Morphological and Molecular Characterization of Selected Chilean Runner Bean (Phaseolus coccineus L.) Genotypes Shows Moderate Agronomic and Genetic Variability

The runner bean is the third most economically important Phaseolus species, which is cultivated on small-scale agriculture for the production of immature pods or to obtain dry seeds. However, despite the economic importance and agronomic potential of this species, the runner bean has been little studied from the genetic standpoint. Therefore, the main objective of this study was to characterize ten selected lines of runner bean obtained from Central (Santiago) and Southern (Valdivia and Villarica) Chile based on morphological and agronomic traits. In addition, the genetic variability of these lines was determined using 12 Inter-Simple Sequence Repeat (ISSR) markers to evaluate the potential of this germplasm for breeding and commercial purposes. As a result, the lines from Central Chile were characterized, and had a higher number of pods per plant compared to the Southern lines, although the size and weight of their seeds were lower. Moreover, a low level of genetic diversity (He = 0.251) was encountered in this population. Finally, this is one of the first studies that generate relevant and novel information on the morphological, agronomic and genetic characterization of the P. coccineus germplasm present in Chile.

Characterization of Colletotrichum lindemuthianum Races in Zambia and Evaluation of the CIAT Phaseolus Core Collection for Resistance to Anthracnose

Colletotrichum lindemuthianum, the causal pathogen of common bean (Phaseolus vulgaris) anthracnose, is highly variable. Therefore, understanding its race structure and identification of new sources of resistance is necessary for the development of varieties with durable resistance. The objectives of this study were (i) to characterize isolates of C. lindemuthianum collected from three major bean-growing regions in Zambia, and (ii) evaluate the CIAT Phaseolus core collection for resistance to C. lindemuthianum races 37, 73, and 566, and a blend of 20 races. Isolates collected from three major bean-growing districts in Zambia, namely Mporokoso, Mpika, and Mbala, were characterized as race 37, 73, and 566, respectively. A subset of the CIAT core collection comprised of 885 accessions of common bean, 13 accessions of scarlet runner bean (P. coccineus), and 11 accessions of year bean (P. dumosus) were evaluated for resistance to races 37, 73 and 566, and a blend of 20 races in a greenhouse at University of Zambia, Lusaka, Zambia. A total of 72%, 66%, 48% and 9% of P. vulgaris accessions evaluated were highly resistant to races 37, 73, 566 and a blend of 20 races, respectively. Also, accessions of P. coccineus and P. dumosus, highly resistant to races 37, 73 and 566, were identified. Only eight of the 331 P. vulgaris accessions were highly resistant to all three individual races (37, 73, and 566) and to a blend of 20 races. These eight accessions constitute a valuable breeding resource for developing varieties with durable resistance to C. lindemuthianum.

The genomic signature of wild-to-crop introgression during the domestication of scarlet runner bean (Phaseolus coccineus L.)

SummaryThe scarlet runner bean is an open-pollinated legume from the highlands of Mesoamerica that is cultivated in small-scale agriculture for its dry seeds and immature pods. Demographic bottlenecks associated with domestication might reduce genetic diversity and facilitate the accumulation of deleterious mutations. Conversely, introgression from wild relatives could be a source of variation.Using Genotyping by Sequencing data (79,286 SNVs) from 237 cultivated and wild samples, we evaluated the demographic history of traditional varieties from different regions of Mexico and looked for evidence of introgression between sympatric wild and cultivated populations.Traditional varieties have high levels of diversity, even though there is evidence of a severe initial genetic bottleneck, followed by a population expansion. Introgression from wild to domesticated populations was detected, but not in the opposite direction. This asymmetric introgression might contribute to the recovery of genetic variation and it has occurred at different times: constantly in the center of Mexico; recently in the North West; and anciently in the South.Several factors are acting together to increase and maintain genetic diversity in P. coccineus cultivars, such as demographic expansion and introgression. Wild relatives represent a valuable genetic resource and have played a key role in scarlet runner bean evolution via introgression into traditional varieties.

Comparative analysis of embryo proper and suspensor transcriptomes in plant embryos with different morphologies

An important question is what genes govern the differentiation of plant embryos into suspensor and embryo proper regions following fertilization and division of the zygote. We compared embryo proper and suspensor transcriptomes of four plants that vary in embryo morphology within the suspensor region. We determined that genes encoding enzymes in several metabolic pathways leading to the formation of hormones, such as gibberellic acid, and other metabolites are up-regulated in giant scarlet runner bean and common bean suspensors. Genes involved in transport and Golgi body organization are up-regulated within the suspensors of these plants as well, strengthening the view that giant specialized suspensors serve as a hormone factory and a conduit for transferring substances to the developing embryo proper. By contrast, genes controlling transcriptional regulation, development, and cell division are up-regulated primarily within the embryo proper. Transcriptomes from less specialized soybean and Arabidopsis suspensors demonstrated that fewer genes encoding metabolic enzymes and hormones are up-regulated. Genes active in the embryo proper, however, are functionally similar to those active in scarlet runner bean and common bean embryo proper regions. We uncovered a set of suspensor- and embryo proper–specific transcription factors (TFs) that are shared by all embryos irrespective of morphology, suggesting that they are involved in early differentiation processes common to all plants. Chromatin immunoprecipitation sequencing (ChIP-Seq) experiments with scarlet runner bean and soybean WOX9, an up-regulated suspensor TF, gained entry into a regulatory network important for suspensor development irrespective of morphology.

Comparative Analysis of Embryo Proper and Suspensor Transcriptomes in Plant Embryos With Different Morphologies

An important question is what genes govern the differentiation of plant embryos into suspensor and embryo-proper regions following fertilization and division of the zygote. We compared embryo proper and suspensor transcriptomes of four plants that vary in embryo morphology within the suspensor region. We determined that genes encoding enzymes in several metabolic pathways leading to the formation of hormones, such as gibberellic acid, and other metabolites are up-regulated in giant Scarlet Runner Bean and Common Bean suspensors. Genes involved in transport and Golgi body organization are up-regulated within the suspensors of these plants as well – strengthening the view that giant specialized suspensors serve as a hormone factory and a conduit for transferring substances to the developing embryo proper. By contrast, genes controlling transcriptional regulation, development, and cell division are up-regulated primarily within the embryo proper. Transcriptomes from less specialized soybean and Arabidopsis suspensors demonstrated that fewer genes encoding metabolic enzymes and hormones are up-regulated. Genes active in the embryo proper, however, are functionally similar to those active in Scarlet Runner Bean and Common Bean embryo proper regions. We uncovered a set of suspensor- and embryo-proper-specific transcription factors (TFs) that are shared by all embryos irrespective of morphology, suggesting that they are involved in early differentiation processes common to all plants. ChIP-Seq experiments with Scarlet Runner Bean and soybean WOX9, an up-regulated suspensor TF, gained entry into a regulatory network important for suspensor development irrespective of morphology.SignificanceHow plant embryos are differentiated into embryo proper and suspensor regions following fertilization is a major unanswered question. The suspensor is unique because it can vary in morphology in different plant species. We hypothesized that regulatory genes controlling the specification of embryo proper and suspensor regions should be shared by all plants irrespective of embryo morphology. We compared embryo proper and suspensor transcriptomes of plants with distinct suspensor morphologies. Scarlet Runner Bean and Common Bean have highly specialized giant suspensor regions, whereas soybean and Arabidopsis suspensors are smaller and less specialized. We uncovered a small set of embryo-proper- and suspensor-specific transcription factors shared by all embryos irrespective of morphology, suggesting that they play an important role in early embryo differentiation.

Effects of Electromagnetic Fields and their Shielding on the Growth of Dwarf Runner Beans

The aim of the study was to determine the effect of electromagnetic fields and their shielding on the growth of dwarf runner bean Phaseolus coccineus L. Three sectors were separated on the device emitting electromagnetic fields: “E” - sector emitting electromagnetic radiation with the predominance of the electrical component, “EM” - sector emitting electromagnetic radiation without domination of its components and “M” - sector with a predominance of magnetic component. Fields generated by the device were also shielded with ADR TEX, a screen based on a nanocomposite in which the electric component of the electromagnetic radiation is absorbed by water dispersed within a dielectric matrix in various ways. The composites exhibit high dielectric absorption and shield electric fields within the frequency range from ~100 mHz to ~100 kHz. Electromagnetic fields with the predominance of the electrical component and without domination of its components delayed the initial emergence of runner bean seedlings. Shielding of electromagnetic field without domination of its components with ADR TEX screen protected against this negative impact on the emergence rate of young runner bean seedlings. Exposure of plants to differentiated electromagnetic fields adversely affected their growth. Plants exposed to electromagnetic radiation without domination of its components had the lowest height and the shortest internodes. Shielding of electromagnetic fields with ADR TEX screen efficiently protected against their negative impact on the plant growth. Electromagnetic fields and their shielding did not influence the size of leaves and the index leaf greenness (SPAD).