Field Applications of Some Bioagents and Safety Chemicals to Control Stem Rot Disease of Jerusalem artichoke (Helianthus tuberosus L.)

Four bioagents i.e. yeast (Saccharomyces cerevisiae), Trichoderma viride, Bacillus subtilis, and Pseudomonas fluorescens in addition to humic acid, sulphated canola oil (sulphex 0.5%) and Paclobutrazol (PBZ) were applied to study their effect on disease incidence caused by Sclerotium rolfsii. Also, some vegetative parameters, tuber yield and enzymes activity of Jerusalem artichokes (Helianthus tuberosus L.) plants under field conditions were detected. Results indicated that, under laboratory conditions, all treatments significantly reduced the linear growth of Sclerotium rolfsii. The highest reduction was obtained with sulphated canola oil (sulphex 0.5%) and Paclobutrazol (PBZ) which reduced the linear growth by 94.4 and 88.9 % respectively, followed by B. subtilis which reduced the linear growth by 71.5 %. Meanwhile, T. viride, P. fluorescens and yeast (S. cerevisiae) showed moderate effect. Under field conditions results revealed that all tested treatments significantly reduced the disease incidence and disease severity of Jerusalem artichokes plants as compared with untreated plants during the periods between April and November of 2009 and 2010 growing seasons. The highest reduction was obtained with T. viride, B. subtilis, sulphated canola oil (sulphex 0.5%) and the fungicide Vitavax-200 which reduced the disease incidence and disease severity more than 70.0 and 54.2% respectively. The same trend was observed in the second seasons. Also, all tested treatments significantly increased the tested parameters of Jerusalem artichokes plants under field conditions compared with untreated plants during 2009 and 2010 growing seasons. As for tuber yield, all tested treatments significantly increased the tuber yield of Jerusalem artichokes plants under field conditions. The most effective treatments are T. viride, B. subtilis, sulphex 0.5% and fungicide Vitavax-200 which increased the tuber yield by 180.7, 180.7 and 145.6% respectively in the first season. Meanwhile, a moderate increas in tuber yield was obtained with P. fluorescens, humic acid and Paclobutrazol (PBZ) which increased tuber yield more than 93.0%. The same trend was observed in the second season. The four bioagents i.e. yeast (S. cerevisiae), T. viride, B. subtilis, and P. fluorescens in addition to humic acid, sulphated canola oil (sulphex 0.5%) and Paclobutrazol (PBZ) increased the activity of all assessed enzymes compared to untreated control during two growing seasons. It could be suggested that bioagents and safety chemicals could be commercially used for controlling stem rot disease for Jerusalem artichokes plants under field conditions.