Breeding for Tolerance of Cowpea to Low Phosphorus Soil Conditions through Physiological and Genetic Studies
Abstract
Cowpea (Vigna unguiculata (L.) Walp.) is a major food legume across Sub-
Saharan West Africa where its leaves, pods and seeds are consumed as food and its
residues are fed to livestock as protein rich fodder. However, soils of West Africa are
poor in phosphorus (P), a soil macro-nutrient all crops need for growth. Fertilizer with P
is not readily available and is too expensive for West African farmers. This research was
therefore, undertaken to identify cowpea lines that inherently grow well in P-deficient
soils and use them to breed improved cowpea varieties that require less phosphorus
fertilization. A hydroponic phenotypic screening method with silica sand was used to
identify cowpea varieties that have tolerance to low soil P as measured by shoot dry
biomass production. Both tolerant and susceptible varieties from the screen were further
analyzed for root biomass, internal shoot P content, and internal root P content. Seed P,
particularly the effect of cotyledon P, and total root production were investigated as
physiological sources of tolerance. Tolerant cowpea varieties were crossed with
susceptible varieties, and the resulting F_(1), F_(2) and BC_(1) seeds were screened to determine
the inheritance and genetic control of tolerance. A Recombinant Inbred Line (RIL)
population of a tolerant by susceptible cross was mapped using SSR markers to identify
linkage groups or QTL for tolerance to low soil P.
Phenotypic screening results identified four cowpea varieties to have P-deficiency
tolerance (Big John, IT97K-1069-6, IT98K-476-8, and TX2028-1-3-1) and
three cowpea varieties (Big John, CB-46, and Golden Eye Cream) to have partial P-deficiency tolerance via high seed P content. All varieties experienced increases in root production under low P treatments relative to normal P treatments. Phenotyping of F_(1), F_(2), and BC_(1) populations showed that low P tolerance is a heritable trait in cowpea with significant additive effects and narrow-sense heritability. Estimates of gene number suggested the tolerance to be a single-gene trait. Mapping linkage groups or QTL for low P tolerance identified QTL in which three SSR markers – CLM0269, 221/222, and CLM0298 – were significantly associated with tolerance and are potential candidates for marker-assisted selection (MAS).
Citation
Rothe, Julie C (2014). Breeding for Tolerance of Cowpea to Low Phosphorus Soil Conditions through Physiological and Genetic Studies. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /152599.