Meta-analysis is a powerful tool to summarize variety mixture effects - exemplified by grain yield and weed suppression of spring barley

In a new project, we aim to increase the general understanding of the power of meta-analysis to combine existing experimental results on variety mixtures. In this way, explanatory power can be increased compared to separate analyses and overall measures and relationships may be revealed. We will thus pursue to uncover a number of critical issues, including the relative importance of various traits and trait combinations on mixing success. To demonstrate the methods of meta-analysis applicable for variety mixture data, we considered a data set consisting of grain yield and weed ground cover assessments in 16 field trials of six 3-component variety mixtures and their components (part of the Danish BAR-OF field trials). The effects of mixing were analysed separately for each field trial and the results used in a meta-analysis in combination with their standard errors. We also analysed the mixing effects of each mixture by fitting a linear model to the entire data set. Both methods showed an overall positive mixing effect on grain yield and a trend for less weed to be found in variety mixtures. Finally, strengths and shortcomings of the methods are highlighted

Yield of spring barley mixtures as a function of varietal and environmental characteristics

To design good variety mixtures it is important to understand the influence of varietal and environmental characteristics on mixing effect, e.g. what characteristics are more beneficial when all mixed varieties express it highly and what characteristics are more beneficial when the mixed varieties express it to varying extent. However, as it is generally impossible to manage more than a few experimental combinations in each field trial, information on general relationships and factors of importance for the successful design of variety mixtures may be overlooked. Using meta-regression (e.g. Houwelingen et al. 2002), numerous results of such trials can be combined, and the influence of varietal and environmental factors on mixing effect can be elucidated. Here, two specific hypotheses were investigated: 1. Variation in straw length among component varieties will increase mixing effect due to enhanced potential for resource utilization. 2. Mixing effect will increase with more stressful environments due to increased importance of mechanisms like complementarity and compensation. Meta-analyses with and without covariates were applied to test the hypotheses and elucidate factors of importance for mixing success. The simple meta-analysis showed significant overall increase in yield due to mixing of varieties in spite of slightly opposing results between individual trials. However, the meta-regressions were unable to support the two hypotheses: the mixing effect was not affected by component variation in straw length, and the mixing effect was slightly increasing with environmental yield potential, which was actually arguing against the hypothesis. Further analyses must be done to investigate whether these trends can be found in other data sets and whether further covariates may assist interpretation. The results also show that experimental trials with extraordinarily small experimental variation may influence the conclusions of the analysis. The excluded trial was performed at an experimental farm which is known to provide rather homogenous growing conditions. This information is not readily included in the current use of weighting. In the work to come, we will assess the appropriateness of the current application of inverse variance as weights in meta-analysis of field trial data. Other critical issues that need further investigation include the possible lack of independence between estimates due to shared environments and common component varieties of mixtures

Effects of inter-varietal diversity, biotic stresses and environmental productivity on grain yield of spring barley variety mixtures

Varietal seed mixtures tend to increase and stabilize crop yields, yet their application is sparse. Large-scale cultivation of variety mixtures may require a better understanding of how inter-varietal interactions and their interaction with the environment may influence the grain yield of variety mixtures relative to their component varieties. For this purpose, six variety mixtures of spring barley and 14 component varieties were grown in each of 17 trial environments. A total of 28 observed and a priori plant characteristics, including grain yield, disease severity and weed competitiveness, were derived for each component variety in each trial. The relationship between inter-varietal diversity of each characteristic and the mixing effect on grain yield was analysed. Additionally, various types of yield stability were estimated and compared among mixtures and component varieties. One mixture out-yielded all of its component varieties in almost half of the trial environments. Inter-varietal diversity in grain yield potential correlated significantly with mixing effect, as did straw length diversity when weighted with weed pressure. The grain yields of most mixtures were more stable across environments than their component varieties when accounting also for the general response to environmental productivity. Hence, most mixtures adapted slightly better to environmental productivity and were less sensitive to environmental stress than their component varieties. We conclude that the efficacy of variety mixtures may be enhanced by mixing relatively high-yielding varieties differing in responsiveness to environmental productivity

Meta-Analysis on grain yield effects of cereals-legume intercropping

Meta-Analysis on grain yield effects of cereals-legume intercroppin

Evaluation of reproductive barriers contributes to the development of novel interspecific hybrids in the Kalanchoe genus

Background: Interspecific hybridization is a useful tool in ornamental breeding to increase genetic variability and introduce new valuable traits into existing cultivars. The successful formation of interspecific hybrids is frequently limited by the presence of pre- and post-fertilization barriers. In the present study, we investigated the nature of hybridization barriers occurring in crosses between Kalanchoe species and evaluated possibilities of obtaining interspecific hybrids. Results: The qualitative and quantitative analyses of pollen tube growth in situ were performed following intra-and interspecific pollinations. They revealed occurrence of pre-fertilization barriers associated with inhibition of pollen germination on the stigma and abnormal growth of pollen tubes. Unilateral incongruity related to differences in pistil length was also observed. The pollen quality was identified as a strong factor influencing the number of pollen tubes germinating in the stigma. In relation to post-fertilization barriers, endosperm degeneration was a probable barrier hampering production of interspecific hybrids. Moreover, our results demonstrate the relation of genetic distance estimated by AFLP marker analysis of hybridization partners with cross-compatibility of Kalanchoe species. At the same time, differences in ploidy did not influence the success of interspecific crosses. Conclusions: Our study presents the first comprehensive analysis of hybridization barriers occurring within Kalanchoe genus. Reproductive barriers were detected on both, pre- and post-fertilization levels. This new knowledge will contribute to further understanding of reproductive isolation of Kalanchoe species and facilitate breeding of new cultivars. For the first time, interspecific hybrids between K. nyikae as maternal plant and K. blossfeldiana as well as K. blossfeldiana and K. marnieriana were generated.Danish Agency for Science, Technology and Innovatio

I did it - Om ph.d.- og efteruddannelseskurset, ”Applied Statistics for Researchers and Developers”, afholdt som interaktiv e-læring

Med ordene ”I did it” indleder deltageren fra Sudan et indlæg i gruppens diskussionstråd, da det en lille uge inde i kurset lykkes ham at få knækket et teknisk problem. Han fortsætter med at takke en anden gruppedeltager for det indlæg, som har fået ham til at se løsningen. Diskussionsindlægget, som er typisk for stemningen i kurset, er udtryk for to ting: at diskussionsindlæg kan fungere i et teknisk fag, og at fornemmelsen af gruppetilhør kan opnås på tværs af landegrænser i en sådan grad, at deltagerne vil dele deres begejstring med resten af gruppen. Artiklen beskriver, hvordan kurset er opbygget med en indledende gruppesocialisering på få dage, med aktiviteter med obligatorisk deltagelse, men uden ”karakter-straf” for fejltagelser, med speakede PowerPoint forelæsninger og med en fleksibel tidsstyring inden for snævre rammer. Vi beretter om gode erfaringer med kurset og forsøger at klarlægge, hvilke pædagogiske elementer og tiltag, der gav de gode resultater i form af gruppediskussioner med frembringelse af faglig viden på højt niveau samt en gennemførselsprocent på ca. 90 i første gennemløb af det krævende kursus. Til sidst i artiklen diskuterer vi spørgsmålet, om det ligefrem kan være en fordel kun at mødes online

The prognostic value of FET PET at radiotherapy planning in newly diagnosed glioblastoma

BACKGROUND: Glioblastoma patients show a great variability in progression free survival (PFS) and overall survival (OS). To gain additional pretherapeutic information, we explored the potential of O-(2-(18)F-fluoroethyl)-L-tyrosine (FET) PET as an independent prognostic biomarker. METHODS: We retrospectively analyzed 146 consecutively treated, newly diagnosed glioblastoma patients. All patients were treated with temozolomide and radiation therapy (RT). CT/MR and FET PET scans were obtained postoperatively for RT planning. We used Cox proportional hazards models with OS and PFS as endpoints, to test the prognostic value of FET PET biological tumor volume (BTV). RESULTS: Median follow-up time was 14 months, and median OS and PFS were 16.5 and 6.5 months, respectively. In the multivariate analysis, increasing BTV (HR = 1.17, P < 0.001), poor performance status (HR = 2.35, P < 0.001), O(6)-methylguanine-DNA methyltransferase protein status (HR = 1.61, P = 0.024) and higher age (HR = 1.32, P = 0.013) were independent prognostic factors of poor OS. For poor PFS, only increasing BTV (HR = 1.18; P = 0.002) was prognostic. A prognostic index for OS was created based on the identified prognostic factors. CONCLUSION: Large BTV on FET PET is an independent prognostic factor of poor OS and PFS in glioblastoma patients. With the introduction of FET PET, we obtain a prognostic index that can help in glioblastoma treatment planning. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00259-016-3494-2) contains supplementary material which is available to authorized users

Angiotensinogen and HLA class II predict bevacizumab response in recurrent glioblastoma patients

Background Bevacizumab combination therapy is among the most frequently used treatments in recurrent glioblastoma and patients who achieve response to bevacizumab have improved survival as well as quality of life. Accordingly, the aim of this study was to identify predictive biomarkers for bevacizumab response in recurrent glioblastoma patients. Methods The study included a total of 82 recurrent glioblastoma patients treated with bevacizumab combination therapy whom were both response and biomarker evaluable. Gene expression of tumor tissue was analyzed by using a customized NanoString platform covering 800 genes. Candidate gene predictors associated with response were analyzed by multivariate logistic and Cox regression analysis. Results Two genes were independently associated with response: Low expression of angiotensinogen (2‐fold decrease in AGT; OR = 2.44; 95% CI: 1.45–4.17; P = 0.0009) and high expression of a HLA class II gene (2‐fold increase in HLA‐DQA1; OR = 1.22; 95% CI: 1.01–1.47; P = 0.04). These two genes were included in a model that is able predict response to bevacizumab combination therapy in clinical practice. When stratified for a validated prognostic index, the predictive model for response was significantly associated with improved overall survival. Conclusion Two genes (low angiotensinogen and high HLA‐class II expression) were predictive for bevacizumab response and were included in a predictive model for response. This model can be used in clinical practice to identify patients who will benefit from bevacizumab combination therapy