Development of Seeded and Parthenocarpic Fruits in Mulberry (Morus RubraL.)

SummaryOpen-pollinated fruits of the ‘Tufts’ mulberry (Morus rubra L.) were studied throughout the 1969 growing season. Growth of the multiple fruit followed the double sigmoid pattern characteristic of drupaceous fruits. Growth of the accessory fruitlet (pistil plus persistent calyx), the sepals, which become succulent as the fruitlet ripens, and the ovary also followed the double sigmoid curve. Since the mulberry ovary is similar to that of fleshy drupaceous fruits both morphologically and in growth pattern, it should be classified as a drupelet rather than as an achene or nutlet. The growth pattern for seeds is a single sigmoid curve, but growth continues during the plateau (period 2) of the ovary growth curve. In typical drupes the integuments attain their ultimate size during period 1 of the curve.About 45% of the open-pollinated fruitlets examined in 1969 were seedless, but had growth curves similar to those of their seeded counterparts. ‘Tufts’ and ‘Hicks’ inflorescences bagged in 1970 to prevent pollination produced as many fruits as did hand-pollinated inflorescences. All fruitlets from the bagged controls were parthenocarpic, whereas most of those from the pollinated inflorescences contained seeds. Seeded and parthenocarpic fruits and fruitlets differed only slightly in size.