A study on the pollination mechanism in field beans (Vicia faba L.)

Abstract

Inbred lines and hybrids of English tick and horse beans and exotic stocks were studied with respect to pod set, floral structure and pollen production and germination to find out why most inbred lines set few or no seeds without tripping whereas most hybrids and some inbred lines set equally well with or without tripping. The most important outcome was new information on variation between genotypes in flower structure and pollen quantity and on how these two characters affect the mechanics of self-pollination. Though heterosis in terms of abundant pollen production could be a factor in the self-pollinating ability of hybrids, some of the inbred lines were capable of self pollination despite limited pollen production, because the structure of the flower permitted the pollen to reach the stigma via a short route. The floral features associated with the ability to self-pollinate in the inbred lines included a relatively short style bending at more or less a right angle, few and short stylar hairs and stigmatic papillae, and less pronounced ridges on the inside of the keel petals. The implications of these findings to the development of self-pollin ated varieties of field beans are briefly discussed. barrier to pollination, which is absent in the flowers of self-pollinating plants. The present investigation Field beans are intermediate in breeding be-was undertaken with the objective of throwing haviour between completely cross-pollinated and some light on the nature of this barrier and how completely self-pollinated crops (Fyfe & Bailey, hybrids and self-pollinating lines overcome it. Such 1951) and their seed set is markedly reduced in the knowledge is of interest both intrinsically and as an absence of pollinating bees (Riedel & Wort, 1960; aid in the development of self-pollinated varieties Scriven, Cooper & Allen, 1961;Free, 1966). Devel-of field beans, opment of completely self-pollinated varieties is being sought (Lawes, 1973) to eliminate dependence MATERIALS AND METHODS on bees for pollination, thereby avoiding fluctuations in yield caused by variations in the availaThe material studied (Table 1) comprised inbred bility and activity of bees. lines selfed for four or more generations and F t The ability of field-bean plants to set seeds with-hybrids, derived from stocks of English spring and out flower manipulation (tripping) is known as winter beans and exotic material from Sudan and autofertility and this varies with the genotype and India. The plants were grown, during the spring of level of inbreeding, hybrids being usually more 1975, singly in 18-cm pots filled with John Innes autofertile than inbred plants. Although in most No. 2 compost and placed on a capillary bench in a cases highly inbred plants set practically no seeds bee-proofed glasshouse, without flower manipulation, the existence of selfpollinating lines has been reported (Hayes & Pod set with and without tripping Hanna, 1968;Kambal, 1969; Toynbee-Clarke, Flowers were tripped by depressing the wing 1974).petals thus releasing the style and s...

Pollination, Fertilization and Floral Traits Co-Segregating with Autofertility in Faba Bean

“…The heterotic autofertility of F 1 plants was initially considered to be a result of the presence of a larger quantity of pollen grains over their inbred parents (Drayner 1959;Kambal, Bond, and Toynbee-Clarke 1976;Stoddard and Bond 1987). In contrast, additively inherited autofertility in inbred lines may involve subtle changes to floral morphology (Kambal, Bond, and Toynbee-Clarke 1976;Suso and Moreno 2004) together with early rupture of the stigmatic cuticle and release of the stigmatic exudate (Paul et al 1978;Lord and Heslop-Harrison 1984).…”

Controls over pollination and ovule fertilization in Vicia faba

“…Variations in floral structure have been associated with differences in the amount and timing of the deposition of pollen on the stigma (Kambal et al ., 1976 ;Lord & Heslop-Harrison, 1984), and advanced to explain autofertility . We consider these less likely to be important in moderate to highly autofertile genotypes, because pollen can usually be found on stigmas of such plants prior to flower opening .…”

“…Ambiguity surrounds the relative importance of each mechanism, but it seems reasonable to suppose that the chemistry of the pollenstigma interaction should exert greater control in autofertile genotypes than would spatial separation of pollen . In some genotypes, self pollen is found on stigmas before the flower opens (Kambal, 1969 ;Paul et al ., 1978) but it need not necessarily germinate on every stigma (Kambal et al ., 1976 ;Rowland et al ., 1983), nor guarantee the pistil will be fertilized . A high correlation between pollination (pollen on stigma) and pistil fertilization has been observed in crops of spring beans in England (Stoddard, 1986a), and also under Australian conditions (Marcellos & Perryman, 1988) .…”

How can an understanding of plant–pollinator interactions contribute to global food security?

“…These factors should enhance overall pollination rates of a crop but may also increase the proportion of self pollen received [52]. For crop systems such as the field bean, which benefit from both self and non-self pollen [53], this will not necessarily have a negative impact, but for others the optimum size of the reward to deliver maximum yields may need to be more carefully assessed.…”