USA
Source: The Agronomic Insider, Bayer CropScience
Root-knot nematode damage
Nematodes are the most numerous multi-cell organisms on the planet and cost U.S. farmers more than $3 billion annually in crop losses. Root-knot nematodes thrive in much of the soils throughout the Cotton Belt, and as the cotton season progresses, Bayer CropScience cotton agronomists, technical service and sales representatives begin to receive calls from growers or consultants about root-knot nematode (RKN) damage on cotton. RKN symptoms usually appear sporadically throughout a field or within a row. Nematode hot spots are identified where cotton plants appear stunted or drought-stressed compared to nearby plants.
In advanced stages of infection, cotton leaves often display symptoms of potassium or nitrogen deficiencies, with high frequencies of interveinal chlorosis and leaf scorching. These symptoms are often confused with fertility problems such as low potash (especially from mid-bloom to final boll filling), but low potassium (K) symptoms are often evidence of nematode infection interfering with nutrient uptake, not low soil levels of potassium.
Diagnosing an infection
The best way to diagnose RKN infection is to look at the roots of stressed plants. It is better to dig up plant samples then to pull them. This saves more feeder roots for observation and leaves fewer roots in the ground. If heavy galling is found on most roots, nematode infection is advanced. At this stage in the season, there are few options for correcting the problem, but you can maximize yield in the rest of the field and choose a root-knot nematode tolerant variety for next year.
Nematodes can cause root galling in cotton.
Photo accessed from http://edis.ifas.ufl.edu/ng015
RKN tolerance varies in commercial cotton varieties, as high-pressure fields can still cause a tolerant variety to express stressed symptoms. It is important to understand the difference between RKN tolerance and resistance. Nematode resistance refers to the suppressive effect of the plant on the nematode’s ability to reproduce. Tolerance describes a variety's ability to absorb a degree of nematode damage to the roots while still maintaining acceptable yields. Currently, there are no known commercial varieties that can claim true RKN resistance.
Tolerant varieties
Bayer CropScience offers two Stoneville® cotton seed varieties with excellent root-knot nematode tolerance: ST 5458B2RF and ST 4288B2F. Farmers have seen improved yields with these varieties in fields with known nematodes when compared to varieties without nematode tolerance. ST 5458B2RF is a mid-maturing variety with moderate levels of tolerance that can continue to perform well under some root-knot nematode pressure. ST 4288B2F is an earlier maturing variety that appears to have even higher levels of root-knot nematode tolerance than ST 5458B2RF.
In addition, Bayer CropScience cotton breeders and cotton agronomists are evaluating multiple experimental varieties that exhibit root-knot nematode tolerance, full crop tolerance to Liberty® herbicide and glyphosate, as well as dual gene insect protection. These new varieties are being evaluated for commercial release for the 2013 growing season.
Species
