Graduation date: 1998

Graduation date: 1996

Cucurbit yellow stunting disorder virus (CYSDV) is a relatively new virus affecting cantaloupe production in South Texas and worldwide. No resistant commercial cultivars are available. A cross of ‘Dulce’ (susceptible) x ‘TGR1551’ (resistant) was made and populations were developed for screening. Although no complete resistance was recovered, ‘TGR1551’ showed some tolerance and may be useful in breeding efforts. Sugar components such as sucrose, fructose, glucose, and total soluble solids are major factors in determining mature melon fruit sweetness, and Vitamin C is important for human health. A F2 population was developed from the melon cross ‘Dulce’ (high values) x ‘TGR1551’ (low values) and bulked segregant analysis was used to detect random amplified polymorphic DNA (RAPD) markers associated with quantitative trait loci (QTL) for each trait. Out of 500 primers, fifteen RAPD markers were found to be significantly associated with fruit quality QTL. These markers could be useful in a marker assisted selection program to transfer these genes into a low quality cultivar or breeding line to enhance fruit quality. Gummy stem blight (Didymella brioniae) affects melon production in South Texas as well as other melon production areas in the U.S. A cross between ‘TMS’ (susceptible) and PI 140471 (resistant) was made and a F2 population was screened with a strain of the disease from South Texas. F2 plants exhibited symptoms ranging from resistant to susceptible. PI 140471 may be useful in developing commercial varieties of melon resistant to the disease in Texas. Monosporascus root rot and vine decline (Monosporascus cannonballus) affects melon production in South Texas as well as other melon production areas in the US. A cross was made between ‘TGR1551’ (moderately resistant) and ‘Deltex’ (resistant) to develop a F2 population. Both parents and the F2 were planted in infested soil. Once symptoms appeared, plant roots were removed from the soil and rated. ‘TGR1551’ showed greater resistance than ‘Deltex’ and should be utilized in breeding to develop improved resistant cultivars.

Three cultivators, Rabewerk, Kongskilde and Hiniker, and three intercrops, soybean, lupin and red clover + rye grass were investigated for their impact on the incidence of ear rot of corn, a common disease of maize in eastern Canada. Wheat was seeded in the corn rows to serve as an additional indicator of cultivation and intercropping effects on the pathogen. An artificial inoculum of F. graminearum that produced perithecia and ascospores was used to mimic natural inoculum. / In 1993 and 1994, the infection in the corn was not very severe and there were no differences between the treatments and the controls. / In 1993 and 1994, at both sites, wheat seeds from cultivation trials showed a tendency for greater disease incidence in the non-cultivated herbicide treatment when compared to any of the other cultivator treatments. Cultivators till the soil and bury corn residues, this action led to the destruction of some of the inoculum and a subsequent reduction of the disease incidence in the cultivated plots. / In the intercrop trial of 1993 and 1994, wheat infection was moderate to severe, except at L'Assomption in 1993, but no significant differences were observed among the treatments. It is believed that interplot interference, due to ascospores moving from one plot to the next, masked differences. / The results indicated that weed cultivation would have a negligible or no effect on the development of fusarium ear rot of corn in Quebec. (Abstract shortened by UMI.)

Fusarium graminearum causes Fusarium Head Blight, (one of) the most destructive cereal diseases in Canada. Yield loss, quality degradation and mycotoxin production make Fusarium a multifaceted threat. Regulated production of reactive oxygen species by Nox enzymes is indispensable for fungal pathogenesis. F. graminearum Nox mutant ∆noxAB produced equivalent mycotoxin but caused reduced virulence than wild-type. We hypothesized that Nox mediated redox signaling may participate in F. graminearum pathogenicity. Two-DE and gel-free biotin affinity chromatography, followed by LC-MS/MS analysis were employed for a comparative redox-proteomics analysis between wild-type and ∆noxAB to identify proteins oxidized by Nox activity. Total 35 proteins, 10 by 2-DE and 29 by gel-free system, were identified. 34% proteins participated in fungal metabolism, 20% in electron transfer reactions and 9% were anti-oxidant proteins. The findings suggested that Nox mediated thiol-disulfide exchange in proteins provide a switch for redox-dependent regulation of metabolic and developmental processes during induction of FHB.

Fusarium head blight (FHB), a fungal disease caused principally by Fusarium graminearum, and barley yellow dwarf (BYD) caused by BYD luteoviruses are two serious fungal and viral diseases of wheat resulting in high economic losses annually. Wuhan, a Chinese wheat cultivar resistant to FHB, and Maringa, a Brazilian cultivar tolerant to BYDV were inter-crossed and crossed with Roblin, a Canada western red spring wheat susceptible to both FHB and BYDV, to determine the genetic basis of resistance/tolerance and to combine the two traits. Four hundred ninety nine F1-derived doubled haploid (DH) lines were generated from reciprocal crosses using corn pollen-mediated DH technology. The DH lines and the parents were evaluated for disease symptoms, reduction in height and spike mass for BYD and for disease incidence, disease severity and Fusarium-damaged kernels for FHB in field and controlled environments. A subset (20/150) of the best performing DH lines from Wuhan/Maringa populations for both BYD and FHB were further evaluated. Plants were point inoculated with F. graminearum in greenhouse experiments, and macroconidial spray inoculations and spread of corn inoculum were used in field environments to evaluate FHB. BYDV inoculations were performed by placing ten to fifteen viruliferous aphids (Rhopalosiphum padi infected with BYDV-PAV isolate 9301PAV), at the one to two leaf stage for both greenhouse and field trials. The studies showed that both FHB and BYDV are quantitatively inherited. Transgressive segregants were observed and the broad sense heritability was high (0.90 to 0.97) for all traits evaluated. Results from independent testing of diseases on Wuhan/ Maringa populations showed fourteen DH lines were as, or more resistant than Wuhan for FHB and Maringa for BYDV tolerance and have combined both BYDV tolerance and FHB resistance. Identifying such lines facilitates the pyramiding of independent genes to obtain adequate levels of enduring resistance. A further experiment was conducted on the 14 lines by inoculating them with BYDV and F. graminearum successively on the same plant. Six out of 14 selected DH lines demonstrated high resistance to FHB and tolerance to BYDV. These six lines can be used in FHB/BYDV resistance/tolerance breeding programs.

Fusarium graminearum, the causative agent of Fusarium head blight, is an economically important pathogen of wheat (Triticum aestivum). Breeding Fusarium head blight (FHB) resistant wheat requires knowledge of the underlying genetic control of FHB resistance. Genetic parameters for FHB resistance and five related traits were estimated in three populations at two locations and in two years. Moderate broad sense heritabilities for FHB severity and Fusarium damaged kernels (FDK) were observed. Incidence of FHB and the toxin deoxynivalenol (DON) accumulation had low to moderate broad sense heritabilities. Correlations between FDK and severity and FDK and DON were moderate to high in the three populations and do support indirect selection for FHB severity or DON based on FDK data alone, but it is important to be cautious in years with a high disease pressure when FHB resistance could be masked. A cycle of among-family and within-family selection cycle was conducted in 2003. Actual selection gain was higher than predicted gain based on variance components in 2003 in the within-family selection study. One population had also a strong response for low DON in the among-family selection study. The observed results suggest that selection for FHB resistant genotypes could be achieved with a recurrent selection scheme. Along with conventional breeding, molecular techniques are being used in breeding for FHB resistance. A first genotypic screening of the three populations showed Population 2 had the presence of a resistance allele form the resistant Chinese cultivar Sumai 3. Although Populations 1 and 3 did not have the resistance allele, the results suggest other sources of resistance might be present in these two populations.

Fusarium graminearum, the causative agent of Fusarium head blight, is an economically important pathogen of wheat (Triticum aestivum). Breeding Fusarium head blight (FHB) resistant wheat requires knowledge of the underlying genetic control of FHB resistance. Two nine-parent diallel analyses were completed in greenhouse and field environments. Combining abilities, variance component ratios, and narrow sense heritabilities for FHB resistance and deoxynivalenol levels were calculated. Significant general and specific combining ability effects were observed. Resistance to FHB seems to be mostly controlled by additive genetic effects with some dominance noted in the field. Resistance noted in the greenhouse environment may not hold up in the field. Genetic parameters for FHB resistance and four related traits were estimated in three populations. Moderate to high broad sense heritabilities for FHB severity and Fusarium damaged kernels (FDK) were observed. Incidence of FHB had low to moderate broad sense heritabilities. Correlations between FDK and severity and FDK and incidence were moderate and low, respectively, and do not support indirect selection for FHB severity or incidence based on FDK data alone. Substantial predicted gains from family selection were observed and therefore selection of FHB resistant wheat lines should be based on family means and not individual selection.

The use of exotic resistance quantitative trait loci (QTL) provides one strategy for breeding wheat cultivars resistant to Fusarium Head Blight (FHB), a devastating disease of wheat. The objective of this study was to evaluate the effectiveness of two QTL, Fhb1 and QFhs.nau-2DL, in diverse genetic backgrounds and to evaluate their effects on agronomic and quality traits. Five populations from crosses between FHB susceptible parents (26R58, KY97C-0574-01, 25R54, KY97C, KY97C-0554-02, 25R78 and KY93C-1238-17-1) and FHB-resistant VA01W-476, were evaluated in the FHB nursery at Lexington, KY in 2010 and 2011. The populations were also grown in yield trials at Lexington (2010 and 2011) and Princeton (2011), KY, to measure agronomic and quality traits. Fhb1 reduced Fusarium damaged kernels (FDK) by 32% and the toxin, deoxynivalenol (DON) by 20%. QFhs.nau-2DL significantly reduced mean FDK by 29% in two of five populations and DON by 24% in four of five populations. While the effects of these QTL on agronomic and quality traits were significant, the impact was small. One cycle of either direct or indirect simulated phenotypic selection was effective at reducing DON levels and the frequency of Fhb1-homozygous resistant lines among the selects was higher than the frequency of QFhs.nau-2DL-homozygous resistant lines.

Fusarium Head Blight (FHB) is a destructive disease caused by Fusarium graminearum that affects wheat (Triticum aestivum L.) worldwide. Breeding for resistance to FHB is arguably the best way to combat this disease. However, FHB resistance is highly complex and phenotypic screening is difficult. Molecular markers are a promising tool but breeding programs face the challenge of allocating resources in such a way that the optimum balance between phenotypic and genotypic selection is reached. An F2:3 population derived from a resistant x susceptible cross was subjected to phenotypic and genotypic selection. For phenotyping, a novel air separation method was used to measure percentage of damaged kernels (FDK). Heritability estimates were remarkably high, which was attributed to the type of cross and the quality of phenotyping. Genotypic selection was done by selecting resistance alleles at quantitative trait loci (QTL) on the 3BS (Fhb1) and the 2DL chromosomes. Fhb1 conferred a moderate but stable FHB resistance while the 2DL QTL conferred a surprisingly high level of resistance but with significant interaction with the environment. Phenotypic selection conferred higher or lower genetic gains than genotypic selection, depending on the selection intensity. Based on these results, different selection strategies are discussed.