The effect of irrigation management on damage caused by rhizomania in sugar beet cultivars

Rhizomania disease has attracted most attention in recent years. One of the cultural practices that have been suggested to reduce the incidence and severity of rhizomania or to limit the spread of the pathogen includes limiting irrigation duration and increasing frequency. Two separate furrow irrigated experiments in non-infested vs. infested fields (in 2002) and low infested vs. high infested (in 2003) were conducted at Zarghan station, Fars Agricultural and Natural Resources Research Center. The experimental design was split plot with randomized complete block with four replications. The irrigation management as a main plot consisted of: 1-every furrow irrigated (EFI) at the conventional irrigation interval (as a control treatment), 2-every-other-furrow irrigated (EOFI) with the irrigation interval equal to the control treatment, 3-EFI, 50% of the applied water and half of the irrigation interval of the control treatment, and 4-EOFI, 50% of the applied water and half of the irrigation interval of the second treatment. Sub plots were composed of three cultivars: Rhizofort and Dorothea (as tolerant cultivars), and IC-1 (as a susceptible cultivar). The irrigation management in non-infested field significantly affected root yield (RY), sugar yield (SY), white sugar yield (WSY), water use efficiency (WUE) in first year, but in infested field was not significant. In second year, water management affected all these characteristics significantly. Maximum yields and WUE were produced on EFI, 50% of applied water and half of irrigation interval. There were significant differences for yields and WUE between cultivars in both fields. In two years, Rhizofort and Dorothea produced most yields and WUE but rhizomania destroyed IC-1. Rhizomania significantly decreased RY, SY, WSY, WUE, sugar content (SC), and white sugar content (WSC). The effect of disease on yields and WUE reductions (78%) was more than (two-fold) the reduction in SC and WSC (35%). In low infestation, the irrigation management can be useful if using tolerant cultivar, but in high infestation the effect of irrigation management was nil.