Anthracnose caused by Colletotrichum lindemuthianum is a major disease of common bean (Phaseolus vulgaris) worldwide. Yellow beans are a major market class of common bean especially in eastern and ...southern Africa. The Yellow Bean Collection (YBC), which is comprised of 255 genotypes, and has not been used previously in genetic studies on anthracnose, is an excellent genetic resource for understanding the extent of anthracnose resistance and its genetic architecture in the yellow bean market class. The objectives of this study were i) evaluate the YBC for resistance to races 5, 19, 39, 51, 81, 183, 1050 and 1105 of C. lindemuthianum. and ii) conduct genome-wide association analysis to identify genomic regions and candidate genes associated with resistance to C. lindemuthianum. The YBC was genotyped with 72,866 SNPs, and genome-wide association analysis was conducted using Mixed Linear Model in TASSEL. Andean and Middle American genotypes with superior levels of resistance to the eight races were identified. YBC278 was the only one among 255 genotypes that was highly resistant to all eight races. Resistance to anthracnose in the YBC was controlled by major-effect loci on chromosomes Pv01, Pv03, Pv04, Pv05 and Pv07. The genomic region on Pv01, which overlapped with the Andean locus Co-1 provided resistance to races 81, 1050 and 1105. Significant SNPs for resistance to race 39 were identified on Pv02. The genomic region on Pv04, which overlapped with known major-effect loci Co-3, Co-15, Co-16, Co-y and Co-z, provided resistance to races 5, 19, 51 and 183. Novel genomic regions for resistance to race 39 were identified on Pv05 and Pv07. Plant resistance genes (R genes) with NB-ARC and LRR domains, which occurred in clusters, were identified as positional candidate genes for genomic regions on Pv02 and Pv04.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Anthracnose, caused by the fungus
, is a major disease of common bean (
L.) worldwide.
is genetically highly variable, and understanding the pathogen's diversity and distribution is a key step in ...developing common bean varieties with durable anthracnose resistance. The objectives of this study were to (i) characterize the race structure of
in Zambia and (ii) assess the molecular diversity of
in Zambia. A field survey was conducted in 20 bean-growing districts in Zambia to collect anthracnose symptomatic bean plants. A total of 103
isolates were collected and characterized based on their reactions on 12 common bean race differential cultivars. RAM and ERIC-BOX DNA markers were used to assess molecular diversity of 60 isolates. A total of 58 races were characterized from the 103 isolates. Race 5 was the least virulent, and race 1631 was the most virulent based on their reaction on the 12 race differential cultivars. Race 19 had the highest recovery frequency (11%) and was the most extensively dispersed among the 22 bean-growing districts from where the isolates were collected. Only six races had previously been reported in Zambia, and 52 races were identified as new races reported for the first time in Zambia. Two races were virulent only on Andean cultivars, 11 races were virulent only on Middle American cultivars, and 45 races were virulent on both Andean and Middle American cultivars. No individual isolate showed pathogenicity on all the differential cultivars, and no isolate overcame the
,
, and
resistance gene pyramid that naturally exists in G2333. Phylogenetic analysis categorized the 60 isolates in six major clusters and six subclusters. The 60 isolates showed high genetic heterogeneity among and within a race of the same virulence. The study has revealed the existence of both Andean and Middle American races and extensive molecular diversity of
in Zambia. The knowledge on the race structure of
that this study has provided will be valuable for making breeding decisions on the host plant resistance genes required for developing common bean varieties with durable resistance to anthracnose in Zambia.
ABSTRACT
Common bean (Phaseolus vulgaris L.) is an important crop grown for household revenue, food, and nutrition security in many parts of the world, especially in Africa and Latin America. ...Anthracnose caused by Colletotrichum lindemuthianum is a major disease of common bean globally. The objective of this study was to determine the response of selected pinto bean genotypes to seven races of C. lindemuthianum the causative fungus for anthracnose. A total of 56 pinto bean genotypes and three checks were evaluated for resistance to C. lindemuthianum races 51, 65, 73, 247, 253, 263, and 1085. Significant differences were observed among the 56 pinto genotypes in their reaction to the seven races, which was generally skewed towards susceptibility except for races 51 and 73. There was no genotype that was resistant to all seven races. In general, the genotypes that showed resistance to most of the races were those that carried Co‐42, which highlighted the importance of this locus to anthracnose resistance in pinto beans. Three genotypes—NDZ14006‐4, NDZ14110‐4, and NDZ14043—showed superior resistance (resistant to six of the seven races).
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT
The common bean weevil (Acanthoscellides obtectus Say) is a major post‐harvest pest of common bean (Phaseolus vulgaris L.) in tropical regions. Developing and using weevil‐resistant ...varieties is the most environmentally and cost‐effective means of mitigating the losses caused by the common bean weevil. The arcelin–phytohemagglutinin–alpha‐amylase (APA) locus, originally from tepary bean (Phaseolus acutifolius A. Gray), provides effective resistance against the common bean weevil. The APA locus is currently deployed in very limited market classes, and knowledge of the stability of its resistance across different market classes of common bean is limited. The objectives of this study were to (i) introgress the APA locus into selected market classes of Andean gene pool of common bean and (ii) determine the stability of APA‐based resistance to A. obtectus (AO) in multiple market classes of common bean. A total of 571 F5:7 breeding lines derived from crossing the weevil‐resistant breeding line AO‐1012‐29‐3‐3A (AO‐3A) possessing the APA locus with seven Andean genotypes belonging to five market classes were evaluated for resistance to AO. Of the 571 breeding lines screened, 16 were resistant, representing a low weevil resistance recovery rate of 2.8%. These lines are across diverse market classes, including those preferred in African countries. Of the 16 newly developed resistant breeding lines, six were more resistant to AO (scores ranging from 1–1.3) than AO‐3A (score of 2), and these can be used for further genetic enhancement of common bean resistance to AO.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Key Message
Quantitative Trait Loci “hotspots” for drought tolerance were identified on chromosomes Pv06, Pv07 and Pv10 of common bean.
Drought is a major production constraint of common bean (
...Phaseolus vulgaris
L.) worldwide. The objective of this study was to identify the Quantitative Trait Loci (QTL) for drought tolerance in an Andean population of Recombinant Inbred Lines (RILs). A total of 155 F
5:7
RILs derived from a cross between Kijivu (drought tolerant) and Bukoba (drought susceptible) were evaluated for drought tolerance in field and pot experiments. Four field experiments were conducted at three locations in Zambia in 2020 and 2021. All field trials were conducted in the dry season under irrigation. The 155 RILs were genotyped with 11,292 SNPs, and composite interval mapping was conducted to identify QTL for drought tolerance. Seed yield for Kijivu under drought stress was consistently higher than for Bukoba across all four field trials. A total of 60 QTL were identified for morphological, agronomic, and physiological traits under drought stress and non-stress conditions. However, the majority of these QTL were specific to drought stress. QTL “hotspots” for drought tolerance were identified on chromosomes Pv06, Pv07, and Pv10. Extensive co-localizations for agronomic and morpho-physiological traits under drought stress were observed at the three drought-tolerance QTL hotspots. Additionally, these three QTL hotspots overlapped with previously identified QTL for drought tolerance, while several others identified QTL are novel. The three identified QTL hotspots could be used in future marker-assisted selection for drought tolerance in common bean.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The current standard for treatment of high grade tendon tears is surgical replacement grafts, however they present the challenge of limited tissue availability (allografts and autografts), donor site ...morbidity (autografts), and immune rejection (allografts and tissue engineered grafts). In recent years, several research groups have attempted to address this problem using scaffold-based tendon replacement grafts, and are faced with the challenge of developing a scaffold-based graft that (i) is biocompatible, ( ii) emulates the properties of normal tendon tissue, and ( iii) degrades at the ideal rate for successful tissue remodeling at the site of implantation, which if too soon, would lead to reinjury at the site, and if too late, would shield the endogenous tissue from the therapeutic benefits of gentle dynamic stretching and result in degeneration. Engineered scaffold-based tendon replacement grafts have yet to reach clinical implementation, and it is clear that a deeper understanding of how to enhance these grafts would help to advance these therapies and, potentially, improve the lives of patients. Primed with this knowledge, our laboratory has taken a more biomimetic approach to tendon tissue engineering—a scaffold-free approach that is inspired by key aspects of embryonic tendon development. By seeding a high density of cells into a growth channel without a provisional scaffold, and subjecting the cells to controlled mechanical and chemical cues, we are harnessing the cells’ innate ability to self-assemble, as seen in embryonic tenogenesis. It is a model of tissue regeneration rather than tissue remodeling. In the first aim of my doctoral thesis, I developed a method to engineer individual scaffold-free tendon fibers using a micro-molded growth channel, which yielded higher throughput, greater consistency, and higher repeatability in the design of the growth channels than our laboratory’s previous technique for tendon fiber engineering. This micromold-based technique also enabled more extensive characterization of the response of engineered tendon fibers to mechanical and chemical cues. The second aim examined the response of engineered, scaffold-free, dermal fibroblast-derived fibers to mechanical stimulation, namely cyclic uniaxial strain (designed to mimic motion-induced loading in the embryo), and quasi-static strain (to mimic limb lengthening-induced loading in the embryo). The results showed enhanced mechanical properties, collagen alignment, and collagen III deposition in the presence of loading and with loading duration. Moreover, cyclic strain increased stress-based properties (i.e., failure stress, Young’s modulus), but did not affect fiber extensibility. Conversely, the introduction of quasi-static strain increased fiber extensibility without affecting stress-based values. Taken together, these findings suggest distinctly different roles of cyclic and quasi-static strain in tendon development. In addition, the second aim assessed the response of a tendon-specific, progenitor cell type in this system, by using tendon stem/progenitor cells (TSPCs). There was limited success using TSPCs to engineer the tendon fibers. TSPC-derived fibers exhibited reduced extensibility after 34 hours in static culture and were too weak to be subjected to loading. The final aim of this dissertation investigated the influence of macromolecular crowders on the mechanical properties of engineered scaffold-free tendon fibers. Two crowders, dextran sulfate (DsX) and Ficoll-cocktail, were tested. Fiber formation was unsuccessful in the presence of DsX. However, conditioning with Ficoll yielded significantly stronger, stiffer, and tougher fibers. This thesis has provided unique insight on the roles of distinct mechanical stimuli and macromolecular crowding on tendon fiber development and maturation. The knowledge gained on cyclic uniaxial strain, quasi-static loading, and Ficoll-conditioning shows great promise for the advancement of tendon engineering strategies.
Abstract Purpose The accepted mechanism explaining the accelerated growth following periosteal resection is that the periosteum serves as a mechanical restraint to restrict physeal growth. To test ...the veracity of this mechanism we first utilized Second Harmonic Generation (SHG) imaging to measure differences of periosteal fiber alignment at various strains. Additionally, we measured changes in periosteal growth factor transcription. Next we utilized SHG imaging to assess the alignment of the periosteal fibers on the bone both before and after periosteal resection. Based on the currently accepted mechanism, we hypothesized that the periosteal fibers adjacent to the physis should be more aligned (under tension) during growth and become less aligned (more relaxed) following metaphyseal periosteal resection. In addition, we measured the changes in periosteal micro- and macro-scale mechanics. Methods 30 seven-week old New Zealand White rabbits were sacrificed. The periosteum was imaged on the bone at five regions using SHG imaging. One centimeter periosteal resections were then performed at the proximal tibial metaphyses. The resected periosteal strips were stretched to different strains in a materials testing system (MTS), fixed, and imaged using SHG microscopy. Collagen fiber alignment at each strain was then determined computationally using CurveAlign. In addition, periosteal strips underwent biomechanical testing in both circumferential and axial directions to determine modulus, failure stress, and failure strain. Relative mRNA expression of growth factors: TGFβ-1, -2, -3, Ihh, PTHrP, Gli, and Patched were measured following loading of the periosteal strips at physiological strains in a bioreactor. The periosteum adjacent to the physis of six tibiae were imaged on the bone, before and after, metaphyseal periosteal resection, and fiber alignment was computed. One-way ANOVA statistics were performed on all data. Results Imaging of the periosteum at different regions of the bone demonstrated complex regional differences in fiber orientation. Increasing periosteal strain on the resected strips increased periosteal fiber alignment (p < 0.0001). The only exception to this pattern was the 10% strain on the tibial periosteum, which may indicate fiber rupture at this non-physiologic strain. Periosteal fiber alignment adjacent to the resection became less aligned while those adjacent to the physes remained relatively unchanged before and after periosteal resection. Increasing periosteal strain on the resected strips increased periosteal fiber alignment (p < 0.0001). The only exception to this pattern was the 10% strain on the tibial periosteum, which may indicate fiber rupture (and consequent retraction) at this non-physiologic strain. Increasing periosteal strain revealed a significant increase in relative mRNA expression for Ihh, PTHrP, Gli, and Patched, respectively. Conclusion Periosteal fibers adjacent to the growth plate do not appear under tension in the growing limb, and the alignments of these fibers remain unchanged following periosteal resection. Significance The results of this study call into question the long-accepted role of the periosteum acting as a simple mechanical tether restricting growth at the physis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
