Soybean Pest Resistance Updates
I have often stated that genetic resistance to pests of soybean is the most effective and sustainable IPM practice. This is especially so since it is now common to find selection against pesticide chemistry among disease and insect pests.
The opening statement in the above paragraph is good on the surface, and certainly is worthy of achievement. The sticking point is that identifying pest resistance in soybean genotypes and then transferring that resistance to acceptable agronomic types is a difficult task that requires much time and resources. However, breeders and geneticists in both the public and private sectors continue to constantly work toward that goal.
The successes in this endeavor are numerous. Following are examples.
• My favorite example is the genetic resistance to stem canker that was incorporated into soybean varieties in the late eighties/early nineties. That resistance is still pivotal to the avoidance of devastating yield losses from this disease, especially since there are no efficacious fungicides against the causal fungal pathogen.
• Another example of genetic pest resistance (or host plant resistance) in soybean is that of resistance to soybean cyst nematode (SCN). This resistance has long been a major effective and economical defense against this pest, and breeders/geneticists have continued to thwart the effects of SCN adaptation by releasing soybean varieties with resistance to evolving types of the pest.
The continued effectiveness of genetic resistance to SCN is recently documented in a paper entitled “Impact of Cyst Nematode Resistance on Soybean Yield” that will appear in the latest issue of Crop Science Journal. Results from 11 years of yield tests that were conducted over 1,247 test-environment combinations in the north-central US and Canada confirm that soybean genotypes that are resistant to SCN yield more than susceptible entries, and this yield advantage increased at locations that had higher initial SCN egg counts. Thus, growing soybean varieties that are resistant to SCN remains an important management component at locations with known infestations of this pest.
• An example of how scientists are continually working toward developing soybean genotypes with pest resistance is reported in a paper entitled “Characterization of seed rot resistance to Pythium aphanidermatum in soybean” that will appear in the latest issue of Crop Science journal.
Results from the latest survey of soybean disease and nematode pests in the Midsouth show that seedling diseases have contributed significantly to yield losses over the last 6 years; Pythium is the predominant pathogen in the seedling disease complex. In the above article, Univ. of Arkansas scientists report that crosses made with the cultivars Archer (previously shown to have resistance to Pythium spp.) and Hutcheson (susceptible) produced progeny that had a high level of resistance to Pythium. The high level of heritability of this resistance, plus the identification of QTL’s associated with this resistance, suggest that Archer is an excellent source of resistance that could be incorporated into soybean breeding programs to develop varieties that are resistant to Pythium seed rot. This finding is of special significance since effective seed treatments only protect the seed and the developing seedling for a short time, and do not protect the emerging root.
With increased scrutiny being applied to the use and application of all pesticides in agricultural settings, plus the continual selection among pest species for resistance to pesticides, efforts to identify sources of genetic resistance to the most damaging pests of soybean and to incorporate those traits into superior agronomic types must be continued at the very least, and increased where possible.
Composed by Larry G.Heatherly, Mar. 2017, larryheatherly@bellsouth.net