Abstract
The many reported inherent nutritional potential in African yam bean (Sphenostylis stenocarpa (Hochst. Ex. A. Rich.) Harms) seem to provide platform for the need of its genetic improvement. A good understanding of the breeding system of the crop species is a needed criterion in plant breeding program. Four accessions of African yam bean (AYB) collected from the Genetic Resources Centre of the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria were grown out in a fifteen plants/accession row on a field at IITA, Ibadan (7.5°N, 3.9°E), Nigeria. Five pollination mechanisms were investigated as treatments on the four accessions. The four accessions set fruits and seeds in four treatments: plants left to open-pollination (A), plants isolated with fine net mesh (B), artificially selfed flowers (C) and inter-varietal cross-pollination (D). Emasculated flowers which were not pollinated (treatment E) produced neither fruit nor seed. Treatment A differed significantly (P<0.05) from B, likewise C and D. Fruit set percentage was higher in A (19.7-21.2) than B (18.3–18.7). Higher pollination/fertilization success (46.5%) was obtained in C compared to 32.3% in D. More seeds (88.6%) were set by self-pollination. The four accessions had a mean selfing rate of 89.8% and an outcrossing rate of 10.17%. The observed 1:9 allogamy: autogamy in this study could form the basis for developing the breeding strategy for the genetic improvement of AYB via hybridization.
Highlights
Information on the flowering characteristics and pollination mechanism of African yam bean (AYB) is scarce
The observed 1:9 allogamy: autogamy in this study could form the basis for developing the breeding strategy for the genetic improvement of AYB via hybridization
It is noteworthy to uphold here that the breeding system of legumes is not uniquely the same: while high level of out-crossing are reported among the arboreal species, autogamy predominates among the herbaceous leguminous species (Arroyo, 1981; Bawa, 1992)
Summary
Information on the flowering characteristics and pollination mechanism of African yam bean (AYB) is scarce. Frankel and Galum (1977) documented that pre-anthesis self-pollination is common in many cultivated legumes such as: Phaseolus vulgaris, Vigna radiata, Arachis hypogaea, Cajanus cajan, Glycine max, Vicia angustifolia, V. sativa and Pisum sativum. These species exhibit autogamy; such that successful pollinationfertilization occurs prior to the time of floret opening, leading to fruits and viable seeds production. This according to Dobrenz and Beetle (1966) is possible because of selfcompatibility within the species. The predominant species of insect involved in legume pollination are the bees (Tandon et al, 2003; Maxted et al, 2004)
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