Effect of flower pruning on the tuber yield of four yam bean accessions (Pachyrhizus erosus)

Yam bean, Pachyrbizus erosus, was tested in Southern Benin as a possible protein-rich food, urgently needed to improve child nutrition there. Four accessions (EC040/385, EW053/385, EC120A/39 and EC042/49) were tested; each was seeded in ridges in two groups: a control, without flower pruning; and an experimental group, in which flowers were pruned regularly. Tubers were harvested at 114, 155, and 197 days after sowing. Accessions, dates of harvest and flower pruning all had highly significant effects on tuber yields. The impact of flower pruning on the tuber yield varied according to accession, and the coefficient by which it multiplied the yield ranged from 1.51 to 4.99. The best accession for both total yield and response to flower pruning was EC040/385. Competition between seeds and tubers for photosynthetic products is discussed. The frequency polygons of tuber weight per plant showed a unimodal distribution for control plants from all accessions for the three yield measurements. Conversely, the distributions were multimodal for the pruned plants. This Suggests that flower pruning induced segregation Of sub-populations within accessions and may thus be a way to improve Pachyrbizus tuber productivity: tubers of selected sub-populations may be multiplied simply by planting them. Accession EC042/049 was least productive and also appears most limited in terms of improvement, but accession EC040/385 showed potential for selection to obtain very high tuber yields. Without the use of any input in poor soils the best accession yielded about 10t/ha tubers (dry matter) containing 13% proteins.