COMBATING STRIGA WEED IN SORGHUM BY TRANSFERRING RESISTANCE QUANTITATIVE TRAIT LOCI THROUGH MOLECULAR MARKER ASSISTED INTROGRESSION

Abstract

Sorghum, the second most important cereal crop in Kenya is often attacked by Striga hermonthica weed with grain yields being reduced up to 100%. In the marginal and semi-arid areas, there is urgent need to enhance the genetic resistance to Striga hermonthica in local varieties. The aim of this study was to introgress Striga resistance from a documented resistant donor line N13, into Ochuti, a susceptible farmer preferred variety through molecular marker assisted selection (MAS). Two backcross populations namely, BC₂F₁ and BC₃F₁ were generated by crossing N13, the donor parent to Ochuti, the recurrent parent line and the resultant backcrossed Striga resistant progenies were subjected to phenotypic selection initially. At the BC₃F₁ stage, fore-ground selection for the Striga resistance Quantitative Trait Loci (QTLs) was conducted through Polymerase Chain Reaction (PCR) and N13 and Ochuti alleles sized through capillary electrophoresis. Eleven polymorphic markers identified at least three Striga resistance QTLs, in five plants of BC₃F_1//F₂ generations. Eight progenies from BC₂F₁ and BC₃F₁ backcross populations were evaluated in field trials under artificial Striga inoculation in two locations and for two seasons. The backcrossed genotypes with Striga resistance allowed fewer Striga plants to germinate though in certain cases Ochuti genotypes performed equally the same.  Marker assisted Selection (MAS) can successfully be utilized to transfer Striga resistance QTLs from a resistant donor source to a susceptible sorghum variety but the transfer should be complimented by field evaluation of the resistant progenies under artificial Striga infestation over several seasons, locations and replications.