Author
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Grube, Rebecca |
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Submitted to: Acta Horticulture Proceedings
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/1/2003 Publication Date: 5/31/2004 Citation: Grube, R.C. Genetic analysis of resistance to lettuce drop caused by sclerotinia minor. Proceeding of the 2002 ISHS/ASHS Joint Annual Meeting, Toronto, Canada. Acta Horticulturae. 2004. v. 637. p. 49-55. Interpretive Summary: The fungal pathogen Sclerotinia minor causes the disease lettuce drop, which consistently causes significant crop losses. The disease is only partially controlled by chemical and cultural practices, and resistant lettuce cultivars do not currently exist. Several cultivated varieties and wild relatives of lettuce were tested for resistance to the pathogen. The most resistant type identified thus far, 'PI 251246', has many physiological features that make it commercially unacceptable. Our objectives were to determine how many genes in 'PI 251246' are required for resistance, and whether they may be transferred by hybridization into cultivated susceptible varieties of lettuce, without simultaneously transferring undesirable traits. 'PI 251246' was crossed with a susceptible iceberg variety 'Salinas', and a population of inbred lines containing different combinations of traits from both parents was created. Several horticultural traits and resistance were evaluated for this population. In this preliminary test, several horticultural traits (e.g. early bolting, lack of heading tendency, flat growth habit, and others) were significantly correlated with resistance. Correlations were not absolute, however, suggesting that it may be possible to incorporate resistance from 'PI 251246' into commercially acceptable lettuce cultivars. Technical Abstract: Despite extensive germplasm screening, no lettuce accessions have been identified as possessing immunity to infection by Sclerotinia species. As previously reported, several genotypes have consistently shown a significant reduction in disease incidence compared with susceptible varieties following inoculation with S. minor. Many of these genotypes exhibit architectural features that may promote avoidance or escape from infection, such as upright growth and early bolting. To date, the genetic basis and mechanisms of resistance identified in lettuce remain unknown. Transfer of resistance that is due solely to avoidance into commercial cultivars without simultaneous transfer of unacceptable plant morphology may be difficult or impossible. In contrast, physiological resistance is likely to be more easily incorporated into acceptable cultivars. To facilitate the development of lettuce cultivars with S. minor resistance, we sought to ascertain the genetic basis of resistance from the primitive L. sativa accession 'PI 251246'. Recombinant-inbred lines (RILs) from a 'Salinas' x 'PI 251246' F2 population were developed to determine the heritability and action of genes involved in resistance derived from 'PI 251246' and for mapping of quantitative resistance loci. Results and implications of preliminary evaluation of F2:4 RILs in a replicated field trial will be discussed. |
