RFLP mapping of genes conferring resistance to Erwinia stewartii
--R. Ming, M.D. McMullen, J.L. Brewbaker, H.G. Moon, T. Musket, and
R. Holley
QTLs for resistance to Stewart's bacterial wilt (E. stewartii) were mapped using recombinant inbred lines derived from Hi31 X Ki14 (see accompanying article). Ninety-six RILs and ten sub- lines of each parent had been planted at Henderson, Kentucky, by Dr. Randall Holley of Northrup-King Co., for Stewart's wilt resistance evaluation under natural infection. The bacterium E. stewartii overwinters in mature corn flea beetles. In the disease nursery at Henderson, beetle populations have been high and the field was under severe Stewart's wilt pressure last year. Among the 96 RILs planted at Henderson, 25 were eliminated due to herbicide damage (Beacon). The remaining 71 RILs were scored for Stewart's wilt severity in two replications using a 1-9 scale (1=no symptom, 9=severe symptom). The sub-lines of resistant parent Ki14 and susceptible parent Hi31 averaged 1.91 and 6.50, and ranged from 1.0 to 4.0 and 4.0 to 8.0, respectively. The F1 hybrid was scored 4.08, intermediate between its parents. The RILs ranged from 1.2 to 7.9.
One hundred twenty-seven RFLP loci were analyzed with the disease data using SAS/GLM (Table 1). Markers on the short arm of chromosome 1 showed the greatest effects on conferring resistance, suggesting a major QTL in this region. Another region on chromosome 9 also showed significant association with resistance. On chromosomes 2, 4, 5, 7, and 8, only single markers showed significant association with disease resistance (data not shown). From previous studies, few loci have been suggested to control Stewart's bacteria wilt resistance (Blanco, Phytopathology 69:849-853, 1979).
Table 1. The loci significantly associated with E. stewartii resistance
from single factor analysis of variance.
| Marker | Chrom. | Position | R^2 | Probabil. |
| umc164 | 1 | 4 | 0.0727 | 0.0286 |
| npi262 | 1 | 84 | 0.1191 | 0.0364 |
| umc167 | 1 | 98 | 0.3273 | 0.0002 |
| umc67 | 1 | 111 | 0.1224 | 0.0313 |
| bnl8.29 | 1 | 264 | 0.0754 | 0.0269 |
| umc19 | 9 | 96 | 0.1927 | 0.0083 |
| bnl7.50 | 9 | 101 | 0.1176 | 0.0406 |
| npi291 | 9 | 155 | 0.1360 | 0.0227 |
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