Interspecific compatibility among 15 Leucaena species (Leguminosae: Mimosoideae) via artificial hybridizations.

Abstract

Seed cross-compatibilities were tested among 15 of the 16 well-defined species of the polyploid genus Leucaena to determine whether genes of interest could be transferred between species. Twelve diploid and four tetraploid taxa were artificially hybridized in 118 of all 120 possible two-way combinations and 31 of 32 possible self and intraspecific matings, with 58 218 floret pollinations. Ninety-one combinations (77%) produced well-filled seed, and 73 of these combinations were grown and validated in the field. The qualitative crossability within ploidy levels (diploid, triploid, tetraploid) was 78%, 75%, and 100%, respectively, whereas quantitative crossability (relative to intraspecific matings) of successful matings within identical ploidy levels was 32%, 11%, and 73% respectively. One-third (34%) of the 114 interspecific combinations tested in both directions exhibited weak unilateral incompatibility (UI), due, in part, to reciprocal differences in stylar length. Other mechanisms for UI (embryo-endosperm imbalance, sex-specific use of self-compatible parents) were ruled out. Wide hybridization appears to be 'buffered' by polyploidy in the genus.