Although high pollinator visitation is crucial to ensure the yields of pollinator-dependent crops, the quantitative trait loci (QTL) controlling nectar volume in sunflower (
L.), a pollinator ...preference trait, have yet to be identified. To address this, a recombinant inbred line mapping population, derived from lines with contrasting nectar volume, was used to identify loci responsible for the phenotype. As a result, linkage mapping and QTL analysis discovered major loci on chromosomes 2 and 16 that are associated with variation in nectar volume in sunflower. Increased nectar volume is also associated with increased sugars and total energy available per floret. The regions on chromosomes 2 and 16 associated with the nectar phenotype exhibit indications of chromosome structural variation, such that the phenotype is associated with rearrangements affecting regions containing hundreds of genes. Candidate genes underlying QTL on chromosomes 9 and 16 are homologous to genes with nectary function in
. These results have implications for sunflower breeding, to enhance pollination efficiency in sunflower, as well as current and future studies on sunflower evolution.
The red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), is a primary seed‐feeding pest of cultivated sunflowers, Helianthus annuus L., in North America. Host plant ...resistance is one tool available to complement insecticide‐based management of S. fulvus. Artificial infestations of 30 adult weevils per head were used to determine whether variation for susceptibility to S. fulvus exists in previously released inbred lines, and how a new weevil‐resistant line, HA 488, compares with other putative sources of resistance. Correcting for the number of seeds per head, 13 older inbred lines showed variation in per cent seed damage from 20% to 38%, with two lines (HA 412 HO, HA 821) being more damaged than most of the tested lines. Among four putative resistance sources, HA 488 was significantly less damaged (5%) than two previously identified open‐pollinated varieties (PI 170424, PI 253417, with 13%–14% seed damage), while the source of the resistance in HA 488, PI 431542, was statistically intermediate (12%). The resistance available in HA 488 is a marked improvement, potentially reducing damage per weevil by two thirds or more, but additional work on genetic markers for resistance, economic thresholds and basic weevil biology (e.g. degree‐day models for adult emergence) is needed to support implementation of integrated pest management for this key sunflower pest.
Key message
Floret and seed traits are moderately correlated phenotypically in modern sunflower cultivars, but the underlying genetics are mostly independent. Seed traits in particular are governed ...in part by epistatic effects among quantitative trait loci.
Seed size is an important quality component in marketing commercial sunflower (
Helianthus annuus
L.), particularly for the in-shell confectionery market, where long and broad seed types are preferred as a directly consumed snack food globally. Floret size is also important because corolla tube length was previously shown to be inversely correlated with pollinator visitation, impacting bee foraging potential and pollinator services to the plant. Commercial sunflower production benefits from pollinator visits, despite being self-compatible, and bees are required in hybrid seed production, where “female” and “male” inbred lines are crossed at field scale. Issues with pollination of long-seed confectionery sunflower suggest that there may be an unfavorable correlation between seed and floret traits; thus, our objective was to determine the strength of the correlation between seed and floret traits, and confirm any co-localization of seed and floret trait loci using genome-wide association analysis in the SAM diversity panel of sunflower. Our results indicate that phenotypic correlations between seed and floret traits are generally low to moderate, regardless of market class, a component of population substructure. Association mapping results mirror the correlations: while a few loci overlap, many loci for the two traits are not overlapping or even adjacent. The genetics of these traits, while modestly quantitative and influenced by epistatic effects, are not a barrier to simultaneous improvement of seed length and pollinator-friendly floret traits. We conclude that breeding for large seed size, which is required for the confectionery seed market, is possible without producing florets too long for efficient use by pollinators, which promotes bee foraging and associated pollination services.
The benefits of insect pollination to crop yields depend on genetic and environmental factors including plant self-fertility, pollinator visitation rates, and pollinator efficacy. While many crops ...benefit from insect pollination, such variation in pollinator benefits across both plant cultivars and growing regions is not well documented. In this study, across three states in the northern Great Plains, United States, from 2016 to 2017, we evaluated the pollinator-mediated yield increases for 10 varieties of confection sunflowers, Helianthus annuus L. (Asterales: Asteraceae), a plant that is naturally pollinator-dependent but was bred for self-fertility. We additionally measured pollinator visitation rates and compared per-visit seed set across pollinator taxa in order to determine the most efficacious sunflower pollinators. Across all locations and hybrids, insect pollination increased sunflower yields by 45%, which is a regional economic value of over $40 million and a national value of over $56 million.There was, however, some variation in the extent of pollinator benefits across locations and plant genotypes, and such variation was significantly related to pollinator visitation rates, further highlighting the value of pollinators for confection sunflowers. Female Andrena helianthi Robertson (Hymenoptera: Andrenidae) and Melissodes spp. (Hymenoptera: Apidae) were the most common and effective pollinators, while other bees including managed honey bees (Hymenoptera: Halictidae), Apis mellifera L. (Hymenoptera: Apidae), small-bodied sweat bees (Hymenoptera: Halictidae), bumble bees Bombus spp. (Hymenoptera: Apidae), and male bees were either infrequent or less effective on a per-visit basis. Our results illustrate that wild bees, in particular the sunflower specialists A. helianthi and Melissodes spp., provide significant economic benefits to confection sunflower production.
Floral nectar and other reward facilitate crop pollination, and in so doing, increase the amount and breadth of food available for humans. Though abundance and diversity of pollinators (particularly ...bees) have declined over the past several decades, a concomitant increase in reliance on pollinators presents a challenge to food production. Development of crop varieties with specific nectar or nectar-related traits to attract and retain pollinating insects is an appealing strategy to help address needs of agriculture and pollinators for several reasons. First, many crops have specific traits which have been identified to enhance crop-pollinator interactions. Also, an improved understanding of mechanisms that govern nectar-related traits suggest simplified phenotyping and breeding are possible. Finally, the use of nectar-related traits to enhance crop pollination should complement other measures promoting pollinators and will not limit options for crop production or require any changes by growers (other than planting varieties that are more attractive or rewarding to pollinators). In this article, we review the rationale for improving crop-pollinator interactions, the effects of specific plant traits on pollinator species, and use cultivated sunflowers as a case study. Recent research in sunflower has (i) associated variation in bee visitation with specific floral traits, (ii) quantified benefits of pollinators to hybrid yields, and (iii) used genetic resources in sunflower and other plants to find markers associated with key floral traits. Forthcoming work to increase pollinator rewards should enable sunflower to act as a model for using nectar-related traits to enhance crop-pollinator interactions.
Nectar-related traits influence the number of bee visits to sunflowers, but the effects of floret size on the diversity and composition of bee communities are unknown. In 4 year × planting date ...combinations, bees were collected from sunflowers with small (< 7.5 mm), medium (7.5–9 mm), or large (> 9 mm) florets, and counts of foraging bees were used to clarify bee responses to plant traits. No effect of floret size on diversity of foraging bees was found, but associations of bee tongue length and floret size led to differences in the communities foraging on sunflowers with small, medium, or large florets. Though most wild bees preferred to forage on plants with more nectar and smaller florets (≈ easier access to nectar),
Bombus
spp. showed an opposite response to floret size, foraging preferentially on lines with large florets. Changes in
Melissodes
spp. foraging preference in the presence of
Bombus
spp. also suggest interactions between small- and large-bodied bees may be important.
Embryos of the sunflower moth, Homoeosoma electellum (Hulst), were cryopreserved after modification to the method that was previously described for Pectinophora gossipiella. The workflow to develop ...the protocol consisted of methods to weaken the embryonic chorion followed by the application of various methods to disrupt the sub-chorionic wax layer. These steps were necessary to render the embryos permeable to water and cryoprotectants. Initially, the embryos were incubated at 21° and 24 °C, and the development of the double pigment spots/eyespot and eclosion were tracked every two hours. The embryos at 24 °C showed eyespots as early as 30 h, while in the case of the embryos that were incubated at 21 °C, there was a developmental delay of approximately 20 h. The embryos at 24 °C showed peak eclosion between 55 and 70 h, and the embryos at 21 °C eclosed between 80 and 100 h of development. Estimating this range is crucial for the purposes of stage selection and treatment initiation for cryopreservation protocol development for the embryos. The control hatch percentage at either developmental temperature was >90%, and the sodium hypochloride, 2-propanol and alkane-based treatments reduced the embryo hatchability to <10%. Hence, a modified surfactant—hypochlorite mixture—was used to destabilize the chorion and solubilize the hydrophobic lipid layers. Water permeability assessments using the dye-uptake method show that polysorbate 80 in combination with sodium hypochlorite alone is capable of permeabilizing the embryo as efficiently as sequential hypochlorite—alkane treatments, but with significantly higher hatch rates. A vitrification medium consisting of ethane diol and trehalose was used to dehydrate and load the embryos with the cryoprotective agent. The median hatch rates after vitrification were 10%, and maximum was 23%.
The red sunflower seed weevil, Smicronyx fulvus L., is a univoltine seed-feeding pest of cultivated sunflower, Helianthus annuus L. Artificial infestations of S. fulvus onto sunflowers with ...traditional (<25% oleic acid), mid-oleic (55–75%), or high oleic (>80%) fatty acid profiles were used to test if fatty acids could be used as natural markers to estimate the proportion of weevils developing on oilseed sunflowers rather than wild Helianthus spp. and confection (non-oil) types. Oleic acid (%) in S. fulvus confirmed the fatty acid compositions of mature larvae and weevil adults reflected their diets, making primary (oleic or linoleic) fatty acids feasible as natural markers for this crop-insect combination. Oleic acid in wild S. fulvus populations in North Dakota suggests at least 84 and 90% of adults originated from mid-oleic or high oleic sunflower hybrids in 2017 and 2018, respectively. Surveys in 2017 (n = 156 fields) and 2019 (n = 120 fields) extended information provided by S. fulvus fatty acid data; no significant spatial patterns of S. fulvus damage were detected in samples, damage to oilseed sunflowers was greater than confection (non-oil) types, and the majority of damage occurred in ≈10% of surveyed fields. Combined, data suggest a few unmanaged or mismanaged oilseed sunflower fields are responsible for producing most S. fulvus in an area. Improved management seems possible with a combination of grower education and expanded use of non-insecticidal tactics, including cultural practices and S. fulvus-resistant hybrids.
Most natural mortality of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), occurs while larvae overwinter in the soil. To test the hypothesis that S. fulvus ...mortality is related to low temperatures, experiments were used to (i) evaluate the temperature at which larvae freeze (= supercooling point SCP), (ii) assess possible vertical movement between entry into the soil in fall and adult emergence in summer, and (iii) determine if realistic soil temperatures could explain patterns of overwintering mortality. Mean SCP for groups of S. fulvus larvae differed between years and months, but only ranged from –20.93 to –22.68 °C. Most overwintering larvae were found within 6 cm of the soil surface, but larvae appeared to move 1–2 cm deeper between pairs of successive sample dates (September to January, January to April). Significant larval mortality that occurred between January and April 2021 was tentatively attributed to a period in February where daily minimum soil temperatures ranged from –8 to –12 °C. When overwintering under control conditions (constant 4 °C) was interrupted with week-long exposure to –4, –8, or –12 °C in a cold bath, significant S. fulvus mortality was seen for temperatures at or below –8 °C. Combined results suggest that mortality of overwintering S. fulvus is likely caused by continuous exposure to low temperatures that may not be cold enough to freeze larvae. Additionally, the shallow overwintering by S. fulvus supports the idea that routine farm management, including tillage and herbicide incorporation, may help limit populations of this sunflower pest.
Extracts from capitate glandular trichomes (CGT) of wild and cultivated sunflowers, Helianthus spp., have repellent or toxic effects on sunflower specialists and generalist herbivores less closely ...associated with sunflower. Though CGT have been primarily examined for their potential to provide partial resistance to the sunflower moth, Homoeosoma electellum Hulst (Lepidoptera: Pyralidae), a floret- and seed-feeding pest, the banded sunflower moth (Cochylis hospes Walsingham Lepidoptera: Tortricidae) is a similar species more common in the primary sunflower-producing states of North Dakota and South Dakota. Replicated field trials using partially inbred lines with low or high CGT densities were used to evaluate possible reductions to seed damage by C. hospes larvae in 2016–2017. Results failed to support the idea that CGT are a useful defense against larvae of C. hospes; the putative plant defense of high trichome density corresponded to slightly more, rather than less, insect damage. A test of a secondary explanation, that strength of sunflower hulls could help determine patterns of seed damage among tested lines, produced similarly negative results. Though timing of bloom differed between groups of most- and least-damaged lines, prior research and pheromone-trapping data suggest differences in plant maturity also cannot adequately explain the observed results. While the specific mechanisms remain unclear, significant differences in susceptibility to C. hospes exist for cultivated sunflower and limit losses from this primary insect pest.
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