Pest Resistance Traits Research Articles

Assessment of Balkan Pepper (Capsicum annuum L.) Accessions for Agronomic, Fruit Quality, and Pest Resistance Traits

To maintain the continuous genetic variation and increase the genetic gain, appreciable germplasm diversity and its comprehensive characterization is necessary to further utilize gene sources for pre-breeding. The diversity of pepper forms, cultivation traditions and diverse fruit usages are typical for Balkan countries. Considering this rich diversity, 21 pepper accessions from the Balkan region were evaluated for morphological, biochemical, and insect resistance traits during 2018 and 2019 at Maritsa Vegetable Crops Research Institute, Plovdiv, Bulgaria. Among the studied accessions, the highest productivity was observed in pumpkin shape K1115 and kapia type K1081 accessions, with 0.74 kg and 0.70 kg per plant, respectively. Concerning fruit quality, the highest total polyphenols and ferric reducing antioxidant power (FRAP) were observed in pumpkin shape K712 (203.44 mg GAE/100 g FW) and K1103A (11.49 µmol Fe2+/g FW) accessions, respectively. Concerning insect resistance, 38% of studied accessions showed no infestation of green peach aphid. The kapia type K697 accession was seen as the most reliable resistance source, as it was not infested by aphids and had the least thrips (20% on plants) and cotton bollworm (6.67% on plants and 8.34% on fruit) damage. Based on examined traits, accessions were identified for enhanced fruit quality and promising insect resistance and have been included in further pre-breeding efforts.

Asexual Epichloë Fungi—Obligate Mutualists

Asexual Epichloë are obligate fungal mutualists that form symbiosis with many temperate grass species, providing several advantages to the host. These advantages include protection against vertebrate and invertebrate herbivores (i.e., grazing livestock and invertebrate pests, respectively), improved resistance to phytopathogens, increased adaptation to drought stress, nutrient deficiency, and heavy metal-containing soils. Selected Epichloë strains are utilised in agriculture mainly for their pest resistance traits, which are moderated via the production of Epichloë-derived secondary metabolites. For pastoral agriculture, the use of these endophyte infected grasses requires the balancing of protection against insect pests with reduced impacts on animal health and welfare.

Genetic structure of Malus sylvestris and potential link with preference/performance by the rosy apple aphid pest Dysaphis plantaginea

The European crabapple Malus sylvestris, a crop wild relative of Malus domestica, is a major contributor to the cultivated apple genome and represents a potential source of interesting alleles or genes, particularly pest resistance traits. An original approach was used to explore the trophic interaction between M. sylvestris populations and its pest, the rosy apple aphid (Dysaphis plantaginea). Using 13 microsatellite markers, population genetic structure and level of crop-to-wild introgressions were inferred between M. sylvestris seedlings from three sites in Europe (Denmark, France, Romania), and M. domestica seedlings. Genetically characterized plants were also used to analyze aphid feeding behavior and fitness parameters. First, aphids submitted to two genetically close M. sylvestris populations (the Danish and French) exhibited similar behavioral parameters, suggesting similar patterns of resistance in these host plants. Second, the Romanian M. sylvestris population was most closely genetically related to M. domestica. Although the two plant genetic backgrounds were significantly differentiated, they showed comparable levels of sensitivity to D. plantaginea infestation. Third, aphid fitness parameters were not significantly impacted by the host plant’s genetic background. Finally, crop-to-wild introgression seemed to significantly drive resistance to D. plantaginea independent of host plant population genetic structure, with hybrids being less suitable hosts.

Phenotypic diversity and population structure of Ethiopian barley (Hordeum vulgare L.) landrace collections

Landraces play a key role in crop breeding by providing beneficial trait for improvement of related crops and their genetic diversity studies are very important for breeding program and identification of parental lines. In this study, 585 barley (Hordeum vulgare L.) landraces collected from 13 agro-ecological zones of Ethiopia were evaluated along with 10 cultivars for their phenotypic diversity and population structure in relation to agronomic traits, resistance to major diseases and barley shoot fly. Data on 22 agronomic traits, three major diseases and barley shoot fly resistance-related traits were recorded. Univariate and multivariate approaches such as principal component and cluster analyses were applied to assess the genetic diversity and population structure. The analysis of variance indicated significant genotypic main, accessions x year and accession x environment interaction effects for almost all the traits evaluated. However, the accessions x environment interactions were mainly due to changes in magnitude rather than crossover types of interactions. The diversity analysis indicated that the population was highly structured according to kernel row-type, region (geographic) origin and altitude classes. Since the population is highly structured, appropriate statistical models will be needed when this population is used for association mapping studies. Eight principal components (PCs) in principal component analysis (PCA) accounted for the variation of 83.01%. The most related traits were included in the same PC, implying that results from PCA could give clues as to the relationship among traits. Though variability existed within and among clusters, useful germplasm clustered together. These materials are important sources of germplasm for the improvement of agronomic, disease and insect pest resistance traits. Keywords: Barley, diseases, genetic diversity, landraces, multivariate, shoot fly

Cotton extrafloral nectaries as indirect defence against insect pests

Knowledge about indirect defences that mediate the ecological interactions between plants and their beneficial and harmful insects are needed to better incorporate pest resistance traits in breeding programs. “Top-down” pest control by natural enemies has not been considered in most plant breeding strategies and, in many cases, beneficial interactions of crops with the third trophic level have been reduced through breeding processes. Extrafloral nectaries (EFNs) are plant structures that provide indirect defences to plants through nectar rewards attracting arthropods that may act as predators of pests. Recent studies have demonstrated that EFNs may play an important role in herbivore suppression in agricultural systems. The main objectives of this study were to quantify the leaf extrafloral nectar production of cotton plants, to identify natural enemies of crop pests visiting these EFNs, and to assess the biological control and occurrence of various cotton pests. To address these objectives, we performed both greenhouse and field experiments in which we compared three wild varieties of cotton plants with EFNs, two cultivated varieties with EFNs and two nectariless varieties. Results showed that wild cotton varieties produced greater quantity of nectar per leaf than cultivated varieties. In addition, wild varieties bearing EFNs enhanced the diversity of natural enemies (especially ants) which could, in turn, increase biological control under certain conditions. However, the association between the community of insects visiting EFNs and pest suppression was not clear and depended on the pest species. Indirect defences associated to EFN need to be better explored to enhance selection of pest-resistant cotton cultivars.

Genetic variation in resistance of Norway spruce seedlings to damage by the pine weevil Hylobius abietis

Regeneration of northern conifer forests is commonly performed by reforestation with genetically improved materials obtained from long-term breeding programs focused on productivity and timber quality. Sanitary threats can, however, compromise the realization of the expected genetic gain. Including pest resistance traits in the breeding programs may contribute to a sustainable protection. Here we quantified the variation in different components of resistance of Norway spruce to its main pest, the pine weevil Hylobius abietis. We followed insect damage in two large progeny trials (52 open-pollinated families with 100–200 individuals per family and trial) naturally infested by the pine weevil. Pine weevils damaged between 17 and 48% of the planted seedlings depending on the trial and year, and mortality due to weevil damage was up to 11.4%. The results indicate significant genetic variation in resistance to the pine weevil, and importantly, the variation was highly consistent across trials irrespective of contrasting incidence levels. Individual heritability estimates for the different components of seedling resistance were consistently low, but family heritabilities were moderate (0.53 to 0.81). While forward selections and breeding for higher resistance seem not feasible, backwards selections of the best parent trees emerge as a putative alternative to reduce weevil damage. A positive genetic correlation between early growth potential and probability of being attacked by the weevil was also observed, but the relationship was weak and appeared only in one of the trials. Overall, results presented here open the door to a new attractive way for reducing damage caused by this harmful pest.

High-carotenoid maize: development of plant biotechnology prototypes for human and animal health and nutrition

Carolight® is a transgenic maize variety that accumulates extraordinary levels of carotenoids, including those with vitamin A activity. The development of Carolight® maize involved the technical implementation of a novel combinatorial transformation method, followed by rigorous testing for transgene expression and the accumulation of different carotenoid molecules. Carolight® was envisaged as a way to improve the nutritional health of human populations that cannot access a diverse diet, but this ultimate humanitarian application can only be achieved after extensive testing for safety, agronomic performance and nutritional sufficiency. In this article, we chart the history of Carolight® maize focusing on its development, extensive field testing for agronomic performance and resistance to pests and pathogens, and feeding trials to analyze its impact on farm animals (and their meat/dairy products) as well as animal models of human diseases. We also describe more advanced versions of Carolight® endowed with pest-resistance traits, and other carotenoid-enhanced maize varieties originating from the same series of initial transformation experiments. Finally we discuss the further steps required before Carolight® can fulfil its humanitarian objectives, including the intellectual property and regulatory constraints that lie in its path.

Identification of Loci Underlying Seed Yield in Recombinant Inbred and Near Isogeneic Soybean Lines Derived from Flyer by Hartwig

Two major determinants of soybean [Glycine max (L.) Merr.] seed yield were resistances to the soybean cyst nematode (SCN) and sudden death syndrome (SDS). Two loci were identified rhg1/Rfs2 and rhg3/rfs5 (for resistance to SCN, Heterodera glycines (I.) HG Type 1.3- (race 14), HG Type 0 (race 3) and SDS caused by Fusarium virguliforme (Roy & Rupe)). The aim of this study was to identify quantitative trait loci (QTL) underlying seed yield. Used were 142 microsatellite markers and the recombinant inbred line population (RIL) ‘Flyer’ × ‘Hartwig’ (F × H; n=92). Flyer (F) was high yielding but SCN and SDS susceptible. Hartwig (H) was lower yielding but resistant to all SCN Hg Types and SDS. Four regions on 3 chromosomes were associated with seed yield. The first region on chromosome 9 (Gm9, qYld09.1), identified by the microsatellite marker Satt539-Satt242 (LOD 2.9, 13% variation) derived the beneficial allele from Hartwig (F allele 2.76 ± 0.06 Mg/Ha; H allele 2.98 ± 0.03 Mg/ha). The second region on Gm9 (qYld09.2) between Satt337 and Satt326 spanned 1.4 cM (LOD of 5.31, 20.2% variation) and the beneficial allele derived from Flyer (0.22 Mg/ha F allele 2.98 ± 0.03, H allele 2.77 ± 0.04 Mg/Ha). The third and fourth QTL were identified in genetic linkage groups D2 (qYld19.1) and G (qYld18.1) in regions previously associated with resistance to SCN. The region encompassing rhg1/Rfs2 on Gm18 between the microsatellite marker TMD1 and Satt610 spanned 15.5 cM (LOD 3.05, 15.8 % variation, F allele 2.37 ± 0.035; H allele 2.91 ± 0.058 Mg/Ha). The region on linkage group D2 between Satt514 and Satt488 spanned 32.6 cM (LOD 2.57, Kas13.3% variation, F allele 2.79 ± 0.049; H allele 3.1 ± 0.043 Mg/Ha). The QTL detected will allow marker assisted selection to stack seed yield, with pest resistance traits (rhg1/Rfs2/qYld18.1; H/H/H allele) and recombinant loci (Rhg5/Rfs2/qYld19.1; H/F/H alleles).

Gene technology in agriculture, environment and biopharming: beyond Bt-rice and building better breeding budgets for crops

Applications of gene technology in agriculture, the environment and human health fields are reviewed. This case study of the intricate historical details of the development of Bt crops like cotton and rice unveils essential elements of productive funding schemes and effective multinational collaborations. Gene technology applied to pest resistance traits in global cotton is analyzed using nation-specific data from India to demonstrate ‘ricochet’ results: Regulatory approval for one crop catalyzes an ‘Enhancer Effect’ for promoting more research funding and more competitive results for other crops-in-waiting, namely rice. Just as cotton commerce promoted philanthropy in unpredictable situations like the Kreenholm dynasty of Ludwig Knoop, research budgets for pesticide and biocide technology have yielded intended effects, but several surprising unintended effects as well. Finally, the case is made for greater control of gene flow and identity preserve issues in plant biotechnology research by invoking Appellation d’Origine Controlee for Bt genes.

Flavor Profiles of Wild Species-Derived Peanut Breeding Lines

Abstract Several diploid wild species of the genus Arachis L. have been used as sources of resistance to common diseases of cultivated peanut (Arachis hypogaea L.). Because flavor is among the most important quality attributes for commercial acceptance of roasted peanuts, sensory attributes of interspecific hybrid derived breeding lines were evaluated to determine if transfer of disease resistance from wild species is associated with concomitant changes in flavor. Sixteen interspecific hybrid derivatives with five diploid species in their ancestries and the commercial flavor standard, NC 7 were evaluated for sensory quality. Significant variation among entries was found for the roasted peanut, sweet, and bitter sensory attributes, but not for the overall contrast between NC 7 and the wild species-derived breeding lines. The variation was either between two groups of wild species-derived breeding lines or within one or both groups. Introduction of disease and pest resistance traits from Arachis species did not result in degradation or improvement of the flavor profile. This suggests that flavor of wild species-derived germplasm will not prevent its use either as parents in peanut breeding programs or as cultivars.

Pest Resistance Traits Controlled by Quantitative Loci and Molecular Breeding Strategies in Tuber-bearing Solanum.

Pest Resistance Traits Controlled by Quantitative Loci and Molecular Breeding Strategies in Tuber-bearing Solanum.

Selection for Monogenic Pest Resistance Traits with Coupling‐ and Repulsion‐Phase RAPD Markers

The random amplified polymorphic DNA (RAPD) assay has recently provided a marker system that may be useful for indirect selection and pyramiding of monogenic pest resistance traits in crop species. Our objective was to investigate the efficiency of marker‐assisted selection with RAPD markers linked in coupling and in repulsion with a single resistance allele. Common bean (Phaseolus vulgaris L.) near‐isogenic lines differing for the recessive bean common mosaic virus (BCMV) resistance allele bc‐3 were screened to identify linked RAPD markers. Two cosegregating RAPD markers were identified and scored across an F2 population of 103 individuals segregating for the bc‐3 allele. One RAPD marker was linked in coupling (1.9. ± 1.4 cM) and one in repulsion (7.1 ± 2.6 cM) with the bc‐3 allele. Categorization of the bc‐3 genotypes in the F2 population revealed that selection against the repulsion‐phase RAPD, as opposed to selection for the coupling‐phase RAPD, provided a greater proportion of homozygous resistant (81.8 versus 26.3%) selections, and a lower proportion of both segregating (18.2 versus 72.5%) and homozygous susceptible (0.0 versus 1.2%) selections. Selection of individuals based on the phenotype of both RAPD markers (i.e., the plus form of the coupling‐phase RAPD and simultaneous with the minus form of the repulsion‐phase RAPD) was identical to selection based solely on the repulsion‐phase RAPD alone. The selection results obtained in our case study were consistent with the theoretical expectations, and both demonstrated that repulsion‐phase linkages provided greater selection efficiency than coupling‐phase linkages, even when the former have greater linkage distances from the pest resistance allele. Because repulsion‐phase RAPD markers are more useful in marker‐assisted selection for monogenic pest resistance traits, researchers will want to design their screening experiments in ways that will optimize the discovery of these.

Reaction of Two Maize Synthetics to Anthracnose Stalk Rot and Northern Corn Leaf Blight Following Recurrent Selection for Resistance to Diplodia Stalk Rot and European Corn Borer

Reaction of Two Maize Synthetics to Anthracnose Stalk Rot and Northern Corn Leaf Blight Following Recurrent Selection for Resistance to Diplodia Stalk Rot and European Corn Borer

Cytogenetics of a Trispecific Hybrid (<i>N. benthamiana×N. glutinosa)×N. tabacum</i> and its Allopolyploids in Genus <i>Nicotiana</i>

The study pertains to the cytogenetics of a newly synthesised trispecific hybrid N. benthamiana (n=19)×N. glutinosa (n=12)×N. tabacum and its allopolyploids. The F1 (n=55) plants were phenotypically identical and by colchicine treatment 2 partial and 2 complete allopolyploids were obtained. The study show that it is not possible to maintain the stability in these allopolyploids, when chromosome number is increased beyond certain limit. However they are useful to understand certain fundamental aspects of evolution. Recently the trispecific hybrids have gained additional importance as they offer an excellent tool to combine two non-crossable species through a ‘bridge’, thus makeing it possible to transfer disease or pest resistance traits from wild species to the species of commerce, N. tabacum.

Effects of Low and High Saponin Selection in Alfalfa on Agronomic and Pest Resistance Traits and the Interrelationship of these Traits1

Six alfalfa (Medicago sativa L.) cultivars, ‘DuPuits,’ ‘Ladak,’ ‘Lahontan,’ ‘Ranger,’ ‘Uinta,’ and ‘Vernal’ were selected for low and high saponin concentration and tested at various locations for seven agronomic traits and resistance to six diseases, five insects, and two nematodes. Although the selection for saponin concentration was effective, none of the agronomic traits (yield, foliage color, frost damage, lodging, digestibility, fraction I protein, and soluble protein) was consistently affected by the selection. High saponin concentration retarded the in vitro growth of southern blight (Sclerotium rolfsii Sacc.) but had very little effect on any of the other disease organisms studied: anthracnose (Colletrotrichum trifolii Bain); bacterial wilt (Corynebacterium insidiosum (Mc‐Cull.) H. L. Jens.); common leafspot (Pseudopeziza medicaginis (Lib.) Sacc.); downy mildew (Peronospora trifoliorum deBary); and phytophthora root rot (Phytoph‐thora megasperma Drechs.). High saponin concentration was also correlated with resistance to pea aphids (Acyr‐thosiphon pisum (Harris)) but had no appreciable effect on chalcids (Bruchophagus roddi (Gussakovsky)), clover root curculio (Sitona hispidulus (F.)), spotted alfalfa aphid (Therioaphis maculata (Buckton)), alfalfa weevil (Hypera postica (Gyllenhal)), northern root‐knot nematode (Meloildogyne hapla Chitwood), or stem nematode (Ditylenchus dipsaci (Kühn) Filip.). Significant correlations among the pest resistance traits suggest the possibility of linkages or pleiotropic factors.