Resistance Of Breeding Lines Research Articles

A reproducible methodology for absolute viral quantification and viability determination in mechanical inoculations of wheat streak mosaic virus

Wheat streak mosaic virus (WSMV) is a common wheat virus causing economic losses to production in the Great Plains of North America. Reproducible inoculation of WSMV by mechanical methods is essential to evaluate the resistance in breeding lines and relies on successful inoculation and infectivity of the virus particles. We used reverse transcription-quantitative PCR (RT-qPCR) for absolute quantification of viral genome copy numbers in both WSMV inoculum and in infected wheat leaves. A time-course study was designed to determine the viability of WSMV in inoculum over time as well as the copy number related to the phenotypic rating scale. In the phosphate inoculation buffer, WSMV was stable with average viral genome copy number 1.86 × 106 ± 4.85 × 105. Plants inoculated with this inoculation buffer using finger rub mechanical inoculation contained WSMV genome copy numbers in the infected leaves ranging between 2.66 × 104 and 4.69 × 106 at 21 to 28 days post-inoculation. Viral copy numbers were statistically similar between leaves inoculated immediately and those inoculated at later time points. There was a weak linear relationship between phenotypic rating score and copy number in infected leaves with the linear model explaining 40% of the variability (R2 = 0.40) indicating the difficulty in disease assessment based solely on phenotypic symptoms. This work describes an accurate methodology to quantify virus concentration in the inoculum and infected plants, as well as emphasizes the demand for absolute measurement of virus load to validate the subjective assessment for unbiased viral disease assessment.

Development of Pea Breeding Lines with Resistance to Orobanche crenata Derived from Pea Landraces and Wild Pisum spp.

Pea (Pisum sativum) is an important grain legume worldwide whose cultivation is severely constrained by the root parasitic weed crenate broomrape (Orobanche crenata), which is widespread in the Mediterranean Basin and Middle East. No resistance is available in commercialized cultivars but some levels of incomplete resistance has been reported in pea landraces and Pisum spp. relatives. In this paper we report the development of a number of advanced pea breeding lines with resistance derived from wide crosses with resistant P. fulvum, P. sativum ssp. elatius, P. sativum ssp. syriacum, and with pea landraces, and critically discuss current progress and future perspectives on pea breeding for broomrape resistance. Resistance of breeding lines was confirmed over five field trials, showing markedly reduced broomrape over ground emergence, and in rhizotron experiments, showing either reduced tubercle formation or, in some of the lines, also hampered tubercle development that might grow slower or even become necrotic and die. Breeding lines performed well agronomically, having similar or mostly higher yields than the parental pea cv. Messire in environments with high broomrape incidence.

A Turnip Mosaic Virus Determinant of Systemic Necrosis in Nicotiana benthamiana and a Novel Resistance-Breaking Determinant in Chinese Cabbage Identified from Chimeric Infectious Clones.

Infectious clones of Korean turnip mosaic virus (TuMV) isolates KIH1 and HJY1 share 88.1% genomic nucleotides and 96.4% polyprotein amino acid identity, and they induce systemic necrosis or mild mosaic, respectively, in Nicotiana benthamiana. Chimeric constructs between these isolates exchanged the 5', central, and 3' domains of KIH1 (K) and HJY1 (H), where the order of the letters indicates the origin of these domains. KIH1 and chimeras KHH and KKH induced systemic necrosis, whereas HJY1 and chimeras HHK, HKK, and HKH induced mild symptoms, indicating the determinant of necrosis to be within the 5' 3.9 kb of KIH1; amino acid identities of the included P1, Helper component protease, P3, 6K1, and cylindrical inclusion N-terminal domain were 90.06, 98.91, 93.80, 100, and 100%, respectively. Expression of P1 or P3 from a potato virus X vector yielded symptom differences only between P3 of KIH1 and HJY1, implicating a role for P3 in necrosis in N. benthamiana. Chimera KKH infected Brassica rapa var. pekinensis 'Norang', which was resistant to both KIH1 and HJY1, indicating that two separate TuMV determinants are required to overcome the resistance. Ability of diverse TuMV isolates, chimeras, and recombinants to overcome resistance in breeding lines may allow identification of novel resistance genes.

Resequencing of Common Bean Identifies Regions of Inter-Gene Pool Introgression and Provides Comprehensive Resources for Molecular Breeding.

Common bean ( L.) is the most important grain legume for human consumption and is a major nutrition source in the tropics. Because bean production is reduced by both abiotic and biotic constraints, current breeding efforts are focused on the development of improved varieties with tolerance to these stresses. We characterized materials from different breeding programs spanning three continents to understand their sequence diversity and advance the development of molecular breeding tools. For this, 37 varieties belonging to , (A. Gray), and L. were sequenced by whole-genome sequencing, identifying more than 40 million genomic variants. Evaluation of nuclear DNA content and analysis of copy number variation revealed important differences in genomic content not only between and the two other domesticated species, but also within , affecting hundreds of protein-coding genomic regions. A large number of inter-gene pool introgressions were identified. Furthermore, interspecific introgressions for disease resistance in breeding lines were mapped. Evaluation of newly developed single nucleotide polymorphism markers within previously discovered quantitative trait loci for common bacterial blight and angular leaf spot provides improved specificity to tag sources of resistance to these diseases. We expect that this dataset will provide a deeper molecular understanding of breeding germplasm and deliver molecular tools for germplasm development, aiming to increase the efficiency of bean breeding programs.

Identification and mapping of net form of net blotch resistance in South African barley

Net form of net blotch (NFNB) caused by the fungus Pyrenophora teres f. teres is an economically important foliar disease of barley (Hordeum vulgare) in southern and eastern Africa. Little attention has been given to disease resistance breeding, and knowledge about the presence of NFNB resistance in breeding lines is limited. Deploying resistance into varieties used in this region is important for future control of the disease. We have identified NFNB disease resistance in existing South African breeders’ lines and have mapped the resistance in line UVC8. Six different trials, three conducted in South Africa and another three in Australia, were used to identify resistance QTL. A major QTL was identified on chromosome 6H having a LOD score of 40.5 and 55% of the phenotypic variance explained. Kompetitive Allele Specific PCR (KASP™) markers were designed for this QTL region. These and microsatellite markers can now be used to routinely select for NFNB resistance.

Genome-wide association mapping of preharvest sprouting resistance in a diversity panel of European winter wheats.

Global wheat production will benefit from cultivars showing genetic resistance to preharvest sprouting (PHS). Working on PHS resistance is still challenging due to the lack of simple protocols for the provocation of symptoms for appropriate trait differentiation under highly variable environmental conditions. Therefore, the availability of molecular markers for enhancing PHS resistance in breeding lines is of utmost importance. Genome-wide association mapping was performed to unravel the genetics of PHS resistance in a diversity panel of 124 winter wheat genotypes using both random and targeted marker locus approaches. Data for grain germination tests, spike wetting treatments, and field sprouting damage measurements of grains were collected in 11, 12, and four environments, respectively. Twenty-two quantitative trait loci (QTL) linked with 40 markers were detected for the three traits commonly used for assessing the PHS resistance of cultivars. All but five QTL on chromosomes 1B, 1D (two QTL), 3D, and 5D showed locations similar to previous studies, including prominent QTL on chromosomes 2BS, 3AS, and 4AL. The highest retrieval rate across environments was found for QTL on chromosomes 1D, 2BS, 3D, 4AL, and 7B. The study identified genomic signatures useful for marker-assisted improvement of PHS resistance not only in European breeding programs, but of global significance.

Leaf rust resistance of bread wheat (Triticum aestivum L.) lines derived from interspecific crosses

Wheat lines which possess resistance to leaf rust were developed from the cultivar crosses between bread wheat (Triticum aestivum L.) and wild cereal species: jointed goatgrass (Aegilops cylindrica Host), tausch’s goatgrass (Aegilops tauschii Coss.), wild emmer (Triticum dicoccoides Koern.) and synthetic species Triticum erebuni Gandil. Resistance of breeding lines was examined at the seedling stage of wheat plants after artificial inoculation. Resistance genes Lr21, Lr22a, Lr24 (T1BL.1BS-3Ae#1L), Lr32, Lr34, Lr39, Lr42, Lr53 and T1AL.1RS were identified by a molecular analysis using sequence-tagged sites (STS) and simple sequence repeats (SSR) markers. Comparison of data of phytopathological evaluation and molecular-genetic analysis of breeding lines revealed that leaf rust resistance was conferred by a combination of several genes. The combination of genes Lr24+Lr34+T1AL.1RS conferred resistance, Lr24+Lr34+Lr21, T1AL.1RS+Lr24 and Lr21+T1AL.1RS+Lr24 conferred resistance and moderate resistance.

Patates Y Virüsü (Potato Virus Y = PVY)’ne dayanıklı sivri biber hatlarının geliştirilmesi

Pepper (Capsicum annuum L.), is one of the most important vegetable species produced both in the world and in Turkey. Turkey is in third place in pepper production in the world. There are many viruses affecting and limiting pepper production. Potato Y virus (PVY), a member of the genus potyvirus, is one of the most common viruses infecting pepper crops. Improving resistant pepper varieties against the disease is more advantageous and easy way to control disease in production area. There are 4 races such as PVY0, PVY1 and PVY1-2 in the world. The dominant Pvr4 resistance gene in wild type SCM 334 pepper confers a complete resistance to the three pathotypes of potato virus. In this study, resistant genotype SCM 334 and susceptible long pepper inbred line were crossed to improve resistance in breeding lines. To eliminate the undesirable characteristics of the resistant genotypes, resistant line was backcrossed three times with susceptible genotypes. Mechanical inoculation and molecular methods were used to determine the reaction of backcross progenies to the disease. The dominant CAPS markers were used to determine resistant and susceptible plants and results from the mechanical inoculation method were verified with the CAPS marker. This study is a part of “Improvement of F1 Hybrid Vegetable Varieties and Qualified Lines in Turkey” basic project and financed by Scientific and Technological Research Council of Turkey (TUBITAK-KAMAG 109G029).

Methods for characterization of preharvest sprouting resistance in a wheat breeding program

Preharvest sprouting (PHS) can be a serious problem in western Canada resulting in economically important yield and grade losses for wheat producers. Improved PHS resistance is an important breeding objective and wheat breeders require effective and reliable methods to select for PHS resistance. The objective of this study was to evaluate whether differences exist between field and artificial weathering in the evaluation of PHS resistance in breeding lines and to determine whether sprouting scores are a good estimator of PHS resistance when compared to Hagberg falling numbers. Results suggest that both field and artificial weathering can be effectively used to screen for PHS resistance in wheat breeding lines. Although in this study, field weathering resulted in greater sprouting damage than artificial weathering, the ability to control conditions may make artificial weathering the more reliable test for PHS resistance in a breeding program. Mean sprouting scores greater than 7.5 consistently identified lines with low PHS resistance; hence, sprouting scores can be used to discard the most sprouting susceptible lines. However, falling numbers appear to be more reliable to evaluate the PHS resistance of advanced lines.

Resistance of leaves of Brassica species to Leptosphaeria maculans

Under controlled conditions, the range of responses in Brassica napusssp. oleiferaand its two putative parents, B. rapa and B. oleracea, were tested by inoculating leaves with a mixture of eight isolates or two separate isolates of Leptosphaeria maculons. Infection resulted in a hypersensitive reaction, or localized lesions of various sizes, or systemic colonization of the lamina and petiole. Although not apparently associated with hypersensitive resistance, levels of alkenyl glucosinolates in leaves were inversely correlated with lesion extension. The value and limitations of these various sources of resistance in breeding lines of B. napus ssp. oleifera are discussed.