Abstract:
Striga gesnerioides is a devastating parasitic weed of cowpea, especially in Ghana and the rest of West Africa. It is the major cause of cowpea yield reduction in Ghana. Despite seven different races being known acrossWest Africa, the races of the parasite present in Ghana and their diversity have not been studied. This study investigated the distribution and diversity of Striga gesnerioides on cowpea in Ghana. The study revealed widespread distribution of the parasite within the Northern, Upper East and Upper West regions of the northern sector of the country. Morphological variation within the parasite showed two flower colour types: purple and white, with a ratio of purple to white being 3:1. The parasite was also found parasitizing two weeds: Tephrosia pedicellata, a leguminous weed, and Ipomoea tribola a non-leguminous weed. The reaction of 29 cowpea genotypes to eight Striga populations from endemic zones revealed that some cowpea genotypes were resistant to all Striga populations, some susceptible to all Striga populations and others showed differential response. The genotypes which showed differential responses probably indicated the presence of more than one race of Striga gesnerioides in Ghana. Molecular studies on 35 Striga gesnerioides collections using 73 markers designed using Striga gesnerioides sequences retrieved from the National Centre of Biotechnology Information (NCBI) database revealed two main clusters. This shows the probable existence of multiple strain of Striga gesnerioides in Ghana. The combined results of response of differential cultivars and the molecular study revealed the probable races of Striga gesnerioides in Ghana from this study are SG3, SG2 and SG5. More studies however are needed to positively confirm the presence of these races in the country.
