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Acreage of dry field pea (Pisum sativum) in North Dakota has increased approximately eightfold from the late 1990s to the late 2000s to over 200,000 ha annually. A coincidental increase in losses to root rots has also been observed. Root rot in dry field pea is commonly caused by a complex of pathogens which included Fusarium spp. and Rhizoctonia solani. R. solani isolates were obtained from roots sampled at the three- to five-node growth stage from North Dakota pea fields and from symptomatic samples received at the Plant Diagnostic Lab at North Dakota State University in 2008 and 2009. Using Bayesian inference and maximum likelihood analysis of the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA), 17 R. solani pea isolates were determined to belong to anastomosis group (AG)-4 homogenous group (HG)-II and two isolates to AG-5. Pathogenicity of select pea isolates was determined on field pea and two rotation hosts, soybean and dry bean. All isolates caused disease on all hosts; however, the median disease ratings were higher on green pea, dry bean, and soybean cultivars when inoculated with pea isolate AG-4 HG-II. Identification of R. solani AGs and subgroups on field pea and determination of relative pathogenicity on rotational hosts is important for effective resistance breeding and appropriate rotation strategies.

Dry bean (Phaseolus vulgaris L.) is an important worldwide legume crop with low to moderate levels of resistance to common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli. A total of 852 genotypes (cultivars, preliminary and advanced breeding lines) from the North Dakota State University dry bean breeding program were tested for their effectiveness as populations for genome-wide association studies (GWAS) to identify genomic regions associated with resistance to CBB, to exploit the associated markers for marker-assisted breeding (MAB), and to identify candidate genes. The genotypes were evaluated in a growth chamber for disease resistance at both the unifoliate and trifoliate stages. At the unifoliate stage, 35% of genotypes were resistant, while 25% of genotypes were resistant at the trifoliate stage. Libraries generated from each genotype were sequenced using the Illumina platform. After filtering for sequence quality, read depth, and minor allele frequency, 41,998 single-nucleotide polymorphisms (SNPs) and 30,285 SNPs were used in GWAS for the Middle American and Andean gene pools, respectively. One region near the distal end of Pv10 near the SAP6 molecular marker from the Andean gene pool explained 26.7–36.4% of the resistance variation. Three to seven regions from the Middle American gene pool contributed to 25.8–27.7% of the resistance, with the most significant peak also near the SAP6 marker. Six of the eight total regions associated with CBB resistance are likely the physical locations of quantitative trait loci identified from previous genetic studies. The two new locations associated with CBB resistance are located at Pv10:22.91–23.36 and Pv11:52.4. A lipoxgenase-1 ortholog on Pv10 emerged as a candidate gene for CBB resistance. The state of one SNP on Pv07 was associated with susceptibility. Its subsequent use in MAB would reduce the current number of lines in preliminary and advanced field yield trial by up to 14% and eliminate only susceptible genotypes. These results provide a foundational SNP data set, improve our understanding of CBB resistance in dry bean, and impact resource allocation within breeding programs as breeding populations may be used for dual purposes: cultivar development as well as genetic studies.