Genetic mapping of genes controlling two leaf surface chemistry traits and identification of quantitative trait loci (QTL) associated with resistance to Phytophthora nicotianae in tobacco ( Nicotiana tabacum L.).

摘要

The ultimate objective of a tobacco breeder is to use genetics to improve traits contributing to improved crop production efficiency and that affect product quality. Two leaf surface chemistries, cis-abienol and beta-methylvaleric acid-containing sucrose esters (BMVSEs), are known to be associated with organoleptic properties of tobacco products and may contribute to resistance against insect pests and fungal pathogens. The black shank disease, caused by Phytophthora nicotianae, causes severe crop losses annually in many tobacco growing regions of the world. Multiple races of this pathogen make it difficult to develop tobacco cultivars with high levels of resistance to all races. In the current study, an investigation was carried out to gain insight into the genetics controlling two leaf surface chemistry traits and black shank resistance using the assistance of microsatellite markers. A cigar tobacco line, 'Beinhart 1000,' was chosen as a source of the ability to accumulate the two leaf surface chemistries and as a source of high levels of resistance against multiple races of the black shank pathogen. A doubled haploid population of 118 lines was developed from a cross between Beinhart 1000 and the flue cured cultivar, Hicks, which lacks the ability to produce the two leaf surface chemistries and is highly susceptible to the black shank disease. Field evaluations in disease nurseries were conducted using replicated trials in three environments. A genetic linkage map with 24 linkage groups was constructed by genotyping the mapping population with 190 microsatellite markers. Both genes controlling leaf surface chemistry traits were positioned on linkage group 4 and were separated by a genetic distance of 8.5 centimorgans (cM). Multiple interval mapping (MIM) analysis identified a total of six quantitative trait loci (QTL) (on linkage groups 2, 4, 8, 9, 11, and 14) associated with black shank disease resistance in Beinhart 1000. Two QTLs on linkage groups 4 and 8 were identified as having major effects and explained 20.5% and 23.5% of the phenotypic variation for end percent survival, respectively. The QTL on linkage group 4 was found to be strongly linked with the gene, Abl, controlling cis-abienol accumulation. Growth chamber evaluations of the mapping population with specific races (Race 0 and Race 1) revealed that the two major QTLs on linkage groups 4 and 8 were significantly associated with resistance to both races. The QTL on linkage group 8 was observed to have consistent large effects in both field and growth chamber evaluations. An attempt was also made to draw genetic comparisons between Beinhart 1000 and the currently most widely exploited source of black shank disease resistance, 'Florida 301'. A mapping population of 125 recombinant inbred lines (RILs) developed from the cross between Florida 301 and Hicks was used for this study. Microsatellite markers representing the six genomic regions identified to be associated with resistance in Beinhart 1000 were tested for their association with resistance in Florida 301. Markers on linkage group 8 and 2 were identified to be associated with resistance in Florida 301. Markers on linkage group 4 and other regions of interest were not significantly associated with resistance in Florida 301. Results may be useful for transferring the two leaf surface chemistry traits and black shank resistance into new cultivars using marker assisted breeding.