|Mcgrath, J Mitchell - Mitch|
Submitted to: Annual Beet Sugar Development Foundation Research Report
Publication Type: Other
Publication Acceptance Date: 9/5/2002
Publication Date: N/A
Technical Abstract: Aphanomyces seedling disease is one of the causal agents preventing good stand persistence in sugarbeet. Aphanomyces generally becomes more of a problem for growers when plants are four to six weeks old, especially after a heavy rain and in flooded areas of the field. There has been no reliable seedling resistance screen. The major focus of this work has been analyses of Aphanomyces resistance in two- to three-week old seedlings. A method was developed for testing seedlings for reaction to Aphanomyces. The major considerations to accept a method were that it be able to reasonably follow field evaluation scores, able to discriminate reactions in a segregating population, and that a genetic association be evident between Aphanomyces reaction and at least one molecular marker. Two of the more important developments for this assay were to minimize zoospores from encysting, and inducing seedling vigor with hydrogen peroxide during germination. After germination, seedlings were grown in shallow water to simulate a flooding-like stress, and roots and hypocotyls were briefly bathed with a zoospore suspension. Infection was scored on appearance of hypocotyls after three to five days, with brown, water-soaked lesions indicating a severe infection. Laboratory inoculation with field results had an acceptable correlation (r = 0.79). Each of 145 F2 individuals were genotyped with 163 AFLP markers, and F3 seed from many F2 individuals were screened for Aphanomyces reaction. Resistance was heritable in this population (H2 = 67%), and QTL analyses showed that two or three loci contribute to resistance in this population.