Challenges for self-compatibility identification in almond

Abstract

Several approaches have been used to assess self-compatibility in almond, such as fruit set after self-pollination and bagging, pollen tube growth, and the more recent Sf allele identification by molecular markers and gene sequencing. However, none of these methods has given fully reliable results and all show advantages and limitations. An active Sf allele that does not confer self-compatibility, in spite of its full identity with the inactive Sf allele conferring self-compatibility, has been identified recently, showing that the presence of the Sf allele is not the only requirement for self-compatibility expression in almond and that the coding region of the Sf allele may not be involved in that expression. Mis-sequencing of alleles has also created confusion for allele identification. Thus, a better knowledge of the plant as a whole, and not only of its genotype, is fundamental to understand self-compatibility in almond and evaluate new selections in a breeding program.