Verticillium wilt in transgenic sugar beet cultivars in Cassia County, ID, 2006

Transgenic (resistant to glyphosate) sugar beet cultivars were evaluated in a commercial sprinkler-irrigated sugar beet field near Heyburn, ID where winter wheat was grown in 2005. The field trial relied on natural infection of Verticillium dahliae. The plots were planted on 28 Apr to a density of 142,560 seeds/A, and thinned to 47,520 plants/A on 15-20 Jun. Plots were four rows wide (22-in. row spacing) and 34.5 ft long. The experimental design was a randomized complete block design with eight replications per cultivar. The field was cultivated on 8 and 20 Jun. The crop was managed by the grower according to standard cultural practices except for herbicide applications. Transgenic cultivars were sprayed with broadcast applications of glyphosate at 32 fl oz/A on 30 May and 22 fl oz/A on 27 Jun. The study area was also hand weeded to keep all plots free of weeds. The percentage of plants with leaves that had dead vein delimited sectors was recorded for the center two rows on 6 Sep. The center two rows were harvested on 25-26 Sep with the aid of a mechanical topper and small plot harvester. The sugar content of the beets was determined by the Amalgamated Sugar Co. laboratory, and recoverable sugar was estimated. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher's protected least significant difference was used for mean comparisons. Yields from this field were below normal for this growing region. Verticillium dahliae symptoms and yield parameters varied significantly between cultivars. Root shape and root hair proliferation indicated that Beet necrotic yellow vein virus (BNYVV) also was present in the field although the foliar symptoms of this disease were not particularly evident. An interaction between BNYVV and V. dahliae may have been present in this field. Based on Spearman's rank correlation coefficient, the mean values for leaf symptoms were inversely related with those for root yield (r = -0.3667, P = 0.0504) but not sugar content or estimated recoverable sugar (P = 0.1277 and 0.2182, respectively). Good resistance to V. dahliae exists in some transgenic cultivars based on the reduction in foliar symptoms. Numerous transgenic cultivars with resistance to both V. dahliae and BNYVV had better yield parameters than the commercial check cultivars indicating growers should be able to switch to some of the resistant transgenic cultivars without experiencing yield loss.