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Phenotyping crop performance is critical for line selection and variety development in plant breeding. Canola (Brassica napus L.) flowers, the bright yellow flowers, indeterminately increase over a protracted period. Flower production of canola plays an important role in yield determination. Yellowness of canola petals may be a critical reflectance signal and a good predictor of pod number and, therefore, seed yield. However, quantifying flowering based on traditional visual scales is subjective, time-consuming, and labor-consuming. Recent developments in phenotyping technologies using Unmanned Aerial Vehicles (UAVs) make it possible to effectively capture crop information and to predict crop yield via imagery. Our objectives were to investigate the application of vegetation indices in estimating canola flower numbers and to develop a descriptive model of canola seed yield. Fifty-six diverse Brassica genotypes, including 53 B. napus lines, two Brassica carinata lines, and a Brassica juncea variety, were grown near Saskatoon, SK, Canada from 2016 to 2018 and near Melfort and Scott, SK, Canada in 2017. Aerial imagery with geometric and radiometric corrections was collected through the flowering stage using a UAV mounted with a multispectral camera. We found that the normalized difference yellowness index (NDYI) was a useful vegetation index for representing canola yellowness, which is related to canola flowering intensity during the full flowering stage. However, the flowering pixel number estimated by the thresholding method improved the ability of NDYI to detect yellow flowers with coefficient of determination (R2) ranging from 0.54 to 0.95. Moreover, compared with using a single image date, the NDYI-based flowering pixel numbers integrated over time covers more growth information and can be a good predictor of pod number and thus, canola yield with R2 up to 0.42. These results indicate that NDYI-based flowering pixel numbers can perform well in estimating flowering intensity. Integrated flowering intensity extracted from imagery over time can be a potential phenotype associated with canola seed yield.

Silene latifolia Poiret of Eurasia has established in North America, prompting this structural study of its mature unisexual buds and flowers. Floral nectaries, anther and stigma changes, and vestigial reproductive structures were studied using light and scanning electron microscopy. In staminate flowers, anthers dehisced before anthesis and >90% of their pollen was liberated within 36 h. Accumulated in the tubular calyx, nectar descended an anthophore from the stomatal-bearing nectary at the stamen bases. Nectary tissue surrounded the pistillode, a central filamentous organ lacking ovules but tipped by hairs resembling stigmatic papillae. In pistillate flowers, nectar flowed into an inflated calyx. The annular nectary had 10 regularly spaced, stomatal-lined craters and was continuous with the adaxial surfaces of the infertile antisepalous and epipetalous staminodes. Key elements of entomophilous pollination leading to successful sexual reproduction of this invasive species include secondary nectar presentation from disparate floral nectaries that, for pistillate flowers, also incorporate the staminodes; rapid pollen release from anthers; and elongation of papillae by tip growth that enhances each stigma’s receptive surface. Context is also provided for future studies of floral nectary development in this model dioecious species.

With the increasing resistance of wild oat (Avena fatua L.) to herbicides, there is a need to evaluate the potential of alternative cropping systems based on integrated weed management principles. A 5-yr field study at eight sites across Canada was used to evaluate the profitability of alternative cropping systems that have the potential to control wild oat using cultural practices in conjunction with herbicides. Cultural practices included twice the recommended seeding rates, fall-seeded winter crops, barley (Hordeum vulgare L.) silage, fallow, and alfalfa (Medicago sativa L.). Seven of the 14 cropping systems in this study did not include wild oat herbicide for three consecutive years, controlling wild oat entirely by cultural practices. Cropping system profitability varied by location. For many locations, combinations of barley silage and fall-seeded winter crops without wild oat herbicide application were as profitable as a system of canola (Brassica napus L.) and wheat (Triticum aestivum L.) with wild oat herbicide applied every year. Unprofitable systems generally included those with fallow, alfalfa, and fall-seeded winter crops in regions with rates of high winter kill. Wild oat control can be achieved with diverse cropping systems that are as profitable as conventional annual cropping that relies on herbicide control of wild oat.

Traditional methods of estimating frost damage to crops are labor-intensive and time-consuming. Remote sensing imagery and vegetation indices can be used for condition assessment, however, the util...

Interrow cultivation is a selective, in-crop mechanical weed control tool that has the potential to control weeds later in the growing season with less crop damage compared with other incrop mechanical weed control tools. To our knowledge, no previous research has been conducted on the tolerance of narrow-row crops to interrow cultivation. The objective of this experiment was to determine the tolerance of field pea and lentil to interrow cultivation. Replicated field experiments were conducted in Saskatchewan, Canada, in 2014 and 2015. Weekly cultivation treatments began at the 4-node stage of each crop, continuing for 6 wk. Field pea and lentil yield linearly declined with later crop stages of cultivation. Cultivating multiple times throughout the growing season reduced yield by 15% to 30% in both crops. Minimal yield loss occurred when interrow cultivation was conducted once at early growth stages of field pea and lentil; however, yield loss increased with delayed and more frequent cultivation events.Nomenclature: Field pea; Pisum sativum L.; lentil; Lens culinaris L.

Concern over the development of herbicide-resistant weeds has led to interest in integrated weed management systems that reduce selection pressure by utilizing mechanical and cultural weed control practices in addition to herbicides. Increasing crop seeding rate increases crop competitive ability and thus can enhance herbicide efficacy. However, it is unknown how increasing the seeding rate affects an herbicide’s efficacy. The objective of this study was to examine the interaction between increasing seeding rate and herbicide dose to control weeds. To meet this objective, the herbicide fluthiacet-methyl was applied to field-grown lentil, with Indian mustard, a proxy for wild mustard, used as a model weed. The experiment was a factorial design with four lentil seeding rates and seven herbicide rates. Overall the herbicide dose response was altered by changing lentil seeding rate. Increasing lentil seeding rate decreased the weed biomass production when herbicides were not applied. In two of the four site-years, increasing lentil seeding rate lowered the herbicide ED50, the dose required to result in a 50% reduction in weed biomass. Increasing the crop seeding rate altered the dose response to provide greater weed control at lower herbicide rates compared with normal crop seeding rates. Increased seeding rates also resulted in higher and more stable crop seed yields across a wider range of herbicide dosages. These results suggest that dose–response models can be used to evaluate the efficacy of other weed management practices that can interact with herbicide performance.

Canola (Brassica napus L.) often experiences high seed losses prior to and during harvest operations. Pod drop and pod shatter are responsible for pre-harvest seed losses in canola although relatively little is known about the significance of pod drop to total pre-harvest seed losses in canola. This research describes a method to measure the predisposition for pod drop among canola genotypes that was developed and tested across different sites from 2013 to 2015. This method, referred to as pod-retention resistance, consists of the use of a force gauge to quantify the force required to break the pod pedicle at the pedicle-rachis junction. Two sets of field experiments were used, the first developed and modeled the factors that influence pod-retention resistance, pod drop and seed shatter. A second set of experiments was used to validate these findings on a broader range of genotypes and determine whether a relationship between pod retention resistance and pod drop could be determined. Results showed that the pod-retention resistance was significantly greater for pods on the proximal half of the rachis compared to the distal half of the rachis. Several factors contributed strongly to variation in pod retention resistance (rachis position, genotype and site) and pod drop (site, rachis position and genotype). The relative importance of individual factors varied between pod retention resistance and pod drop suggesting no relationship between the two. However, weight-adjusted pod retention resistance, i.e., average pod retention resistance corrected for the average weight of dropped pods, was strongly correlated with pod drop, particularly in the validation experiments. This method could be used by canola breeders to select for and develop genotypes with reduced predisposition for seed losses via pod drop.

In western Canada, more money is spent on wild oat herbicides than on any other weed species, and wild oat resistance to herbicides is the most widespread resistance issue. A direct-seeded field experiment was conducted from 2010 to 2014 at eight Canadian sites to determine crop life cycle, crop species, crop seeding rate, crop usage, and herbicide rate combination effects on wild oat management and canola yield. Combining 2× seeding rates of early-cut barley silage with 2× seeding rates of winter cereals and excluding wild oat herbicides for 3 of 5 yr (2011 to 2013) often led to similar wild oat density, aboveground wild oat biomass, wild oat seed density in the soil, and canola yield as a repeated canola–wheat rotation under a full wild oat herbicide rate regime. Wild oat was similarly well managed after 3 yr of perennial alfalfa without wild oat herbicides. Forgoing wild oat herbicides in only 2 of 5 yr from exclusively summer annual crop rotations resulted in higher wild oat density, biomass, and seed banks. Management systems that effectively combine diverse and optimal cultural practices against weeds, and limit herbicide use, reduce selection pressure for weed resistance to herbicides and prolong the utility of threatened herbicide tools.

Silene latifolia Poir. (white cockle or white campion) is an important invasive weed in North American agriculture. It exhibits dioecy, therefore, both male and female plants are required in order for seed production to occur. However, dioecious species being invasive is not common because of their limitations in pollination and subsequent seed production. The objective of this study is to determine the effect of pollination timing and distance on seed production of Silene latifolia. A series of experiments including pollination exclusion, timing and pollination distance were conducted in 2009 and 2010 at or around Saskatoon, Saskatchewan. For pollination exclusion, exclosures were built around the natural female plants for exclosure, sham-exclosure, and male and female combined treatments. Pollination timing was studied by applying exclosure, non-exclosure, night-exclosure, and day-exclosure treatments to individual female plants. Female plants were transplanted along a linear interval at six different distances from the pollen source to study the effect of pollination distance. S. latifolia was exclusively insect-pollinated and pollination occurred both day and night; however, in one year, pollination occurred mainly at night. Female plants that were in the range of 0–4 m from a compatible pollen source experienced no limitation to pollination. However, when the distance was increased further up to 128 m, pollination levels and subsequent seed production were declined. Moreover, there were differences in seed production between years suggesting that pollination was affected by the environmental conditions during pollination and the crop that white cockle was grown in. These experiments indicate that seed production in S. latifolia is limited by insect-pollination. Although there was pollination limitation for seed production at greater distances from a pollen source, the high fecundity rate (3000–18000 seeds per plant) resulted in a large seed output. Thus, we believe that a dioecious species may require characteristics that compensate the pollination limitation for a successful invasion.

Domestication is the process by which a wild plant evolves into a cultivated plant by undergoing morphological, physiological or molecular changes. These changes may be due to conscious selection (primary cultivated plant) or unconscious selection (secondary cultivated plant) by man. These evolutionary changes need to be studied to understand the transition from wild to cultivated plant. Cow cockle (Vaccaria hispanica) is a summer annual species introduced to North America from Europe. It is being considered for commercial production because of its seed constituents. The purpose of this study is to determine which cow cockle populations are best adapted to cultivation and the plant characteristics that are responsible for such adaptation. We compared 15 cultivated and wild cow cockle populations from different parts of the world for 12 agronomic and morphological traits. Multivariate analyses were performed to group populations according to their agronomic and morphological similarity. Cluster analysis revealed three main population groups among the 15 accessions based on the traits studied. Two linear discriminants were obtained by discriminant function analysis accounting for 96 % of the variability among the populations. Analysis of variance showed significant (P

Weed control with herbicides is not possible in several systems including control of wild oat (Avena fatua L.) in tame oat (Avena sativa L.), red rice (Oryza sativa L. var. sylvatica) in rice (Oryza sativa L.), and in organic systems. Competitive crop cultivars can be used to manage weed competition if selective weed control by herbicides is not possible. However, most existing competitive crop cultivars often have low weed-free yield and poor grain quality. We hypothesize that the progeny of a cross between a competitive forage-type oat cultivar and a high-yielding and high grain quality grain oat cultivar will have high yield and good grain quality as well as high competitive ability (CA). The objective of this study was to evaluate progeny lines from a cross between a tall, competitive, forage-type oat cultivar with a semidwarf, high-yielding milling oat for their CA against wild oat. A field study was performed in two locations in Saskatoon, SK, Canada, in 2008 and 2009 using seven progeny lines and the two parents. Oat was seeded with and without wild oat at a target crop and weed density of 250 plant m⁻² in a randomized block design with four replicates. All the genotypes were high yielding and did not differ in grain yield or quality either in weed-free or weedy conditions. Some of the tall (CDC Baler, SA050498, and SA050479) and short (SA050040 and Ronald) genotypes had high average grain yield under both weed-free and weedy conditions compared with the other genotypes. The tall oat line SA050479 was among the most weed suppressive, which resulted in less wild oat biomass. The seedling total leaf area, crop height, and the seedling third leaf area were negatively correlated with wild oat biomass. This study demonstrates that a cross between a high-yielding and a highly competitive genotype can result in progeny with high CA, yield, and crop quality.

Legume crops are known to have low soil N uptake early in their life cycle, which can weaken their ability to compete with other species, such as weeds or other crops in intercropping systems. However, there is limited knowledge on the main traits involved in soil N uptake during early growth and for a range of species. The objective of this research was to identify the main traits explaining the variability among legume species in soil N uptake and to study the effect of the soil mineral N supply on the legume strategy for the use of available N sources during early growth. Nine legume species were grown in rhizotrons with or without N supply. Root expansion, shoot and root biomass, nodule establishment, N2 fixation and mineral soil N uptake were measured. A large interspecific variability was observed for all traits affecting soil N uptake. Root lateral expansion and early biomass in relation to seed mass were the major traits influencing soil N uptake regardless of the level of soil N availability. Fenugreek, lentil, alfalfa, and common vetch could be considered weak competitors for soil N due to their low plant biomass and low lateral root expansion. Conversely, peanut, pea, chickpea and soybean had a greater soil N uptake. Faba bean was separated from other species having a higher nodule biomass, a higher N2 fixation and a lower seed reserve depletion. Faba bean was able to simultaneously fix N2 and take up soil N. This work has identified traits of seed mass, shoot and root biomass, root lateral expansion, N2 fixation and seed reserve depletion that allowing classification of legume species regarding their soil N uptake ability during early growth.

Seed shatter of wild oat (Avena fatua L.), green foxtail [Setaria viridis (L.) P. Beauv.], wild mustard (Sinapis arvensis L.), cleavers (Galium spurium L. and G. aparine L.), wild buckwheat (Polygo...

Organic farmers in western Canada rely on tillage to control weeds and incorporate crop residues that could plug mechanical weed-control implements. However, tillage significantly increases the risk of soil erosion. For farmers seeking to reduce or eliminate tillage, potential alternatives include mowing or using a roller crimper for terminating green manure crops (cover crops) or using a minimum tillage (min-till) rotary hoe for mechanically controlling weeds. Although many researchers have studied organic crop production in western Canada, few have studied no-till organic production practices. Two studies were recently conducted in Saskatchewan to determine the efficacy of the following alternatives to tillage: mowing and roller crimping for weed control, and min-till rotary hoeing weed control in field pea (Pisum sativum L.). The first study compared mowing and roller crimping with tillage when terminating faba bean (Vicia faba L.) and field pea green manure crops. Early termination of annual green manure crops with roller crimping or mowing resulted in less weed regrowth compared with tillage. When compared with faba bean, field pea produced greater crop biomass, suppressed weeds better and had less regrowth. Wheat yields following pea were not affected by the method of termination. Thus, this first study indicated that roller crimping and mowing are viable alternatives to tillage to terminate field pea green manure crops. The second study evaluated the tolerance and efficacy of a min-till rotary harrow in no-till field pea production. The min-till rotary hoe was able to operate in no-till cereal residues and multiple passes did not affect the level of residue cover. Field pea exhibited excellent tolerance to the min-till rotary hoe. Good weed control occurred with multiple rotary hoe passes, and pea seed yield was 87% of the yield obtained in the herbicide-treated check. Therefore, this second study demonstrated that min-till rotary hoeing effectively controls many small seeded annual weeds in the presence of crop residue and thus can reduce the need for tillage in organic-cropping systems.

The current recommended plant density in field pea (Pisum sativum L.) in western Canada is 88 plants m–2. This rate may exceed the optimum for yield in cultivars with more basal branching than typical. The objective of this research was to determine how the seed yield of pea cultivars differing in basal branching ability responds to changes in plant density. Ten pea cultivars were sown at target plant populations of 10, 30, 90, 120, and 150 plant m–2 for 3 yr at Rosthern and Saskatoon, Saskatchewan. At very low plant densities there was greater than a twofold difference in branching potential between cultivars (range 0.85 to 1.99 branches plant–1). Increasing field pea plant density reduced branching by 0.097 branches for each additional plant. The response of yield to plant density differed, as the forage cultivars 40-10 and CDC Sonata reached their potential yield at lower densities, while Courier required higher densities to reach the same proportion of yield. Field pea cultivars with greater basal branching achieved their maximum yield at lower plant densities compared with cultivars with low basal branching. The optimum economic plant density for the pea cultivars ranged from 59 to 84 plants m–2, which is below the current recommended plant density. However, with the exception of the forage cultivars and the low-branching cultivar Courier, the optimum seeding rate was within 8% of 88 seeds m–2. It is recommended that pea growers avoid low-branching pea cultivars and seed at a rate of 88 viable seeds m–2.Key words: Basal branching, seeding rate, plant density, light interception, leafed pea, semi-leafless pea, forage pea

Phosphorus (P) can be low in soil under low input organic management; however, beneficial crop plant associations with arbuscular mycorrhizal fungi (AMF) are known to promote crop nutrition and increase phosphorus uptake. Thus, management strategies that promote AMF associations are particularly desirable for low-input cropping systems. The objectives of this study were to determine the impact of seeding rate on AMF colonization and the impact of AMF colonization on P concentration and uptake by organically grown field pea and lentil. Field experiments examined the impact of three seeding rates of field pea and lentil on P uptake and crop yield. Phosphorus accumulation was examined further in a controlled growth chamber experiment, in which field pea was sown at rates corresponding to those used in the field and harvested at 10-day intervals until 50 days after emergence. In the field, the level of AMF colonization of roots remained at 80% for field pea, while colonization of lentil increased with increasing seeding rates from 77% to 88%. The level of AMF colonization of field pea achieved in the growth chamber after 50 days was 80% for the two highest seeding rates and 60% for the low seeding rate. The rate at which AMF colonization occurred did not vary between treatments. Ultimately, AMF colonization level did not affect P accumulation. In contrast to several previous studies, both field and growth chamber experiments revealed that AMF colonization was not reduced at higher seeding rates. These results suggest that organic farmers may increase seeding rates without adversely affecting P nutrition.

Traditionally, farmers have delayed seeding to manage wild oat (Avena fatua L.) in tame oat (Avena sativa L.) crops, but this practice can adversely affect grain yield and quality. The objectives of this study were: (1) to evaluate the effectiveness of using high seeding rates with early-seeded oat to maintain grain yield and quality, and (2) to determine an optimum seeding rate to manage wild oat and maximize grain yield and quality. The factors of interest were wild oat density (low and high density), seeding date (early May, mid May, early June and mid June), and tame oat seeding rate (150, 250, 350 and 450 viable seeds m-2). The study was conducted at Indian Head and Saskatoon, SK, in 2002, 2003 and 2004, at Winnipeg, MB, in 2002, and at Morden, MB, in 2003 and 2004. Wild oat biomass, wild oat panicle density and wild oat seed in the harvested sample decreased as seeding rate increased, while tame oat biomass and grain yield increased. Wild oat density ranged between 0 and 100 plants m-2 with averages of 10 plants m-2 in the low density treatment and 27 plants m-2 in the high density treatment. At low seeding rates, grain yield decreased with increasing wild oat density. The difference in grain yield between the two wild oat densities decreased as the seeding rate increased. There was a curvilinear decrease in grain yield as seeding was delayed. A seeding date × seeding rate interaction was noted for test weight, plump seed, thin seed and groat yield. Seed quality improved as seeding rate increased for only the mid-June seeding date. Even though the mid-June test weight increased as the seeding rate increased it was always lower than the early May test weight at any seeding rate. The results from this study established that in the presence of wild oats, early seeding of tame oat is possible providing high seeding rates, 350 plants m-2 are used.Key words: Wild oat competition, wild oat density, wild oat biomass, grain yield, grain quality

Successful chickpea production in western Canada typically requires multiple applications of fungicides to minimize the severity of ascochyta blight (AB) caused by Ascochyta rabiei (Pass.) Lab. Although planting resistant cultivars could be economical and environmentally safer than fungicide use, varieties with a high level of resistance are not available. The objective of this research was to identify potentially useful parents for breeding programs aimed at the northern Great Plains by assessing the AB reaction of 12 desi and 12 kabuli chickpea varieties for their AB reaction on leaves, stems and pods under two fungicide regimes. The experiment was conducted at Swift Current and Shaunavon, Saskatchewan, in 2004 and 2005. Differences in AB severity on leaves, stems and pods, seed yield and 1000-seed weight occurred among varieties at all site-years tested. The variation was greater among kabuli varieties than desi varieties. Ascochyta blight severity was generally lower under the high fungicide regime. A positive correlation in AB severity on leaves, stems and pods was observed, suggesting a lack of organ-specific reaction. Several promising varieties that combined improved levels of AB resistance, high yield, and large seed size were identified. Key words: Didymella rabiei, Ascochyta rabiei, Cicer arietinum, fungicide efficacy

Flaxseed is known to have significant health benefits in human nutrition and when included in animal rations. There is pressing need to improve flaxseed production to meet the growing demand. The objective was to study the effects of three seeding rates (22, 45 and 67 kg ha-1), two seeding dates (early May and late May), three rates of nitrogen (66, 100 and 133% of recommended) and three cultivars (Norlin, AC McDuff and CDC Valour) and at five locations representative of the flax-growing area of the Canadian prairies from 1999 to 2001. The variables of interest were plant density, seed yield and yield formation, seed oil content and oil quality. Plant establishment was always highest with Norlin, but bolls m-2 was similar between the three cultivars. Plant density was always highest with the later plantings. No overall effect of seeding date was observed on grain yield, but the site-year by seeding date interaction showed that the later planting was favoured by the most northerly sites and early planting at the most southerly sites. The sites intermediate in latitude showed little response to seeding date. This finding provides important information with respect to the inclusion of flax in cropping systems depending on the latitude and deciding on the order of planting. Later planting resulted in a small decrease in oil content. Seed yields were increased with seeding rates going from 22 to 45 kg ha-1, which corresponded to plant populations > 300 plants m-2, with no increases thereafter. Increases in seeding rates always reduced the number of bolls plant-1 with little effect on seeds boll-1. Seeding rate had no effect on seed oil quantity and quality and maturity. A seed yield increase was observed with nitrogen when going from 66 to 100% of the recommended rate with no increases past 100%. Adding nitrogen resulted in a small drop in seed oil content. The seeding date × nitrogen rate interaction revealed a lack of response to nitrogen with the later planting date beyond 66% of the recommended N rate, suggesting reduced nitrogen rates with later plantings are possible. The absence of a site-year by seeding date by nitrogen rate interaction implies that findings of this study can be applied to a wide geographical area. In conclusion, attention needs to be given to seeding rates to target plant density > 300 plants m-2. Even with the high seeding rates, the target plant population was achieved only 60 and 73% of the time for the early and late planting, respectively. Using soil test recommendations for nitrogen will maximize seed yields under most situations. Best agronomic practices to maximize seed yield were found to maintain adequate seed oil quality and quantity. Key words: Linum usitatissimum L., nitrogen rate, seeding rate, seeding date, cultivar

Oat (Avena sativa L.) yield and quality on the northern Great Plains are consistently reduced by frequent drought and wild oat (Avena fatua L.) competition. Wild oat cannot be selectively removed from oat with herbicides. Identifying genotypes or seed size(s) with high germination potential under moisture stress may facilitate improved seedling vigor, stand establishment, and crop competitiveness. Therefore, a germination study was conducted to determine the effects of genotype and seed size on the germination of oat seed subjected to moisture stress. Large, medium, and small seeds of six common western Canadian oat genotypes were germinated in polyethylene glycol (PEG 8000) solutions with initial osmotic potentials ranging from 0 to -0.4 MPa at 5°C. Generalized linear mixed models fit to the data provided a statistically valid, appropriate, and convenient method to analyze germination data. In all genotypes examined, decreasing seed size and osmotic potential increased median germination time (MGT) and lowered final germination percentage (FGP). Among genotypes, CDC Bell had the fastest MGT while AC Mustang had the highest FGP. Delays in MGT and reductions in FGP resulting from increased moisture stress were similar to those observed in other cereals, suggesting that oat may be as capable of germinating under low spring soil moisture conditions as wheat and barley. The results of this study also indicate that large seed of genotypes such as AC Mustang and CDC Bell appear better suited to germinate under the range of osmotic potentials in this study. Although differences in MGT and FGP between seed sizes in this study were statistically significant, they were generally small and thus, oat germination characteristics may not be substantially improved by screening out small seed from farm-saved seed.

Combine harvesters have the potential to disperse weed seeds great distances. Reducing this dispersal may be important in an integrated weed management system. The objectives of this study were to determine the distance that wild oat seeds are dispersed by a combine harvester and the effect of chaff collection on combine harvester seed dispersal. This was measured by sampling wild oat seeds at varying distances behind a combine equipped with a removable chaff collection system after it passed through a wild oat patch. Chaff collection consistently reduced the amount and distance that wild oat seeds were dispersed. This occurred because more than 74% of the total wild oat seed that were ejected from the combine were in the chaff. Because most of the chaff falls in a row directly behind the combine, chaff collection only affected dispersal in this area. In 1996, chaff collection reduced wild oat seed dispersal past the wild oat patch to less than 10 seeds m−2at 45 m, whereas without chaff collection, there was greater than 10 seeds m−2up to 145 m. At distances beyond 145 m, chaff collection had no significant effect on seed dispersal. Chaff collection may be an important tool in an integrated weed management program because it may slow weed invasions and reduce the expansion of weed patches.

Selective control of wild oat with herbicides is not possible in oat (Avena sativa L.) crops and, consequently, the high quality that is imperative to market success is continually jeopardized. Field experiments were conducted to determine the effects of relative time of emergence and density of wild oat on oat kernel size and weight. Thousand-kernel weight and percentage plump kernels were generally reduced, and percentage thin kernels were generally increased with increasing wild oat densities and earlier wild oat emergence. However, reductions were generally small and occurred only at the highest wild oat densities, which are not commonly observed in commercial fields. These findings suggest that oat growers should not control wild oat based on perceived reductions in oat physical grain quality. Key words: Competition, emergence, physical grain quality, test weight, 1000-kernel weight

The inherent similarity between wild oat (Avena fatua L.) and oat (A. sativa L.) precludes selective herbicide control of wild oat. Previous studies have reported improved crop yield and competitiveness with the use of large seed. Therefore, a greenhouse experiment was conducted in 2002 and 2003 to examine the effect of caryopsis (dehulled kernel) size and genotype on wild oat-oat competition. Seeds of three oat cultivars (AC Assiniboia, CDC Boyer, CDC Orrin) were classified into three size classes based on caryopsis size (large, approximately equal to 35 mg; medium, approximately equal to 25 mg; and small, approximately equal to 15 mg). Whole oat seeds of each genotype and caryopsis size treatment were grown either in monoculture or in mixture with wild oat (250 plants m(-2)). Neither genotype nor caryopsis size significantly influenced (P < 0.05) oat emergence. Nonetheless, oat plants established from large caryopses produced 17% more biomass (P < 0.001) and 15% more panicles m(-2) (P < 0.001) than plants established from small caryopses. Wild oat produced 23% less biomass (P = 0.004) and fewer panicles m(-2) when grown with oat plants established from large caryopses. Genotype only influenced oat panicle production (P = 0.05) and did not affect oat (P = 0.09) or wild oat (P = 0.34) aboveground shoot biomass production. These results suggest that oat plants derived from large-seeded caryopses may be better able to tolerate wild oat interference. However, further investigation is needed to examine the response of oat-wild oat competition to oat caryopsis size and genotype under field conditions.

Wild oat is a serious weed in cultivated oat because there are no herbicides to selectively control it. Considering the effect of time of emergence on weed–crop interference is critical for the development of accurate crop yield loss models and weed density thresholds. Therefore, field experiments were conducted at two locations in Saskatchewan, Canada, in 2002 and 2003 to determine the effect of wild oat density and time of emergence on cultivated oat yield and quality. Wild oat was planted at 50 growing degree day (GDD) intervals ranging from 100 GDD before to 100 GDD after crop planting. Wild oat density ranged from 0 to 320 plants m−2. High densities of early emerging wild oat greatly reduced cultivated oat yield and increased wild oat contamination, with observed oat yield losses as great as 70% and wild oat contamination levels of 15%. Wild oat that emerged before cultivated oat caused considerably more yield and quality loss and had higher reproductive output than wild oat that emerged aft...

Polymer coatings have recently been developed to prevent germination and thereby reduce undesirable emergence of fall-seeded canola (Brassica napus L.) in western Canada. However, recent observations suggest that if seeds are not exposed to moist soil conditions in the fall, these polymer coats may prevent imbibition and subsequent germination during the following spring. Our objective was to determine the effects of moisture stress and polymer coat on canola seed germination characteristics in the laboratory. Polymer-coated and non-polymer-coated canola seeds were germinated in polyethylene glycol (PEG 8000) solutions with initial osmotic potentials ranging from 0 to -1.25 MPa at 5 and 15°C. Polymer coat treatments caused higher median germination times and lower final germination percentages compared with film-coated and uncoated control seeds. Germination characteristics of polymer-coated seeds were negatively influenced by decreasing initial osmotic potential, particularly at 5°C. Although not always significantly different from the uncoated control, film-coated control seeds behaved similarly to those coated with polymers. Among the three polymer coat treatments examined, one polymer coat treatment consistently exhibited higher germination compared with the other two. The results of this study help explain the occurrence of low spring seedling populations of fall-seeded, polymer-coated canola following a dry fall, particularly under low spring soil temperatures.

In western Canada, seasonal seedling recruitment has been reported in weedy canola populations, and seed persistence has been linked to the secondary seed dormancy potential of a genotype. Temperature influences secondary seed dormancy induction in this species. In these experiments we (1) investigated the influence of temperature and osmotic potential on secondary seed dormancy induction in canola, (2) related these to seedbank dynamics and seedling recruitment of two canola genotypes with different seed dormancy potentials in the field, and (3) investigated the influence of residue, burial depth, and soil type on seedbank dynamics and seedling recruitment in the field. In the laboratory, rates of seed dormancy induction were positively correlated to increasing temperatures and water stress. The role of temperature was approximately threefold more important to seed dormancy development than was osmotic potential within the tested ranges of these variables. In the field, seasonal seedbank dynamic...

Summary Secondary seed dormancy has been linked to seedbank persistence of volunteer oilseed rape (Brassica napus) in western Canada. It has been suggested that there is a genetic component to secondary seed dormancy expression in oilseed rape, but little is known of its importance in relation to non-genetic factors. In a series of experiments we investigated the relative importance of genotype, seed size, time of windrowing and pre- and post-harvest environment on the expression of secondary seed dormancy. We found that genotype contributed between 44 and 82% to the total variation in secondary seed dormancy. A broad range in secondary seed dormancy expression was observed among 16 genotypes examined. Nevertheless, three-quarters of the genotypes investigated exhibited relatively high potential for the expression of secondary seed dormancy (back-transformed mean 71% dormant seeds). Seed size contributed 21% to the total variation, while the influence of seed maturity (harvest regime) on secondary seed dormancy expression was negligible. Despite diverging environmental conditions during the four growing seasons spanning these experiments, the influence of pre-harvest environment on seed dormancy expression was relatively small and ranged from 0.1% to 4.5%. Secondary seed dormancy potential decreased over time during seed storage. This decrease was greatest when seeds were stored at ambient temperatures and least when seeds were stored at −70°C.

In western Canada, little is known about the seedbank ecology of volunteer canola. Therefore, integrated recommendations for the management of this weed are limited. In this study, we investigated the seedbank persistence and seedling recruitment of two spring canola genotype groups with different secondary seed dormancy potentials under contrasting tillage systems. The study was conducted at two locations with different soils in the Mixed Moist Grassland ecoregion of Saskatchewan. A single cohort seedbank was established in 1999 and was followed for 3 yr in successive wheat crops. In a separate laboratory study, the six canola genotypes examined were classified as those with high and those with medium potentials for the development of secondary seed dormancy (HD and MD, respectively). After one, two, and three winters, maximum persistence of 44, 1.4, and 0.2% of the original seedbank was observed among the treatments, respectively. In 2001, HD canola genotypes tended to exhibit 6- to 12-fold greater persistence than MD canola genotypes, indicating lower seedbank mortality in HD canola. Seedling recruitment of HD canola also was higher than MD canola when differences were observed between these genotype groups. Therefore, long-term seedbank persistence of canola can be reduced by growing genotypes with low inherent potential for the development of secondary seed dormancy. The proportion of persisting seeds tended to be higher under conventional tillage than under zero tillage because of lower seedbank mortality, but no clear distinction in seedbank persistence in terms of absolute time could be made between these two tillage systems. Volunteer canola seedling recruitment followed the pattern of a typical summer-annual weed, where seedling emergence was observed only during May and June.

The occurrence of volunteer canola has been increasing in western Canada. The objective of this study was to determine the canola seedbank additions incurred during crop harvest on commercial farms. Over 2 yr, 35 fields of 15 different producers were sampled after harvest using a vacuum cleaner. The canola seeds were separated from the crop residue and soil, and yield loss, 1,000-seed weight, and seedbank additions were determined for each field. Further information for each field was obtained through a producer survey questionnaire. Average yield losses of 107 kg ha−1 or 5.9% of the crop seed yield were observed. This amounted to seedbank additions of approximately 3,000 viable seeds m−2. The yield losses among producers ranged from 3.3 to 9.9% or 9 to 56 times the normal seeding rate of canola. Even with relatively low persistence rates, seedbanks of this magnitude could result in significant volunteer populations for several years, without further seedbank additions from escaped volunteers. No...

There is relatively little agronomic information on solid-seeded production of dry bean in western Canada. Recommended seeding density for dry bean can depend on the growth habit of the plant, the yield–density relationship, percent emergence, seed cost and environment. The objective of this study was to determine the yield–density relationships in two determinate bush type cultivars of dry bean and the optimum plant population under solid-seeded production in Saskatchewan. CDC Camino, a late-season pinto bean and CDC Expresso, a medium-season-length black bean were the cultivars evaluated. In most sites, the yield-density relationship of the cultivars was asymptotic and an optimum plant density for maximum yield could not be determined. Camino generally required a lower plant population to reach a given yield than Expresso. Increasing plant population did not affect 1000-seed weight. Higher seeding rate did result in a greater number of seeds produced m-2, with Expresso having a greater increase in seed produced m-2 compared with Camino. Expresso was required to be at higher plant densities than Camino to maximize economic returns. This reflects the differences between cultivars in yield-density relationship and seed cost, as Camino has a heavier 1000-seed weight than Expresso. Saskatchewan bean growers wishing to maximize profit should target plant populations for Expresso and Camino of approximately 50 and 25 plants m-2, respectively. Key words: Saskatchewan, yield components, non-linear regression, seeding rate, narrow rows, solid-seeded

Avena fatua seeds remaining on the plant at harvest and taken into the combine harvester may be dispersed over large areas. The objective of this study was to characterize the development of A. fatua in comparison to spring Triticum aestivum. As part of this objective, the rate of seed shed in A. fatua relative to development of T. aestivum was determined. Avena fatua and T. aestivum had similar phyllochron intervals within locations but differed between locations. Plant development as measured by the Zadoks plant development scale was consistent within plant species between locations. Seed shed in A. fatua was also consistent between locations. Most of the seed shed occurred within 2 wk, and the cumulative seed shed followed a sigmoidal pattern. The seed shed occurred as T. aestivum was ripening, and the percentage of seed shed appears to be related to the water content of the T. aestivum spike. Because of this relationship, the proportion of seed remaining on A. fatua at harvest could be manage...

Phenotypic characterization of two nodulation mutants (R69 and R99) of Phaseolus vulgaris L. was undertaken. The nodule anatomy of R69 (Nod+Fix−), was examined and compared to its wild-type parent, OAC Rico. The arbuscular mycorrhizal (AM) status of R69 and R99 (Nod−) was also compared to OAC Rico. Small whitish growths resembling nodules were produced on the roots of R69 in response to inoculation with Rhizobium leguminosarum biovar phaseoli. These nodule-like structures were variable in shape and occasionally had lateral roots growing from them. A layer of crystalline inclusions (possibly calcium oxalate) occurred between the periderm and parenchyma cells in the mutant nodules. A central infected zone was not present and the vascular system occupied the centre of the nodule instead of the periphery, as seen in wild-type nodules. Given the distinctive phenotype of the nodules of R69, they were designated Pvb− (peripheral vascular bundles, minus). The Nod− mutant, R99, could establish a symbiosis with AM (Myc+), however, R69 was resistant to infection by AM (Myc−). Appressoria would form on the roots and internal hyphae would start to develop, but these would fail to develop into a normal AM symbiosis. We suggest that specific anatomical characteristics of the Nod+Fix− and Myc− phenotypes in R69 supports the hypothesis of a common regulation of the development of the two symbioses.

Nodulation mutants are present in many species of legumes and have potential as ideal reference crops in field measurements of N2 fixation. The objective of this experiment was to characterize the growth, development, mineral-N accumulation, and N2 fixation of two nodulation mutants of common bean (Phaseolus vulgaris L.), R69 (nod+/fix−) and R99 (nod−) in comparison with the wild type parent OAC Rico. The mutants were incapable of N2 fixation. With dual dependence on N2 fixation and [Formula: see text] as N sources, OAC Rico accumulated more N than R69 and R99. However, when supplied with mineral [Formula: see text] sufficient to prevent N2 fixation in OAC Rico, its growth and N accumulation did not differ from those of the mutants. There were differences in internode length that resulted in different heights among the three lines. The addition of silver to the nutrient solution failed to restore nodulation to R99. As a result, it was determined that the nod− phenotype is not a result of an ethylene-related mutation. The nodulation mutants R69 and R99 appear to be good choices as reference crops for common bean in N2 fixation studies. Key words: Common bean, N accumulation, N2 fixation, nodulation mutants, Phaseolus vulgaris, Rhizobium leguminosarum bv. phaseoli

The plant hormone abscisic acid (ABA) has been implicated in the inception and maintenance of seed dormancy, while gibberellins promote dormancy breakage and germination in some species. We investigated whether osmotic stress induced secondary dormancy in Brassica napus L. is associated with changes in ABA sensitivity and metabolism, as well as changes in gibberellin levels. Seeds of two genotypes, one with low dormancy potential (LDP) and one with high dormancy potential (HDP) for secondary dormancy, were exposed to a dormancy-inducing osmotic treatment for up to 4 weeks and then germinated in the presence of increasing ABA concentrations. Even at relatively high concentrations of supplied ABA, germination of LDP seed was not inhibited, while relatively low ABA concentrations inhibited the germination of HDP seed after osmotic treatment. Fluridone was highly effective in suppressing secondary dormancy development in HDP seed, but had no effect on germinability in LDP seed. Despite the lack of differences in nonosmotically treated seed, ABA and ABA-glucose ester accumulated to higher levels, and gibberellin A1 accumulated to lower levels, in HDP relative to LDP seed by the end of the osmotic treatment. Our findings indicate an association among ABA sensitivity, biosynthesis and accumulation, and secondary dormancy potential in B. napus seed.Key words: abscisic acid (ABA), Brassica napus, fluridone, induced dormancy, osmotic stress, sensitivity.