Evaluation location: Iowa, United States
Three hundred and seventy-three maize accessions were tested for resistance to Stewart's wilt, caused by Pantoea (Erwinia) stewartii. Plots were planted on 06-May-2004 at the NCRPIS farm at Ames, IA. Accessions were grown in three replicate plots with 15-18 plants per plot (row). Inoculations were done by the pinprick method on 08-JUN-2004 at the 6 to 8-leaf stage and again on 24-JUN-2004. Inoculum was produced from a mixture of two P. stewartii isolates (Iowa origin). Ratings were done between 29-JUL-2004 and 02-SEP-2004, based on plant maturity (silks brown and dry). Individual plant scores (10-12 plants) were averaged to obtain a disease rating for each plot. Scores for the three replications were averaged for each accession. 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 3.1 and 4.8, respectively. Disease development was slowed by the cooler than normal summer. The susceptible accessions seemed to rate slightly lower than normal (less systemic infection) while the resistant accessions seemed to respond normally.