Floral structure and pollinizer tree as reliable factors for cross-breeding system of Argania spinosa

Abstract

In most breeding programs the pollen donor parents (pollinizers) are characterized by a strong flowering rate and very low fruit set, even after hand pollination. Hence, the notion of pollinizers in the argane species was born, first mentioned, checked, documented and confirmed like in the other conventional tree species. Since the argane tree is completely self-incompatible, the presence of compatible pollinizers is necessary for the fruit set. Indeed, pollinizers need to be selected accurately based on the synchronization of bloom periods and compatibility to receiver trees (females). The pollinizer is essential in any breeding program and as well as for any new orchard plantations. The current study was carried out on 13 argane genotypes including two pollinizers. The flowering period, bloom phenology, floral structure and fruit set of crossed genotypes were monitored, illustrated and a season phenogram was established. The pollen viability and germination were also evaluated. Concerning compatibility trials, the hand pollination, using two selected pollinizers pollens, was compared to open pollination. Then, the compatibility system was monitored and evaluated through the index of self-incompatibility. It has been observed that the flowering periods are genotype depending, that there is one to three blooms during the two years study (2018-2019) and that the argane tree is a tristylous species (Mesostylous, brevistylous and longistylous flowers). The in vitro tests showed that the pollen originated from crossed genotypes were viable and able to germinate. The cross-compatibility rate depends on cross associations and it varies from 39 to 84 %. It was observed, for the first time, that all compatible pollinizers have metaxenic effects of pollen on argane fruit.

Keywords

• arganier
• amélioration génétique
• pollinisateurs
• auto-incompatibilité
• croisements diallèles
• compatibilité
• métaxénie