A Canister Assay for Evaluating Host Status of Potato to Meloidogyne Chitwoodi

Abstract

New, reliable strategies are needed to control Meloidogyne chitwoodi in potato; plant host resistance is central to this effort. While efforts to breed potato for resistance to M. chitwoodi are underway, a major bottleneck in this process is phenotyping plant genotypes for nematode resistance. Currently, time and resource consuming phenotyping takes place in the greenhouse or field. The objective of this study was to establish a high throughput methodology for screening potatoes against M. chitwoodi and quantify nematode egg densities at the end ofscreening using qPCR. Various parameters were evaluated for a canister assay where soil was added to a small container, planted with potato seed tuber, inoculated with nematode eggs, and incubated at a constant temperature in the dark. To obtain maximum reproduction factor (RF = final population density/initial population density) values, a minimum of 6 weeks after inoculation was required. Timing of inoculation was also important, with higher RF values when inoculation with eggs occurred at planting compared to 2 weeks after planting. The volume of water in which inoculum was delivered to soil did not impact RF values, nor did inoculation density (0.5, 1, or 5 eggs/g soil). The canister assay was evaluated using genotypes from a breeding population with varying levels of resistance to M. chitwoodi. Egg enumeration by qPCR was more sensitive than by microscopy, however, this increased sensitivity did not result in a significant difference in RF values nor the designation of a genotype being a good or poor host for M. chitwoodi. This method has the potential to greatly decrease the amount of time and resources needed to phenotype potato against M. chitwoodi and can allow for multiple screenings throughout the year, regardless of the season.