Evaluation of Fumigation and Rhizomania-Tolerant Cultivars for Control of a Root Disease Complex of Sugar Beets. R. M. HARVESON, Department of Plant Pathology, Texas Agricultural Experiment Station, Bushland 79012. C. M. RUSH, Department of Plant Pathology, Texas Agricultural Experiment Station, Bushland 79012. Plant Dis. 78:1197-1202. Accepted for publication 9 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1197.

Field studies were conducted in 1991 and 1993 to evaluate the effectiveness of Telone II fumigation and rhizomania-tolerant cultivars to control a complex of Soilborne pathogens (Rhizoclonia solani, Aphanomyces cochlioides, Fusarium oxysporum f. sp. betae, and beet necrotic yellow vein virus). Fifteen cultivars (13 rhizomania-tolerant and two rhizomania-susceptible) were included in a randomized complete block split-plot design with six replications in which main plots were fumigated or nonfumigated and cultivars were subplots. Data collected included root yield, gross sucrose, percent sucrose, disease index, and final stand. Although there were yield differences between repeated studies, similar trends were observed both years, including a significant fumigation ? cultivar interaction. Yield of Txl8, HH67, and Maribo Record was consistently improved by fumigation, whereas yield of 881139-03, Rhizosen, Maribo Turbo, and TxMH2 responded least to fumigation. Disease index, root yield, and gross sucrose were the variables most improved by fumigation, whereas percent sucrose and final stand were seldom affected. The rhizomania-tolerant cultivars, whether fumigated or not, did not yield as well as the locally adapted T x l8 check. T x l8 responded well to fumigation and even without fumigation yielded as well as or better than the rhizomania-tolerant (but not locally adapted) cultivars with fumigation. To our knowledge, this is the first report of a fumigation X cultivar interaction. Thus, fumigation can be beneficial to Texas sugar beet growers for control of multiple Soilborne pathogens, depending on the cultivars planted.

Keyword(s): Beta vulgaris, fungal root rots, furoviruses, resistance