Pollen physiology and fertilisation in Vicia faba L.
Abstract In many legume crop species, early-formed fruits or those located closest to the photosynthate are more likely to mature than other fruits. This is so in the Vicia faba crop. Based on physiological, nutritional and genetical aspects of seed development, several hypotheses are documented. However, Vicia faba pollen fertility has not been adequately studied. Thus, a series of experiments, consisting of studies of both in vitro and in vivo pollen viability, pollen tube growth and fertilisation ability were conducted using highly inbred lines (6-13 generations). Some of the in vivo experiments were conducted under Ethiopian field conditions. In some lines, even a low level of stress at 20 ºC for 4h at 100% relative humidity (RH) caused a dramatic drop in mean percent pollen germination. The overall results indicated that there was considerable variation (p≥0.001) among the Hues studied, in response to high temperature (20 to 35 C) and 100% RH. Vicia faba pollen showed high variability in fertility level. Overall significant differences exist in fertility (p≥0.01) among the genotypes studied. A fertility gradient exists along the stem: in most genotypes the fertility declining towards the upper nodes. In all of the genotypes, the first nodes carried more highly fertile pollen than the middle and the last flowering nodes. Also the middle nodes were more highly productive than the last nodes in all the genotypes. Thus, success of fertilisation depends to a degree on the source of pollen used. In an experiment concerning pollen storage, freshly dehiscent anthers desiccated at 25 C/6h and freeze dried for 45min, stored in either LN2 or at -80 ºC, gave more than 80% viability after 9 months of storage. Desiccation at RT for 24h and storage in either LN2 or at -80 C and at -20 C, still maintained pollen viability ≥80%. Mixed pollination studies conducted indicated that pollen from one or other of each pair of inbred fines, mixed on an equal weight basis, performed better as pollen parents on some maternal fines than on others. The importance of these findings with respect to synthetic variety and hybrid seed production in the text is discussed. The probable existence of genetic self-incompatibility is also discussed.