Suitability of four different methods to identify self-compatible seedlings in an almond breeding programme

Obtaining self-compatible almond cultivars from controlled crosses has become one of the most important aims in almond breeding programmes. Self-compatible seedlings from such crosses have been identified by different methods. Determination of fruit set in bagged branches and observing self-pollen growth along the pistil by fluorescence microscopy are methods traditionally used. Non-equilibrium pH gradient electro-focusing (NEPHGE) of stylar S-RNases is a more recent method, which reveals self-compatibility by partial or total absence of ribonuclease activity in heterozygous and homozygous self-compatible individuals respectively. To date, the most recent method is S-allele PCR, which identifies the presence of the S-f allele in genomic DNA. In this work, reliability, ease of performance, economic cost and time spent in obtaining the results of these four methods were compared in a progeny of 74 seedlings. The results showed that, considering its moderate cost and time spent, NEPHGE of stylar S-RNases was the most convenient method. However, as PCR of S-alleles can be applied in the first year to plantlets in the nursery. an early selection of self-compatible seedlings is possible. On the other hand, bagging is essential in a further stage of the selection process, thus ensuring good yields in single-cultivar almond orchards.