In lettuce (Lactuca sativa), the dominant gene Tu confers resistance to turnip mosaic virus (TuMV) infection. In order to eventually clone and characterize the Tu gene using a map-based cloning strategy, the chromosome region in which Tu is located needs to be saturated with molecular markers. Random polymorphic DNA (RAPD) markers were screened using bulked segregant analysis. Nine new RAPD markers, UBC431$ rm sb{420}, UBC431 sb{940}, UBC434 sb{360}, UBC434 sb{1000}, UBC439 sb{520}, UBC448 sb{685:750}, UBC135 sb{240}, OP108 sb{410} and OP108 sb{1305},$ were identified as linked to Tu. Each marker was mapped relative to Tu using F$ sb2$ individuals previously known to be recombinant in the area surrounding the Tu locus. Three new markers, UBC431$ rm sb{420}, UBC439 sb{520} and UBC135 sb{240}$ are within a 5 cM area of Tu. As the number of DNA markers on the map increased map expansion and difficulties in determining a unique order were encountered. To increase the confidence in the estimate of genetic distances, a population of 500 F$ sb2$ plants was screened in order to identify more recombinant individuals around the Tu locus. The population was screened using markers UBC431$ sb{420}$ and UBC135$ sb{240}.$ Thirty-three recombinants were identified in an interval of 6.6 cM. Two markers, UBC346$ sb{1067}$ and OP108$ sb{634},$ tightly flanking Tu were converted to sequence characterized amplified regions (SCAR 346 and SCAR L08). No polymorphism was detected among the SCARs generated. The area surrounding Tu now includes 24 RAPD markers in an interval of 44 cM.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves [179]-196). / Microfiche. / xv, 196 leaves, bound ill. 29 cm

Stripe rust (Puccinia striiformis f. sp. hordei) is a serious disease of barley that can cause up to 70% yield loss in susceptible varieties. The fungus is moving northward, threatening major barley production areas in the US, where most cultivars are susceptible. Fungicides are available for control of stripe rust, but economic and environmental considerations favor genetic resistance. Two stripe rust resistance quantitative trait loci (QTLs) located in chromosomes 4 and 7 have previously been reported. One hundred and ten doubled haploid progeny from a stripe rust susceptible x resistant cross were derived using the Hordeum bulbosum technique and phenotyped for agronomic and malting quality traits in order to assess the importance of linkage drag associated with the mapped stripe rust resistance QTLs. Data on 33 markers were combined with phenotypic data for QTL analysis. A molecular marker-assisted backcross program was implemented to initiate the transfer of the stripe rust resistance loci into susceptible US germplasm. No negative QTLs for agronomic or malting quality traits were detected within or adjacent to the intervals that were targeted for marker-assisted selection. A minor leaf rust resistance QTL, however, was found adjacent to the stripe rust locus on chromosome 7. Linkage drag in this region could operate in favor of the breeder. Epistatic interaction between the two stripe rust resistance QTLs confirms the necessity of introgressing both chromosome intervals. / Graduation date: 1994

Bibliography: leaves 137-163. / vii, 163, [25] leaves, [13] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / his is a comprehensive study of induced homoeologous recombination along most of the complete genetic length of two homoeologous chromosomes in the Triticeae (7A of common wheat and 7Ai of Agropyron intermedium), using co-dominant DNA markers. Chromosome 7Ai was chosen as a model alien chromosome because is has been reported to carry agronomically important genes conferring resistance to stem rust and barley yellow dwarf virus on its short and long arms, respectively. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1997

Bibliography: 136-146 / v, 146 leaves, [9] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Agronomy, University of Adelaide, 1987

X-disease, caused by phytoplasmas, is one of the destructive diseases in stone fruit trees, causing yield loss and poor fruit quality. So far no effective methods are available to control X-disease. X-disease resistance has been first discovered in chokecherry (Prunus virginiana, 2n=4x=32), which is a native woody species of North America. To identify molecular markers linked to X-disease resistance, simple sequence repeat (SSR) markers were used to construct genetic linkage maps for chokecherry and to identify markers associated with X-disease resistance in chokecherry. In this research, three segregating populations of chokecherry were developed by crossing one X-disease resistant (CL) with three susceptible chokecherry lines (a, c, and d), of which the progenies were 101, 177, and 82, respectively. In order to construct a genetic map for chokecherry, 108 pairs of SSR primers were employed from other Prunus species. Additionally, a set of 246 SSRs were developed from chokecherry sequencing by Roche 454 sequencing technology. A total of 354 pairs of SSR primers were used to screen individuals of all three populations. Two software programs, TetraploidMap and JoinMap, were used to construct linkage map based on single-dose restriction fragments (SDRFs) and two parental linkage maps were generated for each population from both software programs. Bulked segregant analysis (BSA) was applied for identification of X-disease resistance markers. As a result, one SSR marker was found to be linked to the X-disease resistance. The set of 246 chokecherry SSRs was later used to test transferability among another 11 rosaceous species (sour cherry, sweet cherry, wild cherry, peach, apricot, plum, apple, crabapple, pear, june berry, and raspberry). As a result, chokecherry SSR primers can be transferable in Prunus species or other rosaceous species. An average of 63.2% and 58.7% of amplifiable chokecherry primers amplified DNA from cherry and other Prunus species, respectively, while 47.2% of amplifiable chokecherry primers can be transferable to other rosaceous species. The genetic information, including genetic map, disease linked marker, chokecherry sequence, and confirmed transferability of the identified chokecherry SSRs to other species, will benefit the genetic research in Prunus and other rosaceous species.

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