Pollen-cone Production Research Articles

Pollen cone production in jack pine: spatial and temporal patterns subject to natural disturbance by the jack pine budworm

Patterns of jack pine (Pinus banksiana Lambert) pollen cone production are of interest because they may help explain jack pine budworm (Choristoneura pinus pinus Freeman) outbreak patterns. We used generalized linear mixed models to analyze pollen cone production in 180 permanent plots in Ontario, Canada between 1992 and 2008. Pollen cone production increased with stand age, and large trees in sparsely-populated stands produced more pollen cones. Defoliation decreased the propensity of trees to produce pollen cones for at least two years. We also identified important patterns that are not explained by defoliation and stand characteristics. Pollen cone production is spatially synchronized among years, trees in central Ontario produced more pollen cones than trees in northwestern Ontario, and background cone production increased over time in the central region but not in more northwestern plots. Synchronized reproduction is common among tree species, but has not previously been noted for jack pine pollen cones. Increasing cone production in central Ontario may be evidence of changing forest and (or) climatic conditions and deserves further investigation. Our model can be used to quantitatively predict pollen cone production and assess the risk of jack pine budworm defoliation.

Sex allocation, pollen limitation and masting in whitebark pine

Summary Masting, the synchronous and episodic production of seed crops, is thought to benefit plant reproductive success through positive density‐dependent effects on pollination, dispersal and seed survival. Of these, only increased pollination efficiency in mast years can be a proximate mechanism for masting by synchronizing reproductive effort across individuals through pollen coupling. Increased pollination efficiency requires synchronous investment in male and female function during mast years. Sex allocation theory, however, predicts a trade‐off in investment between male and female reproductive allocation dependent on total resources invested in reproduction. We describe patterns of sex allocation in Pinus albicaulis (whitebark pine), using data on pollen and seed cone counts over 5 years for 29 trees across 7 sites in Montana, U.S.A. Whitebark pine seed cone maturation increased with site pollen cone production, indicating pollen limitation, and pollen and seed cone production were positively correlated across years. Simulating mature seed cone production from these empirical relationships resulted in greater average mature seed cone production than alternative scenarios of (i) no synchrony between pollen cone production and pollen cone initiation, (ii) negative correlation (trade‐off) between seed cone initiation and pollen cone production or (iii) no masting. Synthesis. Our data support a role for pollination efficiency in both increasing long‐term seed production and as a proximate mechanism for synchronizing masting in Pinus albicaulis. Increased pollination efficiency joins greater seed dispersal and survival in mast years seen in other studies, as an additional positive density‐dependent benefit of masting. Positive density‐dependent fitness benefits may therefore influence patterns of sex allocation in relation to total resources invested in reproduction. The pollen limitation found here combined with stand isolation and reduced tree density due to mortality from forest pests and other environmental stressors may lead to reduced seed cone maturation and changes in masting patterns.

Branching habit and the allocation of reproductive resources in conifers

Correlated relationships between branch thickness, branch density, and twig and leaf size have been used extensively to study the evolution of plant canopy architecture, but fewer studies have explored the impact of these relationships on the allocation of reproductive resources. This study quantifies pollen cone production in conifers, which have similar basic reproductive biology but vary dramatically in branching habit, in order to test how differences in branch diameter influence pollen cone size and the density with which they are deployed in the canopy. Measurements of canopy branch density, the number of cones per branch and cone size were used to estimate the amount of pollen cone tissues produced by 16 species in three major conifer clades. The number of pollen grains produced was also estimated using direct counts from individual pollen cones. The total amount of pollen cone tissues in the conifer canopy varied little among species and clades, although vegetative traits such as branch thickness, branch density and pollen cone size varied over several orders of magnitude. However, branching habit controls the way these tissues are deployed: taxa with small branches produce small pollen cones at a high density, while taxa with large branches produce large cones relatively sparsely. Conifers appear to invest similar amounts of energy in pollen production independent of branching habit. However, similar associations between branch thickness, branch density and pollen cone size are seen across conifers, including members of living and extinct groups not directly studied here. This suggests that reproductive features relating to pollen cone size are in large part a function of the evolution of vegetative morphology and branching habit.

Prevalence of Nosema sp. (Microsporidia: Nosematidae) during an outbreak of the jack pine budworm in Ontario

Microsporidia are believed to play little or no role in outbreaks of the jack pine budworm, Choristoneura pinuspinus Freeman (Lepidoptrera: Tortricidae), because the short duration (2–4years) of those outbreaks may not permit significant build-up of the pathogen. We conducted the first survey of Nosema sp. (Microsporidia: Nosematidae) over the course of a recent jack pine budworm outbreak in Ontario. Between 2004 and 2010 the outbreak defoliated a cumulative total of 1.78 million ha. Microscopic examination of ∼15,000 overwintering larvae collected over 6years in sites with densities of 3 larvae per branch or more revealed widespread occurrence of Nosema at generally high infection intensities. The pathogen was present in 69.5% of the 518 plots that were monitored. Prevalence of infection was generally low (below 40% in 84% of plots with infected larvae) but reached high levels (80–95%) locally and increased rapidly in most infestations within 1–2years of onset. We hypothesize that the habit of early-instar larvae to feed on developing male flowers (pollen cones) after spring emergence is critical in allowing rapid build-up of Nosema by increasing efficiency of horizontal transmission (higher density of both infected larvae and egested spores). Nosema infection may contribute to the complexity of jack pine budworm outbreak patterns by affecting egg recruitment and early-instar survival at the stand level in concert with known effects of budworm-induced reductions in pollen cone production on those processes.

Congruence between parental reproductive investment and success determined by DNA-based pedigree reconstruction in conifer seed orchards

Seed orchards’ parental reproductive success is often assessed through surveys of seed- and pollen-cone production (reproductive investment). Although the reliability of this approach has been questioned, its speed and ease made it the method of choice for providing approximate estimates for the genetic quality and quantity of seed orchard crops. In this study, reproductive investment data from various female and male phenotypic assessment methods from three seed orchards (lodgepole pine ( Pinus contorta Dougl. ex. Loud. var. latifolia Engelm.), Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), and western larch ( Larix occidentalis Nutt.)) were compared with reproductive success estimates based on DNA fingerprinting and parentage analyses. The use of reproductive investment as a proxy to reproductive success on estimating seed crop’s volume genetic worth and diversity (measured by effective number of parents) was evaluated. Regression analyses indicated that the phenotypic assessment methods reflect the true parental reproductive success and that estimates of seed- and pollen-cone volume production appear to be the most appropriate indicators of female and male reproductive success, respectively. Although the best combination of female–male survey methods produced inflated effective number of parents estimates, the genetic worth estimates were similar to those based on DNA, highlighting their robustness to fertility variation assessment.

A review of factors affecting the population dynamics of jack pine budworm (Choristoneura pinus pinus Freeman)

AbstractJack pine budworm (Choristoneura pinus pinus Free.) (Lepidoptera: Tortricidae) is a native insect that periodically defoliates areas of jack pine (Pinus banksiana Lamb.) in the subboreal forests of North America east of the Rocky Mountains. Outbreaks of jack pine budworm generally occur at 6‐ to 12‐year intervals and collapse after 2–4 years. Periodicity of outbreaks varies and is associated with site‐related factors. Survival of early‐instar larvae during spring dispersal is tied to the abundance of pollen cones (microsporangiate strobili), which provide a refuge for larvae until current‐year needles expand. Jack pine trees that have been heavily defoliated produce few pollen cones in the following year, often resulting in high mortality of early‐stage larvae. A diverse guild of generalist parasitoids attack jack pine budworm, but only a few species account for most mortality in any area. Collapsing jack pine budworm populations are characterized by sharp declines in early instar survival, coupled with an increased rate of parasitism in the late larval and pupal stages. The reciprocal interaction between heavy defoliation and low pollen cone production, and increased parasitism of late‐stage larvae or pupae, are consistent with second‐order density dependence factors identified in analysis of a long‐term population data set. Since the 1950s, several jack pine budworm outbreaks have been roughly synchronous over a large geographic area, suggesting that Moran effect processes, as well as moth dispersal or other factors, may be involved in jack pine budworm dynamics. Although the short duration of outbreaks enables most trees to recover, over time dead trees and top‐killed trees accumulate in jack pine stands. Jack pine is well adapted to fire and when fires ignite, the accumulation of dead trees and woody debris often leads to intense wildfires followed by prolific regeneration. The three‐way interaction of jack pine, jack pine budworm, and fire ultimately serves to maintain vigorous stands and ensures continued hosts for jack pine budworm.

Seed cone production enhanced by injecting 38-year-old Larix occidentalis Nutt. with GA4/7

The influence of injecting 38-year-old Larix occidentalis with gibberellin A4/7 (GA4/7) on seed and pollen cone production was studied in western Montana, U.S.A. Two natural stands thinned to several spacings in 1961 were chosen. The two widest spacings were used. In 1991, 60 trees selected for study at each site were randomly divided into two groups of similar DBH, half as controls and half injected in June 1991 with a solution of GA4/7 in ethyl alcohol. The volume injected was adjusted to the DBH of each tree (60 mg per 5 cm diameter). In June 1994, half the trees treated with GA4/7 in 1991 and half the untreated trees were injected with GA4/7 in the same manner as before. In 1992 and 1995, seed cone production increased on GA4/7-treated trees compared to the controls. Pollen cone production was significantly increased by GA4/7 treatment but only at one site. Delayed effects of GA4/7 on seed cone production was not evident in subsequent years after treatment. Foliar and shoot damage on treated trees was attributed to GA4/7 treatment but most trees recovered completely the following year. Finally, GA4/7 treatment did not affect cone length, potential seed per cone or filled seed per cone.

Effects of stem injections of gibberellin A4/7 and paclobutrazol on sex expression and the within-crown distribution of seed and pollen cones in black spruce (Picea mariana)

Two experiments in black spruce (Picea mariana (Mill.) BSP) seedling seed orchards were established to determine if a stem injection of paclobutrazol (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl) could be used as an adjunct treatment to increase the efficacy of stem injections of gibberellins A4 and A7 (GA4/7). Trees received a single injection of GA4/7 and (or) paclobutrazol shortly after vegetative bud burst. There was a dose-dependent but nonlinear increase in the production of cones of both sexes in response to stem injections of either GA4/7 or paclobutrazol. The optimum rate of GA4/7 for stimulating pollen-cone production was 3.3 mg, whereas the most seed cones were induced on trees receiving 11 mg. The sex ratio (number of seed cones/number of pollen cones) increased with the rate of GA4/7 applied. Injecting paclobutrazol also promoted cones of both sexes equally, resulting in sex ratios comparable with that of the control trees. Treatments did not affect the total numbers of buds (vegetative, latent, and cone) produced. Seed- and pollen-cone buds occurred in positions that would have otherwise developed vegetatively and become latent, respectively. The mechanisms whereby paclobutrazol could affect flowering in black spruce are discussed. The use of paclobutrazol as an adjunct to GA4/7 treatments in black spruce seedling seed orchards appears effective, practical, and safe.

Effects of crown-pruning on seed and pollen cone production in two lodgepole pine seed orchards in British Columbia

The effects of top pruning on subsequent seed and pollen cone production in lodgepole pine (Pinus contorta Dougl.) grafted clones in two seed orchards were evaluated. In the older orchard (14 years old), three pruning regimes were applied: an untreated control, a moderate pruning where 25% of the crown was removed and a severe pruning where 40% of the crown was removed. In the younger orchard (ten years old), only a control pruning and a severe pruning (50% of crown removed) were applied. Five-year seed cone production was lower in treated ramets compared to controls in both orchards. However, when cumulative seed cone yields were adjusted for reduced tree heights after pruning, differences were no longer significant in the older orchard. Strong clonal variation was observed in seed cone yields in both orchards. Pollen cone development was less variable among treatments in the older orchard. In the younger orchard, controls consistently produced heavier pollen crops. Pruning recommendations for similar orchards are made and results discussed for reducing the impacts of losses in seed cone yields.

Effects of gibberellin A4/7, root pruning and cytokinins on seed and pollen cone production in black spruce (Picea mariana)

Stem injections of 8-9-year-old black spruce (Picea mariana (Mill.) B.S.P.) trees with gibberellin A(4/7) (GA(4/7)) alone and in combination with root pruning increased both seed and pollen cone production in both 1991 and 1992. Combining GA(4/7) and root pruning produced a larger increase in reproductive bud production than either treatment alone, but the complementary effects were less during the warm dry summer in 1991 than during the wet summer in 1992. Cytokinin applications reduced the stimulatory effects of GA(4/7) and root pruning, and the degree of reduction varied with the amount and timing of application. Reduced reproductive bud production was attributed to cytokinin countering the effects of root pruning and natural drought on the GA(4/7) response.

Influences of crown size and maturation on flower production and sex expression in Picea glauca treated with gibberellin A(4/7).

We evaluated the effects of exogenous gibberellin A(4/7) (GA(4/7)) on the production of seed and pollen cones in four stock types of Picea glauca (Moench) Voss. From 1987 to 1991, a combined treatment that included GA(4/7), root pruning and heat stress was applied to 5- to 10-year-old container-grown grafts, representing over 90 clones and originating from 17- to 27-year-old ortets. Hormonal treatments were applied to pruned field-grown grafts in 1991 and 1992, and to unpruned field-grown grafts from the same set of clones in 1990, 1991 and 1992. In 1992, 26-year-old mature trees in a progeny test were treated with GA(4/7). The GA(4/7) treatment was effective in promoting seed-cone production in all four stock types, whereas it promoted pollen-cone production only in unpruned field-grown grafts and mature trees. The older and taller a tree, the less the response to the GA(4/7) treatment was influenced by the climatic conditions prevailing during the differentiation phase.

Promotion of cone production on field-grown eastern white pine grafts by gibberellin [formula omitted] application

Field-grown 4- and 9-year-old grafts of eastern white pine ( Pinus strobus L.) were sprayed or injected with gibberellin A 4 7 . Treatments in May–June significantly increased pollen-cone production. Spraying produced more pollen-cone clusters per tree. Injection increased the number of clusters per branch and the number of whorls per tree producing pollen cones. Injection, but not spraying, in May–June produced more seed cones. However, spraying in August–September did not promote either pollen-cone or seed-cone production. Injection in August–September decreased the number of pollen cones per cluster and inhibited seed-cone production. Present resutls indicate that treatments for pollen- and seed-cone production are best carried out in May and June during the period of rapid shoot elongation.

Seed-cone and pollen-cone production models for young black spruce seedling seed orchards: a first approximation

Seed orchard managers wanting to predict potential seed-cone (Sc) and pollen-cone (Pc) production 1 year in advance of seed release and pollen dissemination need predictive models. The present study proposes the use of cone-crop models based on tree age in young black spruce (Piceamariana (Mill.) B.S.P.) orchards. Sc and Pc production was monitored from 1987 to 1993 in each of five seedling seed orchards. Some trees began bearing Sc and Pc by tree age 6. The relationships of Sc and Pc production with tree age were each represented by three sigmoid equations: one for light crop years, one for heavy crop years, and one for light plus heavy crop years. The rate of cone increase for heavy and light crop years differed for both Sc and Pc. Sigmoid equations representing heavy Sc and Pc crop years in orchards had the highest r2 (0.8462 and 0.9381, respectively) and the lowest standard error. Sigmoid model of heavy crop years with plantation data also had the highest r2 value (0.8066) and the lowest standard error. The rate of Sc and Pc increase versus tree age was higher for orchards than for plantations. To select the best of three sigmoid models, one must take into account the early buildup phase of cone production in young trees, the yearly fluctuation in cone crops, previous-year cone production, and environmental factors that can affect cone crops.

Effects of cultural treatments and gibberellin A4/7 on flowering of container-grown European and Japanese larch

Gibberellin A4/A7 (GA4/7) was injected into the main stem of container-grown Larixdecidua Mill, and Larixkaempferi (Lamb.) Carr. grafts, using different quantities and times of application of GA4/7 and applying it both alone and in combination with heat, drought, girdling, or root pruning. The GA4/7 did not increase flowering, and girdling and root pruning alone were ineffective. In contrast, flowering was substantially increased when grafts were placed in a polythene house from May (beginning of long-shoot elongation) to June or early September (depending on experiments), in three separate experiments, with mean maximum temperatures of 29–30 °C. This heat treatment significantly increased both seed- and pollen-cone production, and drought treatment significantly increased seed-cone production. Treatment means of up to 143 seed cones and between 250 and 1000 pollen cones per graft, on 1.5 m tall grafts, were observed. In one experiment heat treatment in the polythene house did not increase flowering. In that experiment vegetative buds reflushed during treatment in the polythene house, which could have reduced potential flowering sites; the reflushing may have been associated with needle damage possibly caused by higher than usual temperatures, of over 40 °C.

Seasonal Variation in Pollen Catch in a Black Spruce Orchard

Abstract Pollen monitoring was conducted over three years (1987–1989) in a 12.4 ha Picea mariana (Mill.) B.S.P. (black spruce) seedling seed orchard established from 1979 to 1984. Pollen traps were installed around and within the orchard and collected daily. Pollen-cone production was highest in 1988 with an average of 0, 11, 20, and 38 cones per tree for 5-, 8-, 9-, and 10-year-old trees. Trees of the oldest section of the orchard bore about 60% of the total number of orchard pollen cones in 1987 and 1988 but only 26% in 1989. Pollen contamination during seed-cone receptivity was important in all three years assessed. The increase in pollen contamination from 1988 to 1989 resulted, in part, from 1) the roguing of 63% of trees in the oldest section of the orchard and 2) a 17-fold decrease in orchard pollen production from 1988 to 1989 compared to a 5-fold decrease from contamination sources.

Host‐plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract. Newly‐emerged, second‐instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb. Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect. In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring. Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k‐values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones. Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones. We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density‐dependent factor governing the density of early‐stage jack pine budworm. The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

Pollen contamination in a small black spruce seedling seed orchard for 3 consecutive years

Pollen monitoring was conducted in 1987, 1988, and 1989 in the 2.8 ha Second Falls black spruce ( Picea mariana (Mill.) B.S.P.) seedling seed orchard established in 1978. The objectives of the study were to evaluate (i) the orchard pollen-cone production, (ii) the level of orchard pollen production, and (iii) the level of pollen contamination for 3 consecutive years. Pollen traps were established around the orchard and collected on a daily basis. Pollen-cone production per tree averaged 3, 40, and 76 in 1987–1989, respectively. Pollen contamination during seed-cone receptivity was estimated to be 32%, 83%, and 58% in 1987, 1988 and 1989, respectively. The important increase in pollen contamination from 1987 to 1988 resulted, in part, from (i) the roguing of 40% of orchard trees and (ii) a 37-fold increase in pollen catch from contaminant sources from 1987 to 1988 compared to a 3.6-fold increase in pollen production by orchard trees. Supplemental mass pollination and synchronization of high orchard seed-cone and pollen-cone production with low pollen production from contaminant sources are suggested to reduce the level of pollen contamination, to increase panmixis and seed yield, and to maximize genetic gain.

Gibberellin A(4/7) promotes cone production on potted grafts of eastern white pine.

Potted grafts of eastern white pine (Pinus strobus L.) growing in a heated greenhouse were sprayed weekly with 0, 250 or 500 mg l(-1) of gibberellin A(4/7) for four different 6-week periods between mid-May and mid-September. At different periods, gibberellin A(4/7) concentrations of 250 and 500 mg l(-1) were effective in promoting pollen- and seed-cone production. Spraying in May and June, during the period of rapid terminal shoot elongation, significantly increased pollen-cone production, whereas spraying in August and September, about a month after terminal shoot elongation, significantly increased seed-cone production.

Gibberellin A4/7 Enhanced Cone Production in Tsuga heterophylla: The Influence of Gibberellin A4/7 on Seed- and Pollen-Cone Production

Pollen-cone and seed-cone production in 7-8-yr-old rooted and grafted propagules of western hemlock (Tsuga heterophylla) was increased with weekly foliar sprays of gibberellin A_4/7 between March 17 and July 27. In a second study, timed fortnightly applications made over the same interval showed that GA_4/7 had its greatest promotive effect on pollen- and seed-cone bud production when applied shortly before the onset of cone-bud differentiation. However, treatments made during axillary bud initiation also seemed to promote pollen-cone production. The following year, two GA_4/7 stem injections timed to cone-bud differentiation led to increased pollen- and seed-cone production in almost all clones.

Gibberellin A4/7 enhanced flowering in Pinuscaribaea var. hondurensis

Gibberellin A4/7 was applied to field-grown grafts of sexually mature poor and good flowering clones of Pinuscaribaea Morelet var. hondurensis. Barr. & Golf. Continuous applications of gibberellin A4/7 over a 6-week period significantly enhanced seed-cone production in poor flowering clones but had no effect on good flowering clones. Poor flowering clones also showed slight decreases in pollen-cone production with gibberellin A4/7, while clones that normally flowered well did not. Gibberellin A4/7 increased final shoot lengths in the lower (male) and upper (female) crown region of both poor and good flowering clones. A series of timed gibberellin A4/7 applications suggested that a single treatment near the onset of reproductive bud development may be used to enhance seed-cone production.