Identification Of Black Spot Disease And How It Infects Post-harvest Broccoli

Broccoli(Brassica oleacea L.var.italica) is nutritional and regarded as one anti-cancer vegetable.However,it is vulnerable to various pathogens and senescences rapidly after harvest,which remarkably shortens its market life.So it's meaningful to separate and identify these broccoli post-harvest pathogens so as to make effective control protocol.Our research identified the black spot disease pathogen of post-harvest broccoli with the help of morphological and molecular methods and explored its contribution to the senescence of the plants.The results are as follows,a.According to our market research,Black spot disease seems to be one of the most common diseases on post-harvest broccoli.This pathogen is also related with the aging of the plants.The infected plants senescenced rapidly and lost its market value.b.According to Koch's Postulates,pathogens on post-harvest broccoli are identificated as Alternaria spp.And strain HLYB-4 was proved to be the cause of the black spot,which produced a green-brown colony and whose spores are 24 to 51.5×7.5 to 23μm grenade-like with two to six transverse septa,zero to three mediastinal septa and fake rostrum.It was identified as Alternaria brassicicola by morphologically analysis and further proved by the rDNA-ITS blast and particular primers Abral andAbra2.c.The optimal temperature and pH of A.brassicicola are 25℃and pH 5-8 respectfully.Low storage temperature(5℃) can't block its hypha growth and sporation totally.However,high temperature(35℃) seems to effectively restrain its growth and sporation both in vitro and in vivo.In addition,its spores could germinate from pH 2-12 and the germination rate reached 100%within 3 hours at pH 5-9.Moreover,50ppm exogenous ethylene seems to contribute to its germination.d.After pathogen inoculating on the healthy head of broccoli,obvious yellowing could be seen within 72 hours with the degradation of its chlorophyll.High ethylene output and respiration rate could be measured while the inoculated group could be tested 24 hours earlier than the control.However,the rapid descendant of Vitamin C seems not to be related with the infection.e.The RT-PCR result indicates that the transcription of Bo-ACS2 enhanced in the first 72h in the inoculated group and Bo-ACO2 have up-regulated in the first 24 hours in the inoculated group as well,which is one day earlier than the control group.And the transcription of Bo-CLH1 of infected group in the first 72 hours is obviously higher than the control group.So both physiological and molecular results indicated that A.brassicicola induced the senescence of post-harvest broccoli.Above all,in order to improve the preservation of broccoli and extend its market life,it is critical to prevent the occurrence of black spot caused by A.brassicicola.