Determination of optimum irrigation regime and water use efficiency of sugar beet grown in pathogen-infested soil

A field experiment was conducted to quantify the effects of different irrigation frequencies on sugar beet yield in pathogen-infested soils. Four irrigation regimes (every 2, 3, 4, and 5 weeks) and four inoculation treatments (beet necrotic yellow vein virus [BNYVV], beet soilborne mosaic virus [BSBMV], BNYVV+BSBMV, and a noninoculated control) were arranged in a split-plot design and replicated four times. Irrigation frequency and virus infection affected disease severity and yield. Sugar beets irrigated every 4 weeks had the lowest disease severity, and yield was not significantly different from the every 2 weeks frequency. Sucrose content was higher for beets in the 4-week irrigation treatment compared with the 2- and 3-week frequencies. Beets inoculated with BNYVV had higher disease severity and lower root yield than beets inoculated with BSBMV and BNYVV+BSBMV. A greenhouse experiment was conducted to evaluate the effect of water level on disease severity and water use in sugar beet. Four treatments (BNYVV, BSBMV, BNYVV+BSBMV, and a noninoculated control) and three water levels (pot capacity [PC], 75% PC, and 50% PC) were arranged in a split-plot design and replicated five times. Pots of each treatment were weighed every other day to determine evapotranspiration. Evaporation was determined from unplanted pots, and plant transpiration was calculated by the difference. Beets irrigated at 75% pot capacity showed minimal disease incidence and a root weight comparable to the fully irrigated healthy control. Plants in the BNYVV treatment had a significantly higher disease severity than beets infected by BSBMV or BNYVV+BSBMV. Root weights and plant water use were significantly affected by virus infection. Beets in the BNYVV+BSBMV treatment had a significantly higher root dry weight and water use than beets in the BNYVV treatment, suggesting that BSBMV reduced the impact of disease caused by BNYVV.