| Dwarf The plant is smaller than any other primary trisomic and
has longer, wider leaves. They are more waxy than those of disomics. Hairiness
of the neck in this trisomic is expressed to an exceptionally high degree.
This type is also characterized by its extra empty glume. The seedlings
have rather thick, wide and deep green leaves. The extra chromosome is VI
with submedian primary constriction and a very small terminal satellite
on the short arm. This chromosome has been described as the "hairy neck"
chromosome because it has been associated with the gene for this character
(O'MARA 1951; RILEY and CHAPMAN 1958; EVANS and JENKINS 1960). Bush Plants of this type are like Slender in appearance at maturity but slightly smaller. They have comparatively long and narrow leaves. The spike shape is similar to that of Slender but the density is obviously less. In the seedling stage the plants tiller profusely and have pale green leaves. Thus Bush is easily recognized around the middle seedling stage. This trisomic has extra chromosome VII which is the shortest of the rye chromosomes and is characterized by a very pronounced satellite at the end of the short arm. Trisomics and disomics grown in a growth cabinet in 1959 were utilized for checking their pollen and seed fertility. In general the pollen fertility of the trisomics is fairly good and is not much different from that of the disomics except for Stout which showed 63.4% in pollen fertility. Pollen fertility varied from 63.4% (Stout) to 92.8% (Pseudonormal), and the average was 79.3%. The seed fertility obtained from trisomics x disomics varied from 38.7% (Feeble) to 70.5% (Dwarf), and the average was 48.4% Nearly the same results were obtained from crosses between disomics and trisomics. The seed fertility varied from 37.2% (Semi-stout) to 79.9% (Dwarf), the average being 52.6%. In all types but Stout and Semi-stout, the seed fertility from disomics x trisomics is slightly higher than in the reciprocal cross. Seed fertility in open pollination was not precisely examined but was fairly high. In Bush whose extra chromosome VII has the largest satellite, almot all pollen mother cells showed a trivalent attached to a nucleolus. In the other six trisomics no cells with a trivalent attached to a nucleolus have been observed. Consequently, chromosome VII is obviously the nucleolus organizing chromosome. All possible types of trivalents, that is, chain, frying-pan, Y shape and triple-arc, were observed at diakinesis. The first type was most frequently observed, its average frequency in the seven trisomics being 46.5% (31.8-74.6%), it was followed by the second type with the frequency of 33.3% (4.2-56.3%). The frequencies of the last two types were 8.2% (0.9-40.3%) and 4.8% (0.9- 16.6%), respectively. At first metaphase the frequency of 1III + 6II conjugation was decreased and the configuration 7II+1I was correspondingly increased (Tab. 4). The types of trivalents at this stage were mostly chain (84.3%), followed by frying - pan (11.7%) and Y shape (4.0%). In all trisomics no pollen mother cells with a triple - arc trivalent were observed. |
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