The genotype at the Q locus on chromosome 5A of Triticum durum Desf. (2n = 28, AABB), a species with keeled glumes and tough rachis, was studied by either crossing the species with, or substituting its 5A into, a hexaploid common wheat, T. aestivum (L.)Thell. ssp. vulgare (Vill.) MK. cv. Chinese Spring (2n = 42, AABBDD, QQ genotype). Contrary to the opinion of previous researchers that keeled-glumed wheats always have the spelta gene, q, the durum strains studied had a hypermorphic allele, the vulgare gene, Q. No speltoid plants appeared in the progeny of the crosses, and disomic substitution lines (2n = 2) had squareheaded (= vulgare type) spikes. Also, three doses of the long arm of 5A of durum produced compactoidy. Apparently, Q does not produce round glumes in the genetic backgrounds of most tetraploids except T. carthlicum Nevski. The phenotype conditioned by Q, which is evidently present in all free-threshing tetraploid wheats, is somewhat different at the tetraploid level from that in hexaploids. The presence of Q tends to magnify the differences in the degree of expression of certain minor characters.Key words: Triticum, phylogeny, vulgare gene, pleiotropic gene, dosage effect, interaction.
A dosage effect of chromosome 5A (formerly IX) of common wheat, Triticum aestivum L. emend Thell. ssp. vulgare, has been well established. With increasing dosage from monosomic to tetrasomic, the phenotype changes from speltoid to normal vulgare type (squarehead) to subcompactoid to compactoid (HUSKINS 1946;SEARS 1952 SEARS , 1954 (Figure 1 and Table 3 ) . This is due to the pleiotropic gene Q located near the distal end of the long arm of the chromosome (UNRAU, SMITH and MCGINNIS 1950;MACKEY 1954). The two major effects of Q, speltoid suppression and squareheadedness, were thought to be controlled by two different genes, k and q, until MACKEY (1954) found that the two genes were actually identical and incorporated them into a single dominant gene Q. It is the gene Q which makes ssp. vulgare different from ssp. spelta, and spontaneous or induced speltoid mutation (similar to ssp. spelta) in ssp. uulgare is considered to be a deficiency for a segment including Q (SMITH, HUSKINS and SANDER 1949;MACKEY 1954). MACKEY also suggested that the difference between the spelta and speltoid effects is simply due to the modifying effect of genes at other loci.In ssp. vulgare there are many varieties which are squarehead. The difference between squareheadedness and non-squareheadedness is also attributed to genes that modify Q rather than to any difference in Q itself (SEARS 1956). SEARS (unpublished) demonstrated this by substituting chromosome 5A from the non-squarehead strain "Hope" into the squarehead variety Chinese Spring. using a monosomic method (SEARS 1953). The resulting plant was as squarehead as Chinese Spring. Thus Chinese Spring provides a background that leads to squareheadedness in the presence of two Q genes. This dependence of squareheadedness on modifiers fits well with the fact mentioned by HUSKINS and SANDER (1949) that there is little difference in glume characters among speltoid mutants, although the parent strains show wide variation.The dosage series of the spelta gene q (an allele of Q) was also obtained up to four doses (SEARS unpublished). The gene behaved as a null allele. This result tends to favor MACKEY'S (1954) suggestion that ssp. spelta originated as a speltoid mutation-i.e., as a deficiency for Q locus. As SEARS (1954, 1956) ' From part of a thesis submitted to the University of Missouri in partial fulfillment of the requirements for the Ph.D. degree. The work was supported by grants from the National Science Foundation to DR. E. R. SEARS. Contribution from the Missouri Agricultural Experiment Station, Journal Series Number 2506. Approved by the Director.
In their classical study on photoperiodism, Garner and Allard found that various strains of soybean show different photoperiodic behaviors), and later this was studied in detail2~. Similar results have been reported for many other plants , such as Xan-thium3~, Chenopodium4'5~, Oryza6'7~, Solidago3~, Andropogon9_11) , Eupatorium12>, Gossy-piuml3, and Hordeum14~. That Pharbitis nil is also one of them has been reported by Muzamatsu and Sakamoto15~. They planted several strains of Pharbitis from December to June in conditioned greenhouses of Kyoto and Misima which locate at about 35'N. Under constant temperature of 30° in the greenhouse, the position of node bearing the first flower bud of a strain from North China was. always lower than in the southern strains. This varietal difference was conspicuous especially under long-day condition of the summer15~. This paper deals with (1) photoperiodic behavior of six strains of Pharbitis nil and (2) physiological basis of the photoperiodic difference investigated by grafting two strains with different photoperiodic behavior.
The multivalents that appeared in the decaploid strain of Agropyron elongatum (2n = 10x = 70), a relative of wheat, ranged from trivalent to decavalent. Few univalents occurred. The metaphase I chromosome association in 12 cells where all configurations could clearly be identified averaged 0.42 ring X + 0.17 chain X + 0.42 ring VIII + 0.17 branched VIII + 0.25 chain VIII + 0.17 chain VII + 1.17 ring VI + 0.33 branched VI + 0.5 chain VI + 1.67 ring IV + 0.42 branched IV + 0.58 chain IV + 0.08 branched III + 0.17 chain III + 12.58 ring II + 3.75 open II + 0.25 I. The occurrence of decavalents, up to two in one cell, and of a cell with five multivalents, each of which involved more than five chromosomes, and many multivalents of ring shape indicated that the strain is autodecaploid.The chromosome associations of each cell can be interpreted as seven groups of 10 homologous chromosomes. The high frequency of bivalents indicated a tendency toward reduced multivalent formation, for which an explanation is suggested.Key words: Agropyron elongatum, meiotic configuration, decaploid, multivalent.
The number of spikelets per rachis node is a key taxonomic character in the tribe Triticeae. In intergeneric F 1 plants, including wheat (Triticum) and barley (Hordeum), the single spikelet trait was epistatic, whereas it showed intermediate response in the interspecific hybrids involving the genus Elymus. Further genetic analysis has been hindered by the high sterility of the F 1 hybrid plants. In the F 1 E. tsukushiensis × H. vulgare, occasional variation in the number of spikelets was seen, apparently due to somatic chromosome instability. This indicates that these aneuploids should provide useful material for further analysis. A series of nullisomics and nulli-tetra compensation lines of Triticum aestivum ssp. vulgare cv. Chinese Spring was observed. From a consideration of all these results, it is proposed that a dosage of six genes on the homoeologous chromosomes of group-2 may suppress the formation of paired spikelets at the rachis nodes at the hexaploid level of wheat.
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