Powdery mildew development on the slow-mildewing conditions disease severity increased greatly on Vermillion wheat cultivar Knox was compared to that on the susceptible but increased little on Knox. The area under the disease cultivar Vermillion over a period of 4 yr in the field at progress curve had a lower error variance than statistics Lafayette, Indiana. Cultivars received three levels of nitrogen associated with the logit transformation of severity data and fertilizer to determine if high levels of N affected the hence was a superior measurement of slow-mildewing. Slowexpression of slow-mildewing in Knox wheat. Knox's mildewing remains effective under the highest rates of resistance was evident under conditions favoring moderate to nitrogen fertilization likely to be applied to wheat. In severe disease on Vermillion. Under low nitrogen fertility or breeding for slow-mildewing, high rates of N provide optimal unfavorable weather there was little difference in level of conditions for recognition of this resistance. mildew on the two cultivars; under more favorable

Fusarium head blight (FHB) is a devastating disease of wheat and barley worldwide. Resistant cultivars could reduce damage from FHB. Chinese wheat cultivar Sumai 3 and its derivatives represent the greatest degree of resistance to FHB known. A major quantitative trait locus (QTL) on chromosome 3BS and other minor QTL for FHB resistance have been identified in these cultivars and used in wheat-breeding programs worldwide. Many breeding lines with the 3BS resistance QTL and improved agronomic traits have been developed. In barley, only limited sources of FHB resistance are available, especially in six-rowed barley, and none of them contains a DON level low enough to meet the safety requirement of the brewing industry. Several QTL have been identified for lower FHB severity, DON content, and kernel discoloration and used to enhance FHB resistance in barley. Marker-assisted selection for FHB resistance QTL on 3BS of wheat and on 2H of barley is in progress.

Wheat and barley are critical food and feed crops around the world. Wheat is grown on more land area worldwide than any other crop. In the United States, production of wheat and barley contributes to domestic food and feed use, and contributes to the export market and balance of trade. Fifteen years ago, Plant Disease published a feature article titled “Scab of wheat and barley: A re-emerging disease of devastating impact”. That article described the series of severe Fusarium head blight (FHB) epidemics that occurred in the United States and Canada, primarily from 1991 through 1996, with emphasis on the unparalleled economic and sociological impacts caused by the 1993 FHB epidemic in spring grains in the Northern Great Plains region. Earlier publications had dealt with the scope and damage caused by this disease in the United States, Canada, Europe, and China. Reviews published after 1997 further described this disease and its impact on North American grain production in the 1990s. This article reviews the disease and documents the information on U.S. FHB epidemics since 1997. The primary goal of this article is to summarize a sustained, coordinated, and collaborative research program that was put in place shortly after the 1993 epidemic, a program intended to quickly lead to improved management strategies and outreach implementation. This program serves as a model to deal with other emerging plant disease threats.

Scab is a destructive disease of wheat. To accelerate development of scab-resistant wheat cultivars, molecular markers linked to scab resistance genes have been identified by using recombinant inbred lines (RILs) derived by single-seed descent from a cross between the resistant wheat cultivar Ning 7840 (resistant to spread of scab within the spike) and the susceptible cultivar Clark. In the greenhouse, F(5), F(6), F(7), and F(10) families were evaluated for resistance to spread of scab within a spike by injecting about 1,000 conidiospores of Fusarium graminearum into a central spikelet. Inoculated plants were kept in moist chambers for 3 days to promote initial infection and then transferred to greenhouse benches. Scab symptoms were evaluated four times (3, 9, 15, and 21 days after inoculation). The frequency distribution of scab severity indicated that resistance to spread of scab within a spike was controlled by a few major genes. DNA was isolated from both parents and F(9) plants of the 133 RILs. A total of 300 combinations of amplified fragment length polymorphism (AFLP) primers were screened for polymorphisms using bulked segregant analysis. Twenty pairs of primers revealed at least one polymorphic band between the two contrasting bulks. The segregation of each of these bands was evaluated in the 133 RILs. Eleven AFLP markers showed significant association with scab resistance, and an individual marker explained up to 53% of the total variation (R(2)). The markers with high R(2) values mapped to a single linkage group. By interval analysis, one major quantitative trait locus for scab resistance explaining up to 60% of the genetic variation for scab resistance was identified. Some of the AFLP markers may be useful in marker-assisted breeding to improve resistance to scab in wheat.

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Three chromosomal regions associated with scab resistance were detected in a common cultivar, Ning7840, by microsatellite and AFLP analysis. Six microsatellites on chromosome 3BS, Xgwm389, Xgwm533, Xbarc147, Xgwm493, Xbarc102, and Xbarc131, were integrated into an amplified fragment length polymorphism (AFLP) linkage group containing a major quantitative trait locus (QTL) for scab resistance in a mapping population of 133 recombinant inbred lines (RILs) derived from 'Ning7840' x 'Clark'. Based on single-factor analysis of variance of scab infection data from four experiments, Xgwm533 and Xbarc147 were the two microsatellite markers most tightly associated with the major scab resistance QTL. Interval analysis based on the integrated map of AFLP and microsatellite markers showed that the major QTL was located in a chromosome region about 8 cM in length around Xgwm533 and Xbarc147. Based on mapping of six microsatellite markers on eight 3BS deletion lines, the major QTL was located distal to breakage point 3BS-8. In total, 18 microsatellites were physically located on different subarm regions on 3BS. Two microsatellites, Xgwm120 and Xgwm614, were significantly associated with QTL for scab resistance on chromosome 2BL and 2AS, respectively. The resistance alleles on 3BS, 2BL, and 2AS were all derived from 'Ning7840'. Significant interaction between the major QTL on 3BS and the QTL on 2BL was detected based on microsatellite markers linked to them. Using these microsatellite markers would facilitate marker-assisted selection to improve scab resistance in wheat.

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