The Pathogenic Fungus and Incidence Regularity of Die Back from Dendrobium officinale

In order to research die back from Dendrobium officinale, the symptoms observation, isolation of pathogenic fungus, pathogenicity test, identification of pathogenic fungus, incidence regularity, as well as control methods were carried out in laboratory and green house in April 2012 to June 2014 respectively. The results showed that die back is a new disease of D.officinale caused by Alternaria alternate, it damages the young leaves and tender tip of D.officinale, result in tops died when the disease is a serious occurrence. Probability of isolation from TP-1201 strain to be 65.8%, all the inoculated points on inoculated D.officinale are infected caused by Alternaria alternate after 14 days, spots diameter approximately 4 mm, the symptoms is similar to those of natural disease, re-isolation of spots again got A.alternata stain. Morphological description and DNA molecular sequence confirm that TP-1201 strain (A.alternata) is a pathogenic fungus of result in die back from D.officinale. The disease may seriously occurs when the temperature at 20-30 ℃ and RH 75%-90%. Using Trichoderma harzianum and Bacillus subtilis before the disease, and 50% iprodione WP, 20% myclobutanil WP and 70% thiophanate-methyl WP after the occurrence of disease is enable to control the disease.