Mechanisms and mode of inheritance for Striga asiatica resistance in IITA derived maize germplasm.

Abstract

S. asiatica is the most common parasitic weed found in Zimbabwe. It causes huge grain losses in resource poor smallholder farming sector characterised by poor soil fertility and low rainfall. S. asiatica resistant maize cultivars provide the lasting solution in resource poor farming communities as less resources would be required to control the parasitic weed. The objectives of this study were: to identify both maize inbred lines and resultant single crosses resistant to S. asiatica and the mechanisms of resistance from a collection of International Institute of Tropical Agriculture (IITA) inbred lines as well as to understand the gene action controlling the mechanisms of resistance to Striga. Thirty maize inbred lines were evaluated for S. asiatica resistance using the pot culture and agar gel techniques. Thirty two maize single-crosses obtained from selected crosses between eight of the IITA inbred lines and four local testers were evaluated for S. asiatica resistance using the agar gel technique. The pot culture experiment was conducted in a 10x6 lattice design with three replications and laboratory experiments were conducted in Randomised Complete Block Design (RCBD) with four replications. Combining ability analysis for low S. asiatica seed germination stimulant production were conducted for the single-crosses using data from the agar gel experiment. Significant differences (P<0.001) were noted among the inbred lines in the amount of Striga seed germination stimulant produced. Inbred lines 2, 32, 28, 29, 27, 33, 7, and 14 recorded less than 10mm in furthest Striga seed germinated and were identified as resistant with pre attachment resistance mechanism. Significant differences (P<0.05) were also noted for the number of Striga root attachments and emerged Striga. Inbred lines 18, 27, 20 and 32 were noted to have low attachment values and were identified as resistant with post-attachment growth inhibition mechanism. Combining ability analysis revealed that General Combining Ability (GCA) components of genotypic variance were significant and Specific Combining Ability (SCA) components of genotypic variances were not significant. Additive gene action was the predominant mode of inheritance for low Striga seed germination stimulant production. Good SCA effects for low stimulant production were identified in 15xA, 17xA, 17xF, 19xB, 22xB, 29xB, 29xF, 3xB and 3xF.