MN HG Type test
Based on field observations and recent surveys, SCN populations in many Minnesota fields have become virulent to soybean varieties carrying resistant genes from PI 88788 and/or Peking. If a resistant variety yields poorly or a field has been planted with the same resistant variety or varieties with the same resistance source (PI 88788) for a number of years (e.g., more than 5 years), it is recommended to have the HG Type in the field evaluated.
Scouting females (cysts) on the soybean roots in field and testing egg population density after harvesting the resistant variety are also useful methods of determining the reproduction potential of the nematode population on the resistant variety planted in the field.
A complete HG Type analysis including seven indicator lines is time-consuming and costly. To reduce the cost, we recommend only including Peking and PI 88788 because most current SCN-resistant varieties are developed from PI 88788 and a few from Peking. Although a few varieties with PI 437654 source of resistance are available in Minnesota, we can exclude PI 437654 from the MN HG Type test because none of the SCN populations in Minnesota could reproduce well on it (FI are 0 to 8.8 with the average only 0.4) based on the soil samples collected in 2007-08. Varieties with PI 437654 source of resistance should be effective in lowering SCN population densities in fields.
Besides the designation of HG Type, the Female Indexes on individual lines will be reported (Table 3). Soil samples can be submitted to a professional lab (e.g., the Nematology Lab, Southern Research and Outreach Center in Waseca) for a MN HG Type test.
Table 3. Example of MN HG Type.
|Indicator line||Females/Plant||FI||HG Type|
|PI 88788 (2)||19||4.0|