Self-incompatibility Expression in Self-compatible Almond Genotypes May Be Due to Inbreeding

Pollen tube growth after selfing was studied in four almond ( Prunus amygdalus Batsch) families derived from crosses between self-compatible `Tuono' and self-incompatible `Ferragnès' and `Ferralise' in both directions, in order to ascertain the phenotypic expressions of the different genotypes. A differential expression of self-compatibility was observed in the seedlings of the different families. The genetic self-compatible offspring of `Ferralise' showed a lower percentage of pistils with pollen tubes at the style base and a lower number of pollen tubes at the pistil base after self-pollination than those observed in the self-compatible offspring of `Ferragnès'. This low level of self-compatibility expression observed in some `Ferralise' seedlings may be due to the inbreeding present in `Ferralise'. As a consequence, caution must be taken in almond breeding to avoid the increase of inbreeding by the utilization of related parents and to diversify the sources of self-compatibility, at present mostly limited to `Tuono.'