Screening Selected Sorghum [Sorghum Bicolor (L.) Moench] Lines for Post- Attachment Resistance against Witch Weed [Striga Hermonthica (Del.) Benth]

Abstract

Sorghum (Sorghum bicolor L. Moench) is the fifth most important cereal crop worldwide. The crop provides food security in most rural African households and is becoming a suitable alternative in many places where maize crop fails. However, its production has been greatly reduced by the parasitic weed Striga hermonthica (Del.) Benth. The intricate biological association between this herni parasite and its sorghum host makes it difficult to control. Most of the control methods currently in use are either too expensive or not consistent with the smallholder farming systems in East Africa. The use of Striga resistant varieties has been envisaged as the most feasible strategy to combat the Striga problem because it does not require additional inputs and intense labour that are expensive to the resource poor farmers. This study evaluated post attachment resistance levels of four SRS sorghum lines against four ecotypes of Striga from Kenya and Tanzania and also characterized the phenotype of resistance mechanisms. Sorghum seeds were grown in rhizotrons (root observation chambers) and the seedlings were inoculated with pre-germinated Striga seeds and on emergence the attached Striga plants were harvested from the roots of sorghum and scored for the number of attachments, length and dry biomass. To characterize the phenotype of resistance the anatomy of the host parasite interface was studied using histochemical techniques. All statistical data collected was analyzed using ANOYA at 95% confidence interval with SPSS statistical computer software (version 21). Mean separation was carried out using Tukey's pairwise comparison test at 5 % probability level. SRS 120812 had the lowest biomass of attached Striga seedlings of 3.86 mg, 11.04 mg, 2.14 mg and 0.975 mg for Mbita, Kibos, Alupe and Tanga Striga ecotypes respectively. There was a significant difference in the biomass and average length of attached Striga seedlings among the three Kenyan Striga ecotYI2~s on>all sorghum lines. The phenotype of a resistance mechanism was characterized by the inability of the parasite to penetrate host endoderm is, necrosis and the browning and death of attached Striga seedlings. This study has therefore shown that SRS 1208/2 sorghum line exhibits very strong broad spectrum resistance whereas SRS 2408, SRS 2208 and SRS 3308/5 exhibit intermediate resistance to the Striga ecotypes used. The elucidation of the genetic basis of resistance in SRS 120812 is recommended for the development of sorghum cultivars with multiple and durable resistance for use in farmers' fields in East Africa and this will have a significant impact on the livelihoods of some of the world's poorest farmers helping them to alleviate poverty and improve food security.