| Hami melon is a nutrient rich specialty in Northwest China,which has the characteristics of wide planting area and large output.However,Hami melon is very susceptible to the infection of spoilage fungi after picking,resulting in a large number of Hami melon rotting,and countless Hami melons are wasted.In this study,the main kinds of extracellular cell wall degrading enzymes produced by Alternaria alternata and Trichothercium roseum were first discussed,and then the disease mechanism and control methods of Hami melon caused by Alternaria alternata and Trichothercium roseum were discussed.The results are as follows:1.The growth rate of Trichothercium roseum on the potato sucrose medium（PSA）was 1.28 times higher than that of Alternaria alternata on the 7th day,and the colony diameter was 63.2 mm larger than that of Alternaria alternata on the 7th day,1.28 times of that of Alternaria alternata;the cell wall degrading enzymes produced by Alternaria alternata and Trichothercium roseum are the same,including carboxymethyl cellulase,polygalacturonase,β-glucosidase,β-galactosidase,polygalacturonase,pectinase,xylanase and filter paper enzyme.Among them,the activities of β-galactosidase,carboxymethyl cellulase,polygalacturonase and β-glucosidase produced by two kinds of spoilage fungi were higher.On the second day,the activity of polygalacturonase was 1.04 times of that of Alternaria alternata;on the third day,the activity of pectinase was 1.1 times of that of Alternaria alternata;on the seventh day,the activity of carboxymethyl cellulase and polymethylgalacturonase were 1.04 times and 1.07 times of that of Alternaria alternata,respectively.2.Using Hami melon as material,inoculate Alternaria alternata and Trichothercium roseum respectively to study the effect of different inoculating methods on the decay of Hami melon;then inoculate Alternaria alternata and Trichothercium roseum respectively by the way of drilling holes,observe the propagation of spoilage fungi and the change of cell wall structure of Hami Melon by scanning electron microscope,observe the decay of Hami melon,the activity of cell wall degrading enzyme and Hami melon products The mechanism of Hami melon rotten was discussed by the correlation analysis of quality.The results showed that compared with skin scraping inoculation,Z inoculation and no injury inoculation,Hami melon was the most serious,and the disease was found after 1 days of storage.The incidence rate of bacteria in the inoculation group reached 100% on the fourth day.Compared with Alternaria alternata,the infection rate of Trichothercium roseum was faster.The results of SEM showed that the cell wall structure of the uninoculated group was complete,and the surface of the uninoculated group had spoilage fungi growth on the 7th day,but the cell structure was not degraded;the cell wall of the inoculated group was full of hyphae and collapsed on the 3rd day,and the cell wall of the uninoculated group was broken on the 7th day.During storage,the activity of β-galactosidase,carboxymethyl cellulase,polygalacturonase and β-glucosidase increased slowly.The activity of the group inoculated with spoilage fungi was significantly higher than that of the control group,which was 1.28-1.85 times higher than that of the control group.Compared with the control group,Hami melon inoculated with Alternaria alternata and Trichothercium roseum had darker color,faster respiration rate,higher weight loss rate,higher relative conductivity and lower hardness.The results can provide a theoretical basis for the analysis of the infection process and the disease control of Hami melon.3.The effects of chitosan coating,chlorine dioxide（Cl O2）fumigation and the combination of the two on the powdery mildew of Hami melon were studied.The results showed that chitosan coating and Cl O2 fumigation could alleviate the disease symptoms of Hami melon caused by Trichothercium roseum,and the effect was positively correlated with the concentration of chitosan and Cl O2.2% chitosan,120 ppm Cl O2 and 2% chitosan + 120 ppm Cl O2 can inhibit the growth of the hyphae of Trichothercium roseum,cell wall rupture and cell collapse of Hami melon peel and pulp by reducing the activities of β-galactosidase,carboxymethyl cellulase,polygalacturonase and β-glucosidase.Chitosan and Cl O2 inhibited the increase of respiration intensity,weight loss rate,relative conductivity and decrease of hardness.Chitosan + Cl O2 treatment is better than chitosan or Cl O2 treatment alone.It is an effective method to reduce the decay of Hami melon,extend the shelf life and maintain the storage quality of Hami melon. |
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