Detection Of DNA Fragment And Caspase-like Activities In Malus Baccata During Infection Of Diplocarpon Mali

Marssonina leaf blotch caused by Diplocarpon mali, leads to apple severe prematuredefoliation, results in huge yield and economic loss. Trees are weakened gradually withannual occurrence of the disease, which poses threaten to apple safety production. Resistanceof apple germplasm to the disease is divergent, but the mechanism is still unclear. In this study,focused on interaction of resistant material Malus baccata and D. mali, detection of fungalgrowth in M. baccata was performed to analyze the process of resistant responses. Evidencesfor DNA fragment of caspase-like activities were also searched during infection of the fungus.Our works were hoping for providing more details for further exploration of apple resistantmechanism. The results are listed as below.1. Growth of D. mali in M. baccatawas detected using quantitative real-time PCR. Theresults demonstrated no significant difference in fungal biomass of M. baccataand susceptibleM. domesticacv. Fuji at1dai (days after inoculation). But the fungal biomass in M. baccatagradually decreased at3dai. In contrast, it fast accumulated in Fuji to an amount of16timesmuch to that in M. baccata. It indicated that the fungal growth in M. baccata was constrainedby resistant responses. However, fungal biomass in M. baccata also fast accumulated at5dai,which suggested that the fungal growth had recovered normal probably for overcoming ofresistance. The qPCR method could be used for resistance evaluation of new cultivars orefficiency assessment of fungicide.2.Detection of DNA ladder was accomplished using2%agarose gel electrophoresis. ButDNA ladder was negatively detected in M. baccataneither at1dai,3dai and5dai. The resultssuggested that DNA ladder did not accompany with cell death of M. baccata during earlyperiod of infection. But DNA fragment was not excluded based on our results.3. Caspase-like activities were detected using artificial4-peptide fluorescentsubstrate.The results showed that activities of YVADase, DEVDase, IETDase and VEIDase in leaves ofM. baccata had no different changes at1dai and3dai, while it significantly decreased at5dai when the fungal growth recovered normal. In contrast, activities of YVADase, DEVDase,IETDase and VEIDase in Fuji were kept at constant level. The results indicated that thedecrease of activities was related to cell death of M. baccata, but possibly it was the pathogen that suppressed cell death of host by decreasing caspase-like activities to facilitate owninfection.