GENETIC-VARIATION IN APICAL DOMINANCE OF CEDRELA-ODORATA SEEDLINGS INRESPONSE TO DECAPITATION

An assessment was made of genetic variation in apical dominance of Ced rela odorata L,. using a decapitation test. Nineteen weeks after sowin g, post-grown seedlings belonging to 30 open-pollinated progenies from 5 provenances were decapitated by removal of the shoot apex, leaving shoots of a uniform height of 20 cm. Foliage was reduced to a single l eaf with 2 pairs of leaflets on each plant. The length and number of l ateral shoots subsequently formed were measured at 2 weeks, 4 weeks an d 8 weeks after decapitation to determine the percentage bud activity and dominance ratio of the shoots. Percentage bud activity increased w ithin the first 2 weeks to 4 weeks and declined thereafter as dominanc e was reimposed. Significant differences between provenances and proge nies were recorded both in the timing and extent of peak bud activity (P < 0.001, ANOVA). Maximum bud activity ranged from 17.7% to 24.2% in the 5 provenances whereas mean values for the progenies differed by m ore than a factor of 2, ranging from 13.6% to 32.3%. Pronounced geneti c variation in dominance ratio was also recorded; maximum values occur red 4 weeks after decapitation in all progenies. Dominance ratio was n egatively correlated with percentage bud activity (r = 0.65, P < 0.001 ). These results indicate that significant potential exists for select ion of Cedrela odorata genotypes with relatively high apical dominance , which may exhibit superior form and pest tolerance.