Studies on Backcross Progeny of N. rustica×N. tabacum Interspecific Hybrids I
Cytological analysis
1994 年 59 巻 3 号 p. 377-384
詳細
1994 年 59 巻 3 号 p. 377-384
The mammoth gene in Nicotiana tabacum causes the tobacco plant, which is otherwise day-neutral to flower under short photoperiodic conditions. The mammoth gene has been transferred to the genome of N. rustica through interspecific hybridization followed by repeated backcrossing to N. rustica. The expression and segregation of the mammoth gene was complex in the N. rustica genetic background. Plants with abnormal floral expressions and altered responses to environmental factors such as photoperiod and thermoperiod frequently appeared in the rustica-tabacum hybrid population.
Three different flowering responses characterized the segregating populations. A small proportion of rustica-tabacum mammoth hybrids remained non flowering with continued vegetative growth for an indefinite period of time irrespective of photoperiod or thermoperiod. Nine percent of plants in the segregating backcross progeny expressed flower reversion phenomenon which was characterized by the appearance of terminal flowers with abnormal floral morphology, later reverting to normal inflorescence as in N. rustica. The remainder of the hybrid segregants were identical to N. rustica in floral morphology as well as in their responses to photoperiod. The segregation of plants with altered flowering expressions among the backcross progeny was highly heterogeneous.
Cytological investigations were carried out both at mitosis and meiosis to find out whether the heterogeneous segregation of plants with altered flowering expressions could be related to abnormal chromosome segregations. The studies revealed variation in chromosome number at mitosis in flower revertant and non-flowering plants. The studies also revealed cytological aberrations in the hybrid progenies segregating for flower revertant and normal plants at meiosis. The results indicate that their genomes are at an unstable state and it was concluded that the heterogeneous segregation in the backcross hybrid progeny with altered responses to environmental factors and abnormal floral expressions may at least in part be due to chromosome instabilities.
