Objective 1. Dr. Helms has made crosses of breeding material to sources of SCN. When he has breeding material ready for further testing, those soybean lines are tested directly against the nematode in the greenhouse. Dr. Helms and Dr. Nelson also test resistance of commercial cultivars on a yearly basis. A large plant growth system utilizing a water bath to maintain the roots in a 270 C environment is used to grow the plants. Three to four day old seedlings are inoculated with SCN (HG type 0) and placed in the growth system. After about 30 days the roots are extracted, the SCN females on the roots are counted, and a Female Index is calculated for each line and compared to a resistant and susceptible check line.
Dr. Helms also has breeding material screened for resistance to P. sojae. The methodology for the screening against P. sojae has already been developed (2). All screening will be conducted under growth room conditions. A virulent isolate of race 3 or 4 will be inoculated onto 7 day old hypocotyls using the injection technique. Resistant and susceptible checks will be used in all resistance tests. Resistance will be measured as surviving plants. Where necessary, other races will be used to test resistance. In addition, breeding material from Dr. Helms's program for resistance to soybean mosaic virus will be screened.

Objective 2. We will continue to collect soil and plants with Phytophhora root rot from fields for another year. In 2014, 60 fields were sampled, but few isolates of the pathogen were recovered. In 2015 more fields were sampled and isolation of the pathogen is still in progress. The pathogen P. sojae is baited from the soil using plants and then the pathogen is isolated from the diseased plants. Isolates of P. sojae will be identified for virulence phenotype (race) based on differential reaction on eight Rps genes (la,lb,lc,ld, 1k,3a,6,7). We will continue our efforts to identify sudden death syndrome or any other unknown disease when plants showing symptoms are brought to our attention.

Objective 3. We are continuing our attempts to determine what factors and pathogens are involved in the late season root rot complex. We will use standard isolation and molecular techniques to identify pathogens and soil analysis to determine if other factors are involved in this problem (1).

Update:

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Dr. Berlin D. Nelson Jr. Principal investigator, Dept. Plant Pathology, NDSU
Cooperator: Dr. Ted Helms, Soybean Breeder, Dept. Plant Sciences, NDSU

There are a number of diseases that affect soybean production in North Dakota. The primary diseases are those that affect the roots. A major focus of this project was to work with Dr. Helms, soybean breeder, to incorporate resistance to major diseases into public soybean cultivars and germplasm. The two soil borne diseases where resistance is available are Phytophthora root rot and soybean cyst nematode (SCN). Another important part of our work is to investigate changes in pathogen populations that would affect soybean production and identify virulent strains of these pathogens. The last few years we identified races of Phytophthora sojae, the cause of Phytophthora root rot, a major disease during periods of high soil moisture or flooded conditions and we have been examining the strains involved in Fusarium root rot.

In cooperation with Dr. Helms, we continued to incorporate resistance to Phytophthora root rot and soybean cyst nematode (SCN) into soybean breeding lines. We must maintain a variety of races of P. sojae and SCN in storage and each year test them for virulence. During 2016 to 2017 we screened 68 breeding lines for resistance to races 3 or 4 and over 40% of those lines were resistant. Many of the public varieties released by Dr. Helms have resistance to various races of P. sojae. ND Bison soybean, an NDSU release in 2016, has resistance to races 3 and 4 and had been through our screening process in previous years. We also screened 16 advanced breeding lines and 80 lines from Bison soybean for resistance to SCN and are currently retesting 40 commercial soybean varieties for SCN resistance. The objective of this screening is to release public cultivars with high levels of resistance to various diseases or supply information to growers on levels of resistance. Drs. Helms and Nelson have been cooperating on this research for the past 30 years.

We completed our recent study on new races of P. sojae in North Dakota. Our results have shown that there are strains of the pathogen that can attack many of the resistance genes used to control this pathogen. A selection of 47 isolates were evaluated for virulence on three of the most common resistance genes used in commercial soybean cultivars in this region, Rps 1c, 1k and 6. Our results showed 57% of the isolates were virulent on Rps 1c, 45% virulent on Rps 1k and 4% virulent on Rps 6. The high percentage virulent on Rps 1k is of concern since this is the most common resistance gene used in commercial cultivars in this area. This increase in the number of isolates of P. sojae that can attack resistance genes 1c and 1k is due to the widespread use of those genes over the past 20 years. The results suggest that new genes, gene stacking, or other management techniques will be needed in the future to control this disease in some fields.