Root rot pathogen: Cylindrocarpon spp. in Douglas-fir forest nursery in the PNW USA and their management

Background/Question/Methods

Cylindrocarpon spp.cause soil-borne diseases in Douglas-fir bare-root nurseries in the Pacific Northwest USA.  These soil-borne diseases are difficult to control and have typically been controlled by fumigating nursery bed soils with methyl bromide.  Newer integrated pest management approaches have been successful to some degree in reducing soil disease populations in combination with fumigation, and include cover crop manipulation, bare-fallow rotation, tillage, improved drainage, and improved seedling grading.  However, some of these pathogens (specifically Cylindrocarpon spp) can survive even when treated with methyl bromide. Methyl bromide, although effective, is about to be phased out because of its negative environmental effects.  Biocontrol agents have some promise for controlling Cylindrocarpon.  Commercial biocontrol agents (such as Cease – Bacillus subtilis, Actinovate - Streptomyces lydicus , Soil Guard – Gliocladium virens , and Root Shield – Trichoderma harzianum) are available, but they have been only sporadically tested . Knowledge of the relative efficacy of biocontrol agents could decrease fungicide use and reduce fears of fungicide tolerance buildup, while improving seedling yield and performance. Furthermore, compared to other pathogens there is not much known about Cylindrocarpon spp and their pathogenicity.  The objectives of this research were to determine (1) the species of Cylindrocarpon present in nursery soils and (2) if commercial biocontrol agents can be used against Cylindrocarpon spp.  We used Polymerase Chain Reaction (PCR) to identify Cylindrocarpon species in soils and roots from Douglas-fir forest nurseries in Oregon and Washington.  Potential growth inhibition of Cylindrocarponby Cease, Actinovate and Soil Guard was tested in culture.

Results/Conclusions

Three different Cylindrocarpon spp were identified using the PCR technique (Cylindrocarpon destructans, Cylindrocarpon liriodendri and Cylindrocarpon pauciseptatum). Overall in the three nurseries C. destructans was dominant (59.0 %), compared to 38.5% for C. liriodendri and only 2.5% for C. pauciseptatum, which was only detected at one of the nurseries.  The biological control agents Cease, Actinovate and Soil Guard were not very effective at inhibiting the growth of any of the Cyclindrocarpon spp in culture.  Cease was better than Actinovate which was better than Soil Guard, but the highest growth inhibition was only 47.6%. There was no difference in inhibition among the three Cylindrocarpon species.