Brent S. Hulke

Increased food and ecosystem security via perennial grains

Perennial grains hold promise, especially for marginal landscapes or with limited resources where annual versions struggle. Despite doubling of yields of major grain crops since the 1950s, more than one in seven people suffer from malnutrition (1). Global population is growing; demand for food, especially meat, is increasing; much land most suitable for annual crops is already in use; and production of nonfood goods (e.g., biofuels) increasingly competes with food production for land (2). The best lands have soils at low or moderate risk of degradation under annual grain production but make up only 12.6% of global land area (16.5 million km2) (3). Supporting more than 50% of world population is another 43.7 million km2 of marginal lands (33.5% of global land area), at high risk of degradation under annual grain production but otherwise capable of producing crops (3). Global food security depends on annual grains—cereals, oilseeds, and legumes—planted on almost 70% of croplands, which combined supply a similar portion of human calories (4, 5). Annual grain production, though, often compromises essential ecosystem services, pushing some beyond sustainable boundaries (5). To ensure food and ecosystem security, farmers need more options to produce grains under different, generally less favorable circumstances than those under which increases in food security were achieved this past century. Development of perennial versions of important grain crops could expand options.

A High-Density SNP Map of Sunflower Derived from RAD-Sequencing Facilitating Fine-Mapping of the Rust Resistance Gene R12

A high-resolution genetic map of sunflower was constructed by integrating SNP data from three F2 mapping populations (HA 89/RHA 464, B-line/RHA 464, and CR 29/RHA 468). The consensus map spanned a total length of 1443.84 cM, and consisted of 5,019 SNP markers derived from RAD tag sequencing and 118 publicly available SSR markers distributed in 17 linkage groups, corresponding to the haploid chromosome number of sunflower. The maximum interval between markers in the consensus map is 12.37 cM and the average distance is 0.28 cM between adjacent markers. Despite a few short-distance inversions in marker order, the consensus map showed high levels of collinearity among individual maps with an average Spearmans rank correlation coefficient of 0.972 across the genome. The order of the SSR markers on the consensus map was also in agreement with the order of the individual map and with previously published sunflower maps. Three individual and one consensus maps revealed the uneven distribution of markers across the genome. Additionally, we performed fine mapping and marker validation of the rust resistance gene R12, providing closely linked SNP markers for marker-assisted selection of this gene in sunflower breeding programs. This high resolution consensus map will serve as a valuable tool to the sunflower community for studying marker-trait association of important agronomic traits, marker assisted breeding, map-based gene cloning, and comparative mapping.

Freezing tolerance of selected perennial ryegrass (Lolium perenne L.) accessions and its association with field winterhardiness and turf traits

Many winter stresses affect the ability of a perennial grass to overwinter in cold, temperate climates. Freezing tolerance is one of the major component traits affecting winterhardiness. Although effective freezing tolerance assessment procedures have long been available for perennial ryegrass (Lolium perenne L.), no work has been done to characterize plant collections in the United States that may possess novel variation for freezing tolerance and winterhardiness. In this study, 21 accessions sampled from a larger set of 300 accessions with known winterhardiness and 3 check varieties were subjected to environmentally-controlled, low temperature acclimation, followed by controlled freezing using a programmable laboratory freezer. Eight freezing treatments from −2 to −16°C were used to determine survival across the known spectrum of freezing tolerance in perennial ryegrass. LT50 values were estimated based on whole plant survival, as well as tiller survival at each of the temperature treatments in the evaluation. LT50 values for the accessions and checks ranged from −10.31 to −13.95°C, with 3 accessions possessing significantly greater freezing tolerance than the most freeze-tolerant check, ‘NK200’. LT50 values were well correlated with winterhardiness in St. Paul during the winters of 2004–2005 and 2005–2006. Lower LT50 values in this experiment were associated with greater spring growth following the stressful winter of 2004–2005 and upright growth habit. The lack of negative biological association between freezing tolerance and turf quality components indicates that freezing tolerance testing could be a useful tool in breeding and selection with landrace germplasm.

Identification of resistance to new virulent races of rust in sunflowers and validation of DNA markers in the gene pool.

Sunflower rust, caused by Puccinia helianthi, is a prevalent disease in many countries throughout the world. The U.S. Department of Agriculture (USDA)-Agricultural Research Service, Sunflower Research Unit has released rust resistant breeding materials for several decades. However, constantly coevolving rust populations have formed new virulent races to which current hybrids have little resistance. The objectives of this study were to identify resistance to race 336, the predominant race in North America, and to race 777, the most virulent race currently known, and to validate molecular markers known to be linked to rust resistance genes in the sunflower gene pool. A total of 104 entries, including 66 released USDA inbred lines, 14 USDA interspecific germplasm lines, and 24 foreign germplasms, all developed specifically for rust resistance, were tested for their reaction to races 336 and 777. Only 13 of the 104 entries tested were resistant to both races, whereas another six were resistant only to race 336. The interspecific germplasm line, Rf ANN-1742, was resistant to both races and was identified as a new rust resistance source. A selection of 24 lines including 19 lines resistant to races 777 and/or 336 was screened with DNA markers linked to rust resistance genes R(1), R(2), R(4u), and R(5). The results indicated that the existing resistant lines are diverse in rust resistance genes. Durable genetic resistance through gene pyramiding will be effective for the control of rust.

Resistance in Cultivated Sunflower to the Sunflower Moth (Lepidoptera: Pyralidae)

Abstract A five-year field study evaluated 42 sunflower (Helianthus annuus L.) accessions, 25 breeding lines, and 40 interspecific crosses for resistance to infestation and damage from larval feeding by naturally occurring populations of the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae). Accessions PI 175728 and PI 307946 had less than 3% feeding damage per head in all three years they were tested. Some interspecific crosses showed evidence of resistance; PAR 1673-1 had less than 2% seed damage in 2002 and 2003 and less than 3% in 2005. PRA PRA 1142 sustained less than 3% seed damage and STR 1622-1 had less than 2% seed damage in three years of trials. Breeding lines with potential resistance included 01-4068-2, which had the least amount of seed damage per head in 2002 (<1%) and in 2003 averaged only 2% damage. Line 01-4080-1, with less than 1% damage in 2002 and in 2003, was the least damaged entry in these evaluations. Hybrid ‘894’ was included as a standard check; however, it consistently had among the lowest average seed damage from H. electellum feeding. Our investigation showed the potential for developing resistant genotypes for the sunflower moth to reduce seed feeding injury and to prevent yield losses for sunflower producers. The development of germplasm with host plant resistance would provide another tool in an integrated pest management approach for H. electellum. Additional effort is in progress to use the identified lines to introgress resistance genes into cultivated sunflower through conventional breeding facilitated by marker-assisted selection.

Resistance in Cultivated Sunflower Germplasm to the Red Sunflower Seed Weevil (Coleoptera: Curculionidae) in the Northern Great Plains

Abstract A 5 yr field study evaluated 49 sunflower, Helianthus annuus L., accessions, and 5 interspecific crosses for resistance to infestation by naturally occurring populations of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae). Germplasm with potential sources of resistance to attack was identified. The accession PI 162453 averaged only 8% damaged seed per head in 3 yr of testing and PI 431545 averaged 8% damaged seed per head in 4 yr of trials. The accessions PI 431542 and PI 650375, which were tested for five years, averaged 5% and 10% damaged seed per head, respectively over the study. PI 431542 averaged less than 6% in all but one year of testing. Additional accessions that appeared promising in two consecutive years of trials included PI 195573, PI 219649, PI 250085, and PI 432516. Hybrid 894 consistently had high seed damage from S. fulvus feeding. Results revealed potential for developing resistant genotypes for decreasing seed feeding injury by the red sunflower seed weevil. Research is in progress to introgress resistance genes from the identified lines into cultivated sunflower through conventional breeding facilitated by the use of marker-assisted selection.

Plant–Herbivore and Plant–Pollinator Interactions of the Developing Perennial Oilseed Crop, Silphium integrifolium

Abstract Sampling in Kansas and North Dakota documented the plant–herbivore and plant–pollinator interactions of the developing perennial oilseed crop, Silphium integrifolium Michx. The larva of the tortricid moth, Eucosma giganteana (Riley), was the most damaging floret- and seed-feeding pest in Kansas, with infested heads producing ≈85% (2015) or ≈45% (2016) fewer seeds than apparently undamaged heads. Necrosis of apical meristems caused stunting and delayed bloom in Kansas; though the source of the necrosis is not known, observations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois; Hemiptera: Miridae), in S. integrifolium terminals suggest a possible cause. In North Dakota, E. giganteana larvae were not found, but pupae of Neotephritis finalis (Loew; Diptera: Tephritidae), a minor pest of cultivated sunflower, were common in the heads of S. integrifolium. Bees appeared highly attracted to S. integrifolium, and in all but one observation, bees were seen actively collecting pollen. The most common bees included large apids (Apis mellifera L., Svastra obliqua [Say], Melissodes spp.) and small-bodied halictids (Lasioglossum [Dialictus] spp.). Controlled pollination experiments demonstrated that S. integrifolium is pollinator dependent, due to both mechanical barriers (imperfect florets and protogyny) and genetic self-incompatibility. Subsequent greenhouse tests and AFLP confirmation of putative self-progeny show that a low (<1%) level of self-pollination is possible. If genetic self-incompatibility is eventually reduced through breeding, mechanical barriers would maintain a reliance on bees to move pollen between male and female florets. Collectively, observations on S. integrifolium show that both herbivore and pollinator management are important to maximize seed production.

Using Nectar-Related Traits to Enhance Crop-Pollinator Interactions

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.

Somatic Embryogenesis from Corolla Tubes of Interspecific Amphiploids between Cultivated Sunflower (Helianthus annuus L.) and Its Wild Species

Abstract Somatic embryogenesis in vitro provides an efficient means of plant multiplication, facilitating sunflower improvement and germplasm innovation. In the present study, using interspecific amphiploids (2n=4x=68) between cultivated sunflower and wild perennial Helianthus species as explant donors, somatic embryos were induced directly from the surface of corolla tubes at the late uninucleate or binucleate microspore development stage. Primary somatic embryos (PSEs) were obtained in amphiploids G08/2280 (H. pumilus×P21) and G08/2260 (NMSHA89×H. maximiliani). The PSE induction frequency of G08/2280 on synthesized Medium A and B was 30.27 % and 42.42 %, respectively, while that of G08/2260 was 5.89 % and 12.16 %, respectively. The difference of PSE induction frequency was significant between G08/2280 and G08/2260 (P=0.0058), but was non-significant between induction Medium A and B (P=0.1997). Secondary somatic embryos (SSEs) were rapidly produced from PSEs on subculture Medium 1 with the induction frequency of 100 %. The mean number of SSEs produced from each PSE was 19.2 and 12.2 in G08/2280 and G08/2260 within 30 d of subculture, respectively. Mature SSEs were gradually converted into young shoots on hormone-free subculture Medium 2, with the mean number of small green shoots produced from each PSE of 22.0 and 18.7 in G08/2280 and G08/2260, respectively. Through the additional process of rooting for some shoots without roots on half-strength of MS medium adding 0.25–0.5 mg/l NAA, 0.5 mg–1.0/l IBA, SE-derived shoots without roots gained about 40 % rooting frequency. Regenerated plants acclimated successfully and displayed similar morphological and chromosome number to the amphiploid donors.

Ovipositional Preference and Larval Performance of the Banded Sunflower Moth (Lepidoptera: Tortricidae) and Its Larval Parasitoids on Resistant and Susceptible Lines of Sunflower (Asterales: Asteraceae)

ABSTRACT Banded sunflower moth, Cochylis hospes Walsingham, is one of the most destructive seed-feeding insect pests of sunflowers, causing significant economic yield losses in the northern Great Plains. In an attempt to understand host-plant resistance mechanisms for this pest, we field-tested, over several years, the effects of seven sunflower accessions, rated as resistant to C. hospes in previous screening trials, and a susceptible control (Par 1673-2), on the ovipositional preference and larval performance of C. hospes and its larval parasitoids. Of the resistant accessions, PI 494859 was the most preferred for oviposition, receiving a significantly greater number of eggs per head than did the susceptible Par 1673-2 in 2 of 3 yr. However, the numbers of larvae, and consequently the rate of seed infestation, found in PI 494859 heads were significantly lower than those in Par 1673-2 heads over all 3 yr. Female moths laid relatively few eggs on accessions PI 170385,291403, and 251902, compared with on Par 1673-2, resulting in lower numbers of larvae per head and lower percentages of seed damaged. No association was observed between the concentrations of two diterpenoid alcohols or two diterpenoid acids in sunflower bracts and the numbers of eggs laid on the heads of the accessions. The number of banded sunflower moth larvae and the proportion of seeds damaged were positively correlated with kaurenoic acid concentrations and negatively correlated with kauranol concentrations. A positive association between resistance to larval feeding and parasitism was found in years 2006 and 2008, with resistant accessions having significantly greater proportions of parasitized larvae than did the susceptible Par 1673-2.