Preliminary Research On Pathogen Species Diversity Of Yellow Blotch Disease And Varieties Resistance Identification In Pleurotus Ostreatus

Pleurotus ostreatus Kummer is one of the most widely cultivated edible fungi.The brown blotch disease of P.ostreatus is mainly caused by Pseudomonas tolaasii Paine.The symptoms usually show a large area of yellowing or yellow rust on the surface of the pileus.Sometimes,a sunken spot was found on the surface of the pileus.In the later stage,all of fruiting bodies turn curly and chlorosis,even totally rotten.Worse cultivation facilities and the relatively extensive cultivation management easily cause the brown blotch disease,leading to a big loss in economy.Research of pathogen species and variety resistance to the brown blotch disease will possess the important significance on further exploration to the occurrence regularity of brown blotch disease and breeding of disease-resistant variety as well as the integrated disease control.In this study,the survey on brown blotch disease of P.ostreatus was undertaken in18 P.ostreatus cultivation areas such as Wuhan,Zhumadian,Fuzhou,Beijing,Zhengzhou and Shenyang.97 diseased samples of P.ostreatus were collected.During survey,it was found that symptoms of brown blotch disease contained six types such as yellow spot,yellow scar,yellow crack,black spot and wet-rot pileus.197 bacterial isolates were obtained from infected samples.By observing the morphology of bacterial isolates,51 strains of isolates with the same morphology were excluded.146 strains of bacterial isolates were used for pathogenicity.It was found that 23 of 146 isolates showed a strong pathogenicity to P.ostreatus,and these bacterial isolates were reobtained from the infected fruiting bodies,by which 23 isolates were treated as the pathogens of the brown blotch disease in P.ostreatus.Based on the morphological characteristics,16 S rDNA molecular sequence and Biolog system,ten different genus 11 species bacteria were identified in 23 bacterial isolates,including in P.tolaasii(5),P.reactans(4),Mycetocola(3),Enterobacter(3),Sphingobacterium(2),Serratia(2),Staphylococcus(1),Ignatzschineria(1),Providencia(1)and Cedecea(1).Biolog system was used to further identificate the dubious pathogens.Three dubious isolates were clearly identified as S.fonticola,S.plymuthica and S.sciuri.It was demonstrated that different bacterial isolates could cause different symptomsof the yellow blotch disease.The sunk brown disease scar and cowered fruiting bodies were caused by P.tolaasii.P.reactans and Sphingobacterium sp.mainly generated the yellowing symptom.Mycetocola sp.caused the yellowing and sunk scar in fruiting bodies,even non-development for pileus.However,Enterobacter sp.and S.sciuri and Ignatzschineria sp.generated the light yellow spots in fruiting bodies.Therefore,it indicated that the brown blotch disease of P.ostreatus possess diverse pathogens and symptoms.The symptoms caused by those isolates were found in filed survey,but could not be fully corresponded.In the spring of 2018,the incidence and disease index of brown blotch disease in 97 cultivation strains of P.ostreatus were investigated in Taian,Shandong province.The correlations between the disease resistance of strains and the softness and hardness degree of the stipe and the shade of the pileus were analyzed.97 cultivation strains were classified into two types based on the color: darker pileus strains(60)and lighter pileus strains(37).They also were classified two types according to the hardness and softness degree of stipe: hard-stipe strains(74)and soft-stipe strains(23).The incidence and disease index of soft-stipe strains reached to 37.0% and 21.12%,which was higher than those of hard-stipe stains.F-test analysis indicated that the resistance-disease between soft and hard stipe strains had a dramatically significant difference.The incidence and disease index of darker color strains were 26.0% and 13.06%,which was higher than those of lighter color strains.However,the significant difference was no found between darker and lighter color strains.Twenty-sixty cultivation strains possessing different resistance-disease were selected to test the resistance to P.tolaasii.The results demonstrated that the disease symptom was found in the sensitive-disease strains,such as Huaping 801,after 10 h of inoculation,yet slight symptom was found in the resistance-disease strains,such as Huaping 36,after 72 h of inoculation.For the sensitive-disease strains,such as Huaping 801,the disease scar became partly yellow,and rapidly expanded.At last,a large area of fruiting bodies turned dry and yellowish and wither.For the resistance-disease strains,such as Huaping 36,light yellow spots were found only in parts,and scarcely expanded.