Quantification of Pratylenchus penetrans in radish fields using a combination method of soil compaction and real-time PCR to determine the economic threshold

Abstract

The objective of this study was to compare the economic threshold (ET) of Pratylenchus penetrans in radish fields of andosols using the Baermann method and the combination method of soil compaction and real-time polymerase chain reaction (PCR). Soil samples were collected from 26 plots at depths of 0 to 30 and 30 to 60 cm before seeding of radishes. The number of P. penetrans in each sample was estimated by the Baermann method and the combination method. No P. penetrans was detected in 13 plots by the Baermann method, while the number of plots in which no P. penetrans was detected was only two by the combination method. The number of spots caused by P. penetrans on radishes harvested from the plots was also counted. It was difficult to determine the ET of P. penetrans estimated by the Baermann method, based on whether severe damage (more than 10 spots on average per radish) was seen. However, the ET of P. penetrans estimated by the combination method was determined at 5.3 J2 equivalents per 20 g dry soil. In plots with P. penetrans densities lower than the ET as evaluated by the combination method, the ratio of plots with no damage was 87%. The results suggest that the combination method has an advantage in the estimation of damage to radish by nematode. © 2011 Japanese Society of Soil Science and Plant Nutrition.