Introgression of Striga (Striga gesnerioides Willd) resistance into cowpea (Vigna unguiculata L. Walp) varieties.

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
The parasitic weed, Striga gesnerioides (Willd) Vatke is one of the most important constraints to cowpea production in the dry savanna (Derived Savanna, Southern Guinea Savanna and Northern Guinea Savanna) of Northern Ghana. Yield losses due to S. gesnerioides range from 83 to 100%. No single method however, seems to be fully adequate in the control of this parasite. Host plant resistance, appears to have merit in effectively and economically controlling the parasite in that it is affordable to farmers. The objective of this study was to introgress Striga resistance into existing farmer-preferred cowpea varieties. Two resistant genotypes IT99K-573-1-1 and GH3684 were crossed to two susceptible varieties “Hewale” and “Asomdwee” respectively. The chi-square test was used to test the goodness-of-fit of the observed ratios to the expected genetic ratio in F2 segregating populations. The results of the cross of genetic of inheritance demonstrated 3R:1S ratio indicating single dominant gene action (monogenic inheritance). The result of the inheritance study indicated that the environment had great influence on a number of agronomic traits. The broad sense heritability for susceptible and resistant were high (63% and 78% respectively). Narrow sense heritability were low for some of the traits which is an indication that environmental factors (Striga) influenced cowpea production in this study. Three simple sequence repeat (SSR) markers SSR-1, C42-2B and 61RM2 associated with Striga resistance were used to screen 93 F2 progenies. The study showed that the three markers had discriminating power to distinguish between the resistant and susceptible genotypes and with presence of bands in resistant genotypes. The allele frequency for marker SSR-1 was 65% and 61RM2 was 73%, suggesting that these markers are highly repeatable within the population. Yield loss due to Striga infestation was estimated to be (78.22 to 87.17%). Other yield component including pods per plant, 100 seed weight, fodder yield, pod length as well as the number of seeds per pod of the susceptible genotypes were affected. There was significant correlation between percentage yield reduction and percentage reduction in various yield components indicating that Striga infestation was responsible for the overall yield reduction. At present very limited sources of Striga resistant varieties are available, therefore there is the need to develop new Striga resistant cowpea varieties that meet end-user preference. Promising lines will be screened with more Striga resistant markers to determine their level of genetic status.
A thesis submitted to the Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfillment of the requirement for the degree of Master of Philosophy in Agronomy (Plant Breeding),