EFFECT OF ASSIMILATE SUPPLY ON DEVELOPMENT AND GROWTH-POTENTIAL OF AXILLARY BUDS IN ROSES

The effect of assimilate supply on axillary bud development and subsequent shoot growth was investigated in roses. Differences in assimilate supply were imposed by differential defoliation. Fresh and dry mass of axillary buds increased with increased assimilate supply. The growth potential of buds was studied either by pruning the parent shoot above the bud, by grafting the bud or by culturing the bud in vitro. Time until bud break was not clearly affected by assimilate supply during bud development, Increase in assimilate supply slightly increased the number of leaves and leaf primordia in the bud; the number of leaves preceding the flower on the shoot grown from the axillary bud substantially increased. No difference was found in the number of leaves preceding the flower on shoots grown from buds attached to the parent shoot and those from buds grafted on a cutting, indicating that at the moment of release from inhibition the bud meristem became determined to produce a specific number of leaves and to develop into a flower. Assimilate supply during axillary bud development increased the number of pith cells, but the final size of the pith in the subsequent shoot was largely determined by cell enlargement, which was dependent on assimilate supply during shoot growth. Shoot growth after release from inhibition was affected by assimilate supply during axillary bud development only when buds sprouted attached to the parent shoot, indicating that shoot growth is, to a major extent, dependent on the assimilate supply available while growth is taking place.