Evaluation location: Iowa, United States
Eight hundred and fifty-one maize accessions were evaluated for resistance to Stewart's wilt, caused by Pantoea (Erwinia) stewartii. Accessions were grown at the NCRPIS farm at Ames, IA in two replicate plots, with 15-18 plants per plot. The first replication was planted on 08-MAY-2002 and the second was planted on 29-MAY. Inoculations were done by the pinprick method, on 21-JUN (1st rep), 03-JUL (2nd rep), and repeated one week later for each replication. Inoculum was produced from a mixture of two P. stewartii isolates (Iowa origin). Ratings were done between 23-AUG and 06-SEP-2002, depending on maturity. Individual plant scores (10-12 plants) were averaged to obtain a disease rating for each plot. Some plots were lost due to spring flooding and only one replication was available for some accessions. A composite disease average was calculated if both replicates were available. Disease reactions were scored on a 1-9 scale where: 1= no appreciable spread of symptoms from pinpricks (within 1 cm); 2= limited spread of lesions from pinpricks (within 3 cm); 3= limited spread from pinpricks with water-soaking, chlorosis, or necrosis; spread occurring mainly toward tips of leaves; 4= abundant spread from pinpricks with water-soaking, chlorosis, or necrosis toward both ends of inoculated leaves, but no evidence of systemic infection; 5= lesions spread to the main stalk; minimal systemic infection observed; 6= moderate systemic infection with 5-25% symptomatic leaf area on non-inoculated leaves; 7= abundant systemic infection and stunting with 25-50% of the leaf area symptomatic; 8= severe systemic infection and stunting with 50-90% of the plant infected; and 9= 90-100% infection, severe necrosis or dead. The checks were B37 (mod. resistant) and A632 (mod. susc.) with average ratings of 2.6 and 5.8, respectively. Disease development was excellent and provided a good test of resistance.