2006 Volume 75 Issue 5 Pages 365-371
We investigated the morphology of seed, particularly of the endosperm of intact and abscising ‘Shimizu Hakuto’ peach (Prunus persica Batsch) subjected to different fruit thinning levels for four years. The objective was to study the anatomical basis for physiological fruit drop which occurs from end of Stage 2 to beginning of Stage 3 of fruit growth. The percentage of physiological fruit drop was significantly higher (P = 0.05) in trees subjected to heavy fruit thinning (HFT) than in those subjected to light fruit thinning (LFT) or standard fruit thinning (SFT). The mean endosperm length in fruit which dropped at the peak of physiological fruit drop from trees under HFT was equal to that of intact fruit collected at 65 days after full bloom (DAFB); the mean embryo length in dropped fruit was shorter than that in the intact fruit collected at the same time. Endosperm and embryo cells in dropped fruit showed typical necrotic symptoms, such as cells with shrunken cytoplasm and collapsing cell nucleus. Collapsing cell nucleus in the endosperm of the intact fruit collected from trees under HFT began at 66 DAFB that corresponded with the time when the endosperm stopped growing. Morphology of chalazal haustorium was observed in the on-tree fruit collected from the beginning to the middle of Growth Stage 2 in trees under HFT and SFT. Although most chalazal haustoria had reached the chalaza at the beginning of Growth Stage 2 in both fruit thinning levels, those in most of HFT fruit exhibited abnormal shrinking at 54 DAFB. These results indicate that a series of events take place in the seeds predestined to drop. That is, after certain factor(s) that cause shrinking of the chalazal haustorium and retardation of embryo growth to occur, assimilated reserves in the endosperm cannot be translocated to the embryo because of shrinkage of the chalazal haustorium. Finally, necrosis of embryo is induced.
