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Title: HERITABILITY OF RESISTANCE TO APHANOMYCES EUTEICHES RACES 1 AND 2 IN ALFALFA

Author
item Vandemark, George
item BARKER, B - UNIV OF ARIZONA
item Hughes, Teresa

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2004
Publication Date: 4/1/2004
Citation: Vandemark, G.J., Barker, B.M., Hughes, T.J. 2004. Heritability of resistance to aphanomyces euteiches races 1 and 2 in alfalfa. Euphytica. 136:45-50.

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 animals or humans. Body weight certainly is controlled in part by genes, but environmental factors, such as caloric intake and exercise, also greatly influence body weight. It is possible to conduct a mathematical analysis and 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. Aphanomyces euteiches is a soilborne plant pathogen that causes plant death in pea, bean and alfalfa. In alfalfa, at least two distinct forms of the pathogen have been identified. Resistance to A. euteiches in alfalfa is considered to be quantitatively inherited. We calculated heritability estimates for resistance to A. euteiches in alfalfa and found that over 80% of the trait was controlled by genetics for form 1, while over 60% of resistance to form 2 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: Aphanomyces euteiches is a soilborne plant pathogen that causes root rot in several leguminous crops including pea, bean and alfalfa. In alfalfa, at least two distinct races of the pathogen have been identified. Although many alfalfa cultivars are resistant to the race 1 isolate of A. euteiches, resistance to race 2 isolates of the pathogen is lacking in the great majority of cultivars. Our objectives were to calculate heritability estimates of resistance to A. euteiches races 1 and 2 in alfalfa. These estimates will be useful in predicting gain from selection for disease resistance. Three different alfalfa populations developed from the cultivars 3452 ML, Affinity + Z and Depend + EV were examined in this study. Each population consisted of 32 randomly selected half-sib families. Heritability on a half-sib progeny means basis was calculated based on data from pathogenicity tests conducted under greenhouse conditions. Confidence intervals were calculated for each heritability estimate. Heritability estimates based on experiments conducted over two years were high for all populations, ranging from 0.84-0.90 for resistance to A. euteiches race 1 and from 0.62-0.66 for resistance to A. euteiches race 2. These results suggest that improving levels of resistance to both races of the pathogen should be possible through selection.