Relationship between damage to burdock caused by Pratylenchus penetrans and cultivation methods in Hokkaido.

Yamada Eiiti, Kawai Masaru

doi:10.3725/jjn.38.19

The relationship between damage to burdock caused by Pratylenchus penetrans after rotary harrow cultivation (20-30 cm depth) and trencher cultivation (1 m depth) was studied. In the past, burdock fields were rotary cultivated prior to planting and these fields were associated with severe P. penetrans damage symptoms of brown or black spots on the root that fused to form black mottles (common name, “Black Symptom”). Currently, rotary cultivation is followed by trencher cultivation before planting which mixes topsoil having the highest P. penetrans densities with deeper soil having much lower nematode densities. Trencher cultivation is associated with less P. penetrans damage than rotary cultivation and has symptoms of small brown spots on the root (common name, “Sesame Symptom”) thought to be due to reduced nematode densities that result from mixing high nematode density soil with low density soil. The relationship between P. penetrans density and burdock damage was examined in trencher cultivation. All roots that had a rootlesion index and root-deformity index of 2 or less (0 to 4, 0 = 0%, 4 = 100% damage) were considered to be marketable burdock roots. The nematode density of the tolerable injury level threshold was defined as the nematode density that corresponded to 80% of the burdock roots being marketable. The tolerable injury level threshold was based on the number of nematodes extracted by the Baermann funnel technique from 25 g of wet surface soil (0-20 cm depth) for 48 hrs. This value was 6.1 P. penetrans / 25 g soil before trencher plowing, and 3.2 P. penetrans / 25 g soil after trencher plowing.

Relationship between damage to burdock caused by Pratylenchus penetrans and cultivation methods in Hokkaido.

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