Self- and cross-incompatibility in Asparagus officinalis and Asparagus densiflorus cv. Sprengeri

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Garden asparagus, Asparagus officinalis L. (off), is dioecious and reproductively isolated from a related ornamental, monoecious Asparagus densifiorus (Kunth) Jessop cv. Sprengeri (spr). Since the latter is a potentially valuable source of germplasm, a study was initiated to identify hybridization barriers. Intra- and inter-specific crosses were made using 32 plants of two commercial cultivars of off and 17 plants of three introductions of spr. Part of the pollinated pistils were fixed and examined via fluorescence microscopy. In some combinations of genotypes, incompatibility reactions were detected: (i) off × off: in the stigmatic tissue, (ii) spr × spr: on the stigmatic surface and in the style, and (iii) spr × off: on the stigmatic surface, in the stigmatic tissue, and in the style. Although pollen tubes reached the ovules in most combinations of genotypes, seeds were only produced in intraspecific crosses. It is concluded that two types of internal barriers are acting: cross-incompatibility at the pollen–stigma and pollen–style levels, and stronger post-stylar barriers that had not been determined yet. Keywords: Asparagus densifiorus cv. Sprengeri, Asparagus officinalis, cross-incompatibility, reproductive isolation.