Analysis of bulk F2 progenies from monotelotrisomic hybrids for two known genes fc and br showed that the gene-centromere distance and frequency of homozygous recessive F2 segregates were inversely related. Based on this relationship the new genes sb, ea, gs3, f5 were assigned to positions on chromosome 1 relative to the previously mapped genes. The centromere position on chromosome 1 was located between the markers rs and n. Two previously undescribed recessive mutants, revoluted leaf (rvl) and Parkland spot (sp,,b), were associated with the long arm of chromosome 5 through the use of monotelotrisomic 14 + 5L.

Linkage markers and translocation stocks were used to identify four monotelotrisomics in barley as 14 + 1S, 14 + 2L, 14 + 4L, and 14 + 5S. In morphology they displayed the same deviations from disomic plants as the corresponding primary trisomics but to a lesser extent, ranging from an approach to the disomic for 14 + 1S to close resemblance to the trisomic for 14 + 2L. At meiotic metaphase, an average of 61.1% of the cells contained heteromorphic trivalents, with tandem-chain and ring-rod configurations predominating. The extra telocentrics were transmitted to 28.3% of selfed progeny, almost exclusively through the female gamete.

1969. A study of factors influencing the genetics of reaction of barley to root rot caused by Helminthosporium snrivu177. Can. J. Botany, 47: 4 2 9 4 3 . The inheritance of seedling reaction to root rot, caused by the 514 isolate of Helrninthospori~ct~ sntiv~tn~, was studied in crosses and backcrosses among the barley varieties CI.8969 and CI.8873, which show resistance, and the variety Olli, which is susceptible. The study was carried out under a controlled environment in growth cabinets. The data from reaction tests of F3 and backcross families were analyzed by Elston's procedure for testing a one-locus hypothesis, and by Powers' partitioning method. Polygenic inheritance for seedling reaction was indicated, but subsequent experiments showed that seed weight strongly influenced the reaction, which could account for the polygenic interpretation. Based on a drastic reduction of resistance in greenhouse-produced seed, irrespective of seed weight, a high positive correlation of seed weight with resistance in field-produced seed, and other evidence of a similar nature, it was assumed that resistance was related to a principle, present in the seed or on the seed surface, the quantity of which was influenced by seed size and modified by environment. Whether there was a genotypic influence on the quantity of the resistance principle, aside from that affecting seed weight, was not established conclusively. A field study involving the same materials, made in an area known to produce natural root-rot infection, showed that no correlation existed between the disease indices of the entries in the seedling stage in the growth-cabinet tests, and their reaction to the disease in the field. CI.8873 showed field resistance, whereas CI.8969 did not.

Distances between pairs of homologous and nonhomologous telocentric chromosomes were measured in root tip cells of barley. The nonhomologous telocentrics were randomly distributed, whereas the homologues were significantly closer than would be expected with random distribution.

A ditelotetrasomic line (14+2−1S) carrying two telocentric chromosomes in addition to the normal complement was isolated in the selfed progeny of a monotelotrisomic (14+1S) of barley. The plants were shorter and later maturing than the disomic, and highly sterile. In diakinesis and metaphase I cells at meiosis, the extra telos showed a high frequency of pairing with each other and with their normal homologues, resulting in 6″ + (t″ + 1″) and 7″ + t″ as the most frequent configurations. Regular meiotic behavior at subsequent stages resulted in a 42.2% frequency of pollen transmission of the extra telos. Selfed progenies gave rise to 7.1% diploids, 45.7% monotelotrisomics and 47.2% ditelotetrasomics.