PHENOTYPIC AND MOLECULAR SCREENING OF THE MAGIC POPULATION FOR SOURCES OF RESISTANCE TO Striga gesnerioides

Abstract

Infestation caused by Striga gesnerioides (Willd) is a major constraint to cowpea production in the dry savanna of Northern Ghana. Among the approaches used to control the parasite, host plant resistance appears to be more efficient and economical. The objective of this study was to identify sources of resistance to Striga gesnerioides in three hundred RILs of the MAGIC population and their eight founder parents using conventional and molecular breeding methods. The MAGIC population were obtained from the University of California, Riverside (UCR), USA. The study also determined the mode of inheritance of MAGIC lines that were found to be resistant. The study involved field evaluation of the MAGIC population to assess their agronomic performance under rain-fed conditions and also in pots to evaluate their resistance to Striga gesnerioides collected from Manga in Upper East Region of Ghana. Four (4) out of the three hundred RILs of the MAGIC population and their eight founder parents screened were found to be resistant to Striga gesnerioides. The result showed that flowering, pods per plant and grain yield of the susceptible RILs were reduced as compared to the resistant ones. Among the three markers used (SSR1, 61RM2 and C42-2B), C42-2B had association with the trait of interest and therefore was able to distinguish resistant from susceptible lines. The SSR1 marker which is known to be a functional marker for Striga resistance could only amplify the resistant checks and not Suvita-2 and its resistant progenies whilst 61RM2 could not distinguish between resistant checks, resistant and susceptible MAGIC lines. The C42-2B marker had discriminating power to distinguish between resistant and susceptible. The marker amplified resistant lines at 490 bp instead of the 280 bp amplified for the resistant checks. In the F2 generation, the C42-2B marker distinguished between the resistant and susceptible MAGIC lines at 490 bp. Out of 102 F2 progenies of Magic 072 × Apagbaala, 51 individuals were identified as resistant by the marker. Out of 69 F2 progenies of Magic 72 × Magic 020, 42 individuals were identified as resistant by the marker. Out of 33 F2 progenies from a cross of Suvita-2 × Magic 020, 14 individuals were identified as resistant by the marker. Segregation distortion were detected for the genotyped segregation populations deviating from the expected 3R:1S Mendelian ratio of the F2 population. The three F2 populations screened for mode of inheritance showed that single dominant gene control Striga resistance in the donor parents. In the F3 generation, Chi-square test showed 1R:2H:1S expected genetic ratio which confirmed the 3R:1S genetic ratio at F2 population which indicated that the gene that caused the resistance is controlled by a single dominant gene. The results of the study therefore revealed that selection for resistance is more effective at F3 progeny testing since planting of families is done on a one progeny one Striga infected pot basis.