Interacting Effects of Soil Temperature and Type on Reproduction and Pathogenicity of Heterodera schachtii and Meloidogyne hapla on Sugarbeets.

In central Washington, Heterodera schachtii Schmidt (the sugarbeet cyst nematode) is associated with sugarbeets (Beta vulgaris L.) growing in fine-textured soils, and Meloidogyne hapla Chitwood (the nor thern root-knot nematode) is associated with sugarbeets growing in coarse-textured soils. T h e opt imum soil temperature for reproduct ion on sugarbeets is between 21 and 30 C for H. schachtii (2, 7, 8, 9, 11, 12) and between 24 and 30 C for M. hapla (unpublished). In 1975-77 temperatures 8-10 inches deep in several sugarbeet fields seldom exceeded 20 C during the growing season (March-October). Despite those relatively low soil temperatures, H. schachtii and M. hapla are important pathogens on sugarbeets in Washington. This study was undertaken to determine any relation between soil temperature and soil type on the reproduct ion and pathogenicity of H. schachtii and M. hapIa on sugarbeets. Preliminary results have been reported (10). H. schachtii was cultured on sugarbeets and M. hapla on tomato. Nematodes for inoculum were extracted by placing H. schachtii cysts and M. hapla-infected roots under mist for 24-48 hr. Inocnlations were made by pipett ing the desired number o[ nematodes into 50 ml of water and pouring the water around the plant roots. Sugarbeet seeds (U 8~ I Hybr id 8) were planted in methyl-bromide-fumigated silt loam (28.2% sand, 45.4~. coarse silt, 5.0% fine silt, 21% clay) or sandy loam (72.4% sand, 20.8% coarse silt, 1.8% fine silt, 5.0% clay) soil in l-liter plastic containers. T h e containers were placed in temperature-controlled water