John Dennis¹ and David Trotter²

Abstract - This paper summarizes the current knowledge on Douglas-fir root decay. An examination of the disease potential in each growth phase of a standard Douglas-fir growth curve is made focusing on ways in which the disease starts and progresses. Cultivation periods examined are: pre-sow planning, seed germination and germinant growth, seedling exponential growth, dormancy induction, hardening off, lifting and storage, followed by outplanting. A list of important environmental and cultural conditions conducive to Douglas-fir root rot is given and recommendations made at each growth phase on how to prevent the disease from occurring in seedling crops. 1 Pacific Forestry Center, Canadian Forest Service, National Resources Canada,   506 W Burnside Rd., Victoria, BC V8Z 1M5 2 Nursery Extension Services, BC Forest Service, 14275 96th Ave., Surrey, BC V3V 7Z2.

Introduction

Root rot has been a continuing problem in container-grown Douglas-fir (Pseudotsuga menziesii (Mirabel) Franco var. menziesii) seedlings. Studies on the cause of the disease, how it impacts plantation success and how to prevent its occurrences have been on-going for several years. The fungi that cause root disease may be present from the beginning of the growing season. Equipment and materials used in nurseries provide a means for the introduction of these organisms (James et al., 1987, Axelrood and Peters, 1993, Sturrock and Dennis, 1988). Seedling environment and culture have a significant impact on whether disease develops (Axelrood and Peters, 1993 and Dennis et al., 1995). Disease causing fungi can infect seedlings at an early stage of development, remain latent and cause disease later in the season when growing conditions stress the plants (James et al., 1991). High temperatures early in the season (Bloomberg 1973), high growing media moisture and neutral pH late in the season are all stressful to Douglas-fir seedlings. It is suggested that they all contribute to the expression of root rot (Dahm et. al, 1987 and Hargreaves and Fox, 1978). Survival and growth of seedlings planted in the field are affected by the levels of root rot in the crop (Axelrood and Chapman, 1992).

Disease prevention should be a prime consideration when planning a crop strategy. With the short growing season allowed for most crops, there is not enough time for diseased seedlings to recover biomass once they have been diagnosed and corrective measures implemented. The best

time to deal with disease is before mixing the growing media, loading the containers, selecting and sowing the seed, and moving stock into the greenhouse. Choosing components wisely and performing the tasks carefully can eliminate many future problems.

The growing media should be designed to provide the right amount of water, nutrients, air and physical support to plants. It should not be an initial source of disease fungi. It should not provide an environment conducive to the growth of disease organisms, either early in the growing season or later, when the media has become compacted and more decomposed. Mixing media and loading container are critical to creating a healthy root environment. Aeration and water drainage are the most critical factors in the growing media/disease relationship. Oxygen and water requirements of seedling root systems are commonly compromised by uneven loading densities early in the growing season and by media settling, compaction and decomposition late in the growing season. It is very important to select the right mix components for each nursery site and watering regimes.

Containers can contribute to the occurrence of root disease by affecting water and nutrient content of the growing media. Drainage and water movement are affected by container material, structure and dimensions. Height and the opening at the bottom of the cavities affect the level of the perched water table. Temperatures are also affected by the type of material and the colour of containers. The ability of a container to insulate against or absorb heat can significantly affect stress levels experienced by plant roots. Styrofoam is better at insulation than hard plastics and white colored containers absorb less heat than dark colored containers.

Pathogenic fungi can be present on previously used styroblocks and slowly build up during the growing season. As the blocks get older and the foam or plastic deteriorates, they become more difficult to sanitize. Containers should be cleaned between each crop. High water pressure, steam and chemicals are used to clean containers.

Seeds vary in the amount and types of fungi found on their seedcoats. In many cases, pathogenic fungi are found which, under favorable conditions, proliferate in container cavities and cause disease. Seedlots that have small numbers of fungi present in storage can have much higher levels after stratification. Routine bioassays to identify pathogen levels on stored seedlots can help nurseries select the best seedlots to be used in a particular situation. Being forewarned of high pathogen levels in a seedlot allows nurseries to prevent disease expression by treating highly infested seedlots with special care. Work done by the BCMF Nursery Extension Services, the BCMF Tree Seed Centre, B.C. Research and the CFS has shown that a running water rather than standing water soak during imbibition can significantly reduce levels of Fusarium. This technique is effective for seedlots identified during storage as having 530% of the seeds infested with Fusarium and has been implemented on a large scale at the seed Centre.

Greenhouses can harbor many types of pathogenic fungi. Floors, benches, water sources, watering lines, weed patches and any equipment used should be considered potential sources and cleaned between crops. The most commonly used sanitation methods are steam, high water pressure and/or a chemical wash (usually chlorine or bromine) for cleaning greenhouses, equipment, floors and benches. Filtration and chlorination are used when water is known to be contaminated. Removal of weeds and cull piles is used to lower inoculum surrounding nurseries.

Generally, the presence of large numbers of fungi does not always translate directly to a root problem but it does allow for a greater disease potential. Therefore, any practices that reduce the level of pathogens present is very important. Pathogen levels in crops can be identified through a routine monitoring system. When levels are high, the sources of fungi can be identified and eliminated with extra attention paid to eliminating disease causing stress on that particular crop.

Part 2 - Seed Germination and Germinant Growth

Seed germination can have an affect on how the crop will perform throughout the rest of the season. Seed should be of the highest quality with, not only high final germination values, but high vigour. This results in seeds that germinate quickly, avoiding attack by pathogenic fungi. Conifers exhibit epigeous germination where the cotyledons are pushed out of the ground by the developing hypocotyl. Growth of the embryo requires both cell division and elongation. All the embryo cells divide early in seed germination. Later, as the seedlings develop, cell division becomes localized at the apices of shoots and roots.

Environmental and cultural conditions for germination consist mainly of temperature and humidity control. Temperatures between 18°C and 21°C and humidities in the 60-80% range are optimum for most conifers. Diurnal temperature fluctuations are beneficial during the germination period. Frequent misting with water may also be required during hot, sunny weather because soil moisture stress is critical for proper germination. However, excess water can kill seeds due to oxygen stress.

Minimal light intensity is required for germination, but wavelength and daylength are very important. Red wavelengths (660 nm) promote germination and most conifers prefer a 16 hour photoperiod. Higher light intensities are desirable when needles are above ground as epigeous cotyledons become photosynthetically active right after emergence. This is also the time for the addition of soluble fertilizers if nutrients have not been incorporated into the growing medium.

As mentioned earlier, damaging fungi are often present in growing media and containers. Also, seeds come with various levels of fungi on the seedcoats. Germination conditions are conducive to growth and sporulation of many disease fungi, such as Fusarium and Cylindrocarpon. Therefore, numbers of the fungi increase in individual cavities as well as spread to other cavities during irrigation.

Disease in the germination phase consists of pre-emergence and post-emergence damping-off. Pre-emergence damping-off is when seeds are killed before radical emergence, whereas, post-emergence damping-off occurs after the radical emerges. All parts of the germling (roots, hypocotyl and cotyledon needles) can be initial points of attack. In most cases, heat stress or excess moisture stress are the most common causes of damping-off. Infection at this time is important to late season root disease because when high levels of inoculum are present, fungi often penetrate plant tissues without causing disease. Stress during other growth phases allows expression of latent infections. Therefore, if some seedlings in a crop are exhibiting damping-off, it is safe to assume other trees in the crop have become colonized by fungi and may be more sensitive to stresses later in the season.

Pre-emergence damping-off is characterized by the seed becoming soft, dark and mushy. There will be decay of the seed with no sign of germinant activity. Certain fungi can mummify seeds which will not show decay. Post-emergence damping-off is characterized by decay, usually at the groundline, but sometimes in the roots or at the tips of the cotyledons. When infection is at the groundline, the germinants will fall over and there will be a dark, collapsed, translucent region at or below the soil level. When infection is in the roots, the shoot will wilt and become orange-red in colour. When cotyledons are infected, the needle tips will become chlorotic, then orange to red and will, often, have fungi fruiting just below the seedcoats.

Following is a list of environmental and cultural conditions that should be carefully monitored during the germination and primary growth phase in order to prevent root disease:
     *Irrigation
     *Humidity and Vapour pressure deficit Light
      pH
      Fertilization
* - Denotes the three most important environmental and cultural factors contributing to the occurrence of root disease during the germination and primary growth phase.

Recommendations:

1) Maintain optimum temperatures for seed germination and do not allow wide fluctuations of temperatures. Where possible, cool the crop with ventilation rather than water.
2) Use light misting to maintain soil moisture and optimum greenhouse humidities. Keep the crop under cover in order to control container mix moisture.
3) Provide adequate light and nutrients once germinants are above ground.

Part 3 - Rapid Growth

The rapid growth phase is a very dynamic period in the course of seedling development and maturation. This period is characterized by accelerated tissue growth and expansion and it is generally considered the time when seedlings are the most "succulent". Seedling development is concentrated on extensive leaf initiation and stem elongation in which there a dominant translocation of photosynthates to the apical meristem. With time, this changes to a bi-directional distribution of photosynthate to the root system. In general, there is reduced and/or cyclic root growth with root development primarily dedicated to the production of smaller elongating and absorbing roots

Environmental and cultural manipulations during the rapid growth phase must concentrate on providing the seedling with select growing conditions in order to accentuate its growth potential. This is characterized by providing an optimal temperature regime to maximize net photosynthesis. Temperatures over 40°C result in CO₂ being taken up in photosynthesis equaling the amount evolved in respiration resulting in no net gain. In addition, the effects of temperature are light dependent as there is a diurnal pattern of synthesis from spring to summer. On a daily basis, this is characterized by net photosynthesis being highest in the morning and then steadily decreasing in the late afternoon and early evening.

During this phase, irrigation strategies are critical to maintaining a continuous availability of water for cell growth, stem elongation and the transport of necessary nutrients and carbohydrates. As such, an emphasis should be placed on maintaining a perched water table within the container media. Also, a significant vapour pressure deficit is desirable to enhance plant transpiration resulting in a dynamic movement of water and nutrients through these actively growing seedlings. A balanced and complete nutrient feed at this stage is paramount to seedling quality with an emphasis on increasing the Ca component. This nutrient is important in the hardening of cell wall structures and reducing the effects of penetrating fungal enzymes. At this point of seedling development, pH is of less concern unless it is found to limit nutrient uptake.

Diseases of most importance during the rapid growth phase are Fusarium, Pythium and Cylindrocarpon. In general, high temperatures coupled with drought conditions tend to pre-dispose the seedlings to Fusarium infection. An affected seedling exhibits chlorosis of the terminal needles and shoot tip deformation. The root system has few laterals and the remaining roots are dark and swollen. In addition, there is usually no evidence of active root tips. The bark of the stem and the cortex of the roots are easily stripped leaving a darkened cambium and root stele. Fusarium requires a well drained & aerated growing media for continued infection and prefers low pH.

In contrast, Pythium needs water for distribution/survival due to its motile zoospores. In containers, this can occur at the bottom of growing cavity that has been saturated for long periods creating deal conditions for infection. Under these conditions, the pathogen enters through the root tips, proliferating in the young cells and causing root collapse and rootlet death. In comparison, the spread of the disease into the older roots is generally limited to the root cortex. For the most part, it is considered a weak pathogen.

In concert with the above pathogens Cylindrocarpon, also considered a weak pathogen, is commonly found on seedling roots but expression is usually later in the growth cycle. Seedlings tend to be pre-disposed to this pathogen when they have been exposed to some osmotic stress coupled with low oxygen conditions in the root system. It is a pioneer colonizer of young root tips and can rapidly colonize a stressed seedling root system. It is known to use organic and inorganic nitrogen and prefers alkaline media conditions.

Following is a list of environmental and cultural conditions that should be carefully monitored during the rapid growth phase in order to prevent root disease:
     *Temperature
     *Irrigation
      Humidity and Vapour pressure deficit
      Light
      pH
     *Fertilization
* - Denotes the three most important environmental and cultural factors contributing to the occurrence of root disease during the rapid growth phase.

Recommendations:

1) Maintain optimum temperatures for seed growth, 18-26°C and do not allow wide fluctuations of temperatures. Where possible, cool the crop with ventilation rather than water.

2) Irrigation schedules should maintain constant media moisture content or block weights coupled with longer wet/dry cycles. Frequency limits should be placed on misting and humidities should be managed to enhance seedling transpiration through VPD.

3) Nutrient levels should be balanced and complete. The NO₃/NH₄ ratio should be about 0.75 - 0.8 with an increase in Ca to enhance cell wall integrity.

Part 4 - Dormancy Induction

During the dormancy induction period, seedlings are forced to change from a rapid growth phase to a hardening off phase that prepares them for storage or overwintering. Physiologically, this is a change from exponential biomass production, with an emphasis on shoot height, to tissue differentiation (bud development), lignification and carbohydrate storage (stem caliper development) as well as root tissue production. It is a critical phase in seedling development because some metabolic processes within the plant need to be reduced or redirected and others need to be initiated. For example, protein synthesis needs to be lowered in stems but must be redirected to shoot tips for bud formation and to the root system for growth. Also, an immediate reduction in use of photosynthate products means that carbohydrates can be stored in stems and roots. At the completion of this phase, seedlings are able to withstand late summer field conditions such as minor drought, full sunlight and light frosts. Seedlings have also formed needle primordia in buds for the next year's flush of growth.

The environmental and cultural conditions necessary for the dormancy induction period are quite different from those used for the exponential growth phase. Shorter daylength, lower temperature, lower nitrogen fertilization and less frequent irrigation are all required to initiate dormancy. Although the techniques are fairly well defined for most species, in practice, their implementation varies greatly. This is due to geographic as well as technical differences at each nursery site. A "green thumb" approach is required because conditions that can put seedlings under stress vary from year to year. Trees can be stressed by extreme fluctuations in growing conditions. Therefore, it is important to change cultural regimes gradually. A desirable change in one condition, for example increasing sunlight by removing the greenhouse roof, may cause an undesirable change in another condition, such as loss of moisture control. Fungi in the growing medium are affected by both environmental and cultural changes imposed on seedlings during dormancy induction. Lower temperatures tend to reduce levels of Fusarium, but may encourage fungi such as Cylindrocarpon and Botrytis. Lower irrigation frequency discourages fungal growth, but can encourage the formation of survival and dissemination structures such as chlamydospores and conidiospores. Fungi are also affected by induced changes in seedling metabolism. Increased carbohydrate reserves in the seedling roots as well as higher concentration of sugars and amino acids in root exudates encourage the growth of both beneficial and pathogenic fungi. When the fungus is a mycorrhizal or biocontrol organism, the results of this increase in fungal activity are beneficial. However, when levels of pathogenic fungi increase, there is increased potential for disease.

Root disease occurring during the dormancy induction phase is not, initially, as noticeable as in the earlier phases of seedling growth. During this period, shoot elongation is slowing down and root function may be affected without visible decay. Bud growth is inhibited and there appears to be an accumulation of carbohydrates in the lower stems. However, these morphological characteristics develop gradually and go easily unnoticed until late in the phase. Eventually, the affected plants exhibit small buds and stems with significant tapering from the ground line to the shoot tip. The root cortex becomes thickened and dark, but most steles remain white and have little decay. It is difficult at this time to determine which seedlings will develop root necrosis and perform poorly.

Following is a list of environmental and cultural conditions that should be carefully monitored during the dormancy induction phase in order to prevent root disease:
     *Irrigation
     *Fertilization
     *Temperature
      Light
      pH
      Relative Humidity
* - Denotes the three most important environmental and cultural factors contributing to the occurrence of root disease during the dormancy induction phase.

Recommendations:

1) Keep the crop under cover in order to control container mix moisture.

2) Continue to use a wet/dry cycle to maintain growing media aeration.

3) Reduce nitrogen and increase phosphorus and potassium fertilizer levels to initiate lignification of shoot tissues early enough in the growing season.

4) Do not allow wide fluctuations of temperatures. Cool the crop with ventilation rather than water and only use heat on the crop if sudden or extremely cold temperatures are expected.

Phase 5 - Hardening-off

The hardening-off phase is relatively short and is used to develop resistance in seedlings to winter environmental conditions as they wait to be lifted for storage or field planting. It appears to be a quiescent period in which seedlings are not visibly changing. This is not true as some photosynthesis and root growth continues and lignification of stem and root tissue occurs. Seedlings become acclimatized to lower and lower temperatures by gradual metabolic changes at the cellular level. Compared to shoots, roots obtain frost hardiness slower and to a lesser degree so special attention should be paid to protecting them from sudden heavy frosts until late in the season.

Environmental and cultural manipulations during the hardening-off phase are basically a continuation of the dormancy induction techniques with the hope that autumn temperatures will drop consistently and gradually. Nitrogen fertilization levels and irrigation frequency are kept low as the cool temperatures slow plant metabolism. Moisture control continues to be critical at this time as saturated growing media can cause oxygen stress on root systems. Low humidities in combination with wind can create a high vapour pressure deficit in the crop, causing winter desiccation damage to foliage, even in seedlings with adequate moisture in the growing media. Warm, sunny days can also disrupt the hardiness process leading to a change in frost susceptibility.

Changes continue to occur with respect to fungi in the growing media. Populations of fungi preferring cooler temperatures, such as Cylindrocarpon, increase and populations of fungi that prefer heat, such as Fusarium, decrease. Although Cylindrocarpon is a weak pathogen, it appears to be able to readily colonize healthy tissues and cause progressive decay in roots that are cold or oxygen stressed. Growing media pH can affect the ability of certain fungi to colonize root systems. Very acidic media promote Fusarium, whereas neutral to basic media promote Cylindrocarpon.

Root disease is often found during the hardening-off phase. Seedling adjudication occurs at this time and roots are still expected to be actively growing. When roots are not actively growing, have dark thickened cortexes that strip easily or have yellow to brown coloured steles and decay, adjudicators and nursery personnel reject the stock. Shoot symptoms are not always reliable in determining which seedlings have root disease. If root decay occurs late in the hardening-off period, buds can be a normal size and no excess stem taper will be noted.

Following is a list of environmental and cultural conditions that should be carefully monitored during the hardening-off phase in order to prevent root disease:
     *Irrigation
     *Temperature
     *Fertilization
      Relative Humidity
      pH
      Light
* - Denotes the three most important environmental and cultural factors contributing to the occurrence of root disease during the hardening-off phase.

Recommendations:

1) Prevent seedling roots from being in saturated growing media for long periods.

2) Allow for a gradual decrease in temperatures.

3) Continue fertigation with low nitrogen fertilizers

4) Prevent shoot desiccation during periods of sudden sunny weather and/or strong winds.

5) Continue to monitor pH of the growing media to maintain a pH as close to 5.5 as possible.

Part 6 - Storage

Lifting and storage of seedlings are the final steps of their production in nurseries and as such the quality of planting stock is influenced greatly by these operations. Certain root rot fungi, in particular Cylindrocarpon, can be carried over into storage and continue to compromise seedling root systems. Other pathogens, such as Fusarium and Pythium, are rarely aggressive due to the current practice in BC of storing all regular 1+0 conifer seedling species at 0 to -3°C. In contrast, Cylindrocarpon has been shown to be active at temperatures as low as 1°C. Therefore, it is important that any lifted stock that has been identified with a Cylindrocarpon root infection be stored correctly. Also, considerations should be made to ensure that seedling plugs are moist but not saturated with water prior to lifting and storage.

Once a planting window has been designated for a particular seedlot, seedlings are taken out of freezer storage to be thawed. The normal procedure is to raise the freezer temperature to 3 to 5°C. At these temperatures, boxed container seedlings will be completely thawed in 3-4 weeks. Once it has been determined that the seedlings are completely thawed and that the planting window has be set, the seedlings are then sent to reforestation sites in refrigerated trucks. Once on site, the seedlings maybe held in the reefer or placed in caches on the reforestation site. Yet this poses a problem for container stock that may have gone into freezer storage with Cylindrocarpon root infection. Thawing temperatures may provide conditions that are conducive to continued root infection by Cylindrocarpon. Under these circumstances, a rapid thaw that normally takes 3-5 days maybe necessary to reduce further root damage.

Following is a list of environmental and cultural conditions that should be carefully monitored during lifting and storage in order to prevent root disease:
*Temperature
*Irrigation
Humidity
pH
Light
Fertilization
* - Denotes the two most important environmental and cultural factors which occur during lifting and storage which may contribute to the enhancement of root disease in reforestation sites.

Part 7 - Outplanting Performance

The final stage of the nursery growth cycle is the resulting performance potential of lifted and packaged seedlings. To date, root rots have impacted on BC's reforestation effort by reducing the number of requested seedlings or undermining their viability and performance once they are outplanted in the field. In container culture, the three pathogens that have been most associated with root dieback problems have been Fusarium, Pythium and Cylindrocarpon. Pythium has been primarily a condition found in spruce container seedlings. Since it is generally associated with water saturated media, cultural techniques for reducing its effects in the nursery have in recent years not translated to problems in outplanting performance of affected seedlings. Drier irrigation cycles, more porous media and enhanced Ca feeds have significantly reduced the incidence of this disease. This has not always been the case with Fusarium and Cylindrocarpon. In the late 80's, numerous Douglas-fir plantations in SW British Columbia were reported to have poor seedling performance coupled with high seedling mortality. Over subsequent years, in-fill and in some cases total replantings have been required to meet reforestation targets. Root dieback of the seedling stock was reported in 1987 B.C. Forest Service Planting reports for a number of sites. Cylindrocarpon and Fusarium were isolated from the roots of diseased seedling stock grown in nurseries in 1986. In 1991, a study was done by BC Research and the BC Forest Service (Axelrood and Chapman, 1992) to assess the presence of Cylindrocarpon and Fusarium root infection of Douglas-fir seedlings from affected plantations and determine any impact on root performance in the field. Seven sites were selected as representative of affected reforestation sites. Five sites were located in the Squamish District and two were located in the Chilliwack District. Twenty-five planted and an equal number of natural seedlings were sampled from each site. Each seedling was assessed for height, rcd, age, root form, root infection and mycorrhizae.

Results of the study were as follows:

• Cylindrocarpon inoculum in the peat surrounding the planted seedlings persisted for up to 4 years

• A greater number of planted seedlings were infected with Cylindrocarpon than naturals. Also the intensity of the infection was greater in planted seedlings (length of root colonized). Cylindrocarpon was present on reforestation sites as indicated by the infection of naturals

• Cylindrocarpon root infection was highest for roots closest to the remnants of the seedling plug and decreased away from the plug. This trend was not observed in the naturals

• Significant difference in root form between planted and naturals. Ninety-three percent of the naturals but only 16% of the planted seedlings had a tap root with uniform lateral root formation.

• Fusarium root infection was low (<20%) on all 7 sites and there was no significant difference between planted seedlings and naturals.

As this study was only a cursory survey of possible root pathogen effects, it was not possible to establish a cause and effect relationship between root infection and poor plantation performance. This was simply due to the fact that root growth and infection rates were not assessed at regular intervals over the outplanting period. In addition, information was lacking on the level of infection present at the time of outplanting. In 1992, a study (Axelrood and Peters, 1993) was done at one coastal nursery with cursory evaluations at 3 other nurseries to identify the inoculum sources and the effect of nursery practices on Cylindrocarpon and Fusarium root infection and seedling growth. Cultural practices included media bulk density, nitrogen source, sanitation and moisture stress. The results showed that Fusarium was ubiquitous while Cylindrocarpon inoculum was detected primarily on pallets and used styrofoam containers. Root colonization by Cylindrocarpon was much greater than Fusarium throughout the growing season but pathogen population levels in the media could not be used to predict the level of seedling infection.

In 1993, as a follow-up to the aforementioned nursery study, a two year field trial (Axelrood et al., 1995)was initiated to determine the influence of root infection by Fusarium and Cylindrocarpon on 1+0 Douglas-fir seedling performance and fungal root colonization patterns on three field sites. Two of the reforestation sites were in the Pemberton area and the third was a farm field site at Surrey Nursery. Seedlings from seedlot 1262 were obtained from 4 container nurseries in BC. The seedlings were then split into three treatment sets. The first treatment set was composed of seedlings grown under operational and sanitized conditions. Both treatments were visually healthy with no root rot. The second treatment set was made up of visually healthy seedlings from either healthy or diseased seedlots. The third set comprised a diseased seedlot from one nursery that exhibited root rot in the majority of seedlings. The seedlings were visually rated and broken down to 3 categories: minimal, moderate and severe rot. A visual rating system was used to categorize the seedlings. In addition, seed from seedlot 1262 was direct seeded on to all field sites to monitor site colonization by Fusarium and Cylindrocarpon. Results of the study were as follows:

• Expression of root rot symptoms prior to outplanting has a negative impact on seedling survival on reforestation field sites.

• Survival of healthy seedlings from healthy seedlots was 77-93% at 17 months after planting

• Survival of seedlings with minimal, moderate and severe root rot was 41%, 20% and 7%, respectively, at 17 months after planting.

• Seedling survival from visually healthy seedlings from a diseased seedlot was found to be significantly less (50% mortality) than healthy seedlings from healthy seedlots.

• Seedlings with root rot showed less growth compared to healthy seedlings from healthy seedlots regardless of site.

• Cylindrocarpon and Fusarium survived in the roots and media at similar levels for all treatments through both growing seasons on the field sites.

• No correlation between the level of Fusarium and Cylindrocarpon root colonization at the time of planting or during the field trial and seedling growth and survival on the field sites.

Recommendations:

1. Seedlings from seedlots with visible root rot should be carefully graded with critical attention given to evaluation of root health and integrity, bud development and uniformity of caliper.

2. Visually healthy seedlings from diseased seedlots may need to be evaluated using root growth potential, bud activity and possibly root electrolyte leakage.

References:

Axelrood, P. M. Lam and R. Radley, 1995. Influence of Root Rot on Douglas-fir Seedling Survival and Growth on Reforestation Sites     and Assessment of Fusarium and Cylindrocarpon Root Colonization. Final Report 1993-95. Ministry of Forests Contract No. 21384, B. C. Research Project No. 3-01-151.

Axelrood, P. and R. Peters, 1993. Final Report: Influence of Nursery Cultural Practices on Cylindrocarpon and Fusarium Root Infection of Douglas-fir. B. C. Ministry of Forests Contract No. 08384, B. C. Research Project No. 3-01-126.

Axelrood, P. and B. Chapman. 1992. Assessment of Cylindrocarpon and Fusarium Root Infection and Root Form of Douglas-fir Seedlings Outplanted for Four years in Southwestern British Columbia. B. C. Research Report No. 3-01-123 and 3-01-124.

Bloomberg, W. J. 1973. Fusarium root rot of Douglas-fir seedlings. Phytopathology 63:337-341.

Dahm, H. and E. Strzelczyk. 1987. Effect of pH, temperature and light on pathogenicity of Cylindrocarpon destructans to pine seedlings in associative cultures with bacteria and actinomycetes. Eur. J. For. Path. 17:141-148.

Dennis, J., D.Trotter, R.A.M. Outerbridge. 1995. The Effect of Biotic and Abiotic Factors on root Rot in container-grown Douglas-fir. Report submitted to Forest Pest Management Alternative/Minor Use Fund.

Hargreaves, A. J. and R. A. Fox. 1978. Some factors affecting survival of Fusarium avenaceum in soil. Trans. Brit. Mycol. Soc. 70:209-212.

James, R. L., R. K. Dumroese, D. L. Wenny, J. I. Myers and C. J. Gilligan. 1987. Epidemiology of Fusarium on containerized Douglas-fir seedlings. 1. Seed and seedling infection, symptom production and disease progression. U.S.D.A. For. Serv. Northern region. Timber, Cooperative Forestry and pest Manage. Rep. 87-13. 22p.

James, R. L., R. K. Dumroese and D. L. Wenny. 1991. Fusarium Diseases of Conifer Seedlings. In Proceedings of the first meeting of IUFRO Working Party S2.07-09 (Disease and Insects in Forest Nurseries), edited by J. R. Sutherland and S. G. Glover. Information Report BC-X-331, p. 181-190.

Sturrock, R. N. and Dennis, J. J. 1988. Styroblock Sanitation: Results of Laboratory assays from Trials at Several British Columbia Forest Nurseries. In Proceedings, Combined Meeting of Western Forest Nursery Associations: Western Forest Nursery Council, Forest Nursery association of B. C. and Intermountain Forests Nursery Association. U.S.D.A General Technical Report RM-167. P.149-154.

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