Papers by Wallace Cowling
Molecular Plant-Microbe Interactions, 2008
Programmed cell death, with many of the morphological markers of apoptosis, is increasingly recog... more Programmed cell death, with many of the morphological markers of apoptosis, is increasingly recognized as an important process in plant disease. We have investigated the involvement and potential role of apoptosis during the formation of leaf lesions by the fungus Leptosphaeria maculans on susceptible Brassica napus cv. Westar. There were no signs of host cell damage until 7 to 8 days postinoculation (dpi), when trypan-blue-stained leaf mesophyll cells were first detected. Hyphae were visible in the intercellular spaces of the inoculated area from 5 dpi and were associated with trypan-blue-stained cells at 8 to 9 dpi. Hallmarks of apoptosis, observed coincident with or immediately prior to the formation of leaf lesions at 8 to 10 dpi, included membrane shrinkage of the mesophyll cell cytoplasm, loss of cell to cell contact in mesophyll cells, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling of nuclei in apparently “healthy” tissue immediately adjacent to dea...
We simulated pre-breeding in evolving gene banks – populations of exotic and crop types undergoin... more We simulated pre-breeding in evolving gene banks – populations of exotic and crop types undergoing optimal contribution selection for long-term genetic gain and management of population genetic diversity. The founder population was based on crosses between elite crop varieties and exotic lines of field pea (Pisum sativum) from the primary genepool, and was subjected to 30 cycles of recurrent selection for an economic index composed of four traits with low heritability: black spot resistance, flowering time and stem strength (measured on single plants), and grain yield (measured on whole plots). We compared a small population with low selection pressure, a large population with high selection pressure, and a large population with moderate selection pressure. Single seed descent was compared with S 0-derived recurrent selection. Optimal contribution selection achieved higher index and lower population coancestry than truncation selection, which reached a plateau in index improvement after 40 years in the large population with high selection pressure. With optimal contribution selection, index doubled in 38 years in the small population with low selection pressure and 27–28 years in the large population with moderate selection pressure. Single seed descent increased the rate of improvement in index per cycle but also increased cycle time.
Canadian Journal of Botany, 1998
ABSTRACT Latent infection and tissue colonization by Diaporthe toxica was examined by light, scan... more ABSTRACT Latent infection and tissue colonization by Diaporthe toxica was examined by light, scanning, and transmission electron microscopy in stems, leaves, and petioles of resistant and susceptible narrow-leafed lupins (Lupinus angustifolius). Resistance was observed during the latent phase of the disease as an incompatible reaction between the host and pathogen that appeared to occur after penetration of the cuticle. Conidia were attached firmly to the cuticle by an extracellular substance presumably exuded from the conidia. Conidia penetrated the cuticle directly via an infection peg and formed subcuticular coralloid hyphae. The frequency of subcuticular coralloid hyphae was similar on stems, leaves, and petioles of each line. At 14 days after inoculation, resistant plants had a high frequency of small coralloid hyphae (10-80 µm length). The epidermal cells beneath these small coralloid hyphae appeared necrotic and collapsed with accumulation of polyphenolics and electron-dense substances and a loss of internal organisation in the cytoplasm. Necrosis was occasionally observed in small coralloid hyphae as well. Susceptible plants had a high frequency of large coralloid hyphae (80-400 µm length) in which intrahyphal hyphae were observed, and host epidermal cells beneath large coralloid hyphae appeared normal. Colonization of tissues below the cuticle began immediately after excision of stems from susceptible plants, but was delayed in resistant plants. At 8 days after excision, hyphae had invaded all stem tissues and initiated the formation of pycnidia in susceptible plants, but few hyphae were observed in stems of resistant plants.Key words: Diaporthe toxica, coralloid hyphae, Lupinus angustifolius, resistance.
Australasian Plant Pathology, 1998
Resistance to Diaporthe toxica in 12 lines of narrow-leafed lupin (Lupinus angustifolius) was ass... more Resistance to Diaporthe toxica in 12 lines of narrow-leafed lupin (Lupinus angustifolius) was assessed by a competitive enzyme-linked immunosorbent assay (ELISA). Seedlings were inoculated with the pathogen and after 21 days resistance was assessed by counting latent infection structures in epidermal tissue under the microscope. Infected stem pieces were then incubated for 6 days in moist chambers before treatment with
... Document details. Title Genetic resources in lupins. Authors Buirchell, BJ; Cowling, WA Edito... more ... Document details. Title Genetic resources in lupins. Authors Buirchell, BJ; Cowling, WA Editors Gladstones, JS;Atkins, CA;Hamblin, J. Book Lupins as crop plants: biology, production and utilization. 1998 pp. 41-66 ISBN 0-85199-224-2 Record Number 19991602498. Abstract. ...
New Phytologist, 2016
Adaptation of Lupinus angustifolius (narrow-leafed lupin) to cropping in southern Australian and ... more Adaptation of Lupinus angustifolius (narrow-leafed lupin) to cropping in southern Australian and northern Europe was transformed by a dominant mutation (Ku) that removed vernalization requirement for flowering. The Ku mutation is now widely used in lupin breeding to confer early flowering and maturity. We report here the identity of the Ku mutation. We used a range of genetic, genomic and gene expression approaches to determine whether Flowering Locus T (FT) homologues are associated with the Ku locus. One of four FT homologues present in the narrow-leafed lupin genome, LanFTc1, perfectly co-segregated with the Ku locus in a reference mapping population. Expression of LanFTc1 in the ku (late-flowering) parent was strongly induced by vernalization, in contrast to the Ku (early-flowering) parent, which showed constitutively high LanFTc1 expression. Co-segregation of this expression phenotype with the LanFTc1 genotype indicated that the Ku mutation impairs cis-regulation of LanFTc1. Sequencing of LanFTc1 revealed a 1.4-kb deletion in the promoter region, which was perfectly predictive of vernalization response in 216 wild and domesticated accessions. Linkage disequilibrium rapidly decayed around LanFTc1, suggesting that this deletion caused the loss of vernalization response. This is the first time a legume FTc subclade gene has been implicated in the vernalization response.
Grain from self-pollinating crops contributes more than 60% of annual global calories for human c... more Grain from self-pollinating crops contributes more than 60% of annual global calories for human consumption, and demand is increasing. Grain production in self-pollinating crops is extremely sensitive to the effects of heat and drought, and these stresses are increasing as a result of global climate change. The rate of increase in grain yield of the world’s major self-pollinating crops is not keeping pace with demand and is threatened by global climate change. Heat and drought stress tolerance are complex traits often present in wild or landrace relatives of crop plants. They are difficult to transfer by traditional breeding methods. Genomic selection may help this process, but depends on high genetic diversity with associated molecular marker polymorphism in elite breeding populations. The confluence of human population increase, climate change and genomics necessarily promotes change in the underlying methods of crop breeding. The ‘animal model’ provides best linear unbiased predi...
Current Plant Science and Biotechnology in Agriculture, 2000
BMC plant biology, 2015
Development of synthetic allohexaploid Brassica (2n = AABBCC) would be beneficial for agriculture... more Development of synthetic allohexaploid Brassica (2n = AABBCC) would be beneficial for agriculture, as allelic contributions from three genomes could increase hybrid vigour and broaden adaptation. Microspore culture of a near-allohexaploid hybrid derived from the cross (B. napus × B. carinata) × B. juncea was undertaken in order to assess the frequency and distribution of homologous and homoeologous crossovers in this trigenomic hybrid. SNP and SSR molecular markers were used to detect inheritance of A, B and C genome alleles in microspore-derived (MD) progeny. SNP allele copy number was also assessed. The MD progeny were also compared to progeny derived by self-pollination and open-pollination for fertility (estimated by self-pollinated seed set and pollen viability) and DNA ploidy (measured by flow cytometry). In the trigenomic hybrid, homologous chromosome pairs A(j)-A(n), B(j)-B(c) and C(n)-C(c) had similar meiotic crossover frequencies and segregation to that previously observed...
G3 (Bethesda, Md.), Jan 5, 2015
We used the animal model in S0 (F1) recurrent selection in a self-pollinating crop, for the first... more We used the animal model in S0 (F1) recurrent selection in a self-pollinating crop, for the first time including phenotypic and relationship records from self progeny, in addition to cross progeny, in the pedigree. We tested the model in Pisum sativum, the autogamous annual species used by Mendel to demonstrate the particulate nature of inheritance. Resistance to ascochyta blight (Didymella pinodes complex) in segregating S0 cross progeny was assessed by best linear unbiased prediction over two cycles of selection. Genotypic concurrence across cycles was provided by pure-line ancestors. From cycle 1, 102/959 S0 plants were selected, and their S1 self progeny were intercrossed and selfed to produce 430 S0 and 575 S2 individuals which were evaluated in cycle 2. The analysis was improved by including all genetic relationships (with crossing and selfing in the pedigree), additive and non-additive genetic covariances between cycles, fixed effects (cycles and spatial linear trends) and ot...
Current Plant Science and Biotechnology in Agriculture, 2001
Page 219. Chapter 11 Lupins (Lupinus L.) Wallace Cowling 11.1 Introduction Lupins belong to one o... more Page 219. Chapter 11 Lupins (Lupinus L.) Wallace Cowling 11.1 Introduction Lupins belong to one of the most diverse and widespread of flowering plant genera. Wild species of Lupinus ... Anon, 1983). L. micranthus Guss. is serologically ...
ABSTRACT The Brassica genus provides a versatile model for investigating chromosome interactions ... more ABSTRACT The Brassica genus provides a versatile model for investigating chromosome interactions in polyploids. Six species contain the AA, BB, CC, AABB, AACC and BBCC genome combinations, and these species can be hybridised to produce a variety of genome configurations with comparative ease. We are investigating basic questions about how meiotic chromosome behaviour links to sequence similarity, genome dosage and genome differentiation by molecular karyotyping of interspecific hybrid populations using the recently released Illumina Brassica Infinium 60K SNP chip. Much has been discovered previously by genotyping such populations using hybridisation- or PCR-based markers. However, the arrival of the Infinium 60K SNP chip for the Brassica A and C genomes provides a powerful genotyping tool with unprecedented resolution to detect genome interactions in experimental populations. We show examples of how the Infinium 60K chip is allowing us to understand how polyploidy, speciation and genome differentiation affect chromosome behaviour in Brassica.
ABSTRACT Cultivated Brassica crops B. napus (oilseed rape, 2n = AACC), B. carinata (Ethiopian mus... more ABSTRACT Cultivated Brassica crops B. napus (oilseed rape, 2n = AACC), B. carinata (Ethiopian mustard, 2n = BBCC) and B. juncea (Indian mustard, 2n =AABB) are all allopolyploid, with two genomes each resulting from ancestral hybridisation events between diploid species B. rapa (Chinese cabbage, turnip; 2n =AA), B. nigra (black mustard; 2n = BB) and B. oleracea (cabbage, cauliflower, broccoli; 2n = CC). Although no naturally occurring allohexaploid Brassica exists, combining the three genomes to create 2n = AABBCC plants offers significant potential for crop improvement as well as potential elucidation of the mechanisms for polyploid speciation in Brassica. We investigated genome stability and meiotic behaviour in different allohexaploid Brassica populations. Molecular genotyping and cytogenetics approaches were used to track A, B and C genome allele inheritance, DNA content was estimated by flow cytometry and self-pollinated seed set and pollen viability data were collected. Homologous chromosome pairs segregated with moderately high fidelity and with meiotic crossover frequencies similar to those in established Brassica species. However, no strong selective pressure for 2n = AABBCC karyotypes was observed, with frequent aneuploidy and no significant correlations between fertility and DNA ploidy or chromosome fragment loss. Most chromosomes present in only one copy (univalents) were equally likely to be lost as to be retained, and severe karyotype distortions were observed in some second-generation progeny. Production of stable allohexaploid lines is predicted to require rigorous selection for 2n = AABBCC karyotypes.
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Papers by Wallace Cowling