| KIHARA and LILIENFELD (1935; Cytologia 6: 195-210) had observed the occurence
at first metaphase of meiosis in the vulgare-caudata F1
hybrid a range of 3-5 bivalents with a mean of 4 bivalents and trivalents
varying from 0-2. KIHARA (1958; Proc. 10th Intern. Cong. Genetics, Montreal
2 142-171) also reported the occurence of 0-5 bivalents (mode 3) and trivalents
in the F1 of the vulgare-caudata cross, where as
the reciprocal cross had the range of 0-4 (mode 2) bivalents, along with
trivalents and quadrivalents. The present observations and those reported by earlier workers clearly indicate a higher degree of chromosome pairing in 28 chromosome aestivum-caudata hybrids than that observed in euhaploids of aestivum or the 28 chromosome aestivum-longissima or aestivum-rye hybrids. Thus suggesting that the genotype of Ae. caudata seems to modify the potency of chromosome 5B to result in the lowering of the threshold value inhibiting intergenomic chromosome associations. This lowering of the threshold value of chromosome 5B by the caudata genotype results in increased intergenomic pairing in the 28 chromosome aestivum-caudata hybrids. But that this altered threshold value is not of the same magnitude as is brought about by speltoides or mutic genotypes. KIHARA'S data on the occurence of higher frequencies of trivalents and quadrivalents in the caudata-wheat hybrids over that in the reciprocal wheat-caudata hybrids, further indicate that the effect of caudata genotype on chromosome 5B is enhanced by the caudata cytoplasm in the F1 hybrids. The present conclusions are further supported by the observations of KIHARA and LILIENFELD (1935; Cytologia 6: 195-210) on the high degree of chromosome pairing in the triploid F1 hybrid between Ae. caudata and T. durum. The mean chromosome associations per cell, at the first metaphase of meiosis, calculated from their data are 4.8 biv. (range 1-8) and 1.08 triv. (range 0-4). These frequencies are much higher than those observed in the triploid F1 hybrid between Ae. longissima and T. dicoccum by KIHARA (1949; Cytologia 14: 135-144). |
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