The Utilization of Wild Relatives of Cultivated Almond and Peach in Modifying Tree Architecture for Crop Improvement

摘要

Wild populations of almond species representing a wide range of morphological and geographical forms have evolved throughout central and southwestern Asia. Some of the more than 30 species described by botanists may represent subspecies or ecotypes within a broad collection of genotypes adapted to the range of ecological niches in the deserts, steppes and mountains of central Asia. The most northeasterly group located in western China and Mongolia includes P. mongolica, P. pedunulata and P. tangutica (P. dehiscens). The remainder occupy a more or less contiguous area in west central Asia. Those with the most northern range include species in Section Chamaeamygdalus and extend from the Balkan peninsula to the Altai Mountains. The most southern and xerophytic groups includes species in the Spartiodes Section, which can have leafless slender shoots, and the Lyciodes (Dodecandra) Section, which are very dwarfed and thorny. The third group (Section Euamygdalus) resembles cultivated almonds and includes many species extending from central Asia to southern Europe. Because the 2n=16 chromosome number of cultivated almond (Prunus dulcis syn. P. amygdalis, Amydalus cummunis) and peach (Prunus persica) is the same as most related species, this germplasm has proven particularly valuable for cultivar improvement. Successfully introgressed traits include self-fruitfulness, and improved pest and disease resistance and kernel nutrient quality which are typically under oligogenetic control. While such traits are readily introgressed through backcross breeding, undesirable changes in tree architecture remain a major barrier to full commercial utilization. In almond by peach species introgression, undesirable tree architectures are more successfully avoided when backcrossing to cultivated forms of either species. Interspecies transfer from cultivated germplasm avoids the strong promotion or suppression of apical dominance which is inherited from many wild species as a dominant trait. In addition, the use of cultivated almonds and peach as a bridge-species has facilitated the introgression from wild accessions to commercially acceptable types.