Abstract
Apricot (Prunus armeniaca L.) is a species of the Rosaceae that was originated in Central Asia, from where it entered Europe through Armenia. The release of an increasing number of new cultivars from different breeding programs is resulting in an important renewal of plant material worldwide. Although most traditional apricot cultivars in Europe are self-compatible, the use of self-incompatible cultivars as parental genotypes for breeding purposes is leading to the introduction of a number of new cultivars that behave as self-incompatible. As a consequence, there is an increasing need to interplant those new cultivars with cross-compatible cultivars to ensure fruit set in commercial orchards. However, the pollination requirements of many of these new cultivars are unknown. In this work, we analyze the pollination requirements of a group of 92 apricot cultivars, including traditional and newly-released cultivars from different breeding programs and countries. Self-compatibility was established by the observation of pollen tube behavior in self-pollinated flowers under the microscope. Incompatibility relationships between cultivars were established by the identification of S-alleles by PCR analysis. The self-(in)compatibility of 68 cultivars and the S-RNase genotype of 74 cultivars are reported herein for the first time. Approximately half of the cultivars (47) behaved as self-compatible and the other 45 as self-incompatible. Identification of S-alleles in self-incompatible cultivars allowed allocating them in 11 incompatibility groups, six of them reported here for the first time. The determination of pollination requirements and the incompatibility relationships between cultivars is highly valuable for the appropriate selection of apricot cultivars in commercial orchards and of parental genotypes in breeding programs. The approach described can be transferred to other woody perennial crops with similar problems.
Highlights
The pollination requirements of a cultivar can be established by carrying out controlled pollinations in the field and recording the percentage of fruit set
Cultivars were considered as self-incompatible when pollen tube growth was arrested in the style in most pistils from selfpollinated flowers, and as self-compatible when more than half of the pistils displayed at least one pollen tube reaching the base of the style
Half of the cultivars (47) behaved as self-compatible, displaying most pistils with pollen tubes growing along the style (Figure 1B) and at least one pollen tube reaching the base of the style (Figure 1C)
Summary
The pollination requirements of a cultivar can be established by carrying out controlled pollinations in the field and recording the percentage of fruit set. In self-compatible genotypes and compatible crosses, pollen tubes can grow along the style and reach the ovary, where fertilization of some of the two ovules can take place This histochemical approach allows the identification of pollination failure from diverse environmental factors that can affect fruit set under field conditions (Guerra and Rodrigo, 2015). Most traditional apricot cultivars in Europe are self-compatible (Burgos et al, 1997), the use of selfincompatible cultivars developed in North America as parental genotypes in several breeding programs, with the objective of incorporating resistance to sharka (Hormaza et al, 2007; Zhebentyayeva et al, 2012), is leading to the introduction of new self-incompatible cultivars. The pollination requirements of many of these new cultivars are unknown
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