The Frustration with Utilization: Why Have Improvements in Internal Phosphorus Utilization Efficiency in Crops Remained so Elusive?

Despite the attention internal phosphorus utilization efficiency (PUE) of crops has received in the literature, little progress in breeding crop cultivars with high PUE has been made. Surprisingly few studies have specifically investigated PUE; instead, genotypic variation for PUE has been investigated in studies that concurrently assess phosphorus acquisition efficiency (PAE). We hypothesized that genotypic differences in PAE confound PUE rankings because genotypes with higher PAE suffer a lower degree of P stress, resulting in lower PUE. The hypothesis was tested by comparing soil-based screening to a modified technique whereby rice genotypes were grown in individual containers with a single dose of solution P, to eliminate differences in P uptake among genotypes. Genotypic differences in PUE were apparent in root and shoot tissue using the modified nutrient solution technique, but PUE rankings showed no correlation with those from traditional soil-based screening. We conclude that PUE in soil-based screening systems is unavoidably linked with genotypic PAE, resulting in PUE rankings confounded by differences in P uptake. Only screening techniques assuring equal P uptake are suitable for the exploitation of genotypic variation for PUE

A novel allele of the P-starvation tolerance gene OsPSTOL1 from African rice (Oryza glaberrima Steud) and its distribution in the genus Oryza

The deficiency of phosphorus (P) in soil is a major problem in Sub-Saharan Africa due to general nutrient depletion and the presence of P-fixing soils. Developing rice cultivars with enhanced P efficiency would, therefore, represent a sustainable strategy to improve the livelihood of resource-poor farmers. Recently the Pup1 locus, a major QTL for tolerance to P deficiency in soil, was successfully narrowed-down to a major gene, the protein kinase OsPSTOL1 (P-starvation tolerance), which was found to be generally absent from modern irrigated rice varieties. Our target is to improve the tolerance of African mega-varieties to P deficiency through marker-assisted introgression of PSTOL1. As a first step, we have determined the Pup1 haplotype and surveyed the presence or absence of PSTOL1 and other genes of the Pup1 locus in African mega-varieties, NERICAs (New Rice for Africa) and their Oryza glaberrima parents. Here, we report the presence of a novel PSTOL1 allele in upland NERICAs that was inherited from the O. glaberrima parent CG14. This allele showed a 35 base-pair substitution when aligned to the Kasalath allele, but maintained a fully conserved kinase domain, and is present in most O. glaberrima accessions evaluated. In-silico and marker analysis indicated that many other genes of the Kasalath Pup1 locus were missing in the O. glaberrima genome, including the dirigent-like gene OsPupK20-2, which was shown to be downstream of PSTOL1. We have developed several allele-specific markers for the use for molecular breeding to transfer the PSTOL1 gene from Kasalath to African mega-varieties, including NERICAs.Juan Pariasca-Tanaka, Joong Hyoun Chin, Khady Nani Dramé, Cheryl Dalid, Sigrid Heuer, Matthias Wissuw

A PSTOL-like gene, TaPSTOL, controls a number of agronomically important traits in wheat

Background Phosphorus (P) is an essential macronutrient for plant growth, and is required in large quantities by elite varieties of crops to maintain yields. Approximately 70% of global cultivated land suffers from P deficiency, and it has recently been estimated that worldwide P resources will be exhausted by the end of this century, increasing the demand for crops more efficient in their P usage. A greater understanding of how plants are able to maintain yield with lower P inputs is, therefore, highly desirable to both breeders and farmers. Here, we clone the wheat (Triticum aestivum L.) homologue of the rice PSTOL gene (OsPSTOL), and characterize its role in phosphate nutrition plus other agronomically important traits. Results TaPSTOL is a single copy gene located on the short arm of chromosome 5A, encoding a putative kinase protein, and shares a high level of sequence similarity to OsPSTOL. We re-sequenced TaPSTOL from 24 different wheat accessions and (3) three T. durum varieties. No sequence differences were detected in 26 of the accessions, whereas two indels were identified in the promoter region of one of the durum wheats. We characterised the expression of TaPSTOL under different P concentrations and demonstrated that the promoter was induced in root tips and hairs under P limiting conditions. Overexpression and RNAi silencing of TaPSTOL in transgenic wheat lines showed that there was a significant effect upon root biomass, flowering time independent of P treatment, tiller number and seed yield, correlating with the expression of TaPSTOL. However this did not increase PUE as elevated P concentration in the grain did not correspond to increased yields. Conclusions Manipulation of TaPSTOL expression in wheat shows it is responsible for many of the previously described phenotypic advantages as OsPSTOL except yield. Furthermore, we show TaPSTOL contributes to additional agronomically important traits including flowering time and grain size. Analysis of TaPSTOL sequences from a broad selection of wheat varieties, encompassing 91% of the genetic diversity in UK bread wheat, showed that there is very little genetic variation in this gene, which would suggest that this locus may have been under high selection pressure

Enhancing phosphorus and zinc acquisition efficiency in rice: a critical review of root traits and their potential utility in rice breeding

Background: Rice is the world's most important cereal crop and phosphorus (P) and zinc (Zn) deficiency are major constraints to its production. Where fertilizer is applied to overcome these nutritional constraints it comes at substantial cost to farmers and the efficiency of fertilizer use is low. Breeding crops that are efficient at acquiring P and Zn from native soil reserves or fertilizer sources has been advocated as a cost-effective solution, but would benefit from knowledge of genes and mechanisms that confer enhanced uptake of these nutrients by roots. Scope: This review discusses root traits that have been linked to P and Zn uptake in rice, including traits that increase mobilization of P/Zn from soils, increase the volume of soil explored by roots or root surface area to recapture solubilized nutrients, enhance the rate of P/Zn uptake across the root membrane, and whole-plant traits that affect root growth and nutrient capture. In particular, this review focuses on the potential for these traits to be exploited through breeding programmes to produce nutrient-efficient crop cultivars. Conclusions: Few root traits have so far been used successfully in plant breeding for enhanced P and Zn uptake in rice or any other crop. Insufficient genotypic variation for traits or the failure to enhance nutrient uptake under realistic field conditions are likely reasons for the limited success. More emphasis is needed on field studies in mapping populations or association panels to identify those traits and underlying genes that are able to enhance nutrient acquisition beyond the level already present in most cultivars.T. J. Rose, S. M. Impa, M. T. Rose, J. Pariasca-Tanaka, A. Mori, S. Heuer, S. E. Johnson-Beebout and M. Wissuw

Revisiting the role of organic acids in the bicarbonate tolerance of zinc-efficient rice genotypes

It has been hypothesised that enhanced organic acid release from the roots of zinc-efficient rice (Oryza sativa L.) genotypes plays a strong role in plant tolerance to both bicarbonate excess and Zn deficiency. To address several uncertainties in the literature surrounding the tolerance of rice to bicarbonate, we initially assessed the tolerance of six rice genotypes to bicarbonate stress under field conditions and in solution culture. The landrace Jalmagna and its recombinant inbred offspring, RIL46, consistently performed better in terms of maintenance of biomass and root length under high bicarbonate concentrations. In the hydroponic experiments, increased root malate (but not citrate) accumulation and efflux were responses to high solution bicarbonate in the short-term (12 h) in all genotypes. Although both citrate and malate accumulation and efflux increased after long-term exposure (10 days) to high bicarbonate and Zn deficiency, it coincided with amino acid leakage from the roots. Partial least-squares regression showed that this leakage consistently ranked highly as an indicator of poor plant health under all stress conditions, whereas specific malate efflux (the ratio of malate to amino acid efflux) was an important predictor of good plant health. The root leakage of Zn-inefficient genotypes under bicarbonate and dual stress (bicarbonate with low Zn) was typically higher than in Zn-efficient genotypes, and coincided with higher peroxide concentrations, suggesting that bicarbonate tolerance is related to the ability of Zn-efficient genotypes to overcome oxidative stress, maintain root membrane integrity and minimise root leakage

A novel allele of the P‑starvation tolerance gene OsPSTOL1 from African rice (Oryza glaberrima Steud) and its distribution in the genus Oryza

We have developed allele-specific markers for molecular breeding to transfer the PSTOL1 gene from Kasalath to African mega-varieties, including NERICAs, to improve their tolerance to P-deficient soil. The deficiency of phosphorus (P) in soil is a major problem in Sub-Saharan Africa due to general nutrient depletion and the presence of P-fixing soils. Developing rice cultivars with enhanced P efficiency would, therefore, represent a sustainable strategy to improve the livelihood of resource-poor farmers. Recently the Pup1 locus, a major QTL for tolerance to P deficiency in soil, was successfully narrowed-down to a major gene, the protein kinase OsPSTOL1 (P-starvation tolerance), which was found to be generally absent from modern irrigated rice varieties. Our target is to improve the tolerance of African mega-varieties to P deficiency through marker-assisted introgression of PSTOL1. As a first step, we have determined the Pup1 haplotype and surveyed the presence or absence of PSTOL1 and other genes of the Pup1 locus in African mega-varieties, NERICAs (New Rice for Africa) and their Oryza glaberrima parents. Here, we report the presence of a novel PSTOL1 allele in upland NERICAs that was inherited from the O. glaberrima parent CG14. This allele showed a 35 base-pair substitution when aligned to the Kasalath allele, but maintained a fully conserved kinase domain, and is present in most O. glaberrima accessions evaluated. In-silico and marker analysis indicated that many other genes of the Kasalath Pup1 locus were missing in the O. glaberrima genome, including the dirigent-like gene OsPupK20-2, which was shown to be downstream of PSTOL1. We have developed several allele-specific markers for the use for molecular breeding to transfer the PSTOL1 gene from Kasalath to African mega-varieties, including NERICAs

Phosphorus uptake commences at the earliest stages of seedling development in rice

Seed phosphorus (P) reserves are essential for seedling development, however, we hypothesise that the quantity of P in seeds will lose importance in cultivars that rapidly acquire P via roots. Our objective was to investigate the onset of seedling P uptake in rice (Oryza sativa). This question was addressed through 33P labelled P supply and through measuring P depletion in combination with the detection of P transporter activity in root tissue of three rice cultivars during early seedling development.33P supplied to roots four days after germination (DAG) was detected in shoots two days later, indicating P was taken up and translocated to shoots during early seedling development. Measurements of P depletion from the growth medium indicated P uptake occurred even at 2 DAG when roots were only 3 cm long. By day three, P depletion was rapid and P transporter activity was detected in roots, regardless of levels of seed P reserves present. We conclude that P uptake commences at the earliest stages of seedling development in rice, that the amount of P taken up will be limited by root size and that genotypes with more rapid root development should more rapidly complement seed-P reserves by root P uptake

Development of a SNP genotyping panel for detecting polymorphisms in Oryza glaberrima O. sativa interspecific crosses

International audienceOryza glaberrima accessions harbor genes for tolerance to abiotic stresses such as mineral deficiency in problem soils. This genetic potential could be exploited in interspecific crosses with Oryza sativa, as in the case of the ‘New Rice for Africa’ (NERICA) varieties; however, to attain this goal it would be desirable to develop a high-throughput marker system to specifically detect O. glaberrima introgressions in an O. sativa background. Therefore, a single nucleotide polymorphism (SNP) genotyping analysis of an O. glaberrima accession (CG14) with two O. sativa lines (WAB56-104 and WAB181-18) was performed on a genome-wide basis. Comparison of CG14 and the WAB lines resulted in a set of 9,523 polymorphic SNPs which would be suitable to detect O. glaberrima introgressions in upland NERICAs. In addition, a set of 1,540 polymorphic SNPs between O. glaberrima versus O. sativa was identified. A subset of SNPs which were evenly distributed in the genome was then used to design a flexible and cost-effective SNP genotyping panel using the Competitive Allele-Specific PCR technology (KASP). This SNP genotyping panel consists of 2,015 SNPs successfully converted into KASP markers, providing 745 polymorphic SNPs for the parents O. glaberrima CG14/O. sativa WAB56-104 (upland NERICA), and 752 for O. glaberrima TOG5681/O. sativa IR64 (lowland NERICA). KASP markers were successfully validated by mapping O. glaberrima introgressions in NERICA-derived breeding lines. This new SNP genotyping panel will be useful in modern breeding applications such as QTL mapping and/or marker-assisted selection

Educational films on DVD reflected in moderate constructivism

Nach den ersten Filmaufnahmen im ausgehenden 19. Jahrhundert, dauerte es nicht lange, und die neue Technik hielt auch in Forschung und Bildung Einzug. Hier polarisierte der Film Didaktiker seit seiner Existenz und erregte immer wieder neue Diskussionen über seinen Nutzen und die ideale Gestaltung für den Unterrichtseinsatz – bis zu Beginn der 1980er Jahre. Dann wurde es stiller um ihn und das Augenmerk der didaktischen Diskussion verlagerte sich hin zu den entstehenden Möglichkeiten des Computers, den neuen Medien. (Ashauer 1980, S. 122; Ketzer 1980b, S. 10; Kraatz 1997, S. 186; Kuchenbuch 2005, S. 87 ff.). Dies hielt die Produzenten von Unterrichtsfilmen nicht von Weiterentwicklungen ab: Neue Formen des Unterrichtsfilms wurden erst für VHS-Kassette, dann für CD-ROM und seit 1999 für DVD entwickelt. Seit wenigen Jahren wird bereits der Online-Vertrieb erprobt, dessen Produkte jedoch bislang denen des Medienträgers DVD entsprechen (Kap. 2.1.2). Die didaktische DVD, also die DVD für den Unterrichtsfilm, nimmt heute den bedeutendsten Stellenwert bei der Produktion von Unterrichtsfilmen ein und das Institut für Film und Bild in Wissenschaft und Unterricht preist sie als Medium an, „das – bei einfachster Bedienung – mit seinen vielseitigen Möglichkeiten hervorragende Perspektiven für den Einsatz im Unterricht eröffnet“ (FWU o. J., o. S.). Von dieser Ankündigung ausgehend, aber auch vor dem Hintergrund der historischen Entwicklung, formuliert diese Arbeit als erste Hypothese: (Kap. 2.1.2) H1: Die DVD als technische Neuerung bietet neue Nutzungsmöglichkeiten für das Medium Unterrichtsfilm. Der Didaktik war der Vorstoß des Unterrichtsfilms in die digitale Welt und damit auch die Annäherung an die neuen Medien keine Diskussion wert, und auch die Produzenten bemühten sich nicht um das wissenschaftliche Fundament der Neuentwicklungen. Zu belegen ist dies anhand der verschwindend geringen Anzahl der Veröffentlichungen zum Thema Unterrichtsfilm der vergangenen Jahrzehnte. Ein 2005 in der geographie heute erschienener Beitrag beschäftigte sich in knapper Form mit den didaktischen Möglichkeiten. Unkritisch wurde der Neuentwicklung bescheinigt: „Kein anderer Medienträger bietet für den Unterrichtseinsatz größere pädagogische Freiheiten“ (Obermaier 2005, S. 46). Dieses Urteil gründet auf der Vielfalt möglicher Zusatzmaterialien, welche eine DVD neben dem Hauptfilm enthalten kann: Als digitaler Datenträger ist sie in der Lage beliebige, je nach Art mit dem Computer oder dem DVD-Spieler nutzbare Medien i. e. S. (Kap. 2.1.1) zu speichern. Es stellt sich die Frage, ob die neu entwickelten Medien auf DVD vor dem Hintergrund einer sich wandelnden Didaktik tatsächlich aktuelle Medien sind: Die Arbeit legt ein besonderes Augenmerk auf den Konstruktivismus in seiner Ausprägung als Moderater Konstruktivismus sowie auf seine erkenntnistheoretischen Voraussetzungen und die damit verbundenen neurobiologischen Grundlagen. Ausgehend von dieser Betrachtung werden Implikationen für den Unterrichtsfilm untersucht und als zweite Hypothese formuliert: (Kap. 2.2.3) H2: Aus einer moderat konstruktivistischen Betrachtungsweise folgen neue Anforderungen an den Unterrichtsfilm, die den klassischen didaktischen Anforderungen auf Basis einer instruktivistischen Betrachtungsweise widersprechen. Während die Hypothesen einer theoretischen Betrachtung bedürfen, kristallisiert sich als direkte Konsequenz aus H1 und H2 folgende praktisch ausgerichtete Frage heraus: Entsprechen aktuelle Unterrichtsfilme auf DVD den veränderten Anforderungen einer moderat konstruktivistischen Betrachtungsweise unter Einbezug wahrnehmungspsychologischer Erkenntnisse? Dies an konkreten Beispielen zu untersuchen ist Ziel der Analyse. Neben dem Hauptfilm gilt es, eventuell vorhandene Zusatzmaterialien sowie die Gestaltung der DVD selbst in der Einzelanalyse der Fallbeispiele zu berücksichtigen. Um einen unabhängigen Blick auf fachliche und didaktische Inhalte zu ermöglichen, wird vor der genauen Einzelanalyse eine planungsorientierte Materialsichtung durchgeführt. Diese simuliert die Vorbereitungen eines Unterrichtseinsatzes, soweit dies im gebotenen allgemeinen Rahmen sinnvoll ist. Die in der Einzelanalyse entstandenen Filmprotokolle ergeben eine Strukturübersicht des Films, die nach einer ersten Auswertung hinsichtlich der Gestaltungsebenen inhaltlich erschlossen werden muss. Dies geschieht als Gegenüberstellung der Fallbeispiele nach wahrnehmungspsychologischen und didaktischen Anforderungen an Unterrichtsfilme (Kap. 4.5). Hier werden auch die Zusatzmaterialien und die DVD-Gestaltung betrachtet. Die prägnanten Ergebnisse der Analyse werden abschließend hinsichtlich der Eignung für einen moderat konstruktivistischen Unterricht diskutiert. In Hinblick auf den praxisorientierten Ausgangspunkt der Untersuchung werden im Anschluss Vorschläge unterbreitet, wie die untersuchten Medien trotz eventuell inkompatibler Eigenschaften zumindest eingeschränkt im Unterricht eingesetzt werden können.Educational films stirred debates among academics in education since their existence. The discussions lasted until the beginning 1980s and their main topic was the use and ideal arrangement of movies for educational purposes. However, the didactical focus shifted towards the emerging possibilities of computers, the so-called new media (Kraatz 1997, p. 186). This did not prevent producers of educational films to use new techniques for film. Since the DVD replaced the 16 mm-films in 1999 and is the most important carrier of films today the first hypothesis is phrased as follows: H1: The DVD as a technical advance holds new possibilities for educational film as media. The theoretical work in this paper confirms the hypothesis and states a position in-between classical and new media for the DVD. Along with this technical background the question about the ongoing didactical discussion arises. The social turn of the humanities also influenced geographical education. But although the constructivist notion of an individually constructed reality is consistent with recent findings in neurobiological science, dissenting opinions in didactics point out that a radical constructivism cannot justify teaching as being important to learning. As a more pragmatic approach the moderate constructivism accepts both procedures, the instruction of the teaching and the construction of the learning, as being fundamental to gaining knowledge. A modern education, that is willing to comply with this needs media for the classroom that supports such a view on learning. This constitutes the second hypothesis: H2: A moderate constructivist view will manifest new requirements for educational films that oppose to classical instructivist requirements. In correspondence with findings of psychology of perception the theoretical part of this work confirms the hypothesis, which is especially apparent for the conventional requirement of objectiveness as well as for media adequacy. Other classical requirements need to be modified according to constructivist thoughts, too. Bearing in mind the gap in the didactic discussion about the educational film of the last decades and regarding the theoretical discussion of H1 and H2 an evident question for the analysis arises: Do current educational films on DVD satisfy altered requirements of a moderate constructivist view in comprehension with findings of psychology of perception? To answer this question the analysis examined three DVDs of the FWU, the WBF and the fechnerMedia Verlag as case studies, with the basic topic of mega cities. To ensure an independent view on the professional side as well as on the didactical side the first step of the analysis was the simulation of prearrangement for the educational use in class for each DVD. Following this the main features of the DVDs were transcripted, along with a first evaluation of the different levels of film-design in the single-analyses. Here the extra materials of the DVDs and the design of the DVD itself needed to be reviewed, too. Finally the findings of the single-analyses were assessed in a table with moderate constructivist requirements and requirements of psychology of perception. As a guideline the concluding discussion used seven characteristics of moderate constructivist media, elaborated in the theoretical work. Altogether none of the case studies met all characteristics satisfactorily. In terms of psychology of perception only one of the films complies with requirements of arrangement. The origin of the other films as TV-documentaries is obvious and they were not reworked at all or not sufficiently to meet the requirements for teaching. At last the use of the DVD-technique has to be criticised: A creative use of the technology is not featured by any of the analyzed DVDs. Finally the suggestions in this paper on how to use the case studies in school illustrate that also these non-ideal media can support a moderate constructivist education. And yet it would be better, if the media supported modern didactics in the first place. The findings of this study clearly show that the development of educational films lost ties with the intellectual debate in didactics. Indeed it is questionable, what benefit an educational film can offer, that is in fact a TV-documentary. It is not the task of producers to simply sell TV-productions to schools, but to actually rework the materials and make them meet the requirements for school education. Along with this the dialogue between producers and science of didactics needs to be re-established, for educational media must focus on the needs of education. This appeal also addresses to science of didactics, which must not only look at new media. Instead they should revise long known educational media regularly with regards to arrangment, their position and function in the classroom and especially analyze whether existing media fulfils these requirements