Survey of ring nematode in South Carolina peanut fields

Abstract

Peanut (Arachis hypogaea L.) is a worldwide crop rich in protein (25.8%), fat (49.2%), and nutritional value (Kokalis-Bruelle et al., 1997; USDA-ARS, 2019). The United States is the fourth-largest peanut producing country after China, India, and Nigeria (USDA-FAS, 2024) and has produced 143,000 tons in 2021 (USDA-NASS, 2022). South Carolina is ranked sixth in peanut production across the United States. The top peanut-producing counties in South Carolina are Orangeburg, Calhoun, Hampton, Darlington, and Marlboro. Root-knot (Meloidogyne arenaria), lesion (Pratylenchus brachyurus), sting (Belonolaimus longicaudatus), and ring (Mesocriconema ornatum) nematodes are all important pathogens of peanut. All four taxa occur in many agricultural fields in South Carolina. Among these, ring nematode is commonly found in high numbers in peanut fields (Barker et al., 1982; Dickson, 1985). Ring nematodes are obligate ectoparasites abundant in South Carolina's coastal plain region where sandy soils are typical compared to the Piedmont and mountain regions where loamy soils are more predominant (Dickson & Waele, 2005). There are >400 species in the Criconemoides family, and there have been longstanding controversies whether to put Criconemoides and Mesocriconema in the same group as they have many similar characteristics. However, they also have important differences (Brzeski et al., 2002a, 2002b; Hunt et al., 2005). Geraert (2010) reported 400 distinct species in the family Criconematidae (including all ring nematode spp.). At least 90 species of Mesocriconema have been reported worldwide, and at least 12 species have been identified in the United States (Cordero et al., 2012; Powers et al., 2016) with a wide range of morphometric differences. Most of these species are not considered important plant pathogens. Two species of Mesocriconema, M. xenoplax and M. ornatum, are considered important pathogens of peach [Prunus persica (L.) Batsch] and peanut, respectively. They have very similar appearances and overlapping morphometrics, leading to difficulty in identification (Talton & Crow, 2022). Other species of ring nematode, like Criconemella curvata and C. pelerentsi, have been found in peanut fields (Sakwe & Geraert, 1991).

Ring nematode (Criconemoides spp.) was first reported in Georgia peanut fields causing chlorotic symptoms described as groundnut yellows, which were suspected to be caused by Mesocriconema ornatum (Dickson & Waele, 2005; Machmer, 1953). Mesocriconema ornatum is considered a minor pathogen for many crops, including peanut (Kokalis-Bruelle et al., 1997). Occasionally, this nematode has been reported to cause a reduction in peanut yield and quality. Pod yields in a micro-plot experiment were reduced 50% by populations consisting only of ring nematode (Minton & Bell, 1969). In a field experiment where a mixture of plant-parasitic nematodes was present, ring nematode populations were negatively correlated with peanut growth and pod yield (Sasser et al., 1975). High population densities of ring nematodes at planting can cause yellowing and stunting of plants; necrotic lesions on pods, pegs, and roots; apical galling (or galls) in roots; and reduced root volume, ultimately affecting the yield and quality of crops (Barker et al., 1982; Dickson & Waele, 2005; Minton & Bell, 1969; Sharma et al., 1994).

Studies concerning ring nematode in peanut are not abundant. Ring nematodes have been associated with worsening Cylindrocladium black rot disease (caused by Cylindrocladium parasiticum) in susceptible peanut cultivars (Diamonde & Beute, 1981; Kokalis-Bruelle et al., 1997). Previous reports on the presence of specific ring nematode species in South Carolina are lacking. To gain information on ring nematode composition and prevalence in South Carolina, a survey was conducted to determine the ring nematode densities, species, and associations with soil textural characteristics from six peanut-producing counties of South Carolina.

The distribution of Mesocriconema ornatum depends on previous crops and geography. Coastal plains with warm and sandy soils have characteristically been reported to support greater nematode numbers (Dickson & Waele, 2005), which was corroborated by our results where lower clay (and consequently increased sand) content was associated with greater nematode numbers. The presence of ring nematode is dependent on various environmental factors including soil moisture, temperature, and pH. A pH of 7 and temperature of 75—80°F is optimum for its reproduction (Berry & Coop, 2000). The current survey did not examine soil pH or temperature; however, it is plausible that these factors might have contributed to observed differences in nematode numbers among similar soil types sampled. While soil texture is one parameter for ring nematode density prediction, other soil factors like pore size, particle size, and physical and chemical properties of soil can influence the presence and migration of nematodes (Kandji et al., 2001; Norton, 1989). Ring nematode population densities can reach higher levels in coarse compared to finely textured sands, which have smaller pore sizes and thus limit their population development (Pokharel, 2011; Swalem, 2024). Our results showed a negative relationship between total clay content and ring nematodes. However, ring nematodes can also proliferate in the presence of well-structured clay loam soils (Swalem, 2024), which were not observed in the sampled fields.

Peanut is an important commodity in the United States and world. Higher populations of ring nematodes were found in soil with higher sand and lower clay content. The species of ring nematode present in samples collected from peanut fields of South Carolina was Mesocriconema ornatum. While this does not preclude other species of ring nematode from being present in fields planted to peanut in South Carolina, it serves as the first report in South Carolina to document the consistency of the identity of samples that were collected and evaluated as being M. ornatum.

Due to their low expected damage potential in peanuts, ring nematodes are generally neglected. Since ring nematodes can be present in high numbers in peanut-growing fields, it is important to consider their effect outside of yield. Since peanut is an excellent host for ring nematode, supporting up to a 970-fold level of reproduction, and ring nematode has been associated with Cylindrocladium black rot in peanut (Barker et al., 1982; Diamonde & Beute, 1981; Kokalis-Bruelle et al., 1997), further work should be conducted to determine its potential to facilitate other secondary infections.

Sarala Giri: Data curation; formal analysis; investigation; methodology; writing—original draft; writing—review and editing. John Mueller: Methodology; resources; writing—review and editing. Saleh Ahmed: Writing—review and editing. Justin Hiers: Resources; writing—review and editing. Benjamin Fogle: Resources; writing—review and editing. Kendall Kirk: Methodology; resources; writing—review and editing. Weimin Ye: Methodology; writing—review and editing. Daniel Anco: Conceptualization; data curation; formal analysis; funding acquisition; investigation; methodology; project administration; resources; software; supervision; validation; visualization; writing—review and editing.

The authors declare no conflicts of interest.