Etiology, Occurrence And Control Of Figwort (Scrophularia Ningpoensis) Leaf Spot

Figwort (Scrophularia ningpoensis) is a perennial medical plant with an important role in the economic development of local farmers. In recent years, a serious disease with leaf spot on figwort has been occurring in Jianshi county, Hubei province, directly reducing heavy yield loss. The purpose of the current research was to indentify the causal agent of the leaf spot of figwort, to test the biological characteristics of the pathogen, and to determine the control strategies of this disease. The research results had been showed as follows:The strains of Phoma sp. were isolated from the diseased leaves of figwort in nursery of Jianshi county of Hubei province. Pathogenicity was tested by inoculating mycelial plugs or conidial suspension of Phoma sp. onto leaves of healthy plants. The result indicated that Phoma sp. was the causal agent of figwort leaf spot. Isolations were made onto potato dextrose agar (PDA) giving circular colonies. The colonies were initially white and turned yellow. After 7 days of incubations on PDA, the colonies turned grey on the upper surface. After 10 days, the colonies developed numerous spherical dark or flat pycnidia (137-157μm in diameter, 110-126μm in height). Conidiogenous cells were flask-shaped,hyaline nonseptate, 5.7-7.8×3.8-4.5μm, releasing abundant elliptical hyaline, nonseptate conidia measuring by 4.1-6.1×2-2.7μm. Genomic DNA was extracted, and sequences of rDNA-ITS were obtained. Comparison with sequences in GenBank showed 97% similarity with P. herbarum. According to the morphological characteristics, and the DNA sequence of ribosomal ITS, the pathogen was identified as P. herbarum.The result of biological characteristics showed that the pathogen could grow on PDA medium with or without illumination and continuous illumination was the most suitable condition for the growth of mycelia and the germination of conidia. The range of temperature for mycelia growth was 10-35℃, 25℃was the optimal temperature for the mycelial growth and conidial germination. The favorable pH value for mycelia growth was 3.0-11.0, with the optimal pH 6.0. The range of pH value for the germination of conidia is 3.0-11.0, with the optimal pH 7.0-8.0. Among the tested carbon and nitrogen sources in Czapek liquid medium, amylum, glutamic, yeast extract, potassium nitrate and sodium nitrate were the most favorable for mycelial growth. Moreover, amylum, sucrose, galactose, peptone, potassium nitrate, calcium nitrate and urea were the best medium for sporulation. The lethal temperature for mycelia and conidia was 55℃, 10 min and 60℃, 10 min, respectively.To determine host range of P. herbarum, mycelial plugs were inoculated onto the healthy leaves of 18 crops. The result showed that the pathogen could infected Allium fistulosum, Nicotiana tabacum, Lycopersicon esculentu, Solarium melongena, Capsicum annuum, Brassica pekinens, Brassica chinensis, Brassica olerace, Zea mays, Gossypium hirsutum, Arachis hypogaea, Vigna unguiculata, Amaranthus mangostanus, Ipomoea aquatica, Lactuca sativa, Luffa cylindrical, Boehmeria nivea and Sesamum indicum.Mycelia of P. herbarum on diseased plant debris remained viable for over 5 months in each treatment. Percentage recovery of pathogen was the highest in glasshouse at 58% while percentage recovery was the lowest at 4% in ice chamber. Percentage recovery of pathogen from the soil surface (38%) was higher than percentage recovery from the soil depths of 20 cm (12%).The results of observation on occurrence of figwort leaf spot in 2007 and 2008 showed that the disease occured in mid-to-late May with a few spots on leaves, peak of diseasse is from the end of August to mid-to-late September with lots of leaf spots, the disease index is between 12.6 and 30.5. From October to November, disease is a little aggravated, the disease index is between 31.7 and 39.3.Inhibition of mycelia growth of P. herbaurm by six fundicides was assayed on amended PDA medium. 10% Score GR and 30% Armure EC had the highest inhibitory effect with the 50% effective concentration (EC₅₀) at 0.10μg/ml,0.29μg/ml whereas 80% Mancozeb DP and chlorothalonil had the lowest inhibitory effect with the 50% effective concentration (EC₅₀) at 27.94μg/ml, 120.88μg/ml. Field experiment for disease control in 2007 and 2008 indicated that the significant effect was observed with 10% Score GR of 48.38% and 73.62%, The worst effect was observed with 40% Fiusilazole EC of 28.83% and 50.44%.Comparison experiment on eight figwort cultivars in field trial in 2007 and 2008 indicated that disease resistance evaluation of Sichuan-1, Chongqin-1 were best, Shanxi-1 were susceptible to figwort leaf spot.