INCREASE OF FLOWERING IN PINUS-NIGRA ARN SUBSP SALZMANNII (DUNAL) FRANCO BY MEANS OF HETEROPLASTIC GRAFTS

Behaviour of black pine (Pinus nigra subsp salzmannii) ramets grafted in 1987 on P nigra and P brutia rootstocks was compared in a clonal se ed orchard located in Guadalajara (Spain). Graft take percentage was l ower on average and more variable between clones for interspecific uni ons than for intraspecific ones; however, later field survival was rat her similar. Between 1990 and 1994, heteroplastic grafts displayed a f emale flowering ranging from four to 13 times higher than homoplastic ones depending on the year, and with 5 years of age, interspecific gra fts produced male strobili, nearly absent in the second group. Althoug h seed production is still scarce, due to lack of pollination, heterop lastic ramets seem to yield bigger cones with more sound seeds per con e. Significant differences between both types of grafts were observed regarding stem diameter, branching pattern, apical dominance and crown width. Differentiation of lateral shoots, both floral and vegetative, was higher in heteroplastic grafts, resulting not only in more branch es, but also in more strobili of both sexes per branch. Heteroplastic ramets displayed a marked tendency to lose apical dominance. thus supp orting their higher number of shoots since the number of branches per whorl is equal in both groups. These results suggest that utilization of P nigra grafts on P brutia rootstocks, in similar site conditions, may be a helpful tool to obtain more precocious and abundant fruit yie lds than those derived from the more common use of homoplastic grafts.