Sorghum root length density and the potential for avoiding Striga parasitism

Striga hermonthica is a serious root parasite of sorghum in the semiarid tropics. Successful parasitism is dependent on interactions of Striga seeds and host roots. Several sorghum cultivars have been found which resist parasitism. The basis of resistance is not well known. One possible method for reducing the chances of parasitism is by restricted host root development. This research was conducted to evaluate this hypothesis in sorghum known to possess resistance to parasitism by Striga. Root length density of 21-day-old pot-grown resistant cultivars, Framida, N-13, IS-9830, Tetron and P-967083, were compared to that of the susceptible check, Dabar, using the line intercept method of measuring root length. There was no significant difference between resistant cultivars and the susceptible cultivar Dabar. The RLD of resistant P-967083 however was significantly less than Framida, another resistant cultivar. The RLD of Dabar was compared to that of Framida and P-967083 in USA and Niger field trials. Root length density was determined on soil cores taken at flowering with a Giddings Soil Sampler. Each core was divided into 10-cm fractions for estimating RLD by the line intercept method. In the USA Dabar had significantly greater RLD than the two resistant cultivars in the upper 10-cm portion of the soil profile, but only significantly greater than P-967083 in the 10-20-cm portion. Significant differences in RLD between susceptible and resistant cultivars were not found at depths between 20-60 cm. In field trials in Niger, RLD of Dabar was significantly greater than either resistant cultivar in the (0 to 30 cm) portion of the soil core. These results suggest that part of the Striga resistance of P-967083 and perhaps Framida may be a result of avoiding interactions between parasitic seeds and host roots.