The Future of Soybean Variety Development

Before the advent of transgenic or GM (genetically modified) soybean varieties, producers planted “conventional” or non-GM varieties. These varieties had no resistance to any herbicides, which meant that only PRE and non-glyphosate POST herbicides that were labeled for soybeans were used for weed control.

Disease and nematode pests were managed by planting seed of soybean varieties that were either resistant or partially resistant to these pests. There were no effective seed treatment or foliar fungicides at that time. Insects were the only pests that could be managed effectively with applications of pesticides. Soybean cyst nematode (SCN) was managed effectively by planting SCN-resistant varieties and/or by rotation with non-host crops such as corn.

In the mid-1990's, glyphosate-resistant (GR) soybean varieties came on the scene. The cheapness and effectiveness of glyphosate applied POST to these varieties changed the weed control landscape for soybeans. Glyphosate herbicide was used for burndown weed control before planting and for POST weed control after soybean emergence. It was the herbicide used almost exclusively on most soybean acres following this development.

In the late-1990's, seed-applied fungicides that were effective in controlling both seed- and soil-borne pathogens became available, and in a short time they were widely used on all planted soybean seed. In the early 2000's, the strobilurin fungicide Quadris came on the scene as a cure-all foliar-applied fungicide for both foliar and seed diseases that were a serious pest of soybeans during reproductive development.

Now, regrettably, there are problematic weeds that are resistant to glyphosate and problematic fungal pathogens that are resistant to the strobilurin fungicides. There is anecdotal evidence that fungal pathogens may also be developing resistance to some of the seed-applied fungicides. These developments have led to the development and use of soybean varieties that are resistant to other classes of herbicides (e.g., glufosinate, dicamba, 2,4-D), and fungicide use patterns that are based on applying materials that have more than one mode of action. But these alternative approaches are fraught with problems (e.g. risk of new resistance development, applying volatile auxin herbicides on auxin-resistant soybean varieties). Thus the solutions to these new problems are not as foolproof as the earlier solutions were perceived to be in solving the original problems.

As shown in a previous blog, there is no doubt that Midsouth soybean yields have reached a much higher plateau over the last 5 years. In fact, yields in the Midsouthern US are now on a level with soybean yields in the Midwestern US. There is also no doubt that this has resulted in part because of the better weed and pest control afforded by herbicide-resistant (HR) varieties and effective seed- and foliar-applied fungicides.

All of this has come at a cost to the producer. A 50-lb. bag of soybean seed now costs $60-65, and seed-applied pesticides (insecticides, fungicides, and/or nematicides) will cost an additional $7-15/acre, depending on how many of the products are used. This cost is much higher than the previous cost of $10-15 for a bag of seed of a public variety with no GM traits. This means that a producer is now paying about $75/acre for seed of varieties with HR traits and that have been treated with seed-applied pesticides. These are GM seed with HR traits that may not even be effective anymore, or will become ineffective if overused the way the GR seed trait was. Plus, some producers are paying extra for seed of dicamba-resistant soybean varieties just to protect themselves from the effects of now-prevalent dicamba drift. Also, in a “back to the future” moment, producers are now being advised to use PRE and POST herbicides that were being used before the advent of GM seed with HR traits in order to control resistant weeds and/or to introduce more modes of action for weed control so that resistance will not develop to the herbicides used on HR soybeans. In effect, the cost for weed control is now in the neighborhood of the cost for weed control before HR soybeans were introduced, but the cost of seed has not been lowered to offset this increased cost for weed control. So what will be the gain of paying for these traits in the future if they continue to be rendered ineffective?

The increasing presence of yield-limiting fungal pathogens presents another set of problems. As stated above, pathogen resistance to the most-used class of fungicides is present and even increasing among some pathogens. This has come about because of the blanket application of these fungicides regardless of whether or not a target disease was present. The cost of this control measure can be in the $12-25/acre range. Producers are still being advised to apply this blanket fungicide application, but now are being told to use fungicides that represent more than one mode of action. But what happens when resistance to more than one fungicide class develops? There will be no more options for fungal pathogen control.

But let’s go back in time. Prior to the entrance of soybean seed with GM traits into the producer environment, there were control measures that were effective. For instance: 1) When stem canker decimated the Midsouth soybean crop in the late 80's, public and private seed company soybean breeders and geneticists quickly identified resistance genes (click here and here) that were used in the development and release of varieties with excellent resistance to stem canker that is still effective nearly 30 years later (Note: there were not then and still aren’t fungicides to control this disease). 2) Decades ago, public and private soybean breeders and geneticists developed and released varieties that were resistant to prevalent types of SCN, and they still do this because there are no effective pesticide options to control this widespread and yield-limiting pest. In the absence of chemical controls for stem canker and nematode pests, public and private breeders worked and continue to work in consort to develop and release varieties with these resistance traits.

Now back to the present. Public breeders and geneticists have identified genes that will confer resistance to FLS (click here) and soybean rust (click here and here), but there are few public breeders who are developing and releasing varieties (GM or non-GM) that have these resistance traits. (In fact, most if not all Midsouth soybean acres are planted with seed of private company varieties.) To my knowledge, there are no known commercial varieties that have resistance to either pathogen, although FLS tolerance levels of varieties are identified on most private seed companies’ websites (click here for links to company websites).

It is interesting to note that both FLS and soybean rust have effective fungicide controls at this time. The sale of these fungicides to producers is an excellent source of income for providing companies, but as shown above, these products are temporary remedies and their continued use will only lead to resistance development among the pathogens they control. So what happens when the supplying companies can no longer develop fungicides that are effective against these pathogens?

Of special interest here is that companies have not heretofore charged a technology fee (as they have for GM varieties) for genetic resistance to pathogens that have been incorporated into their varieties by conventional or non-GM breeding methods. So it is easy to assume that this approach is not viewed as financially rewarding as either GM varieties or the sale of fungicides that are presently effective.

It appears to me that public and private sector soybean breeders and geneticists should be working in consort to pursue the discovery of resistance genes that can be incorporated into varieties that will then have resistance to these pathogens. This may not be as lucrative as the sale of pesticides to producers or the development of GM varieties that garner a technology fee, but it should lead to a more sustainable production system for soybeans in the US. And it should improve the bottom line for US soybean producers.

It will be interesting to see what the future holds for the development of private varieties that are as resistant to FLS and soybean rust as present varieties are to stem canker. Again, public breeders and geneticists have developed and released germplasm that can be obtained free of charge for this development. However, with the dearth of public breeders who are releasing varieties, and with the low likelihood that this will change with continued tightening of public university and federal agricultural research budgets, it will be up to the private seed companies to adopt this approach rather than their continued emphasis of depending on new pesticides that will replace those that have been rendered ineffective by fungal pathogens continuing to evolve resistance to these pesticides.

It is my opinion that the soybean seed industry needs to get off the train of total dependence on pesticides to control pathogens and nematodes, and revert to the time-proven concept of incorporating newly discovered resistance genes that are effective against some of the major pests of soybeans. However, the goals and objectives of seed companies and those of chemical companies may not necessarily be the same. Plus, there is a potential conflict in overall industry goals since several major seed companies are now owned by chemical companies. Nonetheless, since the source of new varieties is now the private seed companies, the burden is on them to pursue this genetic avenue of protecting soybeans against known pathogens vs. reliance on pesticides that provide only temporary protection against these yield robbers.

Composed by Larry G. Heatherly, July 2017, larryheatherly@bellsouth.net