Development of a Standardized Test for Evaluating Alfalfa for
Resistance to Aphanomyces euteiches Race 2
B. D. Hudelson and C. R. Grau
University of Wisconsin-Madison, Madison, WI 53706
Aphanomyces euteiches causes seedling and root health problems of alfalfa especially when soil moisture is excessively high. WAPH-1 alfalfa germplasm was released in 1992 and was intended as a source of resistance and a resistant check for the alfalfa industry (1). Isolates highly virulent to WAPH-1 were discovered in 1988 and were designated as race 2. Isolates with low virulence to WAPH-1 were designated as race 1. The importance and impact of race 2 has not been documented, but some level of anticipatory breeding is recommended to alfalfa breeders. Thus, a standardized test for A. euteiches race 2 has been developed. WAPH-5 alfalfa germplasm was developed as a resistant standard for race 2 isolates of A. euteiches. Initially, attempts were made to improve WAPH-1 for resistance to race 2 isolates, but genetic gain could not be made after three cycles of selection. Fifty plant introductions (PIs) were identified that expressed variability for resistance to race 2 isolates. Although several PIs were possible candidates, PI 468018, PI 439006, and PI 468471 were used to incorporate resistance to race 2 into an adapted germplasm pool (ADP) derived from WAPH-1. Plants of each plant introductions were challenged with race 2 isolates (NC-1 and WI-98) of A. euteiches. Race 2 resistant phenotypes were selected and intermated with ADP plants which had been previously selected for resistance to Phytophthora medicaginis, Verticillium albo-atrum and Colletotrichum trifolii. A base population was kept separate for each PI source for three cycles of selection. Resistant plants from each PI source were selected in cycle 4 and intermated to develop WAPH-3. Two additional cycles of selection were performed to develop WAPH-5. The development of WAPH-5 and the standardized test was done in collaboration with private sector alfalfa scientists from ABI Alfalfa, FFR Cooperative, Cal-West, Forage Genetics, W-L Research, Pioneer and Dairyland.
Table 1. Reaction of alfalfa populations to isolates of race 1 and race 2 of Aphanomyces euteiches
| Population |
Isolate MF-1 (race 1) |
Isolate NC-1 (race 2) |
||||
|
% |
Transformed |
DSI |
% |
Transformed |
DSI | |
|
Agate |
8 |
0.23 |
3.48 |
3 |
0.15 |
3.84 |
|
Saranac |
3 |
0.12 |
3.65 |
2 |
0.07 |
3.96 |
|
WAPH-1 |
44 |
0.72 |
2.58 |
6 |
0.20 |
3.66 |
|
WAPH-3 |
54 |
0.83 |
2.30 |
26 |
0.50 |
3.00 |
|
WAPH-4 |
71 |
1.03 |
1.88 |
44 |
0.72 |
2.62 |
|
WAPH-5 |
71 |
1.03 |
2.02 |
50 |
0.79 |
2.56 |
|
LSD (0.05) |
--- |
0.13 |
0.30 |
--- |
0.17 |
0.35 |
|
CV% |
--- |
18.6 |
9.8 |
--- |
38.2 |
8.2 |
Literature
Grau, C.R. 1992. Registration of WAPH-1 alfalfa germplasm with resistance to Aphanomyces root rot. Crop Sci. 32:287-288.