Search

The reniform nematode, Rotylenchulus reniformis, is a major yield-limiting pest of upland cotton (Gossypium hirsutum) in the United States that has been steadily increasing in incidence in many states. Reniform nematode-resistant cotton cultivars have recently become commercially available for cotton producers; however, few field trials have evaluated their efficacy as a nematode management tool. The aim of this study was to evaluate reniform nematode population development, plant growth, and seed cotton yield of reniform nematode-resistant cotton cultivars in two nematode-infested fields in Louisiana. Replicated small-plot field trials were conducted in St. Joseph, LA (NERS field) and Winnsboro, LA (MRRS field) during the 2022 and 2023 growing seasons. In 2022, cultivars evaluated included: (1) DP 1646 B2XF (susceptible/tolerant), (2) DP 2141NR B3XF (resistant), (3) PHY 332 W3FE (resistant), (4) PHY 411 W3FE (resistant), and (5) PHY 443 W3FE (resistant). In 2023, an additional susceptible cotton cultivar, PHY 340 W3FE, was also included. All nematode-resistant cotton cultivars evaluated provided suppression of reniform nematode population development relative to that of the susceptible cotton cultivars, with suppression of nematode soil population densities at harvest ranging from 49 – 81% relative to DP 1646 B2XF. The resistant cultivar PHY 411 W3FE provided the most consistent suppression of reniform nematode population development, reducing reniform nematode soil population densities at harvest in both field locations and both trial years. In contrast, DP 2141NR B3XF only reduced soil population densities at harvest in the NERS field in 2023. Despite relatively consistent nematode suppression and improvements in plant vigor ratings and canopy coverage associated with the resistant cotton cultivars, a yield increase was only observed with PHY 332 W3FE and PHY 411 W3FE planted at the NERS field in 2023. Despite strong resistance to reniform nematode in the evaluated cotton cultivars, nematode soil population densities still increased during the growing season in plots planted with resistant cotton cultivars, emphasizing the need for additional management tactics to use alongside host resistance. This study indicates that new reniform nematode-resistant cotton cultivars show promising potential to reduce nematode population development during the growing season in Louisiana.

Reniform nematode (Rotylenchulus reniformis) is a major pest of sweetpotato in many production regions in Southern United States. Applying soil fumigants and non-fumigant nematicides are the primary management strategies available to growers. This study compared the relative efficacy of nematicides (1,3-dichloropropene, fluopyram, oxamyl, fluazaindolizine, aldicarb, Majestene, and fluensulfone) for management of reniform nematode on sweetpotato. Fumigating soil with 1,3-dichloropropene consistently reduced soil population densities of reniform nematode at the time of planting in both trial years (31 – 36% reduction relative to the untreated control); however, the duration of suppression varied greatly by growing season. A similar trend was observed with fluopyram (56 – 67% reduction) and aldicarb (63 – 65% reduction), which provided season-long suppression of reniform nematode population development in 2021 but had no impact in 2022. In 2021, nematicide application had no impact on yield; however, in 2022, oxamyl and aldicarb increased the yield of U.S.#1 grade sweetpotato. Overall, soil fumigation with 1,3-dichloropropene and in-furrow application of fluopyram and aldicarb provided the most consistent suppression of reniform nematode on sweetpotato.

Inoculation with antagonistic soil microorganisms has shown potential to suppress replant disease of apple in orchard soils. Pseudomonas spp. may have the potential to reduce Pratylenchus penetrans populations on apple. Pseudomonas spp. were isolated from the rhizosphere of sweet cherry and screened for antagonistic characteristics. Two highly antagonistic Pseudomonas isolates, P10-32 and P10-42, were evaluated for growth promotion of apple seedlings, suppression of P. penetrans populations, and root colonization in soil from three orchards. During the isolate screening, Pseudomonas fluorescens P10-32 reduced in vitro growth of fungal pathogens, had protease activity, had capacity to produce pyrrolnitrin, suppressed P. penetrans populations, and increased plant biomass. Pseudomonas fluorescens P10-42 reduced in vitro growth of fungal pathogens, had protease activity, suppressed P. penetrans populations, and increased plant biomass. In potted orchard soil, inoculating apple with P. fluorescens P10-32 suppressed P. penetrans populations in one of the three soils examined. Inoculation with P. fluorescens P10-42 improved plant growth in two of the soils and suppressed P. penetrans abundance in one soil. In one of the soils, P. fluorescens P10-42 was detected on the roots 56 days postinoculation. Overall, we conclude that Pseudomonas spp. play a role in suppressing P. penetrans on apple in orchard soil. [ABSTRACT FROM AUTHOR]

Preplant soil incorporation of compost has previously shown potential to suppress Pratylenchus penetrans populations and improve replant establishment of newly planted fruit trees at old orchard sites. Using a greenhouse experiment, we evaluated the effects of preplant incorporation of three compost amendments (agricultural waste compost, yard trimmings compost, and municipal waste compost) on growth of apple seedlings, P. penetrans populations, microbial populations associated with soil suppressiveness, and microbial activity using soil collected from three orchard sites. We also aimed to identify the biological factors that were most strongly associated with enhanced plant growth in compost-amended soil. In four out of nine compost type × soil combinations, compost improved apple seedling growth relative to the control. In four out of nine compost type × soil combinations, compost reduced P. penetrans root infestation relative to the control, and in one compost type × soil combination, compost amendment increased P. penetrans root infestation. Composts stimulated soil microbial activity and abundance, resulting in greater populations of Pseudomonas spp. in soil in seven of the nine compost type × soil combinations. In a step-wise multiple linear regression, P. penetrans root infestation and the total abundance of fungi in soil accounted for the most variance in plant biomass, with increases in both variables correlated with reduced seedling biomass. Overall, composts show variability in the capacity to promote the establishment of fruit trees in orchard soil. Future research should be directed toward understanding variability in compost-induced plant growth promotion among different orchard soils and compost types. [ABSTRACT FROM AUTHOR]

Meloidogyne enterolobii and M. incognita are major pests of sweetpotato. The ability of M. enterolobii to cause symptoms and reproduce on nematode-resistant cultivars threatens the sweetpotato industry. To evaluate the penetration, development, and reproduction of M. enterolobii and M. incognita on sweetpotato, a time-course study was conducted using the genotypes 'LA14-31' (resistant to M. enterolobii and intermediate-resistant to M. incognita ), 'LA18-100' (susceptible to M. enterolobii and resistant to M. incognita ), and 'LA19-65' (resistant to M. enterolobii and susceptible to M. incognita ), with 'Beauregard' (susceptible to both species) and 'Jewel' (resistant to M. enterolobii and intermediate-resistant to M. incognita ) as controls. Sweetpotato roots were collected at 7-, 9-, 11-, 13-, 21-, and 35-days post-inoculation (DPI), stained with acid fuchsin, and analyzed for nematode developmental stages. Nematode reproduction was evaluated by examining egg production at 42 DPI. Results showed that M. enterolobii developed and reproduced only in 'Beauregard' and 'LA18-100'. In resistant genotypes such as 'Jewel', 'LA14-31', and 'LA19-65', M. enterolobii remained at the pre-parasitic J2-stage, with halted development linked to localized cell death in response to M. enterolobii penetration. For M. incognita , the defense response was most notable in 'LA18-100', where infective juveniles either died, matured as males, or experienced delayed development into adult females, with a marked reduction in M. incognita reproduction. These findings suggest that resistance to M. enterolobii likely involves a hypersensitive-like response that prevents feeding site establishment, whereas resistance to M. incognita appears quantitative, as evidenced by delayed nematode development and reduced reproduction in resistant genotypes.

Root-knot nematodes, genus Meloidogyne , are the most damaging nematodes of sweet potato, causing yield reduction and aesthetic damage of the marketable product. Several sweet potato cultivars currently grown in the Unites States have intermediate-to-high resistance to Meloidogyne incognita ; however, many of these cultivars are susceptible to M. enterolobii . Therefore, the response of 69 sweet potato genotypes to M. enterolobii and M. incognita was evaluated under greenhouse conditions to identify potential sources of resistance. The cultivars 'Beauregard' and 'Jewel' were used as controls. Results showed that sweet potato genotypes were either highly resistant or highly susceptible to M. enterolobii , whereas they showed a wide-spectrum response to M. incognita , ranging from highly susceptible to highly resistant. Twenty-six genotypes were resistant to M. enterolobii and 11 genotypes were resistant to M. incognita . Combined resistance to M. enterolobii and M. incognita was observed in three sweet potato genotypes. Selected genotypes from this study will be used to incorporate the observed resistance into a commercially viable sweet potato cultivar., Competing Interests: The author(s) declare no conflict of interest.

Background: Meloidogyne enterolobii (Yang and Eisenback) was recently introduced into Louisiana on contaminated sweetpotato planting material. Given the known variation in sensitivity to nematicides within the genus Meloidogyne, there is question as to whether fluorinated nematicides will be as efficacious toward M. enterolobii as they are with M. incognita (Chitwood). Using a series of in vitro and growth cabinet experiments, this study compared the sensitivity of M. enterolobii and M. incognita to four synthetic non-fumigant nematicides (fluopyram, fluensulfone, fluazaindolizine, and oxamyl)., Results: Meloidogyne enterolobii had lower sensitivity to nematicides than M. incognita in the majority of the in vitro exposure assays. Similar levels of reduction in root infectivity were observed after nematicide exposure among both nematode species. Fluopyram showed high hatching inhibition for both Meloidogyne species at low concentrations [median effective concentration (EC 50 ) values of 0.273 to 0.018 mg L -1 ], whereas fluensulfone showed high root penetration inhibition at low concentrations (EC 50 values of 0.151 to 0.065 mg L -1 ) relative to that of other evaluated nematicides. For both Meloidogyne species, each of the four non-fumigant nematicides reduced root galling (58-96% reduction for M. enterolobii, 71-100% reduction for M. incognita) and egg production (63-99% reduction for M. enterolobii, 58-96% reduction for M. incognita) on sweetpotato when applied at the label recommended rate., Conclusion: Fluorinated nematicides and oxamyl show capacity to suppress M. enterolobii on sweetpotato. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)