Identification Of Pathogen And Its Biological Characteristics Of Blackleg Disease Of Ajuga Multiflora

Ajuga multiflora belonged to Lamiaceae Ajuga Bunge, this plant had a long florescence, with beautiful shape, grown fast and managed easily, worthy to be popularized as one kind of ground cover plant. Since the autumn of 2004, the A. multiflora died in scenic spots of Hangzhou seriously. We found it was a new infected disease result in this damage. Brown water-soaked spots initially appeared on the base of stem, then the lesions rapidly turned into black-rot, followed by wilting and drying of individual leaves, ultimately death. The typical symptom of this disease was black and rot of the stem, so we named this disease as Blackleg disease of Ajuga multiflora.Collected 14 species plants cultivars infected A. multifiora in Hangzhou, and only one pathogen was isolated. The isolate was given a corresponding number such as JGC24. The pathogenicity test showed, the symptom developed on the inoculated plants was consistent with that in field. And the same pathogen was consistently reisolated from infected plants. The isolates were identified as Phoma multirostrata (P.N. Mathur, S.K. Menon & Thirum, Dorenb. & Boerema) based on its morphological characters (Sutton, 1980).The rDNA ITS1-5.8S-ITS2 sequence length of JGC24 is 441bp. A neighbor-joining tree was generated based on the 5.8S gene and internal transcribed spacer (ITS1 and ITS2)sequences of 9 isolates of Phoma, rooted with Phyllosticta sp. Analysis the ITS sequences, the result showed that all they were very similar. The percent identity of sequences of P. exigua,P. exigua var exigua and JGC24 is 100%, Among all the isolates, P. herbarum's relation to JGC24 is the furthest, and the sequences distance is 0.0413.The study of pathogen's characterization showed that the optimum temperature and pH for mycelial growth of the pathogen were 20～25℃and pH 6～9. Different lighting time had no significant effect on mycelium growth of JGC24. Fructose and dextrose were the optimum carbon source, and yeast was the optimum nitrogen source, but Carbamide was not fit for JGC24.The effect of 14 different kinds of fungicides on mycelium growth were studied by means of measuring colony's diameter.The results showed that 7 kinds of fungicides had distinctly depressed the mycelia growth of JGC24 with inhibition rates were up to 100%. In the greenhouse trial, pouring Thiophanate-methyl and Pyrimethanil 1000 times dilution after infected by A. multiflora, the relative cure effects were up to 100%.In the greenhouse trial, P. oliganrum RCul had significantly curative effect against the blackleg disease of A. multiflora, and the control effect up to 70.14% that was equivalent strong with Carbendazim 1000 times dilution (P=0.05).