René I. Alfaro

Wound-Induced Terpene Synthase Gene Expression in Sitka Spruce That Exhibit Resistance or Susceptibility to Attack by the White Pine Weevil

We analyzed the expression pattern of various terpene synthase (TPS) genes in response to a wounding injury applied to the apical leader of Sitka spruce (Picea sitchensis Bong. Carr.) genotypes known to be resistant (R) or susceptible (S) to white pine weevil (Pissodes strobi Peck.) attack. The purpose was to test if differences in constitutive or wound-induced TPS expression can be associated with established weevil resistance. All wounding treatments were conducted on 9-year-old R and S trees growing under natural field conditions within the range of variation for weevil R and S genotypes. Representative cDNAs of the monoterpene synthase (mono-TPS), sesquiterpene synthase (sesqui-TPS), and diterpene synthase (di-TPS) classes were isolated from Sitka spruce to assess TPS transcript levels. Based on amino acid sequence similarity, the cDNAs resemble Norway spruce (Picea abies) (−)-linalool synthase (mono-TPS; PsTPS-Linl) and levopimaradiene/abietadiene synthase (di-TPS; PsTPS-LASl), and grand fir (Abies grandis) δ-selinene synthase (sesqui-TPS; PsTPS-Sell). One other mono-TPS was functionally identified as (−)-limonene synthase (PsTPS-Lim). No significant difference in constitutive expression levels for these TPSs was detected between R and S trees. However, over a postwounding period of 16 d, only R trees exhibited significant transcript accumulation for the mono- and sesqui-TPS tested. Both R and S trees exhibited a significant accumulation of PsTPS-LASl transcripts. An assessment of traumatic resin duct formation in wounded leaders showed that both R and S trees responded by forming traumatic resin ducts; however, the magnitude of this response was significantly greater in R trees. Collectively, our data imply that the induced resinosis response is an important aspect of defense in weevil R Sitka spruce trees growing under natural conditions.

Historical and spatial characteristics of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) outbreaks in northeastern British Columbia

Abstract The historical pattern of outbreaks of the spruce budworm, Choristoneura fumiferana (Clem.), in white spruce stands in the Fort Nelson Forest District of northeastern British Columbia was reconstructed with the use of dendrochronology. Outbreaks occurred on an average every 26 years, with 5–6 outbreaks in the past century in the northern regions of the district, while southern regions experienced between 0 (the most southern sites) and 4 outbreaks. In the northern regions, outbreaks began about 10 years earlier and the period of defoliation was longer than in the southern regions of the district. The southern limit of the range of the spruce budworm in British Columbia is marked by the predominance of the Montane Boreal White and Black Spruce biogeoclimatic subzone that has cool and wet summers that may not favor budworm development. Therefore, outbreaks that begin in the more suitable northern habitat would move southward only when favorable environmental conditions develop. Along with the high number of outbreaks in the northern regions of the district, there has been no direct control of the budworm, and overmature stands are maintained through suppression of fire and lack of harvesting. Many of these stands are entering a state of general decline with protracted mortality, resulting from a complex of secondary insects and pathogens.

Budburst phenology of sitka spruce and its relationship to white pine weevil attack

Abstract Phenology of budburst development of Sitka spruce, Picea sitchensis Bong. Carr., measured at two sites on Vancouver Island, British Columbia, Canada, was under strong genetic control, with family heritability ( h 2 f ) ranging from 0.45 to 1.0, depending on phenology stage. On average, families with resistance to the white pine weevil, Pissodes strobi (Peck), initiated and maintained a faster rate of bud development than families from susceptible parents, requiring lower heat accumulation to reach particular stages of bud development. However, a large overlap occurred, with one resistant family having a budburst phenology not significantly different from the susceptible families and some susceptible families having phenology as early as that of resistant families. It is postulated that resistance is a multicomponent trait based on different resistance mechanisms, some of which may be correlated with phenology but not others. Close observation of weevil behaviour through the season indicated that resistant families experienced reduced weevil presence, copulation and oviposition rate with respect to susceptible families.

WHITE PINE WEEVIL ATTACK ON WHITE SPRUCE: A SURVIVAL TIME ANALYSIS

The survival time of a white spruce tree (Picea glauca (Moench) Voss) with respect to the attack by the white pine weevil (Pissodes strobi (Peck)) was defined as the number of years until an attack occurred. In this context, resistant trees are those capable of delaying attacks rather than preventing attacks. This study investigated the patterns of survival times of resistant and susceptible trees in a progeny trial of white spruce in the interior of British Columbia, Canada. By doing so, we demonstrated that survival time analysis, a technique specifically developed for dealing with clinical medicine and industrial reliability tests, was a very useful approach in analyzing resistance of hosts to herbivore attack. The results suggested that survivorship of resistant trees was significantly different from that of susceptible trees, as expected. The median survival time of susceptible trees was -12 yr after seeding, while it was 21 yr for resistant trees. The survival times of white spruce trees were identified adequately following a lognormal distribution. Based on the estimated hazard functions of the lognormal distribution, the most severe weevil infestation was predicted to occur at 19 yr for susceptible trees, and at 26 yr for resistant trees. Infestation level was affected by several factors, such as tree height, seasonal temperature, and precipitation. An accelerated failure time model was used to evaluate the effect of these factors on survivorship. The identification of resistant or susceptible trees by survival times is to be incorporated into an integrated pest management program for the white pine weevil in British Columbia.

Resistance of white spruce to white pine weevil: Development of a resistance index

Abstract An index of resistance in white spruce, Picea glauca (Moench) Voss, to attack by the white pine weevil ( Pissodes strobi Peck) was developed based on tree variables which measured attack intensity, severity and the tolerance of the tree to attack. The index, derived using principal component analysis, was used to screen 139 white spruce families from the interior of British Columbia in a replicated family trial, for resistance to weevil attack. The resistant ranking of the families was significantly related to the habitat characteristics of the parent trees as measured by elevation, longitude, latitude and by the ecological variables of biogeoclimatic zone, subzone and variant. Geographic sources of white spruce genotypes resistant to weevil attack were identified. These were mainly in the moist-warm habitats of the SubBoreal Spruce biogeoclimatic zone.

Damage assessment and integrated pest management of forest defoliators

Abstract Forest defoliator damage is reviewed and related to the definition of integrated pest management (IPM). Forests are often managed for the production of more than one resource from the same unit of land. Defoliators do not harm all resources to the same extent, and some resources, forage for example, may increase after defoliation, Therefore, to calculate the net damage in multiple-use forestry, positive effects should be substracted from negative effects. For IPM, he severity of defoliator damage must be judged in relation to the degree to which an infestation prevents the forest manager from attaining the objectives for a particular unit of land. Similarly, the benefits of a pest control option must be considered in relation to the attainment of the same objectives.

Genetical Genomics Identifies the Genetic Architecture for Growth and Weevil Resistance in Spruce

In plants, relationships between resistance to herbivorous insect pests and growth are typically controlled by complex interactions between genetically correlated traits. These relationships often result in tradeoffs in phenotypic expression. In this study we used genetical genomics to elucidate genetic relationships between tree growth and resistance to white pine terminal weevil (Pissodes strobi Peck.) in a pedigree population of interior spruce (Picea glauca, P. engelmannii and their hybrids) that was growing at Vernon, B.C. and segregating for weevil resistance. Genetical genomics uses genetic perturbations caused by allelic segregation in pedigrees to co-locate quantitative trait loci (QTLs) for gene expression and quantitative traits. Bark tissue of apical leaders from 188 trees was assayed for gene expression using a 21.8K spruce EST-spotted microarray; the same individuals were genotyped for 384 SNP markers for the genetic map. Many of the expression QTLs (eQTL) co-localized with resistance trait QTLs. For a composite resistance phenotype of six attack and oviposition traits, 149 positional candidate genes were identified. Resistance and growth QTLs also overlapped with eQTL hotspots along the genome suggesting that: 1) genetic pleiotropy of resistance and growth traits in interior spruce was substantial, and 2) master regulatory genes were important for weevil resistance in spruce. These results will enable future work on functional genetic studies of insect resistance in spruce, and provide valuable information about candidate genes for genetic improvement of spruce.

Potential of Beauveria bassiana (Hyphomycetes: Moniliales) for controlling the white pine weevil, Pissodes strobi (Col., Curculionidae)

Abstract:  Studies were conducted under laboratory conditions to document the potential of Beauveria bassiana conidia applications for controlling the white pine weevil, Pissodes strobi (Peck). A screening test including six B. bassiana isolates allowed us to demonstrate that CFL (Centre de Foresterie des Laurentides) and IP‐CPB (Île Perrault‐charançon du pin blanc) were the most virulent isolates among the ones tested, with percentages of mortality after 3 weeks of 73% and 85.5%, respectively. These two B. basiana isolates were applied either onto soil or branch sections to compare the effectiveness of these potential control strategies. Greater than 75% mortality was observed within 3 weeks for both modes of application using suspensions of B. bassiana at a concentration of 1.0 × 108 (soil application) and 1.0 × 109 conidia/ml (branch application). The results demonstrate for the first time that B. bassiana is an effective entomopathogen against P. strobi.

Population genetic structure of Pissodes strobi (Coleoptera: Curculionidae) in British Columbia, Canada.

Abstract The genetic structure of 41 Canadian populations (27 populations from British Columbia, two of which were from east of the Continental Divide, and the remaining 14 representing localities east of the Continental Divide) of the white pine weevil, Pissodes strobi (Peck), was investigated using isozyme markers. Differentiation among populations (FST) was estimated to be 0.084 and inbreeding within populations was low with estimated mean FIS of 0.011. Although overall genetic uniformity among the studied 41 populations was high (mean Nei’s genetic distance = 0.027), differences among groups of populations were revealed in cluster analyses. The 16 weevil populations obtained from areas east of the Continental Divide formed a significant cluster with the 11 populations collected from the Interior British Columbia. The 11 weevil populations examined from the South Coast–Vancouver Island of British Columbia were distinct from this cluster, as were the three weevil populations collected from the North–Central Coast of British Columbia. Populations within the South Coast–Vancouver Island group were the most genetically dissimiliar to each other, with Nei’s genetic distance ranging from 0.004 to 0.108. This was caused, in part, by differences in allele frequencies in the Bella Coola, Eve River, and Nanaimo populations relative to the other eight populations within this group. Genetic diversity estimates, in terms of the mean number of alleles per locus, the percentage of polymorphic loci and the mean expected and observed heterozygosity, were higher in eastern than western populations.

Variation in wood anatomical structure of Douglas-fir defoliated by the western spruce budworm: a case study in the coastal-transitional zone of British Columbia, Canada

Key messageAn outbreak of the western spruce budworm temporarily modifies cellular wood anatomy of stem wood in natural and mature Douglas-fir stands impacting wood quality properties.AbstractWestern spruce budworm (Choristoneura occidentalis Freeman) is a widespread and destructive defoliator of commercially important coniferous forests in western North America. In British Columbia, Canada, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is the most important and widely distributed host. Permanent sample plots were established at a number of locations in southern interior at the beginning of a severe western spruce budworm outbreak in the 1970s. Two of the sites were sampled in 2012 to determine whether modifications had occurred in the anatomical characteristics of stem wood formed during outbreak years. We determined that rings formed during the western spruce budworm 1976–1980 outbreak had a significantly lower proportion of latewood, reduced mean cell wall thickness and smaller radial cell diameters. While the cellular characteristics of the earlywood remained fairly constant, significant reductions in lumen area occurred in 1978 and 1979 at each site. Our study shows that western spruce budworm outbreaks not only reduce annual radial growth, but also temporarily modify cellular characteristics in latewood cells, which has implications for wood density and quality in Douglas-fir.