Browsing by Subject "disease resistance"
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Item Facultative expression of hygienic behaviour of honey bees in relation to disease resistance(Taylor and Francis, 1993) Spivak, Marla; Gilliam, MarthaFour experiments were conducted to examine factors that influence the expression of hygienic and non-hygienic behaviour in honey bees, Apis mel/itera, and to examine the correlation between this behaviour and resistance to chalkbrood, Ascosphaera apis. Colonies were headed by instrumentally inseminated queens selected on the basis of uncapping and removal behaviour expressed by their progeny. In the first experiment, colony strength was altered by transferring hygienic and nonhygienic colonies from 1O-frame field hives to 2-frame observation hives. This treatment significantly reduced the hygienic response of the hygienic bees but did not affect the response of the non-hygienic bees. In the second experiment, hygienic and non-hygienic bees displayed different responses to freeze-killed and live brood which had been partially or entirely uncapped. Both lines of bees recapped both partially and entirely uncapped live brood, but non-hygienic bees also recapped partially uncapped freeze-killed brood, suggesting that non-hygienic bees either could not detect dead or diseased brood or avoided it by sealing it within a comb cell. The third experiment tested whether the degree of hygienic behaviour could be increased by adding hygienic bees to non-hygienic colonies. Adding 20-30% young hygienic bees to nonhygienic colonies did not increase the degree of hygienic behaviour, but adding young nonhygienic bees to hygienic colonies suppressed the behaviour. The results suggest that although hygienic behavior is genetically determined, its expression depends on colony strength and composition of workers within the colony. In the fourth experiment, the hygienic and non-hygienic colonies were fed with pollen patties containing A. apis spores. The weak correspondence that was observed between removal behaviour and physiological resistance to chalkbrood suggested that few colonies are both highly hygienic and physiologically resistant to chalkbrood. Selection against uncapping and removing diseased brood might occur if this behaviour also promotes the spread of disease through the colony. This possibility is discussed in relation to avoidance behaviour of other social insects toward pathogens.Item IDENTIFICATION AND GENETIC CHARACTERIZATION OF BACTERIAL LEAF STREAK RESISTANCE IN BARLEY(2022-03) Ritzinger, MitchellBarley is a globally important crop whose production can be limited by bacterial leaf streak (BLS) caused by Xanthomonas translucens pv. translucens. The deployment of resistant cultivars is the best means for controlling the disease. To identify resistant accessions for use in breeding, 2,094 diverse barley accessions were screened to BLS in the field, and 32 were found to possess a high level of resistance and a desirable maturity time. A genome-wide association study was conducted on two panels of advanced breeding lines from the large-scale screening study to characterize the genetic architecture of BLS resistance. Eight quantitative trait loci for BLS resistance were identified: two each on chromosomes 1H, 2H, and 3H and one each on chromosomes 5H and 6H. The resistant germplasm identified in this study together with data elucidating the genetic basis of the trait will facilitate the development of BLS resistant barley cultivars.Item Identification of markers associated with race-specific resistance to Aphanomyces root rot in alfalfa, Poster at the 2017 APS meeting(2017) Samac, Deborah; Bucciarelli, Bruna; Dornbusch, Melinda; Miller, Susan; Yu, Long-XiAphanomyces root rot, caused by Aphanomyces euteiches, is one of the most important diseases of alfalfa in the United States. Two races of the pathogen are recognized and although most cultivars are resistant to race 1, fewer have resistance to race 2, the predominant race in North America. Molecular markers are needed to facilitate breeding for resistance and to clarify race/resistance gene structure. Resistant and susceptible seedlings were identified from three resistant cultivars, WAPH1, WAPH5 and 53V52, and used as parents to produce F1 populations. Severity of symptoms corresponded with amount of pathogen DNA and oospore density in roots. Race-specific resistance involves a hypersensitive response of individual epidermal or cortical cells upon pathogen attack followed by suberization of cells surrounding the stele and strong autofluorescence in cortical cells, indicating the presence of phenolic compounds. Segregation ratios of F1 populations suggested that resistance to race 1 in WAPH1 is conditioned by a single gene but resistance to race 1 is multigenic in WAPH5 and 53V52, and resistance to race 2 is multigenic in all three cultivars. Segregation for resistance to seven strains of A. euteiches in 70 F1 full-sib plants derived from 53V52 suggested the presence of clustered resistance genes and multiple race types. Identification of resistance gene loci is in progress using genotyping by sequencing and genetic mapping of F1 populations.Item Lignin reduction in alfalfa (Medicago sativa) does not affect foliar disease resistance(2018) Samac, Deborah A; Ao, Samadangla; Dornbusch, Melinda R; Grev, Amanda M; Wells, M Scott; Martinson, Krishona; Sheaffer, Craig CDisruptions in the lignin biosynthetic pathway have been shown to reduce disease resistance in a number of crops. Recently, genetically modified alfalfa (Medicago sativa) varieties have been marketed with reduced lignin and improved forage quality traits, including increased digestibility by ruminants at later stages of plant maturity. The objective of this study was to compare foliar disease resistance in three reference alfalfa varieties, 54R02, DKA43-22RR, WL355.RR, and the reduced lignin variety, 54HVX41, to evaluate the effect of the reduced lignin trait on foliar disease resistance. Alfalfa plants in research plots at three locations in Minnesota were evaluated for percent defoliation caused by foliar pathogens at four maturity stages; early bud, bud, early flower, and flowering; with natural inoculum. Spring black stem and leaf spot, Leptosphaerulina leaf spot, and common leaf spot were observed from June through September in all locations on all varieties. Summer black stem and leaf spot was most prevalent in August on all varieties at one location. The amount of defoliation increased with maturity stage for all varieties. When harvest was delayed until the flowering stage, moderate to severe (32 to 64%) leaf loss occurred, depending on location. Alfalfa varieties did not differ in percent defoliation at any maturity stage indicating that the reduced lignin trait did not affect foliar disease resistance.Item Management Strategies for Hop Downy Mildew Utilizing Fungicides and Host Resistance(2017-07) Havill, JoshHop (Humulus lupulus L.) is an herbaceous perennial plant species that is native to the Northern hemisphere. The hop inflorescences are utilized during the production of beer. Commercial production of hops requires the use of fungicides and host resistance to retain high overall yields and quality characteristics that brewers are satisfied with. The primary objectives of this research were to determine effective fungicidal compounds that can be used to control hop downy mildew (caused by Pseudoperonospora humuli (Miy. et Takah.) Wils.) and to collect and characterize a panel of 112 diverse H. lupulus accessions for resistance to P. humuli. Results from field fungicide trials indicate that significant interactions exist between cultivars, environments, and fungicidal compounds with regards to disease severity. With regards to host resistance, H. lupulus var. lupuloides E. Small accessions originating from the United States were highly-resistant to P. humuli compared to their North American counterparts H. lupulus var. neomexicanus Nelson & Cockerell or H. lupulus var. pubescens E. Small. Comparisons of H. lupulus var. lupuloides from Canada indicated that accessions from the United States were significantly more resistant to P. humuli, but not significantly different from H. lupulus var. lupulus accessions originating from Kazakhstan. These results indicate that control of hop downy mildew can be accomplished through use of resistant cultivars, fungicidal compounds, and selection of proper environments for cultivation. Additionally, utilization of H. lupulus var. lupuloides will increase the diversity of resistant sources to hop downy mildew in the development of new cultivars.Item Misfits of wheat stem rust resistance-‐ Unusual solutions to a consistent problem(2016-12) Briggs, JordanRust fungi include some of the most economically damaging pathogens of wheat. They are notorious for their ability to quickly spread in susceptible host populations and greatly reduce grain yield potential and quality when managed improperly. Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem rust, can cause yield losses exceeding 50%. Stem rust is controlled in the U.S.A. using several methods including the introduction of genetic resistance, selection for earlier maturing varieties, removal of the alternate host Berberis vulgaris, and the application of fungicides. Subsequently, epidemics of stem rust causing greater than 10% yield losses have not been observed in the U.S.A. since the mid 1950’s. Together, removal of B. vulgaris from wheat growing regions and the introduction of genetic resistance have accounted for much of the control of stem rust. Genetic resistance remains the dominant method of controlling stem rust in regions where removing B. vulgaris is not applicable. In more recent years, races of Pgt have been identified that overcome most widely deployed resistance genes. In 1999 race TTKSK was identified in Uganda that overcame stem rust resistance gene Sr31. Following deployment of Sr24 in Kenya, further selection for virulence resulted in the identification of race TTKST, then TTTSK (Sr36 virulence), and more recently TTKTT and TTKTK (SrTmp virulence). Major resistance genes have continually proven to not provide a durable form of resistance to wheat stem rust. Some resistance genes however have proven the test of time and remain effective to date. These resistance genes include Sr2, Lr34, Lr46, and Lr67. Each gene functions in an additive, minor-effect, and in some cases recessive manner, atypical of standard major genes, and provides and/or enhances resistance to multiple diseases including stem rust, leaf rust, stripe rust, and powdery mildew. Additionally Lr34 and Lr67 do not have the NB-LRR protein domains consistent with major genes. Durable genetic resistance to stem rust may require sources of resistance that deviate from standard mechanisms. This dissertation describes such sources of resistance. SrTm4 is a major gene identified in Triticum monococcum that functions in a recessive manner, is broadly effective, and elicits a mesothetic (intermediate-effect) infection type. The adult plant resistance observed in ‘Morocho Blanco’ was found to have two underlying QTL, Qsr.cdl.2BS.2 and Qsr.cdl.6AS.1. These two loci comprise much of the adult plant resistance in ‘Morocho Blanco’ and exhibit interactions with environment or pathogen race. The Sr12 mutants created in this dissertation were made to characterize the disease reducing capabilities of Sr12: a recessive, race specific major gene that co-locates with adult plant resistance to Sr12 virulent races. Lastly, this dissertation also describes the identification of putative susceptibility genes for rust pathogens in barley, maize, soybean, and Brachypodium distachyon. The putative susceptibility gene in B. distachyon was tested with a T-DNA insertion mutant and exhibits enhanced rust resistance, however, may be linked to changes in overall plant growth and development. Each source of rust resistance defies standard systems of characterization and includes some traits that are less desirable along with their resistance capabilities, for example: unstable expression due to environmental interactions, race specificity, or recessive gene action. However, the benefit of these sources of stem rust resistance may compensate for their less desirable traits.Item Reaction of barley seedlings with different stem rust resistance genes to Puccinia graminis f. sp. tritici and P. g. f. sp. secalis(Canadian Journal of Plant Pathology, 2005-03-01) Sun, Y; Steffenson, BrianSeedling tests are desirable for disease resistance screening in breeding programs because a large number of lines can be evaluated in a short period of time and with modest space requirements. This study was undertaken to identify pathotypes of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici) and cultures of the rye stem rust pathogen (Puccinia graminis f. sp. secalis) that might be useful for detecting resistance genes in barley (Hordeum vulgare) at the seedling stage. Barley accessions with different resistance genes (Rpg1, Rpg2, Rpg3, rpg4, and rpgBH) were assessed for their infection types (ITs) to 13 pathotypes of P. graminis f. sp. tritici and two cultures of P. graminis f. sp. secalis at two temperature regimes (18–21 °C and 24–25 °C). The P. graminis f. sp. tritici pathotypes HKHJ and QCCJ were effective for specifically detecting Rpg1 and rpg4, respectively, and will facilitate resistance breeding efforts. No cultures were found to be effective for specifically detecting the resistance of Hietpas-5, PI 382313, or Black Hulless at the seedling stage. Some pathotypes or cultures did, however, produce low ITs on these sources and will therefore be useful for genetic studies involving crosses with susceptible barleysItem A resistance gene to Ustilago nuda in barley is located on chromosome 3H(Canadian Journal of Plant Pathology, 2010-06-07) Menzies, J.G; Steffenson, Brian; Kleinhofs, ALoose smut of barley is a common disease which can be controlled using resistant varieties. Information on the chromosome location of loci controlling loose smut resistance and the development of molecular markers to aid in selection for these genes can be beneficial in the resistant variety development process. The objectives of this work were to determine the resistance or susceptibility of doubled haploid barley lines arising from a cross of the varieties ‘Steptoe’ and ‘Morex’ to Ustilago nuda, the causal agent of loose smut of barley, and map the chromosome location of the loose smut resistance locus in ‘Morex’. The reaction to Ustilago nuda of the doubled-haploid barley plants was determined by inoculating spikelets of each line at anthesis by injection of a teliospore suspension using a needle inoculation method. Mature seeds from the inoculated spikelets were grown to determine the percentage of plants that developed with smutted heads. The lines were classified as susceptible if greater than 10% of the plants were smutted. The loose smut resistance locus from the resistant source ‘Morex’ was mapped using an existing DNA marker map of the ‘Steptoe’/‘Morex’ population. The distribution of the resistant and susceptible progeny from the loose smut testing fit a single gene model. The resistance gene was mapped to chromosome 3 (3H).Item Resistance to American foulbrood disease by honey bee colonies Apis mellifera bred for hygienic behavior(2001) Spivak, Marla; Reuter, Gary S.Honey bee colonies, selected for hygienic behavior on the basis of a freeze-killed brood assay, demonstrated resistance to American foulbrood disease. Over two summers in 1998 and 1999, 18 hygienic and 18 non-hygienic colonies containing instrumentally inseminated queens were challenged with comb sections containing spores of the bacterium Paenibacillus larvae subsp. larvae that causes the disease. The strain of bacterium was demonstrated to be resistant to oxytetracycline antibiotic. Seven (39%) hygienic colonies developed clinical symptoms of the disease but five of these recovered (had no visible symptoms) leaving two colonies (11%) with clinical symptoms. In contrast, 100% of the non-hygienic colonies that were challenged developed clinical symptoms, and only one recovered. All non-hygienic colonies had symptoms of naturally occurring chalkbrood disease (Ascosphaera apis) throughout both summers. In contrast 33% of the hygienic colonies developed clinical symptoms of chalkbrood after they were challenged with American foulbrood, but all recovered. The diseased non-hygienic colonies produced significantly less honey than the hygienic colonies.