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Stem rust resistance in wheat (Triticum aestivum L.) conferred by the Sr2 gene has remained effective against Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn. worldwide for more than 50 yr. Sr2 resistance is associated with variable levels of disease symptoms; it shows recessive inheritance and is expressed primarily during the adult-plant stage. A genetic and physical interval for the Sr2 gene was determined on the short arm of chromosome 3B of wheat. Flanking microsatellite markers were identified and one tightly linked marker (gwm533) was shown to be associated with presence of Sr2. This marker was validated in a wide range of germplasm and can now be implemented in marker-assisted breeding to facilitate selection for this durable, broad-spectrum but difficult to score rust resistance gene., RESISTANCE TO STEM RUST was transferred from Triticum turgidum L. ssp. dicoccum Schrank ex Schubler (cv Yaroslav) into hexaploid wheat by McFadden (1930) producing the variety Hope. Hare and McIntosh [...]

THE ABILITY OF THE PLANT PATHOGENIC fungus Nectria haematococca MP (mating population) VI to infect pea (Pisum sativum L.) is determined in part by whether the fungus can detoxify pisatin, [...], A family of cytochrome P-450 (Pda) genes in the pathogenic fungus Nectria haematococca is responsible for the detoxification of the phytoalexin pisatin, an antimicrobial compound produced by garden pea (Pisum sativum L.). The Pda6 gene was mapped by electrophoretic karyotype analysis to a small meiotically unstable chromosome that is dispensable for normal growth. Such traits are typical of B chromosomes. The strains of Nectria studies here have no sequences that are homologous to the Pda family other than Pda6 and therefore demonstrate that unique, functional genes can be found on B chromosomes. Unstable B chromosomes may be one mechanism for generating pathogenic variation in fungi.

Previous cytogenetic studies of the genus Bromus L. were limited to chromosome counts and construction of karyotypes on the basis of Feulgen staining. Since the chromosomes of Bromus are similar in morphology, these karyotypes are of limited use for chromosome identification and genome analysis. The objectives of this study were to develop and evaluate a Giemsa C-banding procedure to use in identification of individual bromegrass chromosomes and to develop a karyotype for diploid Bromus riparius Rehm. (2n = 14; PI 440215). All chromosomes had one or more C-bands which were located mainly at telomeric regions. A group (I) of four pairs of chromosomes had telomeric bands on only one arm and could be differentiated. In this group, one pair had an interstitial C-band along with a telomeric band, one pair had a nucleolus organizer region (NOR) at a subtelomeric location on the short arm, and the other two pair could be distinguished by centromere location. The other group (II) of three pairs of chromosomes had telomeric bands on both arms. The unequivocal identification of specific chromosomes of Group II was not possible in all cells because of their similarity and differential condensation of chromosomes. Chromosomes of both groups were either metacentric or submetacentric. The total length of individual chromosomes ranged from 5.58 to 6.87 µm and the arm ratios ranged from 1.02 to 1.5. The homologous chromosomes were paired and assigned numbers I to VII in decreasing length. A karyotype was constructed by means of the C-bands, mean chromosome lengths, and arm ratios. The C-banding procedure used in this study could be used to developed karyotypes for the other species of the genus Bromus and these C-banded karyotypes could be used to compare genomes within the genus., THE GENUS BROMUS CONTAINS more than 100 species distributed over all continents (Gould and Shaw, 1983). The ploidy level within the genus varies from diploid to decaploid (Armstrong, 1991). Feulgen [...]