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item Vandemark, George
item Larsen, Richard
item HUGHES, T

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2005
Publication Date: 3/1/2006
Citation: Vandemark, G.J., Larsen, R.C., Hughes, T.J. 2006. Heritability of resistance to verticillium albo-atrum in alfalfa. Plant Disease. 90:314-318.

Interpretive Summary: The simplest method of inheritance of any trait is through the control of a single gene. However, this form of inheritance is more likely the exception rather than the rule. A great majority of important traits for crop improvement, referred to as quantitative traits, are controlled by interactions between environmental influences and several genes. A classic example of a quantitative trait is body weight in humans, which is controlled in part by genes, but also by environmental factors such as caloric intake and exercise. It is possible to determine the relative contributions of genetics and environment towards a quantitative trait. The fraction of the trait that is controlled by genetics is referred to as the heritability of the trait. Plant breeders use heritability estimates to determine what percentage of a population should be kept as parents for subsequent generations. Verticillium albo-atrum is a soilborne plant pathogen that causes plant death in a wide range of crops, including alfalfa, potato, and cotton. The disease can cause up to 50% reductions in yield in infested alfalfa fields. We calculated heritability estimates for resistance to verticillium wilt in alfalfa and found that up to 90% of the trait was controlled by genetics. These values will directly assist plant breeders in optimizing breeding strategies to most rapidly enhance levels of disease resistance in alfalfa.

Technical Abstract: Verticillium wilt of alfalfa, caused by Verticillium albo-atrum, may reduce yields by up to 50% in alfalfa producing areas of the northern United States and Canada. It has been suggested that cultivars require at least 60% resistant plants to afford maximum protection against disease. Our objective was to calculate heritability estimates of resistance to Verticillium albo-atrum in alfalfa. Two alfalfa populations developed from the cultivars Affinity + Z and Depend + EV were examined. Heritability on a half-sib progeny means basis was calculated based on data from greenhouse pathogenicity tests. Heritability estimates based on repeated experiments conducted for single years were high for both populations, ranging from 0.86-0.92. The heritability estimate based on data collected over two years was 0.26 for Affinity + Z and 0.66 for Depend + EV. Disease was more severe in 2005 than in 2004. However, the Spearman rank correlation between mean DSI values for half-sib families over two years was positive and significant for both populations. Results of pathogenicity tests suggested that neither cultivar had resistance levels approaching 60%. The heritability estimates suggest that resistance levels in both Affinity + Z and Depend + EV could be improved through continued selection.