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Sugar and Root Yield of Sugar Beets as Affected by Bacterial Vascular Necrosis and Rot, Nitrogen Fertilization, and Plant Spacing. S. V. Thomson, Assistant professor, Department of Plant Pathology, University of California, Berkeley 94720, Current address of senior author: Department of Biology, Utah State University, Logan 84322; F. J. Hills(2), E. D. Whitney(3), and M. N. Schroth(4). (2)Extension agronomist, University of California, Davis 95616; (3)Research plant pathologist USDA, SEA-AR, Salinas, CA 93915; (4)Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 71:605-608. Accepted for publication 12 November 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-605.

In field experiments at Davis, CA, nitrogen (N) fertilization increased the incidence of rot caused by Erwinia carotovora subspecies betavasculorum. When plants were inoculated, rot per beet root increased from 11% with no fertilizer N to 36% when 336 kg N/ha was applied. The sucrose concentration of roots declined at a faster rate with increasing rates of fertilizer N when plants were inoculated than when not inoculated, and root yield increased at a slower rate with N fertilization when plants were diseased. Sugar yield estimations from regressions increased for healthy plants but decreased for diseased plants as fertilizer N increased. As the in-row spacing between plants was increased from 10 to 46 cm, the percent of diseased roots increased more rapidly when plants were inoculated than when they were not inoculated. Root sucrose concentration decreased with increasing in-row spacing but the rate of decline was more rapid for inoculated than for uninoculated plants. For uninoculated plants, root and sugar yields were maximized at in-row spacings of 1530 cm but, when plants were inoculated, these yields declined linearly as in-row spacing increased from 15 cm. In field tests at Salinas, CA, inoculated plants of Erwinia-susceptible cultivar C17 showed more rot per root with increased in-row spacing than did inoculated plants of moderately susceptible cultivar 546H3.

Additional keywords: cultural control, soft rot, disease assessment, crop loss.