2014 Root-knot Nematode Soybean OVT Gall Ratings and Yield

Over the past several years the number of fields observed to contain root-knot nematodes has increased across Mississippi. The best way to determine the presence of a nematode infestation (whether reniform or root-knot or soybean cyst nematode) is to soil sample.  Not only is soil sampling important from a nutrition standpoint, but determining the specific nematode present in a field can help determine the variety or rotational crop that best suits the field situation.  Presently, commercially available varieties do not contain resistance to the reniform nematode.  However, some tolerance within soybean varieties to the root-knot nematode does exist.

In 2014, and again in 2015 (data forthcoming), a version of the MSU soybean OVT was planted in a field with a known infestation of the root-knot nematode (RKN). A total of 142 entries were planted consisting of the RoundUp Ready entries, minus the conventional (MG IV and V) and LibertyLink (MG IV and V) varieties.  The field was located in northwestern Coahoma County and had a history of cotton production.  Prior to the 2014 season soybean plants from this particular field had been observed to contain a substantial amount of root galling as a result of the RKN.

Immediately prior to harvest, roots were removed from rows 1 and 4 with a shovel and rated on a scale of 0-5, whereby 0=no root galling and 5=severe root galling of the taproot as well as lateral roots. Yield was harvested from the middle (rows 2 and 3) of each plot to assess the impact of RKN on overall yield.

Group IV early entries (2014 MG IV early RKN and yield table)

Within the MG IV early varieties, the lowest yielding variety was Delta Grow 4685RR with a yield of 25.7 bu/A. Morever, this particular variety had the greatest root galling, on average a 4.2 on a scale of 0-5 indicating extreme sensitivity to RKN populations.  The greatest yielding variety in the MG IV early varieties was Mycogen 5N452R2.  However, the Mycogen variety had a root galling of 4 so even though the variety may appear susceptible to RKN based on the appearance of galls on the roots the variety appears tolerant based on yield.  The most tolerant variety based on the lowest amount of root galling was Dyna-Gro S43RY95.  In addition, yields significantly differed between varieties with a range of 31.3 bu/A between the 33 entries.  Root galling also significantly differed between varieties with a low of 2 and a high of 4.2.  No correlation between yield and rot galling was observed for this particular set of entries (Figure 1 – scatter plots).

Maturity Group IV late entries (2014 MG IV late RKN and yield table)

Within the MG IV late varieties, the lowest yielding variety was Progeny P 4848 RYS with a yield of 15.5 bu/A. Even though this particular variety did not have the greatest root galling, the root galling associated with this particular Progeny variety suggests it is extremely susceptible to the RKN.  The greatest yielding variety in this particular group was Delta Grow DG 4970 RR with a yield of 53.4 bu/A.  However, even though this particular variety was a good yielder, the RKN populations present resulted in a high level of root galling, a 4.1, associated with this particular variety.  The root galling encountered with some of the varieties suggests that some varieties, while good yielders in the presence of RKN, can see sustain a high level of root galling.  Yields significantly different between varieties with a range of 37.9 bu/A between the 53 entries.  No correlation between yield and rot galling was observed for this particular set of entries (Figure 1 – scatter plots).

Maturity Group V early entries (2014 MG V early RKN and yield table)

Within the MG V early varieties, the lowest yielding variety was University of Arkansas R10-R130 RY, an experimental variety, with a yield of 20.8 bu/A. In addition, the variety had root galling observed to be greater than 4 out of 5 suggesting the variety is quite susceptible to yield loss as a result of RKN galling.  The greatest yielding variety was Dyna-Gro S52RY75 with a yield of 62.2 bu/A.  However, even though this particular variety was the greatest yielder the root galling that occurred as a result of RKN was still greater than 4, suggesting that the variety can out yield root damage as a result of RKN.  But, it should be noted that root galling was only observed at one time during the season.  Yields significantly differed between varieties with a range of 41.4 bu/A between the 51 entries.  In addition, root galling between varieties significantly differed with a range of 2 to 5.  No correlation between yield and rot galling was observed for this particular set of entries (Figure 1 – scatter plots).

Maturity Group V late entries (2014 MG V late RKN and yield table )

Within the MG V late entries, the lowest yielding variety was University of Arkansas R07-6614RR, an experimental variety, with a yield of 34.3 bu/A. However, this particular variety had the lowest root galling as a result of the RKN populations present, 2.8.  The greatest yielding variety was Asgrow AG 5831 with 62.5 bu/A.  Yields significantly different between varieties with a range of 28.2 bu/A between the five entries.  However, there were no significant differences in the root galling observed between varieties.  A statistical correlation between yield and root galling existed for the MG V late varieties as indicated in Figure 1 (scatter plots).