Cultivated Sunflower Research Articles

Genetic Analysis of Domestication Parallels in Annual and Perennial Sunflowers (Helianthus spp.): Routes to Crop Development.

Parallels exist between the domestication of new species and the improvement of various crops through selection on traits which favor the sowing, harvest and retention of yield potential and the directed efforts to improve their agronomics, disease resistance and quality characteristics. Common selection pressures may result in the parallel selection of orthologs underlying these traits and homologies between crop species can be exploited by plant breeders to improve germplasm. Perennial grains and oilseeds are a class of proposed crops for improving the diversity and sustainability of agricultural systems. Maximilian sunflower (Helianthus maximiliani Schrad.) is a perennial crop wild relative of sunflower (Helianthus annuus L.) and a candidate perennial oilseed species. Understanding parallels between cultivated H. annuus and H. maximiliani may provide new tools for the development of Maximilian sunflower and other wild relatives of sunflower as crops to enhance functional diversity in cropping systems. F2 populations of Maximilian sunflower segregating for traits associated with the domestication ideotype of cultivated sunflower including branching architecture, capitulum morphology and flowering time were developed to investigate parallels between H. maximiliani and H. annuus. Genotype-by-sequencing (GBS) was employed to genotype novel Maximilian sunflower populations and perform quantitative-trait-loci (QTL) analysis. A total of 11 QTL in five regions were identified across 21 linkage groups using 4142 GBS derived single nucleotide polymorphism markers called using the sunflower reference genome as a guide. A major QTL on linkage group 17b, associated with aspects of floral development and apical dominance, was discovered and corresponds with a known domestication QTL hotspot in H. annuus and candidate genes were identified. This suggests the potential to exploit orthologs for neo-domestication of H. maximiliani for traits such as branching architecture, timing of anthesis, and capitulum size and morphology for the development of a perennial oilseed crop from wild relatives of cultivated sunflower.

Susceptibility of sunflower inbred lines and putative resistance sources to Smicronyx fulvus LeConte (Coleoptera: Curculionidae)

AbstractThe 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.

Genetic Diversity, Population Structure and Linkage Disequilibrium Assessment among International Sunflower Breeding Collections.

Sunflower germplasm collections are valuable resources for broadening the genetic base of commercial hybrids and ameliorate the risk of climate events. Nowadays, the most studied worldwide sunflower pre-breeding collections belong to INTA (Argentina), INRA (France), and USDA-UBC (United States of America–Canada). In this work, we assess the amount and distribution of genetic diversity (GD) available within and between these collections to estimate the distribution pattern of global diversity. A mixed genotyping strategy was implemented, by combining proprietary genotyping-by-sequencing data with public whole-genome-sequencing data, to generate an integrative 11,834-common single nucleotide polymorphism matrix including the three breeding collections. In general, the GD estimates obtained were moderate. An analysis of molecular variance provided evidence of population structure between breeding collections. However, the optimal number of subpopulations, studied via discriminant analysis of principal components (K = 12), the bayesian STRUCTURE algorithm (K = 6) and distance-based methods (K = 9) remains unclear, since no single unifying characteristic is apparent for any of the inferred groups. Different overall patterns of linkage disequilibrium (LD) were observed across chromosomes, with Chr10, Chr17, Chr5, and Chr2 showing the highest LD. This work represents the largest and most comprehensive inter-breeding collection analysis of genomic diversity for cultivated sunflower conducted to date.

Phylogeography and the Evolutionary History of Sunflower (Helianthus annuus L.): Wild Diversity and the Dynamics of Domestication.

Patterns of genetic variation in crops are the result of selection and demographic changes that occurred during their domestication and improvement. In many cases, we have an incomplete picture of the origin of crops in the context of their wild progenitors, particularly with regard to the processes producing observed levels of standing genetic variation. Here, we analyzed sequence diversity in cultivated sunflower (Helianthus annuus L.) and its wild progenitor (common sunflower, also H. annuus) to reconstruct phylogeographic relationships and population genetic/demographic patterns across sunflower. In common sunflower, south-north patterns in the distribution of nucleotide diversity and lineage splitting indicate a history of rapid postglacial range expansion from southern refugia. Cultivated sunflower accessions formed a clade, nested among wild populations from the Great Plains, confirming a single domestication event in central North America. Furthermore, cultivated accessions sorted by market type (i.e., oilseed vs. confectionery) rather than breeding pool, recapitulating the secondary development of oil-rich cultivars during its breeding history. Across sunflower, estimates of nucleotide diversity and effective population sizes suggest that cultivated sunflower underwent significant population bottlenecks following its establishment ~5000 years ago. The patterns inferred here corroborate those from previous studies of sunflower domestication, and provide a comprehensive overview of its evolutionary history.

Genetic Dissection of Phomopsis Stem Canker Resistance in Cultivated Sunflower Using High Density SNP Linkage Map.

Phomopsis stem canker (PSC) caused by Diaporthe helianthi is increasingly becoming a global threat for sunflower production. In this study, the genetic basis of PSC resistance was investigated in a recombinant inbred line (RIL) population developed from a cross between HA 89 (susceptible) and HA-R3 (resistant). The RIL population was evaluated for PSC disease incidence (DI) in seven screening trials at multiple locations during 2016–2018. The distribution of PSC DI in the RIL population was continuous, confirming a polygenic inheritance of the trait. A moderately high broad-sense heritability (H2, 0.76) was estimated for the trait across environments. In the combined analysis, both the genotype and the genotype × environment interactions were highly significant. A linkage map spanning 1505.33 cM was constructed using genotyping-by-sequencing derived markers. Marker–trait association analysis identified a total of 15 quantitative trait loci (QTL) associated with PSC resistance on 11 sunflower chromosomes, each explaining between 5.24 and 17.39% of the phenotypic variation. PSC resistance QTL were detected in two genomic regions each on chromosomes 3, 5, 13, and 17, while one QTL each was detected in the remaining seven chromosomes. Tightly linked single nucleotide polymorphism (SNP) markers flanking the PSC resistance QTL will facilitate marker-assisted selection in PSC resistance sunflower breeding.

Pest potential of Neotephritis finalis (Loew) on Silphium integrifolium Michx., Silphium perfoliatum L., and interspecific hybrids

AbstractNeotephritis finalis (Loew), a fly known as a minor pest of cultivated sunflowers (Helianthus annuus L.), has been observed to attack Silphium spp., which are being evaluated as new crops to produce biomass or edible oil. Infestations of Silphium integrifolium Michx., Silphium perfoliatum L. and their interspecific hybrids were assessed by securing bags over heads late in bloom and counting emerged adult flies ∼30 d later. Effects on seed production were assessed by examining the percent of achenes containing fully developed seeds (i.e., seed set). In 2017, more flies emerged from S. integrifolium and hybrids than from S. perfoliatum, but even high numbers of adult flies emerged per head appeared unrelated to seed set in S. integrifolium. In 2018, far fewer flies were found across Silphium spp., but seed set was similar to 2017. Combined, results indicate that N. finalis is unlikely to limit seed production of Silphium spp.

Genetic and Genomic Tools in Sunflower Breeding for Broomrape Resistance.

Broomrape is a root parasitic plant causing yield losses in sunflower production. Since sunflower is an important oil crop, the development of broomrape-resistant hybrids is the prime breeding objective. Using conventional plant breeding methods, breeders have identified resistant genes and developed a number of hybrids resistant to broomrape, adapted to different growing regions worldwide. However, the spread of broomrape into new countries and the development of new and more virulent races have been noted intensively. Recent advances in sunflower genomics provide additional tools for plant breeders to improve resistance and find durable solutions for broomrape spread and virulence. This review describes the structure and distribution of new, virulent physiological broomrape races, sources of resistance for introduction into susceptible cultivated sunflower, qualitative and quantitative resistance genes along with gene pyramiding and marker assisted selection (MAS) strategies applied in the process of increasing sunflower resistance. In addition, it presents an overview of underutilized biotechnological tools, such as phenotyping, -omics, and genome editing techniques, which need to be introduced in the study of sunflower resistance to broomrape in order to achieve durable resistance.

Capitate Glandular Trichomes Fail to Provide Significant Resistance to Banded Sunflower Moth (Lepidoptera: Tortricidae)

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.

Quantitative PCR Assays Developed for Diaporthe helianthi and Diaporthe gulyae for Phomopsis Stem Canker Diagnosis and Germplasm Screening in Sunflower (Helianthus annuus).

Phomopsis stem canker of sunflower is caused by two fungal pathogens, Diaporthe helianthi and Diaporthe gulyae, in the United States. In this study, two quantitative PCR (qPCR) assays were developed to detect and quantify D. helianthi and D. gulyae in sunflower. The two assays differentiated the two fungi from each other, other species of the genus Diaporthe, and pathogens, and they have high efficiency (>90%). The qPCR assays detected the two pathogens on plant samples exhibiting Phomopsis stem canker symptoms sampled from commercial sunflower fields in Minnesota, Nebraska, North Dakota, and South Dakota. Furthermore, the assays were used to screen cultivated sunflower accessions for resistance to D. helianthi and D. gulyae. The disease severity index (DSI) of the accessions significantly correlated (P < 0.0001) with the amount of pathogen DNA from the qPCR assays. The qPCR assays identified PI664232 and PI561918 to be significantly less susceptible (P ≤ 0.05) to D. helianthi and D. gulyae, respectively, when compared with the susceptible check cultivar HA 288, and this was in agreement with the DSI. These results suggest that the qPCR assays for D. helianthi and D. gulyae can be used as a reliable tool to diagnose Phomopsis stem canker and screen sunflower germplasm for disease resistance.

Cytomorphological and molecular characterization of inter-specific hybrid between cultivated sunflower and Helianthus argophyllus

Cytomorphological and molecular characterization of inter-specific hybrid between cultivated sunflower and Helianthus argophyllus

Genetic variation for tolerance to extreme temperatures in wild and cultivated sunflower (Helianthus annuus) during early vegetative phases

Abstract The increased incidence of extreme temperature events due to global climate change poses a major challenge for crop production. Ability to increase temperature tolerance through genetic improvement requires understanding of how crops and their wild relatives respond to extreme temperatures. We developed a high-throughput technique to evaluate tolerance to freezing stress (FS) and heat stress (HS) in wild, crop–wild hybrid and cultivated sunflower (Helianthus annuus L.). We also investigated whether trade-offs exist between stress tolerance and growth under benign conditions. Eleven experiments were performed under a combination of growth-chamber and field conditions. In growth-chamber experiments, FS and HS consisted of exposing acclimated plants at the 2–4-leaf stage to temperatures ranging from to –2.5°C to –4°C for 2–4 h and from 52°C to 54°C for 2–3 h. In the field, plants were grown for 32 days during midwinter (FS: average Tmean = 9.9°C and Tmin = 3.8°C) or for 10 days in a heat tent (HS: average Tmean = 30.1°C and Tmax = 43.3°C). We observed large differences in tolerance to FS and HS between wild and cultivated sunflower. Wild sunflower showed higher FS tolerance than cultivated in both growth-chamber and field experiments, whereas cultivated sunflower showed higher HS tolerance in growth-chamber experiments. No differences in HS tolerance were observed in the field. Crop–wild hybrids generally showed intermediate HS and FS tolerance. We found no evidence of a growth-tolerance trade-off, which suggests that tolerance might be introgressed into elite germplasm without growth penalties. The study reveals that wide genetic variation for the tolerance to extreme temperatures exists in the primary gene pool of sunflower.

Transcriptomic data of leaves from eight sunflower lines and their sixteen hybrids under water deficit

This article describes how the transcriptomic data were produced on sunflower plants subjected to water deficit. Twenty-four sunflower (Helianthus annuus) genotypes were selected to represent genetic diversity within cultivated sunflower and included both inbred lines and their hybrids. Drought stress was applied to plants in pots at the vegetative stage using the high-throughput phenotyping platform Heliaphen. Here, we provide transcriptomic data from sunflower leaves. These data differentiate both plant water status and the different genotypes. They constitute a valuable resource to the community to study adaptation of crops to drought and the transcriptomic basis of heterosis.

RNA expression dataset of 384 sunflower hybrids in field condition

This article describes how RNA expression data of 173 genes were produced on 384 sunflower hybrids grown in field conditions. Sunflower hybrids were selected to represent genetic diversity within cultivated sunflower. The RNA was extracted from mature leaves at one time seven days after anthesis. These data allow to differentiate the different genotype behaviours and constitute a valuable resource to the community to study the adaptation of crops to field conditions and the molecular basis of heterosis. It is available on data.inra.fr repository.

Gene banks for wild and cultivated sunflower genetic resources

Modern breeding of sunflower (Helianthus annuus L.), which started 100 years ago, increased the number and the diversity of cultivated forms. In addition, for more than 50 years, wild sunflower and otherHelianthusspecies have been collected in North America where they all originated. Collections of both cultivated and wild forms are maintained in gene banks in many countries where sunflower is an important crop, with some specificity according to the availability of germplasm and to local research and breeding programmes. Cultivated material includes land races, open pollinated varieties, synthetics and inbred lines. The majority of wild accessions are ecotypes of wildHelianthus annuus, but also 52 other species ofHelianthusand a few related genera. The activities of three gene banks, in USA, France and Serbia, are described in detail, supplemented by data from seven other countries. Past and future uses of the genetic resources for environmental adaptation and breeding are discussed in relation to genomic and improved phenotypic knowledge of the cultivated and wild accessions available in the gene banks.

Pattern Analysis of Visible Faulty Fruits in Capitula: A Case in Cultivated Sunflower (Helianthus annuus L.)

The analysis of spatial arrangement of incompletely developed fruits (IDF) in capitula could be used to understand the nature and the relative arrangement of these fruits at maturity, previously unexplained by current models. The objective of this work was to quantify and define the distribution pattern of visible IDF (IDFvis) at physiological maturity in the capitulum of the cultivated sunflower, in two genotypes with different self-compatibility expression grown in three different environments. Spatial characteristics and the possibility of randomness of IDFvis pattern generation were also evaluated. We were able to define four IDFvis patterns: Type I, where the distribution of the IDFvis was located mainly at the capitulum center, Type II, where the distribution remained grouped at its center but spreads towards the periphery, Type III, where the distribution was more homogeneous over the entire capitulum surface and Type IV with a homogeneous but very dispersed distribution over the entire capitulum surface. Second order spatial point pattern analysis techniques for a plane (Ripley’s K) were applied to the distribution of IDFvis in the four predefined IDFvis patterns. Using the ADE-4 software, spatial distribution patterns contained in a circular surface and corrected for edge effects were analyzed. By grouping the different types of IDFvis patterns by environment and genotype, a tendency was observed to generate preferably two types of patterns, Type I and Type IV, directly related to the genotype and not to the environment. The K index obtained for each type of pattern showed that, for the scales analyzed, Types I, II and III can be defined as grouped, since they laid outside the Poisson confidence limits. The Type IV pattern presented results consistent with a completely randomized distribution. It was observed a low-frequency appearance of the IV (random) pattern and only for one genotype in the different environments studied, while in the rest of the genotype x environment combinations there was always a greater degree of grouping (non random; Type; I, II and III patterns). Proved that mostly of the IDFvis patterns presented in the sunflower capitulum were mainly non random, the results shown here suggest that, to the intrinsic characteristics of the plant to express this character, mainly physiological, intra-receptacle physical factors could be added in the post-pollination stage, capable of altering the normal development of the embryos.

Pericarp features of wild perennial Helianthus L. species as a potential source for improvement of technical and technological properties of cultivated sunflower

Although the anatomy of the sunflower achene has been extensively studied, not enough attention is given to the research of the pericarp characteristics as potentially important parameters in the breeding programme. Therefore, we considered that it was important to make very detail comparative analysis of morpho-anatomical characteristics of achene as well as miromorphological and n-alkane characteristics of epicuticular wax of the 18 wild perennial Helianthus species. For anatomical analyses cross-sections were obtained from the middle part of pericarp using cryotechnique procedure. Micromorphological observation, morphological and anatomical analysis of pericarp were performed using Light and Scanning Electron Microscopy. The composition of the epicuticular n-alkanes was characterized by GC-FID and GC/MS analyses. Results showed differences in the distribution of phytomelanin pigment among the species. Denser phytomelanin network in the species H. salicifolius, H. resinous, H. tuberosus, and H. hirsutus may be connected with better resistance to insects and mechanical damages. Species H. resinosus, H. giganteus, and H. hirsutus are characterized by the highest percentage of cuticle and sclerenchyma thickness in the pericarp which can be a predictor of mechanical resistance to biotic and abiotic factors. Species H. strumosus, H. maximiliani, and H. grosseserratus are characterized with thin pericarp, poorly developed cuticle and epicuticle wax, as well as thin sclerenchyma tissue. In the pericarp waxes, C29 was the dominant alkane but several samples had n-alkanes longer than C33.These long-chain n-alkanes may be related to drought tolerance in some species. Obtained results of pericarp characteristics can be useful for improving technical and technological properties of the achene as well as for preservation of collection of wild sunflower species.

Intraspecific genetic divergence within Helianthus niveus and the status of two new morphotypes from Mexico.

Collecting and characterizing the genetic diversity of wild relatives of crops can contribute importantly to sustainable crop production and food security. Wild sunflower, Helianthus niveus, occurs in arid regions in western North America and is partially cross-compatible with the cultivated sunflower (H. annuus). We assessed phylogenetic relationships and patterns of genetic divergence among three previously described subspecies (subsp. niveus, subsp. canescens, and subsp. tephrodes) as well as two new morphotypes of H. niveus recently discovered in extreme drought and dune habitats in Baja California, Mexico. We measured 50 plants growing in a common garden for 27 morphological traits and conducted principal component analysis to assess patterns of phenotypic variation. Genome size of each accession was determined using flow cytometry. Pollen viability of first generation hybrids between taxa was tested to infer the strength of intrinsic postzygotic reproductive barriers. Finally, genotyping-by-sequencing data were used to investigate the genetic structure and phylogenetic relationships among the previously described subspecies and new morphotypes. The intraspecific genetic and phenotypic divergence of H. niveus populations closely tracks their geographical distribution. Subspecies niveus is phenotypically, genetically, and reproductively distinct from the other two subspecies and has a larger genome. Therefore, H. niveus as currently circumscribed should be considered to contain two distinct species, H. niveus and H. tephrodes. ABBA-BABA tests revealed substantial introgression between subsp. canescens and its sympatric congener H. petiolaris, which might contribute to their morphological similarities. The two new morphotypes collected in Mexico represent local ecotypes of subsp. niveus that occur in extreme drought and dune environments. Mantel tests showed a strong positive correlation between genetic and geographic distances. We conclude that geographic isolation is primarily responsible for intraspecific genomic divergence within H. niveus, while patterns of phenotypic variation appear to have been shaped by ecological selection and interspecific introgression.

Cochylis hospes (Lepidoptera: Tortricidae) damage to male lines varies significantly and inbred susceptibility predicts damage to hybrids

AbstractLarvae of Cochylis hospes (Walsingham) (Lepidoptera: Tortricidae) (banded sunflower moth) are a primary source of insect damage to seeds of cultivated sunflower, Helianthus annuus Linnaeus (Asteraceae), in North America. Field trials were used to evaluate seed damage under natural infestations for panels of publicly released male lines, publicly derived hybrids (females crossed to one common male parent), and commercial hybrids over a total of four years. For trials in 2013–2014 including 17 male lines, seed damage ranged from 3% to 19%. The least damaged male, RHA 266, was statistically similar to one other male, RHA 455. Three commercial hybrids used as checks also received very little seed damage (&lt; 5%). In trials during 2016–2017, hybrids created by pollinating 15 different female lines with RHA 266 showed 4–14% damage. Data from female parents explained about 28% of variation in seed damage for the hybrids. Results confirm cultivated sunflower has greater variation in susceptibility to C. hospes than previously believed, and that seed damage to inbred lines provides some predictive power for hybrids. Though breeding for resistance to C. hospes seems possible, it may be too labour-intensive without relating resistance to more easily measurable traits or genetic markers.

Assessment of Genetic Diversity of Cultivated Sunflower in Terms of Oil Content, Fatty Acid Compositions and Seed Traits

Abstract Sunflower (Helianthus annuus L.) cultivated accessions contains useful genes encoding different phenotypic characteristic through which the origin of sunflower oil could be hypothesized. Those genes could be later used for future breeding programs for providing better quality sunflower oil. The objective of the current study is to discriminate genetic diversity of cultivated sunflower seeds collection through the statistical methods such as PCA (principal component analysis) and Pearson correlation analysis for two characters; seed oil content and fatty acid composition. Materials and methods: In the present study, the genetic diversity of 107 cultivated accessions of Helianthus annuus L. was studied for fatty acid composition and oil content. Pearson correlation and Principal Component Analysis (PCA) were used to determine the correlation between the studied parameters. A dendrogram using Ward’s method and the squared Euclidean distance coefficient was produced. The results showed that the average seed oil content in the accessions was 29.51 % with a profile of 7.23 % palmitic acid (PAL), 5.04 % stearic acid (STE), 36.85 % oleic acid (OLE) and 50.85 % linoleic acid (LIN). The highest oil content was found in accession Hopi Dye (43.66 %). High levels of OLE were observed in the Csehszlovakiai “B” (60.14 %) and Vk-47 (55.73 %) accessions. On the other hand, Fuksinka 10 and Georgia accessions had the lowest mean PAL values (4.98 %) and STE (1.81 %), respectively. Palmitoleic acid (PALM) was identified in 29 accessions and linolenic acid (LIL) in 32 accessions, the highest in Gonondu (0.86 %) and Oleisty Borovskil (0.76 %), respectively. A significant negative relationship between OLE, STE and saturated fatty acids (SFA) with oil content was observed. The Pearson correlation of unsaturated fatty acids to saturated fatty acids ratio (UFA/SFA ratio) with oil content was positive and significant. In the PCA analysis, four major principal components (PCs) were identified, accounting for 87.19 % of the total variations. In PC1, PAL and STE (with positive coefficients) and UFA/SFA ratio (with negative coefficients), had the highest loadings, which determined 41.33 % of the total variations. In PC 2, OLE (with negative coefficient) and LIN (with positive coefficient), had the highest values. According to the dendrogram of the accessions, they were grouped into seven distinct clusters and the accessions in clusters 4 and 7 contained high UFA and low SFA values. The findings of this study showed that there is a significant genetic diversity among the accessions, which can be used to maximize heterosis in sunflower breeding programs.

Concentrations of sunflower phenolics appear insufficient to explain resistance to floret- and seed-feeding caterpillars

Cultivated sunflowers, Helianthus annuus L., show significant variation in susceptibility to insect pests, though specific mechanisms of resistance are not clear. Plant secondary compounds, including phenolics, are often associated with resistance to insects and pathogens. Because several phenolics are present in sunflower florets, wild sunflowers and cultivated inbred lines were sampled to document natural variation in free phenolics and evaluate their potential effects on floret-feeding pests. Four di-O-caffeoylquinic acid isomers were the largest contributors to total phenolic content of disc florets. When identified phenolics were combined with unidentified flavonoid glycosides, total phenolic concentration in inbred lines varied fourfold (≈ 18–72 mg/g), and was significantly greater than that in wild sunflowers. Two lab assays with 50 or 100 mg/g chlorogenic acid showed inconsistent reductions in mass or increases in mortality of sunflower moth (Homoeosoma electellum Hulst) larvae after 9 days, and tests using floret tissue with low or high levels of total phenolics did not show an effect of tissue type on H. electellum development. Tests for correlation between total phenolics and field data on susceptibility of sunflowers to another floret-feeding pest, banded sunflower moth (Cochylis hospes Walsingham), did not show any significant association. Cumulatively, results suggest there may be minor effects of phenolic compounds on floret-feeding insects, but these alone are insufficient for plant defense. However, variation in concentration of phenolic compounds may remain valuable, both as a component of plant defense and a source of oxidative stability in sunflower oil.