ALTERATIONS OF THE MANIFESTATIONS OF HYBRID BREAKDOWN IN LYCOPERSICON-ESCULENTUM L-PENNELLII F2 POPULATIONS CONTAINING LYCOPERSICON-ESCULENTUM VERSUS L-PENNELLII CYTOPLASM

Reproductive abnormalities reduced the percent stainable pollen, and fruit and seed set in interspecific F-2 populations derived from crosses of Lycopersicon esculentum and L. pennellii but were not observed in parental Lines and interspecific F-1 populations. The degree to which these reproductive abnormalities were expressed in the interspecific F-2 populations was affected by cytoplasm. Reproduction was impeded in interspecific F-2 populations containing L. esculentum cytoplasm (F-2(Le)) by reduction in pollen production, the lack of fruit set and a high proportion of parthenocarpic fruit among plants capable of fruit set. The F-2 populations containing L. pennellii cytoplasm (F-2(Lp4)) showed a reduced frequency of reproductive abnormalities at all stages of reproductive development, resulting in higher values for percent stainable pollen, fruit and seed set and higher proportions of the F-2(Lp4) populations being capable of setting fruit or seed than F-2(Le) populations. The major barrier remaining in F-2(Lp4) populations was reduced fruit set compared to parental lines. The barrier to fruit and seed set observed in the F-2(Le) populations, and to a lesser extent in the F-2(Lp4) populations, occurs around the time of fertilization or early embryonic development. The effect of L. pennellii cytoplasm on barriers in the F-2(Lp4) populations is proposed to be due to an interaction between cytoplasmic and nuclear genes during fertilization of the F-1 plants to produce F-2 populations and may also affect subsequent generations.