| Italian ryegrass(Lolium multiflorum)is a high-yield,high-quality forage grass,and widely cultivated in southwestern China.With the increasing of areas,plant disease has become one of the main factors that limits the production and utilization of Italian ryegrass.However,there have been few systematic studies on diseases of Italian ryegrass in the past.In order to find out the main fungal diseases,on one hand,the fields of Italian ryegrass in Sichuan province were successively investigated and researched from 2015 to 2019;on the other hand,the seed-borne fungi of 36 varieties were identified and taken into account for pathogenic studies.The main results are as follows:1.The main fungal diseases on Italian ryegrass were studied in detail.Five new diseases of Italian ryegrass in China were found out and reported: Alternaria leaf spot(Alternaria alternata),Gray mold(Botrytis cinerea),Pyrenophora leaf spot(Pyrenophora nobleae),Gray leaf spot(Pyricularia oryzae)and Sclerotinia rot(Sclerotinia sclerotiorum).2.This is the first report of B.cinerea causing gray mold on Italian ryegrass in the world.The peak period of gray mold is usually from January to February;under wet,humid(15-20 ?)conditions,the disease developed rapidly,and may be potential threat to Italian ryegrass.Studies show that the optimal temperature,media,C source,N source for mycelial growth of B.cinerea were 20–25 ?,PDA,D-galactose,and Dleucine,respectively,and the growth rate was optimum under the 24 h dark;when heated on water bath for 10 min,the lethal temperature for the mycelium was 47?.Pathogenicity tests on detached leaves of 10 varieties showed that L.multiflorum Aabad and wintergreen presented more resistant than others to B.cinerea.3.Pyrenophora leaf spot is one of the most serious diseases affecting Italian ryegrass in southwestern China,and the peak period of this disease is from April to May;however,in some years,the leaf disease incidence could range up to 100%;typical symptoms appeared as brown or tan spots surrounded by a yellow halo,or brown to dark brown net blotch.Pathogenicity tests showed that P.dictyoides was the most important causal agent,followed by P.nobleae.4.Nine hundred twenty-one strains of seed-borne fungi were finally isolated from the 36 ryegrass varieties.According to the identity of ITS sequences in NCBI as well as the similarity of morphological characters,534 strains,representing 58% of all strains,were preliminary identified as Aspergillus,which were the most common seedborne fungi of L.multiflorum;followed by Chaetomium and chaetomium-like(12.7%)species,and Pyrenophora species(12.3%).Finally,33 species,belonging to 14 genera,were accurately identified based on both morphological characters and multilocus phylogenetic analyses;25 of these species were the first report on Italian ryegrass in China: Albifimbria verrucaria,Alternaria dactylidicola,Aspergillis hiratsukae,As.ochraceus,As.protuberus,As.pseudoglaucus,As.ruber,As.sydowii,Arcopilus aureus,Chaetomium cochliodes,Ch.elatum,Ch.rectangulare,Ch.subaffine,Collariella bostrychodes,Co.carteri,Dichotomopilus erectus,Di.indicus,Di.pratensis,Di.variostiolatus,Fusarium torulosum,Paraphaeosphaeria minitans,Pyrenophora avenicola,P.triseptata,P.tritici-repentis and Talaromyces ucrainicus.5.Pathogenicity tests showed that Albifimbria verrucaria,Bipolaris sorokiniana,B.cinerea,Ch.rectangulare,Fusarium torulosum,P.avenicola,P.chaetomioides,P.dictyoides,P.lolii,P.teres and P.triseptata exhibited inhibition on seed germination,with a decrease rate of 100%,14%,9%,12.8%,20.2%,8.6%,8.6%,15.8%,23.3%,18.3% and 8.9% in the final germination percentage(FGP)and 100%,14.3%,13.1%,20%,29.8%,20.2%,11.8%,22.8%,22.5%,19.1% and 12.4% in germination index(GI)compared with the control treatments,respectively. |
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