Abstract

The objective of this study was to determine the stability of Sorghum spp. tolerance to two Striga strains. This was stimulated by the observation that sorghum tolerant to Striga asiatica in a particular area could still lack the same tolerance to a strain native to remote areas. Nine Sorghum bicolor genotypes and one Sorghum arundinaceaum (Wild sorghum) were subjected to two Striga asiatica strains sourced from Rushinga and Chiundura which are 500 km apart together with a control. A 3 × 10 factorial experiment was set up, arranged in a completely randomized design with three replications at two sites. The measured data were sorghum height, chlorophyll content, tiller number and dry matter. The results showed that sorghum genotype and Striga strain differed (P<0.05) in their response to the stunting effects of Striga strains at both the sites. The Chiundura strain was more virulent to Isifumbathe, Zambia, Wild sorghum and Mashava at Henderson Research Station, whilst at BUSE the Chiundura strain was more virulent on wild sorghum and Mashava. The two Striga strains were generally similar on their effects on chlorophyll content and were less than the control. However, different sorghum genotypes responded differently to the effects of various sorghum strains. At Henderson, the Chiundura strain reduced chlorophyll content of Chiredhi, Zambia, Tshwetha and SC Sila. At BUSE both strains were not significantly different (P<0.01) from each other at 10 weeks after crop emergence (WACE). The effects of the two strains were similar for head index, root index, stem index and leaf index at all sites. Chiundura strain reduced the total dry weight at BUSE but not at Henderson. Overally, the Chiundura strain had more deleterious effects on sorghum traits compared to Rushinga confirming the existence of physiological speciation on Striga asiatica.