CHROMOSOME ASSOCIATION AND POLLEN FERTILITY OF PARENTAL AND INTERSPECIFIC HYBRIDS OF LYCOPERSICON-ESCULENTUM X LYCOPERSICON-HIRSUTUM AND LYCOPERSICON-PENNELLII

Cytological studies were carried out on two wild species (L. hirsutum and L. pennellii) and the cultivated species (L. esculentum) of tomato and their F1 hybrids. Both parents and hybrids show a diploid chromos ome number of 2n = 24. The meiotic behaviour of the cultivated species showed a high degree of chromosome homology resulting in a high level of chiasmata frequency per bivalent. In contrast, the two wild specie s showed a slight increase in univalent frequency and a decrease in bi valent formation and chiasmata frequency. The meiotic behaviour of the hybrids showed a high level of univalents and low levels of bivalents as well as trivalents. Highly significant decreases in chiasmata freq uency and increases in meiotic abnormalities, especially in the L. esc ulentum X L. pennellii hybrid, also were detected. The high meiotic ir regularity and low chiasmata frequency recorded in the second hybrid i ndicated the disharmony and difference between its parental genomes an d also served to predict its sterility. With regard to degree of pairi ng recorded in the hybrids, there is a possibility that sterility in s uch cases may refer to genetic factors in addition to the previously m entioned reasons. Pollen fertility showed no great difference between L, esculentum and L. hirsutum and their Fl hybrid, but a significant d ecrease was recorded in the L. esculentum X L. pennellii hybrid, which was clearly associated with high meiotic irregularity, low chiasmata frequency and chromosome association.