| Summary: | Conventional linkage and primary trisomic analyses were undertaken to locate genes conditioning resistance of barley (Hordeum vulgare L.) to Puccinia hordei Otth. The linkage relationships of resistance genes Pa in Speciale (C.I. 7536) and Pa₇ in Cebada Capa (C.I. 6193) with genes known to reside on chromosomes 2 and 3 were studied in crosses involving Speciale and three chromosome 2 markers (e, gs₅, and lr), and in crosses involving Cebada Capa and four chromosome 3 markers (gs₂, uz, als, and yst₂). The location of the resistance gene Pa₃ in Estate was studied by primary trisomic analysis.
Inheritance of leaf rust resistance was determined by seedling reaction to culture 57-19, race UN4 of Puccinia hordei. The inheritance and linkage relationships of marker genes and rust resistance were analyzed from F₂ and F₃ coupling data. A recombination value of 41.0 ± 2.2% was found between Pa and gs₅, a marker for chromosome 2L. No evidence was obtained linking Pa with genes e or lr, but population sizes were too small to detect reliably loose linkages in these populations. A loose association was observed between Pa₇ and yst₂ a marker for chromosome 3S; however, the data were not sufficiently homogeneous to permit estimation of a recombination value. The data from crosses involving Pa₇ and uz were not consistent but one population exhibited a trend which suggested these genes might be linked. No evidence of linkage was observed in crosses between Pa₇ and the genes gs₂ and als, although population sizes were limited.
The assignment of Pa₇ to chromosome 3 was confirmed by primary trisomic analyses. By the same method, the Pa₃ gene in Estate was shown to be independent of chromosome 3. High temperatures during leaf rust inoculation and incubation periods resulted in poor expression of infection type in crosses involving Estate and Triplo 4, 5, and 6. Despite this the data from these crosses indicated that Pa₃ is not likely inherited through chromosomes 4 through 6. Accrued data suggest that Pa₃ may be located on chromosome 1. === Ph. D.
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