THE EFFECT OF IRRADIANCE, DEFOLIATION, AND BULB SIZE ON FLOWERING OF NERINE-BOWDENII WATSON,W (AMARYLLIDACEAE)

Large Nerine bowdenii bulbs (>14 cm in circumference) were exposed to low light intensities for different periods during two successive grow ing seasons. The flowering percentage and number of florets in the cur rent season's inflorescence were recorded at anthesis. Small and large bulbs were subjected to continual defoliation starting at different t imes during the growing season. Bulbs were dissected at planting (26 S ept, 1992) and on 12 Jan. 1993 (nondefoliated control bulbs) to determ ine growth and developmental stage. At anthesis, inflorescences were h arvested and the florets per inflorescence were counted. After anthesi s in the fall, all bulbs were dissected and the following variables re corded: 1) percentage flowering, quiescence, or abortion of the curren t season's inflorescence; 2) developmental stage of quiescent inflores cences; 3) number of florets in the outermost inflorescence; 4) develo pmental stage of the innermost inflorescence; 5) number of leaves or l eaf bases in each growth unit; 6) number of daughter bulbs; and 7) dry weight of new leaf bases. There were three reasons for nonflowering o f the bulbs, viz., failure to initiate an inflorescence, inflorescence s remaining quiescent, and inflorescence abortion. Individual florets that had not reached stage ''Late G'' (gynoecium elongated, carpels fu sed) at the start of rapid inflorescence elongation aborted. The more florets that aborted, the greater the probability that the entire infl orescence aborted. The inflorescence was more vulnerable to stress dur ing the first half of the growing season due to its relatively weak po sition in the hierarchy of sinks within the bulb.