FRUIT AND SEED SET IN THE CUCUMBER (CUCUMIS-SATIVUS L) IN RELATION TO POLLEN-TUBE GROWTH, SEX TYPE, AND PARTHENOCARPY

Pollination of parthenocarpic Dutch slicing cucumbers often yields low numbers of seed per fruit, because only the proximal segment of the fruit contains seeds. In contrast seed yield of short fruited types is usually high. To identify reasons for this inadequate seed set, in vivo pollen tube growth, ovule and seed development, and fruit elongation were studied in cucumber cultivars with different fruit lengths and levels of genetic femaleness and parthenocarpy. Pollen parents had no significant effect on pollen tube growth or seed set. Sex type or parthenocarpy did not affect seed set in any of the fruit types. Genotypes with long fruits also possessed long ovaries, which enlarged quicker than those of short fruited genotypes. Pollen tubes were never found beyond the proximal half of the developing ovary in long fruited types, because fruit elongation proceeded more rapidly than pollen tube growth. Therefore the long ovary and the rapid elongation of the fruits are responsible for the low seed set in long fruited cucumber types.