Temperature, Fruit Set, and Embryo Sac Development in ‘Italian’ Prune1

Abstract

Abstract Initial fruit set in 6 ‘Italian’ prune orchards for 2 years was markedly influenced by post-bloom temperature. In the warm year initial sets ranged from 36 to 64%; in the cool year initial sets were 1 to 13%. Visible frost damage occurred in only 1 orchard and was not responsible for the general failure in the cool year. Embryo sacs were studied in pistils from the same orchards in the 2 years. The cause of erratic fruit setting in ‘Italian’ prune is attributed to its genetically determined sensitivity to cool weather in the post-bloom period. Cool temperature delays pollen tube growth, fertilization, and early embryo and endosperm development so long that the ovule begins to degenerate. Ovule breakdown begins in the nucellus at the chalazal end, so that even if fertilization is finally accomplished, fruit set is not stimulated.