Call number: LD2668 .T4 1955 H39 / Master of Science

LD2668 .T4 1962 S65

Wheat leaf rust, caused by Puccinia triticina Eriks. (= P. recondita Rob. Ex Desmaz. f. sp. tritici), is the most widespread disease of wheat worldwide and causes average annual yield losses of 5 to 25%. The emergence of a new predominant race of leaf rust, TDBG, in the 2004 Canadian virulence survey led to the identification of a second leaf rust resistance gene segregating in the Thatcher-Lr1 near-isogenic differential line, RL6003, which produced an unusual mesothetic infection type. This gene was subsequently isolated in a Thatcher background and temporarily designated as LrCen (Tc-LrCen). A cross was made with a susceptible parent (Tc-LrCen/ Sumai3-lr34) and a doubled haploid (DH) mapping population was generated from the hybrids. Parental lines and 180 double haploid (DH) individuals were phenotyped with race TDBG and a 1:1 ratio was observed in the DH population. Parental lines and 94 DH individuals were genotyped with the Illumina Infinium assay using a custom iSelect 90K wheat SNP array. Two-point linkage between the phenotype and polymorphic SNP markers identified linked markers. A BLAST search of linked SNP sequences was performed against the Wheat Survey Sequence providing a putative chromosomal location of 7AL. Subsequent mapping with microsatellite markers confirmed LrCen was located on the long arm of chromosome 7A flanked by gwm344 (9.5 cM) and cfa2240 (0.6 cM) as well as a group of co-segregating SNPs also at a genetic distance of 0.6 cM. When the SNP sequences were converted to the kompetitive allele specific PCR (KASP) markers they were found to be dominant, making them less useful for marker assisted selection in populations with heterozygotes. LrCen mapped distal to Lr20; the only other Lr gene previously identified on chromosome 7AL. / October 2016

Call number: LD2668 .T4 1950 W6 / Master of Science

Graduation date: 1990

Call number: LD2668 .T4 1952 H8 / Master of Science

Call number: LD2668 .T4 1959 E41

Call number: LD2668 .T4 1960 D73

LD2668 .T4 1962 S57

Doctor of Philosophy / Department of Plant Pathology / Erick D. DeWolf / Stripe rust (caused by Puccinia striiformis f. sp. tritici) and leaf rust (caused by Puccinia triticina) are the top two diseases of winter wheat (Triticum aestivum) with a 20-year average yield loss of 4.9% in Kansas. Due to the significant yield losses caused by these diseases, the overall objective of this research was to identify environmental variables that favor stripe and leaf rust epidemics. The first objective was to verify the environmental conditions that favor P. triticina infections in an outdoor field environment. Wheat was inoculated with P. triticina and exposed to ambient weather conditions for 16 hours. Number of hours with temperature between 5 to 25°C and relative humidity >87% were highly correlated and predicted leaf rust infections with 89% accuracy. The results of this outdoor assay were used to develop variables to evaluate the association of environment with regional leaf rust epidemics. Before regional disease models can be developed for a forecast system, suitable predictors need to be identified. Objectives two and three of this research were to identify environmental variables associated with leaf rust and stripe rust epidemics and to evaluate these predictors in models. Mean yield loss on susceptible varieties was estimated for nine Kansas crop reporting districts (CRD’s). Monthly environmental variables were evaluated for association with stripe rust epidemics (>1% yield loss), leaf rust epidemics (>1% yield loss), severe stripe rust epidemics (>14% yield loss) and severe leaf rust epidemics (>7% yield loss) at the CRD scale. Stripe rust and leaf rust epidemics were both strongly associated with soil moisture conditions; however, the timing differed between these diseases. Stripe rust epidemics were associated with soil moisture in fall and winter, and leaf rust epidemics during winter and spring. Severe stripe rust and leaf rust epidemics were associated with favorable temperature (7 to 12°C) and temperature (15 to 20°C) with relative humidity (>87%) or precipitation in May using tree-based methods of classification, respectively. The preliminary models developed in this research could be coupled with disease observations and varietal resistance information to advise growers about the need for foliar fungicides against these rusts in Kansas winter wheat.