Levels of Sclerotium rolfsii inoculum influence identification of resistant genotypes in Jerusalem artichoke

Abstract

Improvement of Jerusalem artichoke genotypes with resistance to stem rot caused by the soil borne fungus Sclerotium rolfsii is a sustainable means for controlling the disease. However, this crop is rather new to breeders. A consensus screening procedure for resistance to the disease is not yet available. The aim of this study was to determine the level of inoculum that provides the reliable and effective results for screening trials. In the experiment in Khon Kaen, Thailand, four levels of sorghum seed infested with S. rolfsii (1, 2, 3 or 4 seeds/plant) were tested with 10 Jerusalem artichoke genotypes. Plants inoculated with one sorghum seed had the lowest disease incidence, whereas plants inoculated with four sorghum seeds had the highest disease incidence. Most pairings of inoculum levels were statistically different for disease incidence except for two vs. three seeds. In addition, permanent wilting and area under disease progress curve occurred more rapidly with four seeds compared to the other inoculum levels. The highest variation among Jerusalem artichoke genotypes was observed in the plants inoculated with three sorghum seeds. Therefore, three sorghum seeds inoculum was suitable to identify Jerusalem artichoke genotypes resistant to S. rolfsii.  Based on days to permanent wilting, resistant and susceptible genotypes were identified.   Key words: Helianthus tuberosus L., sunchoke, stem rot, disease incidence, genotypes, sorghum seed, area under disease progress curve.