INTRASPECIFIC VARIABILITY IN MARITIME PIN E (PINUS-PINASTER AIT) IN THE SOUTH-EAST OF FRANCE .2. HETEROSIS AND COMBINATION OF CHARACTERS ININTERRACIAL HYBRIDS

This paper deals with a provenance hybridization experiment of maritim e pine (Pinus pinaster Ait) at 8, 9 and 13 years of age that was estab lished in the south-east of France. The hybrids were obtained by cross ing la provenances of the species (table I) according to a complete di allel scheme with, nevertheless, several missing combinations (fig 1). The diallel analysis showed an important proportion of specific combi ning ability variance for vigor characters (height and diameter), form (coefficient of dendrometric stem form) and branch habit (branch angl e), whereas general combining ability effects were prevailing for the trunk straightness and sensibility to Matsucoccus feytaudi (table III) . Our results revealed evidence of heterosis for most characters (tabl e V) except sensitivity to the insect pest The important specific comb ining ability effects in most traits seem to be insufficient to explai n the strong heterotic response observed for these characters. Some hy potheses are discussed for an understanding of such a response. A desi rable parental character combination is also obtained in at least 3 hy brid combinations (Tamjout x Leiria, Tamjout x Cazorla, Tamjout x Viva rio).