Effect of flowering time modulation on fruit set, ripening time and fruit characteristics in almond

Flowering time in Prunus species is highly dependent on chilling requirements of each cultivar. This is an adaptive mechanism that allows flowering to occur under suitable climatic conditions for pollination and fruit development in every area. One of the main objectives of almond (Prunus dulcis (Mill.) D.A. Webb) breeding programs is the delay of flowering time to avoid the late frosts in cold areas. Nonetheless, some extra-late and ultra-late flowering cultivars have shown a low fruit set or small fruits size. The objective of this work was to determine whether these problems are genotype-associated or if they are determined by weather conditions during the late flowering or their shorter period of fruit development. For that purpose, flowering time of the extra-early flowering ‘Desmayo Largueta’ and the ultra-late flowering ‘Tardona’ was modulated by applying controlled temperatures on trees grown in containers. Replications of both cultivars were forced in controlled chambers simulating the autumn, winter and spring seasons to flower each week between the flowering time in the field of both cultivars (the first of February for ‘Desmayo Largueta’ and the first of April for ‘Tardona’). Flowering and ripening time, fruit set, and fruit characteristics were recorded for three years. The culture of trees on containers and the artificial temperature treatments had an important influence on the studied traits. Results pointed to a direct influence of flowering time on ripening time but no effect on fruit set or fruit characteristics could be shown. Generally, the ultra-late flowering ‘Tardona’ presented difficulties for flowering time modulation and it showed an accelerated sprouting respect flowering, which led to flower bud failure.