Accepted for publication 28 October 2002. Published 21 November 2002.
Management of the Peanut Root-knot Nematode, Meloidogyne arenaria, with Host Resistance
J. L. Starr and E. R. Morgan, Department of Plant Pathology, Texas Agricultural Experiment Station, Texas A&M University, TAMU 2132, College Station 77843-2132 and C. E. Simpson, Department of Microbiology, Texas Agricultural Experiment Station, Texas A&M University, Stephenville 76401
Corresponding author: James L. Starr. firstname.lastname@example.org
Starr, J. L., Morgan, E. R., Simpson, C. E. Management of the peanut root-knot nematode, Meloidogyne arenaria, with host resistance. Online. Plant Health Progress doi:10.1094/PHP-2002-1121-01-HM.
Several species of root-knot nematodes are pathogenic on peanut (Arachis hypogaea) and cause considerable yield losses annually. In the United States, Meloidogyne arenaria is the predominant species attacking peanut in Alabama, Florida, Georgia, and Texas (3,9,17), with M. hapla being predominant in the northern production areas of Oklahoma, North Carolina (12), and Virgina. Populations of M. javanica attacking peanut are relatively rare in the United States but have been described from a few fields in Florida, Georgia, and Texas (6,8,16). Additionally, an as-yet undescribed Meloidogyne spp. has been isolated from peanut in north Texas (1).
The common peanut root-knot nematode, M. arenaria, causes substantial yield losses in severely infested fields, resulting primarily from stunted plant growth and premature plant death (Fig.1). Many soilborne fungi, especially Sclerotium rolfsii (which causes southern stem rot) and Sclerotinia minor (which causes Sclerotinia blight), will infect the weakened peanut plants and cause additional plant death. Root-knot nematode infection of the peg (Fig. 2) weakens the peg so that it breaks during harvest, contributing to additional yield losses because the detached pods are then left in the soil. Infections of the pods also contributes to a decline in yield quality.
Management of root-knot nematodes on peanut has traditionally relied primarily on treatment of infested fields with nematicides such as granular aldicarb (Temik) or the fumigant 1,3-dichloropropene (Telone). Two year rotations with cotton, bahaigrass, or velvet bean (10,11) are effective also. Resistance to the peanut root-knot nematode was not available until 1999 when the cultivar COAN with resistance to M. arenaria and M. javanica was released by the Texas Agricultural Experiment Station (13). In 2002, the cultivar NemaTam, which has greater yield potential than COAN with the same level of resistance to M. arenaria and M. javanica, was released by the Texas Agriculture Experiment Station (Fig. 3). The availability of these nematode-resistant cultivars gives growers an additional option for management of M. arenaria and M. javanica, and will reduce the growers reliance on nematicides. As yet, there are no peanut cultivars with resistance to M. hapla.
The yields of COAN and NemaTAM are greater than that of susceptible cultivars in nematode-infested soils (Fig. 4) (15). Both COAN and NemaTAM were developed by backcrossing nematode-resistant peanut lines with the cultivar Florunner. Because NemaTAM was developed by completing two additional backcross generations than were used for COAN, it has greater yield potential than does COAN (2). Neither COAN nor NemaTAM have the yield potential of the best susceptible cultivars in the absence of root-knot disease (Fig. 5). Therefore, these resistant cultivars are recommended only for fields known to be infested with M arenaria or M. javanica.
The damage threshold, or the initial nematode population density at which peanut yields begin to decline, has been reported to be in the range of 1 to 10 eggs and second-stage juveniles per 500 cm3 soil for M. arenaria on susceptible peanut cultivars (1,5,7). When yields of COAN and NemaTAM were compared to two susceptible cultivars in field microplots across a range of initial nematode population densities, yields of the susceptible cultivars were reduced by as much as 50% when nematode population densities at planting were as low as 10 nematodes per 500 cm3 soil (Fig. 6). In contrast, the yields of the resistant cultivars were unaffected by initial nematode population densities as high as 100 nematodes per 500 cm3 soil. Thus, these nematode-resistant peanut cultivars can be grown in nematode infested fields without having to rely on nematicide applications to achieve the genetic yield potential of the crop.
An additional benefit of the resistance of COAN and NemaTAM is that reproduction of the root-knot nematode is inhibited relative to reproduction on a susceptible cultivar (Fig. 7) (2,5). Therefore, these resistant cultivars not only protect the peanut crop from yield loss due to nematode parasitism, but they also suppress the nematode’s population density at crop harvest. Any crop planted after the resistant peanut will be subjected to less disease pressure than it would experience following a susceptible peanut crop.
Neither COAN nor NemaTAM are resistant to the tomato spotted wilt virus, which causes substantial yield losses in Georgia, Alabama, and Florida. Efforts to introgress nematode resistance into high yielding peanut lines that are also resist to TSWV are in progress, but until virus and nematode resistance are combined in the same cultivar, growers in areas where the potential for economic loss due to TSWV is high may need to continue to grow virus resistant cultivars and to use nematicides or crop rotation to manage the root-knot nematodes.
Because the resistance of COAN and NemaTAM is based on the same single, dominant gene there is uncertainty about durability of the resistance. Continued planting of cultivars with the same source of resistance may lead to the develop of nematode populations that are virulent on that resistance as has occurred with M. incognita-resistant tomato (4). There is need to identify additional resistance genes in peanut, and to incorporate these genes into high-yielding cultivars, to increase the durability of resistance.
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