low amounts, respectively. All the 75 genotypes recorded low leaf numbers when compared to the control experiment. It was observed that 25%, 63% and 12% for the genotypes produced high, medium and low fresh panicle weight and dry grain weight values respectively. The panicle size for most (87%) of the genotypes was medium while 13% of the cultivars showed very small sized. Principle component analysis using the scree plot Eigen values shows that the first factor contributes 58% of the cumulative variation. Two principal axes (F1 and F2) were selected, which explained about 74.45% of the total variation. Neighbour-joining hierarchical clustering analysis led to the formation of five groups for Striga*genotype interaction. It can be concluded that Striga hermonthica affects negatively crop morpho-physiologaical aspects such as plant height, chlorophyll content and leaf number as well as yield determining components such as field weight, panicle height which ultimately reduce the yield of sorghum. The existence of high variability in the response to Striga hermonthica infestation in the 75 sorghum genotypes gives the possibility to breeding interventions to improve tolerance to this parasitic weed.