COMPARISONS OF SOMATIC CROSSING OVER FREQUENCY INNICOTIANA TABACUMAND THREE OTHER CROP SPECIES

Tobacco is compared with Glycine max, Gossypium barbadense, and Lycopersicon esculentum. In tobacco, a greater number of D spots (1.37 ± 0.092 per leaf) than of A spots (0.33 ± 0.039) was observed. Double spots were found less often (0.10 ± 0.021) than A spots. Spots occurred equally often among the youngest 4 leaves, among the oldest 4, and among the middle 12, but more often and with more variability among the middle 12. As in G. max, spots occur only on leaves of chlorophyll deficiency heterozygotes, more frequently on upper than lower surfaces, and equally often on right and left halves. Unlike G. max, spots occur more frequently, at all positions in the leaf sequence, more frequently on distal than proximal halves, and proportionally more D spots whether relative to A spots, Db spots, or their sum. Tobacco has the highest, and L. esculentum the lowest, frequencies of total spots per leaf and Db spots per leaf. L. esculentum has the highest D/A ratio. The frequency of somatic crossing over per spot-capable mitosis is established as 5.74 × 10 −5 in G. max and 7.70 × 10 −6 in tobacco.