Abnormal Pollen Germination and Embryo Abortion in the Interspecific Cross, Fragaria x ananassa ×F. vesca, as Related to Cross-Incompatibility

Abstract

To investigate why the interspecific cross Fragaria x ananassa (8x) × F. vesca (2x) gives a lower rate of viable hybrid achenes and seedlings, emasculated flowers of F. x ananassa 'Honeoye' (8x) were pollinated with pollen of 'Changsen', a clone of F. vesca (2x) originally from Changbaishan, Jilin Province, China. The intraspecific cross F. x ananassa 'Honeoye' × 'Hokowase' was used as the control. In the interspecific cross, 6 out of 10 pollinated flowers produced 303 developed achenes of which 167 seedlings were grown ; 84 were hybrids (5x) and 83 were apomicts. The germination of F. vesca pollens on the stigmas of F. x ananassa was rarely observed and the elongation of pollen tubes in the style was irregular. For the interspecific cross, in addition to normal growth of embryos with endosperm, delayed fertilization was observed as well as the suspended growth of embryos at the globular stage. Such abnormal embryos lacked endosperm development. These results indicate that abnormality in pollen germination and pollen tube elongation, and aberrant growth of embryos and endosperm could be the basis of incompatibility in the interspecific cross of F. x ananassa × F. vesca. Embryo rescue culture which prevents abortion of rudimentary embryos, which can occur in the interspecific cross in strawberries, may be the means to develop new hybrids.