Correlation between Yield and Qualitative Traits of Sugar Beet Cultivars with Rhizomania Disease Indices under Field Infection Conditions.

Introduction Rhizomania viral disease is one of the limiting factors of sugar beet cultivation and significantly reduces its yield. The most important way to deal with this disease is to use resistant cultivars. Materials and Methods In order to evaluate the correlation between yield and qualitative traits of sugar beet cultivars with rhizomania disease indices, an experiment was conducted in a randomized complete block design with 12 different sugar beet cultivars in four replications in test site with natural infection with rhizomania in Torbat-e-Jam area at two years (2017 and 2018). The traits studied in this study included root yield, sugar content, sugar yield, white sugar content, white sugar yield, sodium, potassium, trace nitrogen, alkalinity, sugar extraction coefficient, leaf growth score, root growth score, disease severity and ELISA test index (OD). Analysis of variance was performed using SAS v.9.1 statistical software. Mean comparisons of traits were performed using LSD test at the probability level of 5 and 1%. Results and Discussion Analysis of variance showed significant differences among genotypes for all studied traits except for sodium. Cluster analysis of yield, crop quality as well as rhizomania severity of infection divided the sugar beet cultivars into three groups (resistant, semi-resistant and sensitive). Correlation between traits in a rhizomania infected field and different levels of resistance to rhizomania was different. In all cultivars with different levels of resistance, there was a significant correlation between pure sugar yield with leaf growth score (r=0.88 **), root growth score (r=0.85 **), disease severity (r= -0.84 **) and ELISA index (r= -0.67 **) was observed. Therefore, these traits are suitable indicators for evaluation of cultivars for suseptibility or resistance to rhizomania disease. In addition, correlation between ELISA index with disease severity (r=0.83**), leaf growth score (r= -0.61 **) and root growth score (r= -0.67 **) was significant. Conclusion According to the obtained results, because the ELISA test and determining the virus concentration is expensive, and on the other hand, this index had a positive and very significant correlation with the severity of the disease infection, so the disease severity index can be used to evaluate cultivars for resistance to rhizomania disease. [ABSTRACT FROM AUTHOR]