A Nonlinear Mixed-Effects Model for Multivariate Longitudinal Data with Dropout with Application to HIV Disease Dynamics

The main challenge in biomedical and clinical studies which involve collection of longitudinal data is the premature withdrawal of the subjects from the study resulting in incomplete data. Standard statistical analysis approaches usually give biased estimates of the model parameters if the mechanisms that led to dropout are ignored. In this discussion, we consider nonlinear mixed-effects models for multivariate longitudinal data in the presence of subject dropout. We present techniques for estimation of model parameters. These procedures are applied to estimate the parameters in the HIV dynamic system using routine observational data from an HIV clinic.     

Diploid-tetraploid crosses as the instrument for obtaining apomictic maize plants

In this paper, the opportunity to reveal pseudogamous apomixis in maize inbred lines when tetraploids are used as pollinators is demonstrated for the first time. Kernels with hybrid endosperm, from which plants of maternal type developed, were obtained in five of ten studied lines. Hybrid nature of these kernels was proven using SDS electrophoresis of endosperm proteins. In addition to apomictic kernels, the normally developed kernels with di-, three- and tetraploid hybrid embryos were obtained.     

Height-diameter models with random coefficients and site variables for tree species of Central Maine

Height-diameter models were developed for nine tree species common to the northeastern United States: Abies balsamea, Acer rubrum, Betula papyrifera, B. populifolia, Picea rubens, P. mariana, Pinus strobus, Populus tremuloides, and Tsuga canadensis. Stem heights and diameters were collected from 6 146 trees (between 136 and 2615 trees per species) on 50 plots within 10 structurally diverse stands that are part of a long-term silvicultural experiment in central Maine. The models were developed using both generalized nonlinear least squares (GNLS) and multi-level, mixed-effects approaches. Mixed-effects approaches were superior to GNLS, with inclusion of site covariates (tree density and basal area) accounting for some of the variability explained by the random coefficients in the full mixed-effect models. Analysis of plot-level parameter estimates suggested that differences in stand structure (even-aged vs. uneven-aged silvicultural practices) had a significant influence on the height-diameter relationships.     

利用水硼溶液浸泡为哥伦比亚瓜多竹防腐——水硼溶液温度、浓度和浸泡时间对防腐效果的影响

摘要：在哥伦比亚咖啡产区,调查了使用水硼溶液浸泡的化学方法为瓜多竹防腐的效果。将不同径级和壁厚的没经过处理的竹子截取成长度为50-60cm之间的样品。然后将样品浸泡在用硼砂制成的3个不同浓度水硼溶液中：硼酸为1：2,在不同的温度（20-80℃）中浸泡不同时间（3-5d）。防腐质量由主要样品的初级温度、比重、溶液密度、渗透时间和温度控制。同时设定数学模型．以控制溶液浓度．     

A model calculation approach towards the optimization of a standard scheme of seed‐parent line development in hybrid rye breeding

The importance of hybrid rye (Secale cereale L.) breeding has steadily increased over the last decades. This paper presents results of model calculations aiming to optimize the number of candidates, testers to assess combining ability and test locations at each selection stage of a standard scheme of seed‐parent line development. Two variants of the scheme differing in the number of stages and the cycle length are investigated. Optimization criterion is the expected selection gain per year under the restriction of a fixed budget. Prediction of selection gain rests on quantitative–genetic and economic parameters estimated from breeders’ data. Optimization covers different genetical and economical situations. Results show that the optimum number of testers to assess combining ability depends on the relative amount of dominance variance. The efficiency of a breeding scheme strongly increases with decreasing cycle length. A larger budget should mainly be used to increase the number of candidates at all selection stages. Recommendations for practical breeding schemes are given. We conclude that model calculations are a valuable tool for the optimization of breeding schemes.     

Development of a cDNA-AFLP derived CAPS marker co-segregating with the powdery mildew resistance gene Mlg in barley

Powdery mildew is an important pathogen of barley in many barley-growing areas. To identify molecular markers for the resistance gene Mlg located on chromosome 4H, a cDNA-AFLP approach was carried out on near-isogenic lines. Based on the identification of a differentiating fragment of 37 bp, which turned out to be part of a nucleoside diphosphate kinase as estimated by blastn , a CAPS marker has been developed, which co-segregated with Mlg in a population of 738 F₂-plants. Due to its co-dominant inheritance, clear banding pattern and close linkage this marker is well suited for marker-based selection procedures.     

Plant survival after freezing in wheat 'Cappelle Desprez' ('Bezostaya 1') intervarietal chromosome substitution lines

The effect of individual chromosomes of the wheat variety ‘Bezostaya 1’ on plant resistance to low temperatures was studied using the available set of intervarietal ‘Cappelle Desprez’ (‘Bezostaya 1’) chromosome substitution lines. The number of plants surviving after freezing at ?12, ?15 and ?17°C was determined for both parents and lines in trials in 2004/2005 and 2005/2006. Significant differences between the three temperature treatments and between lines were found, implying that two factors, the level of temperature stress and chromosome substitutions, were influencing plant survival. Improved frost resistance in both trials was associated with genes located on five chromosomes: 5A, 2D, 4A, 5D and 6A. An increase in the plant frost resistance because of the effects of 7A and 1A chromosomes was also observed in the 2005/2006 trial, when the overall autumn and winter (January) temperatures were lower than in 2004/2005.     

Radiographic evaluation of internal defects of seeds of forage grasses

The possibility of using the radiographic method for analyzing the viability of seeds of forage grasses and making a differentiated evaluation of the effect of various types of latent defects of the internal structure of seeds on their sowing qualities is shown.     

Morphogeographic and molecular genetic analysis of the VIR white cabbage collection

It is shown that an analysis of microsatellites allows dividing the white cabbage collection into concultivars and geographic groups corresponding to its morphogeographic classification. Despite a different breeding history, cultivars remain belonging to the concultivar.