Causal Agent Identification Of Apricot Fruit Black Spot And Rapd Analysis Of Relate Species Of Alternaria

Apricot fruit black spot was found in 1995. But causal agent of that disease was unknown. The disease was only found on Hongyu apricot and Badan apricot and only infected fruits while branches and leaves were not affected. Little red dots were found and then they changed into black spots on the peel of injured fruits. Most of the infection began from the heads of the fruits. The spots could be stripped with ease and did not deepen into flesh, so it did not affect the taste of the fruit.The causal agent was identified as Alternaria arineniacac T.Y.Zhang, M.Zhang et.W.H.Yangaccording to its pathogenicity, characteristics of culture, morphology and biological characteristics. The optimum range of temperature and pH for the mycelia growth were 25~30癈 and pH 4~8 respectively, but 28癈 and pH 5 were the most favourable. For conidia germination, the suitable temperature was 25-35癈 and 30"C was the most optimum. Illumination favoured the mycelia growth and conidia germination.DNA was extracted from mycelia of Alternaria anneniacae and 19 related strains. 10 primers from 100 random primers for RAPD analysis were screened out which had clear bands and good diversity characters(the rate of diversity was 81.2%). The DNA of 28 tested strains which belongs to 6 species of Alternaria were amplified qualitatively by PCR technique and got 157 very clear bands of DNA totally. The results of DNA amplification were analysed by cluster. The pattern of RAPD showed that their genetic relationships were very close for all the tested strains clustered into one group at linkage distance 6.7. However there was still considerable genetic diversity.9 Alternaria anneniacae strains clustered into one group at linkage distance 4.7 according to the cluster analysis which indicated that Alternaria prunicola was an independent species. The strains of A.alternta dividing into different groups indicated that there was an intiaspecies variation among A.alternta. A.alternta and A.gaisen mixied in cluster tree as well as A.alternta and A.inali. indicated that they were homogeneous in gene.Although the results of genetic analysis and the results of morphological analysiswere not consilient which indicated that species of Alternaria can not be distinguished only depending on IIAPD profiles, the results indicated that RAPD analysis can test genoniic DNA directly and suitable for analysis genetic variations among intraspecies and interspecies,The study of Apricot fruit black spot and RAPD analysis on 28 strains will provide theoretic base for disease diagnosis and control and for identification and classification of Altenuu'ia respectively.