RESUMO
Field experiments were conducted at Gainesville and Marianna, FL in 2004 and 2005 in which severity of spotted wilt, caused by Tomato spotted wilt virus, and pod yield were compared in six peanut (Arachis hypogaea) cultivars. The six cultivars included the moderately field resistant cultivars ANorden, C-99R, and Georgia Green; the highly field resistant cultivars AP-3 and DP-1; and the susceptible cultivar SunOleic 97R. There were four trials at each location, with four planting dates that ranged from late March to early June. Tomato spotted wilt severity in moderately resistant and susceptible cultivars was lower at Gainesville than at Marianna in both years in moderately resistant and susceptible cultivars. Trends in incidence for the two locations were less evident for AP-3 and DP-1. At Gainesville, there were few differences in tomato spotted wilt severity, and severity ratings were similar for Georgia Green and SunOleic 97R in two of four trials in 2004 and across all trials in 2005. At Marianna, severity ratings were lower for Georgia Green than for SunOleic 97R in six of the eight trials, and severity of tomato spotted wilt was lower for AP-3, C-99R, and DP-1 than for Georgia Green in all eight trials. In 2004, there was a trend toward decreasing severity ratings for Georgia Green and SunOleic 97R with later planting dates, but not for AP-3 or DP-1 at Marianna. Split-plot field experiments were also conducted at Tifton, GA in 2005 through 2007 in which incidence of tomato spotted wilt and pod yield were compared for peanut cultivars AP-3 and Georgia Green across planting dates ranging from late April through late May. Incidence of tomato spotted wilt was lower for AP-3 than for Georgia Green within each planting date of all years, and planting date effects were smaller in AP-3, if observed at all, than in Georgia Green. In most planting dates of all three trials, yields were higher for AP-3 than for Georgia Green. The relationships between yield and planting date were not consistent. These results indicate that the level of field resistance in AP-3 and DP-1 cultivars is sufficient to allow planting in late April without greatly increasing the risk of losses to tomato spotted wilt.
RESUMO
Field experiments were conducted at Marianna, FL in 2006 and Tifton, GA in 2006 and 2007 to compare new peanut (Arachis hypogaea) cultivars to the moderately resistant cv. Georgia Green and the highly resistant cv. AP-3 for field resistance to Tomato spotted wilt virus (TSWV), genus Tospovirus, and to determine the effects of in-furrow application of phorate insecticide and use of twin-row versus single-row patterns on incidence of spotted wilt in these cultivars. Cvs. Georgia Green, AP-3, Georgia-03L, Georgia-01R, Florida-07, McCloud, and York were evaluated in all five experiments, and Tifguard was added in experiments at Tifton. All cultivars except McCloud had lower incidence of spotted wilt than Georgia Green in all experiments. McCloud was intermediate in resistance to TSWV and had lower incidence of spotted wilt than Georgia Green in four of five experiments. Use of the twin-row pattern also reduced incidence of spotted wilt in McCloud in both years. On Georgia Green, phorate reduced incidence of spotted wilt in 2007 and twin-row pattern reduced incidence in both years. Phorate had no effect on spotted wilt in AP-3, Georgia-03L, McCloud, Georgia-01R, or Tifguard in either year. Twin-row pattern reduced either final incidence or area under the disease progress curve in all cultivars in at least 1 year of the study. All of these new cultivars should reduce the risk of losses to spotted wilt compared with Georgia Green. In highly resistant cultivars, especially AP-3, York, and Tifguard, use of phorate insecticide or twin-row pattern may not be necessary, and may not provide noticeable benefit in reduction of spotted wilt or increased yield.
RESUMO
The relationship between severity of bacterial streak and yield in winter wheat was studied in field plots and using a single-tiller method. Regression analysis from single-tiller studies showed that the grain weight per spike decreased as bacterial streak severity increased in cvs. Florida 304 and Savannah. The number of kernels per spike decreased as bacterial streak severity increased in Savannah but not in Florida 304. There was no difference in slope of the regression line between different years, locations, or cultivars for grain weight per spike. However, grain weight per spike at 0% bacterial streak (intercept) was different for different years, locations, and cultivars. The average reduction in grain weight per spike was 0.012 g for every 1% increase in bacterial streak severity. Using this relationship for cv. Savannah, average bacterial streak severity of 10% would result in about a 9% reduction in the grain weight per spike. In Florida 304, bacterial streak severity of 10% would result in about a 7% reduction in the grain weight per spike. During 1993-94, the largest difference in bacterial streak severity between inoculated and noninoculated plots was 4% in cv. Pioneer 2548, and the smallest difference was less than 1% in cvs. Terral 101 and Florida 304. There were no yield differences between inoculated and noninoculated treatments for any genotype. In field plot studies at two locations during 1989-90, bacterial streak severity did not differ between inoculated and noninoculated plots in Alexandria, Louisiana; but in Winnsboro, Louisiana, bacterial streak severity was 18 to 40% in inoculated plots and less than 5% in noninoculated plots. Differences in yield between inoculated and noninoculated plots ranged from 1,370 kg/ha (24% loss) to -121 kg/ha in Winns-boro. During the three seasons in which these studies were conducted, bacterial streak severity averaged about 10% or less in susceptible cultivars in all experiments except one. Based on the relationships derived from single-tiller studies, this suggests that yield loss is likely to be low most years. As indicated by the experiment in Winnsboro, however, more severe yield reductions could occur in a susceptible cultivar if weather conditions are favorable for disease development.