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White Clover Response to Nematode Infestation and Plant Density

Crop Science Res. Lab., Forage Res. Unit, USDA-ARS, P.O. Box 5367, Mississippi State, MS 39762

^* Corresponding author.

The southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] reduces the productivity and persistence of white clover (Trifolium repens L.) throughout the southeastern USA. Our objective was to determine the response of two white clovers with differing M. incognita tolerance to nematode infection across a range of plant densities. Nematode-susceptible ‘Regal’ and tolerant germplasm SC-1 were established in the greenhouse at 3, 6, 12, 24, and 48 plants per fiat (0.I m^–2) and root-knot n ematode ( Race 4) eggs were applied to each fiat at 0 (control), 600 (low), or 1200 (high) eggs per 500 cm³ of soil mix. Regal exhibited no tolerance to infection, while SC-1 exhibited tolerance (equivalent dry matter [DM] yield across initial nematode egg levels) in the first repetition of the experiment only. Total DM yield of Regal and SC-1 increased quadratically with increasing plant density across initial nematode egg levels in the first repetition, indicating DM yield suppression was caused by factors related to intraspecific competition, rather than by nematode infection. In the second repetition, DM yield of both clovers increased linearly with increasing plant density at the low and high initial egg levels, indicating that nematode infection had a greater effect on yield than intraspecific competition. Nematode reproduction was not influenced by plant density. Stolon dry weight of both clovers was reduced a mean of 60% by nematode infection. Because total DM yield of nematode-infected white clover increased with increasing plant density due to greater early harvest productivity immediately following nematode inoculation, increasing plant density would not be an effective means of increasing long-term forage productivity.

Received for publication August 16, 1989.