In Vitro Inoculation System For Pathogenicity Evaluation Of Peach Tree Gummosis

Peach (Prunus persica) is one of the most important and widely cultivated fruit trees in China, but has serious gummosis diseases. Gummosis, caused by Botryosphaeria spp., mainly appeared on trunks and branches. The disease can cause a general decline of tree growth, leading to significant economic losses. It is difficult to control, for the lack of studies on regulation of pathogen dissemination, the virulence of pathogen, and a fast and reliable system to evaluate the virulence.In this study, the virulence of JMB-122(Lasiodiplodia theobromae), LHKB-111(Fusicoccum aesculi), and XC-132(Fusicoccum aesculi), which were isolated from different regions in Hubei Province, was evaluated by inoculating detached twigs and leaves. The inoculation experiments were also performed on the lignified branches in the field. Based on the test results, a quick experimental evaluation system and new disease severity grades for peach gummosis were developed. The experiment was also conducted to evaluate susceptibility of the peach cultivar’Spring Snow"(Prunus persica’Spring Snow’) and’Tianxianhong’(Prunus persica’Tianxianhong’). The major results were as follows:1. The virulence of JMB-122(Lasiodiplodia theobromae), LHKB-111(Fusicoccum aesculi), and XC-132(Fusicoccum aesculi) was evaluated via artificial inoculation with detached twigs and leaves. The result shows:JMB-122(Lasiodiplodia theobromae) was highly virulent, LHKB-111(Fusicoccum aesculi) was considered intermediately virulent and XC-132(Fusicoccum aesculi) was shown to be weakly virulent. That is, Lasiodiplodia theobromae was more virulent than Fusicoccum aesculi.2. A quick in vitro inoculation system was firstly established to evaluate the virulence of pathogen by inoculating detached leaves. The detached leaves were pricked once, inoculated with the pathogenic fungal mycelial disc, and then incubated at28℃and2500lux, after4days in a moisture box. Lesion diameters were collected and analysed. The procedure of inoculation on detached leaves could identify the differences of virulence among isolates accurately, which were consistent with the results of inoculation on detached twigs and branches in the field. 3. A new disease severity grade was built, using disease spot size by inoculating detached leaves.4. The experiment was also conducted to evaluate susceptibility of the peach cultivar ’Spring Snow’(Prunus persica’Spring Snow’) and’Tianxianhong’(Prunus persica ’Tianxianhong’), which was performed on leaves by inoculation with the isolate LHKB-111, belonging to the most common species F. aesculi. The results were as follows:’Spring Snow’was more susceptible and’Tianxianhong’was more resistant. The conclusion was consistent with the field investigation.