MORPHOLOGY OF POSTPOLLINATION FRUIT ABORTION IN PECAN

Anatomy of normal and abortive fruit was compared at each of the three postpollination fruit drops characteristic of pecan [Carya illinoensi s (Wangenh.) C. Koch]. Size differences between normal and abortive fr uit decreased during the growing season, but differences in ovule size between normal and abortive fruit increased, During Drop II, normal a nd abortive fruit had an integument enclosing a massive nucellus in wh ich an embryo sac was embedded, but embryo sac shape and constituents differed, Embryo sacs were distended in normal fruit and contained a d efinitive zygote as Evidence of fertilization, i.e., union of egg and sperm, In contrast, embryo sacs in abortive fruit were shriveled and c ontained an egg apparatus as in unfertilized pistillate flowers, Durin g Drop III, normal and abortive fruit had a similar multicellular embr yo. The nucellus in normal fruit was reduced to a cap at the micropyle region and cellular endosperm was evident. In contrast, the nucellus in abortive fruit was abundant and cellular endosperm was not evident, During Drop IV, embryo development in abortive fruit lagged behind th at of normal fruit, Thus, we present the first direct evidence that ab orted pecans deviate from normal fruit by an absence of a zygote at Dr op II, a deficiency in cellular endosperm at Drop III, and a delay in embryo development at Drop IV.