Jk. Pataky et al., Stewart's wilt reactions of an international collection of Zea mays germ plasm inoculated with Erwinia stewartii, PLANT DIS, 84(8), 2000, pp. 901-906
Maize accessions were evaluated in 1997, 1998, and 1999 to identify additio
nal sources of Stewart's wilt resistance and to determine if reactions diff
ered among accessions collected from various regions of the United States a
nd throughout the world. The distributions of Stewart's wilt reactions rate
d from 1 (no appreciable spread of symptoms) to 9 (dead plants) were relati
vely similar among groups of accessions from all regions of the world excep
t for those from the Mid-Atlantic/Ohio River Valley region of the United St
ates, the southern United States, and the northeastern United States. The m
ean and median Stewart's wilt rating for 1,991 accessions evaluated in 1997
was 4. The mean Stewart's wilt rating for 245 accessions collected from th
e Mid-Atlantic/Ohio River Valley region was 3.1, which was significantly lo
wer than that for accessions from all other regions. The mean rating for ac
cessions from the southern United States was 3.7, which also was lower than
mean ratings for accessions from all other regions. Ratings from trials in
1997 and 1998 were highly correlated (r = 0.87) for 292 accessions and 15
sweet corn hybrid checks evaluated in both years. Of 20 accessions rated be
low 2 in 1997 and 1998, seven were from Virginia, seven were from the Ohio
River Valley or central Corn Belt of the United States, four were from the
northern or western Corn Belt of the United States, and two were from Spain
. Ratings for these accessions ranged from 1.7 to 3.1 in 1999. Ratings rang
ed from 2.6 to 3.7 for F, hybrids of these accessions crossed with one of t
wo susceptible sweet corn inbreds, CrseW30 or Crse16, which were rated 5.7
and 5.4, respectively. Based on the reactions of this collection of germ pl
asm, it appears that high levels of Stewart's wilt resistance are prevalent
only among accessions collected from areas where the disease has been ende
mic for several years, whereas moderate levels of resistance can be found i
n accessions collected from nearly everywhere in the world.