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Ebrahiem M. Babiker, Stephen J. Stringer, Hamidou F. Sakhanokho, Barbara J. Smith, and James J. Polashock

Blueberries rank as the second most important berry crop in North America with a total area of 96,869 ha ( Strik, 2006 ). As blueberry acreage increases, pathogen diversity and diseases become a more important issue. Stem blight, caused by the

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Gabriele Gusmini, Luis A. Rivera-Burgos, and Todd C. Wehner

Gummy stem blight is a major disease of watermelon [ C. lanatus (Thunb.) Matsum. & Nakai]. It is caused by three genetically distinct Stagonosporopsis species, S. cucurbitacearum (syn. Didymella bryoniae ), S . citrulli , and S . caricae

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Gang Lu, Wenlei Jian, Jiajing Zhang, Yijing Zhou, and Jiashu Cao

Asparagus officinalis L., a member of the family Liliaceae, is an important vegetable worldwide for its culinary and medicinal properties. The world total yield reached 6,346,000 t in 2006 ( FAO, 2006 ). Stem blight, caused by a complex of fungal

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D.J. McGrath, L. Vawdrey, and I.O. Walker

Resistance to gummy stem blight [Didymella bryoniae (Auersw.) Rehm] was evaluated in two accessions of Cucumis melo L., PI 266935 and PI 266934. Based on disease reaction scores and dry weights, PI 266934 possessed much greater resistance than PI 266935. The quality of resistance of PI 266934 was unaffected by the ranges of seedling ages and inoculum concentrations used. No melon cultivar, to our knowledge, is highly resistant to gummy stem blight in the field, and alternative sources of superior resistance are potentially useful for breeding.

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Luis A. Rivera-Burgos, Emily Silverman, Nebahat Sari, and Todd C. Wehner

Gummy stem blight (GSB) is a major disease of watermelon [ Citrullus lanatus (Thunb.) Matsum. & Nakai] that leads to significant economic losses. This disease is caused by three genetically distinct Stagonosporopsis species, S . cucurbitacearum

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Joseph N. Wolukau, Xiaohui Zhou, and JinFeng Chen

Gummy stem blight (GSB) caused by Didymella bryoniae (Auersw.) Rehm is one of the most important soilborne diseases of melon and causes significant economic losses (30% to 60%) ( Frantz and Jahn, 2004 ). Although chemical control has been

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Joseph N. Wolukau, Xiao-Hui Zhou, Ying Li, Yong-Bin Zhang, and Jin-Feng Chen

Melon production is severely constrained by several soil-borne disease pathogens. Of these pathogens, Didymella bryoniae (Auersw), Rehm that causes gummy stem blight (GSB) is one of the most destructive resulting in substantial economic losses

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Paul C. St. Amand and Todd C. Wehner

Leaf and stem resistance to gummy stem blight [Didymella bryoniae (Auersw.) Rehm.] in five resistant by susceptible crosses of cucumber (Cucumis sativus L.) was investigated using generation means analysis. No single gene of major effect controls either leaf or stem resistance to gummy stem blight in these five crosses. The mean number of effective factors controlling leaf resistance in the cross `Slice' × `Wis. SMR 18' was estimated to be at least five. Estimates of broad- and narrow-sense heritabilities indicated that environmental effects were larger than genetic effects. In general, additive variance was the larger component of genetic variance. Epistasis was significant in most crosses, and dominance was present in several crosses. Additive gene effects contributed more to resistance than to susceptibility in contrast with dominance gene effects. Reciprocal differences for leaf rating were detected in the crosses M 17 × `Wis. SMR 18' and `Slice' × `Wis. SMR 18'. Phenotypic correlations between leaf and stem ratings were moderate (r = 0.52 to 0.72). Estimates of genetic gain for resistance to gummy stem blight ranged from low to moderate. Breeding methods that make best use of additive variance should be used because much of the variance for resistance is additive, and dominance effects, at least in these crosses, tended to contribute to susceptibility.

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James J. Polashock and Matthew Kramer

Stem diseases of blueberry (Vaccinium spp.) can cause significant crop loss as well as loss of entire bushes. Stem diseases are also more difficult to control with fungicides than foliar or fruit diseases. A screening program was initiated to test blueberry cultivars for resistance to two pathogenic fungi: botryosphaeria stem blight and phomopsis twig blight. An attached stem assay was developed to compare the host response with both fungi. The relative resistance of 50 blueberry cultivars was assessed using stem lesion lengths, analyzed on a log scale, taken at 4 weeks postinoculation. For Botryosphaeria stem blight, mean lesion length ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible cultivars. The half-high cultivars Northsky, Northblue, and Chippewa, and the lowbush cultivar Putte were among the most resistant. Phomopsis twig blight lesions ranged in mean length from about 18 to 98 mm. Similar to results for Botryosphaeria stem blight, resistance was limited to half-high (`Northsky' and `Chippewa') and lowbush (`Blomidon', `Chignecto', and `Cumberland') cultivars. Individual cultivars resistant to one pathogen were not necessarily resistant to the other; although, overall, the resistances were correlated. Approximate 95% confidence intervals were established for all cultivars to predict mean performance across years. The cultivars tested varied in resistance, but the largest single factor affecting lesion length was the fungal isolate used for inoculations. These data enable us to identify cultivars resistant to both diseases that can be used for planting in problem areas, as well as selection of parental material for breeding cultivars with improved resistance.

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Takahiro Sonoda, Atsuko Uragami, and Kazuhiko Kaji

Asparagus officinalis L. cultivars were evaluated for resistance to asparagus stem blight caused by Phomopsis asparagi (Sacc.) Bubák under controlled environmental conditions. The plants were inoculated with the vinyl tube and cotton inoculation method. Disease severity assessments, based on the percentage of diseased plants and the disease index, were made 4 weeks after inoculation. Estimates of the percentage of diseased plants ranged from 33% to 80%, and the disease index ranged from 28 to 79. None of the cultivars and lines showed high resistance, but there were significant differences in disease susceptibility among the cultivars and lines.