Position of the Stigma in Relation to Fruit Setting of the Tomato

The relationship between fruit setting and depression of the stigma within the anther tube of the tomato flower was investigated by comparing these two variables in field plantings consisting of two pure-breeding lines-VF36 with a low stigma level and VF6 with a high stigma-and their F~1 and F2 hybrid progenies. The inheritance patterns of stigma position in these progenies as well as in F3 families argue for quantitative determination by relatively few genes with high heritability. The F2 proved to be ideal material for intended tests by providing a complete spectrum of stigma levels from one parental extreme to the other, assorted randomly throughout the field planting. Observed values from test plots grown in two years were pooled into five intrahomogeneous periods. In each period, stigma position was correlated with fruit set-the lower the stigma level, the higher the set-this relationship bordering on statistical significance in four periods, and being highly significant in the fifth. Since the period of highest correlation was also the one of lowest fruit set, stigma position tends to have more impact on fruitfulness during periods of unfavorable environmental conditions. According to all correlated observations, the lower stigma positions afford better self-pollination, hence improved fruit setting. The low fruit set of numerous F2 segregants that had stigmas at levels as low as those of VF36 indicates that stigma level does not completely account for the high fruitfulness of the latter. Developmental studies indicated that the lower stigma positions result from differential growth of stamens versus style in late stages of ontogeny of the flower buds.