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Todd A. Burnes, Robert A. Blanchette, Jason A. Smith, and James J. Luby

Gooseberries and currants (Ribes L.) are the alternate hosts for the fungus Cronartium ribicola J. C. Fischer, the causal agent of white pine blister rust. In this study, 16 black currant (R. nigrum L.) cultivars, including three accessions of the putatively immune cultivar ‘Consort’ and three cultivars developed at the University of Minnesota Horticultural Research Center, were screened for resistance to C. ribicola using artificial inoculation procedures. Twelve of these cultivars were grown in the field and observed for natural infection. Cultivars ‘Ben Sarek’, ‘Ben Lomond’, and ‘C2-2-1’ were infected naturally in the field at the University of Minnesota Horticultural Research Center in 2000, 2001, and 2004. Cultivars ‘Ben Sarek’, one mislabeled ‘Consort’ accession, R. nigrum ‘WI-1’, and ‘Ben Lomond’ had significantly more uredinial sori than other cultivars when inoculated artificially. To determine if the infected and noninfected ‘Consort’ clones were genetically related, DNA microsatellite genotyping was carried out to fingerprint these clones. One of the six microsatellite loci resulted in a polymorphism that indicated the infected clone was genetically different from the noninfected clones. In addition, the inoculation procedures used in these studies are generally efficacious for predicting resistance in the field because none of the field-infected cultivars were resistant in the greenhouse. This study confirms the Cr gene for resistance to C. ribicola in Ribes has remained effective for over 50 years.

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Phillip N. Miklas and J. Rennie Stavely

Foliar diseases are a major constraint to cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) production in some environments. The reactions of 12 cultivated teparies to eight individual races (41, 47, 49, 51, 53, 58, 67, and 73) of the bean rust fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus maintained at Beltsville, Md., were examined under greenhouse conditions. These diverse races, used together, overcome all of the major rust-resistance genes present within the 19 host differential cultivars of common bean (Phaseolus vulgaris L.). Seven lines (GN-605-s, GN-610-s, PI 321638-s, PI 502217-s, Neb-T-6-s, Neb-T-8a-s, and Neb-T-15-s) exhibited similarly high levels of resistance (immunity or necrotic spots without sporulation) to all eight races. Inheritance of resistance was examined across five susceptible × resistant (S × R) and three resistant × resistant (R × R) populations. The rust reactions in the F1, F2, and F3 generations derived from S × R crosses revealed that the immune or necrotic resistance response was conditioned by a single locus exhibiting incomplete dominance. The rust resistance of four lines tested for allelism in R × R crosses was found to be derived from the same gene. This apparent lack of variability for rust resistance suggests that a single introgression event may realize the full potential for cultivated tepary bean to contribute rust resistance to common bean through interspecific hybridization. In addition, the limited variability for resistance to the highly variable rust pathogen in cultivated tepary bean supports the occurrence of a “bottleneck effect” during domestication of this species, as observed in germplasm diversity studies.

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Lisa A. Beirn, William A. Meyer, Bruce B. Clarke, and Jo Anne Crouch

, and have frequently produced nonrepeatable results ( Huang et al., 1990 ; Williams et al., 1966 , 1967 ). Detached leaf assays have been used to maintain cultures of the crown rust fungus ( P. coronata ) from oats ( Avena sativa L.); however, it

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Weining Wang, Yanhong He, Zhe Cao, and Zhanao Deng

), and/or have improved ornamental values. Induced tetraploids may also show improved disease resistance. For example, tetraploid Glycine tabacina became more resistant to the leaf-rust fungus Phakopsora pachyrhizi ( Burdon and Marshall, 1981 ), and

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Michele R. Warmund, Jeanne D. Mihail, and Kaley Hensel

United States HortTechnology 22 556 566 Mohlenbrock, R.H. 1999 The illustrated flora of Illinois. Sedges: Carex. Southern Illinois Univ. Press, Carbondale, IL Petersen, R. 1974 The rust fungus life cycle Bot. Rev. 40 453 513 Saccardo, P.A. 1891 Sylloge