Evaluation location: California, United States
Test (411) was conducted at the Spence Farm in Salinas, CA. The field is infested with the wild type strain of BNYVV. Trial was planted in April/May in a RCBD of single-row plots 2.74 m in planted length with 0.61 m between plots and 0.71 m row spacing. Stand count (number of plants per plot) was recorded 6-weeks post-planting. Plants were rated for disease as signs and symptoms of infection were seen, typically beginning in September. Evaluation for resistance to rhizomania is based on a composite visual score of foliar color and wilting and a root score of bearding (the massive proliferation of necrotic secondary roots), shape, and size. Two methods are used to estimate reaction to rhizomania. First, scores for foliar yellowing attributed to rhizomania are evaluated on 0 to 9 scale, where 0 = very dark green with no yellowish plants, and 9 = 100% of the plants showing yellowing typical of rhizomania-susceptible varieties. Second, a rhizomania disease index (RZDI) is calculated. Plot canopies are mowed and roots are lifted for evaluation. Each beet per plot is given a root score on a severity scale from 0 (a completely clean root) to 9 (where the tap root is completely bearded, replaced by secondary and tertiary roots, due to rhizomania). As bearding increases, so does the RZDI, which is calculated for each plot based on the severity scale as follows: [(number roots X 0) + (number roots X 1) +X + (number roots X 9)] divided by the total number roots harvested. Essentially it is a weighted average of all roots in the variety. When present, natural PM infection is scored from 0, clean leaves, to 9, indicating at least 90% or more of the leaf area is covered with visible mildew.
Excel file from Kelly Richardson 2010, 2011, 2012 and 2013 data with multiplr worksheets
A general overview of the Rhizomania evaluation work at Salinas, California.