Etude des relations entre la precocite du tournesol et son rendement, sa teneur en huile, son developpement et sa morphologie

French. Dans une étude sur 25 hybrides de tournesol, issus d’un plan factoriel de croisement, ainsi que des variétés cultivées, 2 matrices de corrélations linéaires totales entre différents paramètres ont été réalisées afin d’étudier les liaisons entre différents caractères du développement et l’humidité à la récolte, le rendement en grains et la teneur en huile. La précocité à la récolte est corrélée avec la durée totale levée-maturité physiologique (r = 0,74 **), et plutôt avec la durée floraison-maturité physiologique (0,69 **) que la durée levée-floraison (0,54 *). Les caractères morphologiques ne sont pas révélateurs de la précocité. Le rendement est corrélé avec des caractères morphologiques de vigueur, mais parmi ses composantes le nombre de grains par capitule paraît plus important que le poids de 1 000 grains. La teneur en huile est peu corrélée avec d’autres caractères. En l’absence de corrélation rendement-précocité la sélection de tournesols précoces à haut rendement devrait être possible mais nécessiterait des observations en fin de cycle de la maturité des graines.

English. The developmental and agronomic characteristics of sunflowers were observed in trials involving 25 hybrids from a factorial cross and 3 commercial varieties, over 2 years, 1986 and 1987. There were significant differences between genotypes for all characteristics except the duration sowing-emergence (table I). From the results, 2 matrices of total linear correlations were calculated between different parameters in order to study relations between developmental stages and earliness at harvest, yield and oil content (tables II and III). The length of developmental phases before and after flowering are independent. The duration emergencephysiological maturity was correlated with the periods before and after flowering, but more closely with the duration flowering-maturity (r = 0.87 **). Earliness at harvest appears correlated with the total duration emergencephysiological maturity (r = 0.74 **), and follows the same pattern, being more especially related to the duration flowering-physiological maturity (r = 0.69 **) than to the duration emergence-flowering (r = 0.54 *). Of the morphological characters observed, most do not provide any useful indication concerning earliness; only leaf number shows a significant correlation with emergence-flowering and emergence-maturity. In contrast, yield is significantly correlated with morphological characters which vary with plant vigour, such as head and basal stem diameter and plant height. For the components directly determining yield, seed number per capitulum appears more important than 1 000 seed weight. In the conditions of the trials, yield appears most related to characters determined before flowering. Oil content is not closely linked with other characters, except lateness to some extent. It is concluded that since earliness at harvest depends on the sum of all the vegetative stages, more particularly those after flowering, no juvenile character provides a satisfactory forecast. Earliness can only be determined by end of cycle observations on seed maturation. However, the absence of any significant correlation between yield and earliness suggests that it should be possible to select for high yielding early sunflowers.