| The pathogen strain Alternaria citri was obtained from the surface of the naturally rotted Citrus.unshiu Marc cv.fruits. The results of morphological testing and rDNA-ITS sequeces analysis showed that the pathogen was Alternaria citri. The infection ways and biological characters of Alternaria black rot disease were studied. Three antagonist strains Wf-b-1,γ-60-11 and Wm-9 exhibited good inhibit effct against postharvest Alternaria black rot of Citrus. The main results are as follows:1. Identification of the isolated pathogen: through morphological testing, pathogenicity determination and rDNA-ITS sequences analysis, it was determined that the pathogen was Alternaria citri.2. The results of biological characteristics showed that there was significant difference in colony form, growth rate of hypha and yield of conidia in different culture media, among which potato glucose agar played the best role for mycelium growth of pathogens, but citrus leaf medium was the most appropriate for sporulating. Among all of the seven kinds of carbon sources, glucose was the best for mycelial growth; chitosan was better than other carbon sources for the yield of conidial, which could reach 1.80×10~6 spores/mL; among all of the ten kinds of nitrogen sources, beef extract played the best role for both the mycelial growth and sporulation. The suitable temperature for the growth of Alternaria citri ranged from 25℃to 32℃, with the optimum temperature for mycelial growth being at 30℃, and the optimal temperature for producing of conidia was 32℃. Lighting did not show significant effect on the growth of the pathogen, but the treatment of the darkness could promote sporulation. Alternaria citri could grow in the media with pH from 4 to 11, and pH had no evident effect on the growth of the pathogen. The lethal temperature of Alternaria citri was about 55℃. The bio-assessment tests of different fungicides showed that 25% imidazole, 50% carbendazimand and 2,4-Dicholrophenoxyacetic + 70% thiophanate methyl were the best for controlling the pathogen among all the chemicals tested.3. The infection way of Alternaria citri was preliminarily identified: From the flowering season to the harvest time, Alternaria citri could invade potential. In the full flowering stage, it was found that petal, calyx, stigma and ovary were infected by the black rot pathogen, and that the infection rate of petals was 100%. During the development period of Citrus, the peel of the peduncle and the peel of the navel region which carried pathogen rate were the highest. The pathogen could also extend to fruit pulp.4. The isolates which could control Alternaria black rot were screened: 12 strains exhibited inhibitory activity against Alternaria citri by means of primary and further screening in vitro. It was found that isolates Wf-b-1,γ-60-11 and Wm-9 were the most effective against Alternaria citri in vivo.5. The inhibition effects of antagonists with different concentrations were tested. The results showed that: the biocontrol activity was positively correlated to the concentration of yeast antagonist. When the concentration of pathogen was 1×10~5 spores/mL and the antagonist concentration was 1×10~8 CFU/mL, after eight days, the incidence rates of Wf-b-1,γ-60-11 and Wm-9 were 16.49%, 20.74% and 25.44% separately. And the inhibiting rates were 55.57%, 56.65% and 50.48% respectively.6. The Antagonistic isolates were identified: The strains Wf-b-1, and Wm-9 were identified by morphological testing, physiological testing and rDNA-ITS sequences analysis. Wf-b-1 belonged to Torulaspora, Torulaspora globosa and Wm-9 was Hanseniaspora uvarum. Furthermore, it was found that y-60-11 came from the mutation breeding of Kloeckera apiculata. |
PDF Full Text Request