UC Riverside

Cowpea is a multi-purpose leguminous crop, and its importance as a resource to address food security issues plus production constraints imposed by biotic and abiotic stresses has attracted significant research. Aligned with these efforts, this dissertation describes the resistance found among 53 cowpea genotypes from Mozambique, to root-knot nematodes (RKN) (Meloidogyne incognita¬ and M. javanica) and Fusarium wilt (FW) [Fusarium oxysporum f. sp. tracheiphilum (Fot races 3 and 4)]. In the first chapter, an overview is provided about the significance of cowpea as a food security resource, constraints limiting production and research progress and status of cowpea production in Mozambique. Also, available genetic and genomic resources and their utility for cowpea breeding are described. In addition, the concept of plant resistance, types of resistance, mechanisms of plant resistance, disease quantification to RKN and FW, the genetic control of some cowpea diseases and practical example of successful cowpea breeding for diseases is discussed. The second chapter, describes a series of experiments that led to the discovery of seven cowpea genotypes with broad-based resistance to RKN using nematode reproduction and root-galling phenotypes. The effectiveness of resistance in FN-2-9-04 relative to virulence levels in RKN isolates and the relationship between resistances to different RKN isolates is described. In the third chapter, the genomic architecture of resistance to RKN in FN-2-9-04 is determined through a series of genetic analyses and quantitative trait locus (QTL) mapping. Two QTLs on chromosomes 1 and 4 were associated with the strong RKN resistance in FN-2-9-04. The fourth chapter describes the resistance found among the test cowpeas to Fot3 and Fot4 based on wilting and vascular discoloration phenotypes. The virulence profiles of Fot3 and Fot4 are compared, and the effectiveness of FW resistance in FN-2-9-04 and the relationship between wilting and vascular discoloration responses are discussed. In the fifth chapter, the genomic architecture of resistance to Fot4 in FN-2-9-04, determined through a series genetic analyses and QTL mapping, is described. Two QTL on chromosomes 3 and 8 were associated with Fot4 resistance in FN-2-9-04. These novel sources of nematode and Fusarium resistance are important for cowpea genetic improvement.