SCANNING ELECTRON-MICROSCOPY OF FLORAL INITIATION IN SWEET CHERRY

Flower initiation and development in 'Bing' sweet cherry (Prunus avium L,) was examined using scanning electron microscopy. There was a 1- t o 2-week difference in the time of initiation of flower buds on summer pruned current season shoots (P) compared to buds borne on unpruned s hoots (U) or spurs (S). By late July, this difference was obvious in m orphological development. The P buds had already formed floral primord ia, while the S and U buds showed little differentiation in the merist em until early August. In general, buds from unpruned shoots were simi lar developmentally to spur buds. By late August, primordial different iation was similar in the buds from all the wood types; however, buds from pruned shoots were significantly larger (838 mu m) than buds from spurs (535 mu m) and unpruned shoots (663 mu m). Early summer pruning may shift allocation of resources from terminal shoot elongation to r eproductive meristem development at the base of current season shoots. The similarity in reproductive bud development between spurs and unpr uned shoots, given the difference in active terminal growth, might sug gest that developmental resources are inherently more limiting in repr oductive buds on spurs.