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Interseeding camelina crambe and mustard to reduce soybean cyst nematodenematode (Heterodera glycines) (SCN)

Berti, A. Peterson, G. Yan

i)                    Greenhouse experiment to determine hosting and reducing ability of camelina, crambe and brown mustard

Industrial oilseeds have a great potential in the northern Great Plains both as oilseeds and as cover crops sown following wheat harvest and before soybean sowing in the following spring. One of the most important biotic stresses in soybean production is soybean cyst nematode, a serious pest that affects 90% of the soybean areas in the U.S. The objective of this study was to evaluate the hosting and SCN population reduction abilities of winter camelina cv. Joelle, crambe (Crambe abyssinica L. cv. BelAnn), and brown mustard (Brassica juncea L. cv. Kodiak). The experiments were performed in the greenhouse by planting the crops on naturally SCN-infested soils and sandy soil artificially inoculated with two SCN populations HG type 7 and 0 from two fields in North Dakota. Soybean cyst nematode did not reproduce on brown mustard or camelina with a female index (FI) of 0, suggesting these are non-hosts, while SCN reproduced on crambe. The numbers of white females on crambe ranged from 1 to 13 with FI of 0.17 to 1.06 in naturally infested soils, and 1 to 4 with FI of 1.15 to 2.46 in artificially infested soils, classified as a poor-host (FI < 10). All the tested crops were able to reduce the SCN populations by an average of 51% by brown mustard, 48% by winter camelina, and 24% by crambe across all the experiments with naturally infested soils compared with the initial population levels. Both brown mustard and camelina consistently reduced the SCN populations compared with the non-planted control (fallow). Although these crops were non- or poor hosts for SCN, limited reproduction could help reduce SCN survival in fields. Hence, host status and population reduction ability are important while selecting as a cover crop in SCN-infested soybean fields.

ii)                  Interseeding camelina, crambe and brown mustard into standing soybean

The results of the first year of field experiments indicate cover crops did not reduce soybean yield, plant height, crude protein, and oil content at both locations.  Interaction between cover crop treatments and soybean varieties was not significant.  In Prosper, soybean yield in the susceptible variety, averaged across all cover crop treatments, was about half of that of the resistant variety.  Similarly, the susceptible soybean was shorter than the resistant variety.  In Casselton, both varieties yield and plant height were similar but significantly lower than in Prosper. The experiment in Casselton was very dry this year and weed control was delayed at the beginning of the season, which were probably two of the causes of low yield in both varieties.  In addition, the initial SCN egg numbers in Casselton were lower than in Prosper.

Biomass for the interseeded cover crops was similar among cover crops at both locations.  The biomass yield in the resistant variety was less than in the susceptible variety at both locations, indicating the resistant soybean competed with the cover crops suppressing their growth.

In Prosper, SCN egg numbers increased in the susceptible variety in all treatments except in the treatment with camelina interseeded at V6, which reduced the SCN egg numbers in 32%. In the resistant variety, SCN eggs numbers decreased or stayed about the same in all treatments regardless of the initial SCN egg count. Although not significant, crambe and brown mustard interseeded at V6 had the lowest final egg population in the resistant variety, which may indicate these cover crops are providing an additional SCN-reduction to the resistant variety. However, further research will be needed to assess this.

 

in Casselton, the initial and final SCN egg counts were much lower than in Casselton and not significant for any treatment. However, the clear effect of the resistant variety on reducing SCN population observed in Prosper was not observed in Casselton. The populations stayed about the same. Although there were not significant difference due to the uneven distribution of SCN in the soil, the increase in number of eggs in the check treatment before initial and final counts was much greater than for the plot with cover crops.

It is clear that none of the cover crop treatments was able to overcome the SCN reproduction in the susceptible variety. A check treatment with only cover crop (no soybean) would be needed to estimate if the presence of the susceptible soybean is responsible for the increase in SCN egg numbers. Winter camelina and brown mustard are non-hosts of SCN so they should not increase the population of SCN.  

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