First report of the soybean cyst nematode heterodera glycines infecting dry bean (Phaseolus vulgaris l.) in a commercial field in Minnesota

In July 2016, irregular patches of stunted and yellowed plants were observed and reported by a grower in a commercial dark-red kidney bean (Phaseolus vulgaris L. cv. Red Rover) field in Sherburne County, Minnesota. Examination of root tissue revealed many white to yellow females, similar to soybean cyst nematode (SCN). The previous crop in 2015 was corn, and the field was planted to soybean in 2010. Five soil samples were collected from this field. Vermiform nematodes and cysts were extracted from the soil, and then eggs were extracted from the cysts from each sample. Population densities of the cyst nematodes ranged from 1,630 to 3,840 eggs and juveniles/100 cm³ of soil. The soil samples were mixed thoroughly and the resulting field soil with 2,112 eggs/100 cm³ of soil was used to inoculate the three most widely grown kidney bean cultivars (Montcalm, Red Hawk and Pink Panther), each in 5 replicates. After 32 days of growth after planting in a growth chamber maintained at 27°C with 16-h light/day, females were extracted from roots and counted. The mean numbers of white-yellow females formed on cvs. Montcalm, Red Hawk and Pink Panther were 429 ± 180, 452 ± 147, and 620 ± 131, respectively, indicating that this cyst nematode infects and reproduces well on these dry bean cultivars. Cysts were lemon-shaped with a protruding neck and cone, ambifenestrated, underbridged, with well-developed bullae typical of SCN. The key morphometrics of cysts (n = 10) were a mean vulva slit length of 43.5 ± 2.0 (range = 40 to 56) µm, fenestra length 51.8 ± 1.5 (50 to 54), and width 40.3 ± 2.1 (37 to 43). Second-stage juveniles (J2s) were vermiform with a hyaline region in the tail terminus. The key morphometrics of J2s (n = 30) were body length 455.0 ± 35.5 (397 to 508) µm, stylet 24.4 ± 0.8 (23 to 26) µm, tail 47.1 ± 3.0 (39 to 52) µm, and hyaline region 25.2 ± 3.2 (20 to 32) µm. Morphology of the cysts and J2s was in agreement with those of Heterodera glycines (Subbotin et al. 2010). Genomic DNA was extracted from single cysts (n = 12) isolated from both soil and roots. The rDNA of 28S region was amplified from single cysts (n = 6) using D2A and D3B primers (Yan et al. 2013) and sequenced. The consensus sequence submitted to GenBank (Accession No. KX790324) had 100% identity to three H. glycines isolates (GU595446.1, GU475087.1, and DQ328692.1). The identity of the nematode as H. glycines was further confirmed by species-specific sequence characterized amplified region (SCAR) primers SCNF1/SCNR1 (Ou et al. 2008). Heterodera glycines is the most destructive pathogen of soybean in the United States. Dry bean (Phaseolus vulgaris L.) was demonstrated as a host of SCN under artificially infested soil conditions in the greenhouse and outdoor buried pots in North Dakota (Poromarto and Nelson 2009, Poromarto et al. 2010). To our knowledge, this is the first report of the soybean cyst nematode H. glycines in a commercial dry bean production field in Minnesota. Soybean cyst nematode distribution is increasing in the leading U.S. dry edible bean growing area of Minnesota/North Dakota, and will likely become a major yield-limiting threat, especially in highly susceptible kidney bean (Poromarto and Nelson 2009).