Etiology And Control Of Brown Patch On Festuca Arundinacea

Brown patch,which caused symptoms of large brown or straw-coloured patches was a common serious disease on turfgrass in recent years.The outbreak of this disease led to the lack of delight,and quality of golfground.At present,there were a few reports about the investigation and chemical control of brown patch.The objective of this reseach was to indentify the causal agent of Festuca arundinacea brown patch, determine the host range,biological characteristics,the infection process of the pathogen on Festuca arundinacea leaves and screen the fungicides in pot experiment. The results showed as follow:Rhizoctonia sp.was isolated from diseased leaf of Festuca arundinacea in Huazhong Agricultural University.Pathogenicity was tested by inoculating the leaf with mycelial suspension of Rhizoctonia sp.,the result indicated that Rhizoctonia sp.was determined to be the pathogen of Festuca arundinacea brown patch.According to morphological observation,the colonies of pathogen turned to sparse felty texture after 2 days of incubated on PDA medium.Mycelium was variable in colour of white,yellow and grey,and usually maturing to some shade of brown and from sparsely aerial to mealy or felted.Branching of the main or runner hyphae was mostly right-angled,with constrictions where they originate and septate above the junction.The diameter of the runner hyphae was 4-13μm.Young hyphae were multinucleate.Comparion with sequence of ITS1-5.8SrDNA-ITS4 in Genbank showed 99%of identity with R.solani. According to the morphological characteristics and anaysis of rDNA-ITS,the pathogen was identified as R.solani.the pathogen could infected Cynodon dactylis,Lolium perenne,Festuca arundinacea,Poa pratensis,Oryzae sativa,Triticum aestivum,Zea mays,Brassica olerace,Gossypium hirsutum and Capsicum annuum.Test of cross inoculation showed that Rhizoctonia spp.were isolated from different plants,and three R.solani,isolates were are pathogenic to four tested plants at 28℃whereas R.cerealis was not pathogenic to them.The results of biological characteristics revealed that the mycelium of pathogen could grow in the range of the temperature from 10-30℃,the optimal temperature and pH value mycelial growth was 30℃and 7.The range of pH value for mycelia growth were 4-12.The pathogen could utilize various carbon and nitrogen sources,but effects of carbon and nitrogen sources for mycelial growth were significant different.Among the tested carbon and nitrogen sources in Czapek liquid medium,starch and yeast extract were best most favorable.The lethal temperature for mycelial growth and sclerotia germination were 50℃and 55℃for 10 min,respectively.Detached leaves of Festuca arundinacea were inoculated with mycelial suspension of R.solani and incubated at 28℃under high humidity.Samples were collected from inoculated leaves at different timing intervals,and then decolorated and stained.Finally,the infection process on leaves of Festuca arundinacea were observes with optical microscope.The result indicated that hyphae could grow longitudinally along leaves at 3h after inoculation.Some of branches turn to infection cushions or lobate appressoria.Infection cushions were formed via the aggregation of hyphal branches.Lobate appressoria were composed of many short and swollen branches with apical lobes.The mycelia could penetrate into leaves tissues directly or via stomata. The way of direct penetration into epidermis was frequent.Some hyphae in epidermis were found at 6h after inoculation.Inhibition of mycelia growth of R.solani by five fundicides was assayed on amended PDA medium.30%Armure EC had the highest inhibitory effect with the 50% effective concentration(EC₅₀) at 0.00613ug/ml whereas 5%jinggangmycin SP had the lowest mycelial inhibition with EC₅₀ values of 61.46369 ug/ml.Potted experiment for disease control indicated that the significant effect was observed with 5%jinggangmycin SP of 73.67%efficacy,and 20.67%Charisma EC of 70.2%in the treatment of spraying fungicide before inoculating.30%Armure EC and 40%Fiusilazole EC was 68.48%and 61.57%disease suppression in the treatement of spraying fungicide after inoculating,respectively.