Midsouth soybean producers are all too familiar with the problems and issues arising from poor quality of harvested seed. It is generally thought that these problems are mainly caused by Phomopsis seed decay (PSD), or the degrading of seed resulting from infection by the Phomopsis longicolla pathogen during the latter stages of reproductive development. This problem is especially prevalent in seed harvested from ESPS plantings.

Breeding for resistance is perceived to be the most effective and best long-term strategy to control or avoid PSD, and it certainly should play a major role in solving the problem. In fact, MSPB-funded research conducted by USDA-ARS scientists Anne Gillen and Shuxian Li at Stoneville, MS provide promising results that this may in fact come to fruition.

A recent publication entitled “Identification of a single gene for seed coat impermeability in soybean PI 594619" by USDA-ARS scientists Hirut Kebede, James R. Smith, and Jeffery D. Ray at Stoneville, MS sheds light on another possible approach to solving the PSD problem.

The results published in this paper explain how the hard seed or impermeable seed coat (ISC) trait in soybean is controlled by a single major gene (Isc), and how high temperatures during seed fill increase the occurrence of this trait. The ISC trait in soybean seed is associated with non-uniform and delayed germination (in standard germination tests) because the seed fail to imbibe water sufficient for germination. This then is a major problem if soybean seed for future plantings are to be produced in environments such as the Midsouth where high temperatures during seed fill almost always occur.

The authors suggest that selection of the recessive form of the gene (isc) may be important in developing soybean varieties with permeable seed coat for high-heat seed production environments such as the Midsouth. This would then allow seed production for southern soybean plantings to occur in these environs instead of the current situation where seed beans for the midsouthern US are produced in northern states where seed fields mature later under cooler temperatures.

The value of this research may also come in another area that can be very important for southern soybean production, and is alluded to by the authors in their statement “The single-gene nature of impermeable seed coat may also have potential for being utilized in reducing seed damage caused by weathering and mold” during seed fill and maturation. Here is how that might be of value.

Suppose the simply inherited (single gene) ISC trait can protect maturing soybean seed from the effects of adverse environmental conditions that make them vulnerable to infection by the pathogen or pathogens that are associated with in-field seed decay. This would be a cost-free host plant mechanism to avoid this major production problem in the Midsouth.

To pursue this possible benefit, there are several points that must be considered.

• The germination of ISC soybean seed has not been tested when planted in a field environment where soil chemical and microbial properties may overcome the ISC trait so that germination and emergence are normal. In fact, in a preliminary assessment of soybean seed with the ISC trait planted in the field in 1994 at Stoneville, non-scarified ISC seed had the highest emergence of any seed lot in the test. Thus, it appears that the soil environment effects germination unlike the environment of a standard germination test that is normally used to determine the capability of ISC seed to germinate. This indicates that the possible breakdown of the ISC trait when seed are planted in soil should be investigated. If the trait does not inhibit germination of seed that are planted in soil, then it potentially has great utility for protection against in-field seed deterioration prior to harvest without the concern that seed with this trait that are planted will not germinate.


•  When harvested soybean seed are delivered to elevators, they are graded for foreign matter and damaged seed (heat, mold, shriveling, insect, etc.). The subsequent grade is then used to assess dockage. Will the ISC trait result in enhanced quality or appearance of harvested seed, thus resulting in less potential dockage for damaged seed? This should be determined.


•  An oil mill is only concerned about oil and protein content of the seed; thus, there needs to be a determination of how the ISC trait may or may not affect these qualities, as well as the extraction process.


•  Can the ISC trait be maintained over the several-years-life of a particular variety? What is its heritability over the life of a variety?

While there may be multiple genes involved in the ISC trait, the above report is significant in its determination of one gene’s mechanism of inheritance in the ISC trait in soybean. The next steps are determining how this trait may be used to aid in 1) producing planting seed in the Midsouth, and 2) protection of maturing soybean seed from in-field deterioration.

Composed by Larry G. Heatherly, June 2015, larryheatherly@bellsouth.net