No description available.

In this study, RAPD (Randomly Amplified Polymorphic DNA) and SCAR (Sequence Amplified Characterized Region) markers found within 5 centiMorgans of known disease resistance loci in L. sativa were tested for their potential use in MAS. Out of thirty RAPD and SCAR markers evaluated, ten were found to be reliable predictors of disease resistance or susceptibility across a wide range of commercial and reference cultivars. Direct sequencing of seven selected markers did not reveal any significant similarity with known sequences. Three SNPs (Single Nucleotide Polymorphism) associated with two markers found in close proximity to corky root (cor) and Lettuce mosaic virus resistance (mo12) genes were identified. This information was used in the development of a non-electrophoresis PCR-based assay called FRET (Fluorescence Resonance Energy Transfer) hybridization probes assay.

Little is known about the mechanism of virus disease resistance in plants. The aim of the work presented here was to answer whether disease resistance is offered within the cell or at the level of intercellular movement of the virus. The protoplast system was used for this purpose. Conditions were optimized to isolate viable protoplasts from the leaves of Lactuca sativa cultivars. Protoplasts and leaves from resistant and susceptible Lactuca sativa cultivars were inoculated separately with turnip mosaic virus (TuMV) and lettuce mosaic virus (LMV), Virus multiplication was examined over time using enzyme-linked immunosorbent assay. Resistant cv. Kordaat did not support TuMV multiplication in protoplasts as well as in leaves. The results indicated that resistance to TuMV is available within the cell. The results ruled out the possibility of involvement of cell to cell movement and resistance to TuMV seems to be constitutive. On the other hand, protoplasts and leaves from both resistant and susceptible lettuce cultivars supported LMV multiplication. This suggested that resistance to LMV may not be offered within the cell. The results also indicated that the resistance to LMV was partly due to a hypersensitive response though virus was still able to spread systemically. To contribute towards mapping of the Tu resistance gene, the genotype of F$ sb2$ individuals was determined by screening an F$ sb3$ population from 71 F$ sb2$ individuals of a cross between cv. Calmar and cv. Kordaat for TuMV-infection. These data were useful for the production of bulks around the Tu locus to facilitate the search for new molecular markers linked to the Tu gene.

No description available.

In Lactuca sativa, the dominant gene Tu confers resistance to infection by turnip mosaic virus (TuMV). Tu and Dm5/8, a gene for resistance to Bremia lactucae, are linked in L. sativa. The area surrounding Dm5/8 on the genetic map of L. sativa contains restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) markers. The orientation of Tu relative to Dm5/8 was not known. Locating Tu would indicate which markers are on the map of lettuce close to Tu. To locate Tu on the L. sativa genetic map, F$ sb3$ families from recombinant F$ sb2$ in the Dm5/8 area of a cross between TuMV-resistant (Cobbham Green) and susceptible (Calmar) cultivars were inoculated with TuMV and phenotyped for Tu by indirect enzyme-linked immunosorbent assay. Polyclonal antibodies for immunodetection were produced using turnip mosaic virus coat protein expressed in E. coli. Phenotypic ratios within F$ sb3$ families were used to determine individual F$ sb2$ genotypes for Tu. With these genotypes, Tu was located on the genetic map of L. sativa relative to data present for Dm5/8 and surrounding markers, between OPM18 and OPY13. Using bulked segregant analysis, bulks created for the Dm5/8 locus were screened for genetic polymorphisms by the RAPD technique. Five new RAPD markers, UBC346, UBC517, UBC563, UBC599, and UBC675 were found linked to Tu after mapping relative to F$ sb2$ genotypes for Tu and other RAPD markers. The resulting three-point mapping information indicates that Tu is flanked by two markers, OPM18/OPL08 and UBC346, at respective genetic distances of 0.4 and 0.7 cM.

Lettuce mosaic virus (LMV) is an economically important pathogen with worldwide distribution. LMV infection in L. sativa can cause significant yield losses. Resistance to LMV in L. sativa is conferred by the recessive gene mo. We attempted to position the mo gene on the L. sativa map. The ultimate goal is a better understanding of plant-virus interactions. To do so, Random Amplified Polymorphic DNA (RAPD) markers were screened in the near isogenic lines (NILs) Vanguard and Vanguard 75. These NILs differ in the presence of the mo gene in Vanguard 75. Polymorphic markers were screened for linkage to mo in two F$ sb2$ populations segregating for resistance to LMV. The F$ sb2$ populations used were derived from 2 crosses, the first one between the L. sativa cultivars Dwarf 2 (resistant to LMV via the presence of mo) and Saffier and the second one between two breeding lines 87-25M-1 (momo) and 87-1090M-1 (MoMo). In order to develop a highly stringent antibody detection system to phenotype plants infected with LMV, a plasmid construct was developed which overproduces LMV coat protein. This construct will be used in the future to produce enough recombinant LMV coat protein for antibody production. To further characterize mo, a selection of cultivars resistant and susceptible to LMV according to the literature were subjected to various temperature changes to determine the environmental influences on virus movement.

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.

No description available.

No description available.

No description available.