Studies On Etiology And Control Of Rehmanniae Glutinosa Leaf Ring Rot(Phoma Herbarum)

Rehmanniae glutinosa is an important medicinal and economic plant widely grown in China, Henan Province is the main production area with about6000Ha. Diseases are major biological factors that limited production and quality of Rehmanniae glutinosa in Henan, they have brought huge economic losses for the farmers. In recent year, the leaf ring rot breaked out frequently, it has become the most important leaf disease of Rehmanniae glutinosa. Investigation conducted in2010and2011, showed the disease occurrence with the incidence rate of100%and the average disease index40. In this research, we study the etiology of leaf ring rot, screening biocontrol endophytes and fungicides, then develop the strategies of IPM.Through the morphology and molecular identification, the pathogen of leaf ring rot is Phoma herbarum, it is the first report of Phoma leaf ring rot on Rehmanniae glutinosa. The pycnidia of this pathogen were produced on older lesions on the leaf tissue, initially buried, then breakthrough the epidermis, pycnidia were spherical, oblate, diameter of120to210μm. Conidia were monoplast, hyaline, rod or oval-shaped, size were4～5umμ×1.5～2μm.Study of the biological characteristics of Phoma herbarum, it showed that PDA, Rehmanniae glutinosa juice agar and OA are suitable for pathogen, CA(carrot agar) make the best production of pycnidia. Colony growth of the optimum temperature is25℃,12hours light and dark alternately growth fastest, the pathogen can grow well under pH5-7conditions, the optimum growth environment is pH6, the pathogen conidiospore lethal temperature is53℃. Glucose is the best carbon source for Phoma herbarum in solid medium, and soluble starch is the best carbon source in liquid medium, yeast extract is the most suitable nitrogen source of pathogen.The disease appear sporadic in June, wide spread in July, peak incidence of the disease is in August and September. The disease would outbreak in continuous rainfall, leaves become rot in hot and humid environment. From the comparison experiment, Kangyu-831, Guolimao showed high resistance,85-5performed moderate resistant, and Beijin-3was the heaviest susceptible cultivars.Field trials were conducted in2010and2011, the disease index of leaf ring rot was reduced by Azoxystrobin (1000times, spraying) significant to control. Endophytic fungi of Rehmannia glutinosa tested against to P. herbarum in vitro,10of34isolates showed antibiosis,067(Epicoccum nigrum) was the best strains. Endophytic bacteria0831-b and xb, have good antagonist role to P. Herbarum, their biocontrol effect reached to90%and80%in vitro(on leaf), respectively. It showed that endophytes can be used as tool for biocontrol to the diseases of Rehmannia glutinosa.According to the results, we formulated a integrated control strategy to Rehmannia glutinosa.1) Use the resistant varieties Kangyu-831, Beijing-3and85-5, reduce the index of Rehmannia glutinosa.2) Cultivate Rehmannia glutinosa in sandy loam, rigde planting, drainage in time, reduce the temperature and humidity of the field.3) Clean-up the sick plants after harvest, separated from the breeding field and cultivating field.4) Spraying since July, remedy in time after rainfall, suitable fungicides were Azoxystrobin, Tebuconazole, Ningnanmycin and Mancozeb.