Almond fruitfulness and role of self-fertility

The world record of kernel yield is 2.0 t/ha and belongs to the Californian irrigated almond industry. Since the kernel is only 6.6% to 9.0% of the whole fresh fruit weight, a yield of 2.0 t/ha of kernel means a yield 10 to 15 times higher, i.e. 20 to 30 t/ha of whole fruits, depending on the cultivar. Adequate planning of irrigation, fertilization and pruning, reaching the top yield mentioned above should not be impossible, since goals of 30 t/ha and more of fruits are common with oranges, apples, pears, peaches, etc. Considering the variability of the weight of the almond kernel, between 1.0g and 1.6g, depending on the cultivar, a yield of 2.0 t/ha of kernel means 1,250,000-2,500,000 fruit/ha, i.e many thousand fruit/tree. From this second point of view, besides irrigation, fertilization and pruning, an effective pollination by honeybees assumes strategic importance. Correct management of bees for pollination means optimization of fruit set. In addition, the use of self-fertile almonds could really help towards the achievement of the above records. Investigation carried out throughout the ‘70s and ‘90s allowed at least 30 naturally self-fertile almonds to be identified. The common denominator of those cultivars was the same geographic origin: Apulia, southern Italy. It has been supposed that self-fertility appeared following remote and natural hybridization between the cultivated almond and a wild bitter kernel almond living in Apulia from time immemorial: Amygdalus webbii Spach. In addition, self-fertility has been artificially introduced into the genome of the common almond by means of artificial hybridization with peach and induction of mutation. Pluriannual studies have shown that under the same environmental and growing conditions, almonds which are self-fertile and able to set fruit with their own gametes are also able to set kernel per tree and per hectare about twice as big as the most popular self-sterile almonds. In conclusion, the studies carried out have shown that self-fertile cultivars can be grown in solid blocks, eliminating the need for pollinators and the ensuing problems. However, the achievement of horticulturally interesting yields by self-pollination and self-fertilization is impossible without insect vector mediation. The action of the vectors has been interpreted as fundamental to ensure the intimate contact of pollen grains with the stigma of the same flower, between flowers of the same tree, between flowers of different trees of the same cultivar.