by Greg LaBarge, Fulton County
Some new soybean seed genetics are available which include resistance to soybean aphid development through a gene identified as Rag1. This is a traditional genetic selection and not gene transfer process which identified this resistance. In fact 4 genes have been identified and given Rag 1-4 designation for 2011 only Rag1 is available in varieties. The Rag 1 has proven very effective for susceptible populations.
The qualifier “susceptible populations” is the problem in that there have already been populations or races of soybean aphid identified which develop unchecked on the Rag 1 gene and those populations exist in Ohio.
The figure at the left shows a chart of soybean aphis from both Illinois and Ohio being placed on soybean genetics with and without Rag1. Just 15 days after exposure the numbers for the OH soybean aphids have surpassed the threshold of 250. The IL line of aphids were held in check with less than 30 aphids on any variety. Both the OH and IL aphids developed on the susceptible varieties (Dwight & Williams82) at the same pace.
The second chart shows different aphid biotypes and resistance genes. Where an R in red box is seen this combination results in slow or no development of the aphids. Where the (S)Dev is noted the aphids develop on the plant normally for that combination of genes and biotype.
Farmers should be cautious in paying a high premium for this first introduction of aphid resistance for northwest Ohio. As combinations of resistance are incorporated in future varieties we will possible see a greater benefit due to resistance for multiple races of soybean aphid.
This is type of scenario is not uncommon when we deal with adaptive pest and is very similar to what we experienced in the 1990 with genetic resistance and the seedling/stem disease phytophthora where races of the disease adapted quickly to single genes in varieties especially where pressure was high.