Ecological impacts of Phlebiopsis gigantea biocontrol treatment against Heterobasidion spp. as revealed by fungal community profiling and population analyses

Abstract

Wood decay fungi belonging to the species complex Heterobasidion annosum sensu lato are among the most common and economically important species causing root rot and stem decay in conifers of the northern temperate regions. New infections by these pathogens can be suppressed by tree stump treatments using chemical or biological control agents. In Finland, the corticiaceous fungus Phlebiopsis gigantea h a s b e e n f o r m u l a t e d i n t o a commercial biocontrol agent called Rotstop (Verdera Ltd.).This thesis addresses the ecological impacts of Rotstop biocontrol treatment on the mycoflora of conifer stumps. Locally, fungal communities within Rotstop-treated and untreated stumps were analyzed using a novel method based on DGGE profiling of small subunit ribosomal DNA fragments amplified directly from wood samples. Population analyses for P. gigantea and H. annosum s.l. were conducted to evaluate possible risks associated with local and/or global distribution of the Rotstop strain.Based on molecular community profiling by DGGE, we detected a few individual wood-inhabiting fungal species (OTUs) that seemed to have suffered or benefited from the Rotstop biocontrol treatment. The DGGE analyses also revealed fungal diversity not retrieved by cultivation and some fungal sequence types untypical for decomposing conifer wood. However, statistical analysis of DGGE community profiles obtained from Rotstoptreated and untreated conifer stumps revealed that the Rotstop treatment had not caused a statistically significant reduction in the species diversity of wood-inhabiting fungi within our experimental forest plots.Locally, ISSR genotyping of cultured P. gigantea strains showed that the Rotstop biocontrol strain was capable of surviving up to six years within treated Norway spruce stumps, while in Scots pine stumps it was sooner replaced by successor fungal species. In addition, the spread of resident P. gigantea strains into Rotstop-treated forest stands seemed effective in preventing the formation of genetically monomorphic populations in the short run. On a global scale, we detected a considerable level of genetic differentiation between the interfertile European and North American populations of P. gigantea. These results strongly suggest that local biocontrol strains should be used in order to prevent global spread of P. gigantea and hybrid formation between geographically isolated populations.The population analysis for H. annosum s.l. revealed a collection of Chinese fungal strains that showed a high degree of laboratory fertility with three different allopatric H. annosum s.l. taxa. However, based on the molecular markers, the Chinese strains could be clearly affiliated with the H. parviporum taxonomical cluster, which thus appears to have a continuous distribution range from Europe through southern Siberia to northern China.

In vitro interaction between Phlebiopsis sp. and Ganoderma philippii isolates

“…This interaction is similar to that between P. gigantea and H. annosum that was described as structural changes to the hyphae of H. annosum resulting in cytoplasmic vacuolation, granulation and loss of opacity (Ikediegwu ). This response is considered to be one of the expressions of mycoparasitic activity that leads to suppression of the growth of pathogens (Vainio ). Attempts to grow G. philippii from the confrontation zone were generally unsuccessful.…”

Experimental use of a native isolate ofPhlebiopsis gigantea: efficacy and eco-sustainability.

“…Infatti, la presenza in bosco di altri isolati nativi era già stata verificata a suo tempo nella prova preliminare (Annesi et al 2005) ed è stata ripetutamente confermata nel corso di monitoraggi dell'inoculo aereo di H. annosum effettuato nella stessa pineta (D'Amico et al 2008), in quanto dalle rotelle-trappola veniva catturato, anche dopo il trattamento biologico, inoculo di P. gigantea con caratteristiche genetiche diverse dall'isolato ISPaVe PF 52 (dati non pubblicati). In precedenti sperimentazioni la "non persistenza" di un isolato utilizzato per il controllo biologico era stata dimostrata su P. sylvestris (Vainio et al 2001), ma non su P. abies, dove era reperibile sino a sei anni dopo (Vainio 2008). Questa non persistenza è stata qui verificata anche su P. pinea, evidenziando un ulteriore argomento a favore dell'utilizzo di questo organismo per la lotta biologica a H. annosum in ambiente mediterraneo.…”

What Is Important in Selecting Phlebiopsis gigantea Strain for Commercial Use?

“…Fungus strains were obtained from Rotstop and PG Suspension producers and represented P. gigantea mycelium growing on coniferous stumps in Scandinavia (Finland, Sweden) and Great Britain, respectively. It was assumed that the results of molecular analyses carried out with the use of random amplified microsatellite (RAMS) method [27][28][29][30][31] as well as comparisons of strain enzymatic, and wood decay activities would distinguish similarities between the strains tested and point towards the most vigorous ones, in view of treatment efficacy in practice. The results of some enzyme assays and Norway spruce wood decay assessments described below were extracted from the database described by Żółciak et al [17].…”