Factors affecting the proportions of cross-bred and selfed seed obtained from field bean (Vicia faba L.) crops

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Abstract
SUMMARY Winter bean crops, mainly of the variety Throws MS, were surveyed for proportions of cross-bred seed, using hilum colour as a genetic marker. In 1971 a significantly greater proportion of cross-breds was detected in random samples taken from the centre than in similar samples from the border of three fields and from the total of all seven fields. An hypothesis is proposed that pod setting at the centre was limited more than at the border by a factor such as plant competition and chocolate spot at a time when selfing was enforced due to a general lack of bee visitation, or else inbred embryos aborted more under the stress of disease in the centre. No differences between centre and border were found in 1972 except for a greater proportion of cross-breds from the border of a Maris Beagle field and this only applied to parent plants of certain genotypes. Significant differences were also found between fields and between seasons. There was a significant regression of percentage selfing on field size but there was no evidence that bees failed to penetrate to the centre of large fields. Implications for variety development, testing and purity are discussed.