ARS | Publication request: Disease Resistance and Plant Morphology

Submitted to: Lettuce Workshop And Leafy Vegetable International Conference Proceedings
Publication Acceptance Date: March 8, 2004
Publication Date: August 30, 2004
Citation: Grube, R.C., Aburomia, R. Disease Resistance And Plant Morphology - Building A Better Lettuce. Lettuce Workshop And Leafy Vegetable International Conference Proceedings. 2004. No Page Numbers.

Technical Abstract: In many cases, variation in susceptibility to soilborne and foliar pathogens has been attributed to differences in plant morphology or growth habit. Focusing on resistance to lettuce drop caused by Sclerotinia minor, we examined the association between variation in plant growth characteristics and pathogen tolerance. In previous studies, lettuce genotypes with the highest levels of partial resistance to S. minor, e.g. PI 251246, have been non-cultivated lettuces with primitive (usually early bolting and erect) growth habits. We and others have hypothesized that plant growth habit may affect susceptibility indirectly by altering the suitability of the pathogen habitat near the plant. Cultivated varieties of lettuce exhibit considerable variation in growth habit including plant canopy size, vigor/growth rate, and erectness between as well as within the major cultivated lettuce types (e.g. crisphead, romaine, leaf, butter). We sought to evaluate whether there were significant differences in susceptibility to S. minor among cultivars of different types, and if so, to determine whether these differences were associated with any measurable differences in plant growth habit. Cultivars of all major cultivated and non-cultivated lettuce types wee evaluated for resistance to S. minor in replicated field experiments. Significant variation in susceptibility to S. minor was detected among cultivars within as well as between major lettuce types. Field grown plants and seedlings of the same genotypes were also evaluated for several morphological traits including plant canopy size, seedling vigor, and root and shoot growth. The correlations between lettuce drop susceptibility and various aspects of plant morphology were determined. We will discuss the implications of our results for lettuce breeding. Specifically, we will address the relative feasibility of transferring resistance from primitive lettuce compared with cultivated lettuces with very different growth habits, and whether higher levels of resistance to lettuce drop and other diseases may be obtained without sacrificing desirable plant morphology.