Predicting the spread of postharvest disease in stored fruit,with application to apples

Postharvest diseases can cause considerable damage to harvested fruit in controlled atmosphere storage. Since there is a large cost associated with opening the storage rooms, regular assessment of damage levels is not feasible, and many experts agree on the need for a reliable predictive model. Presented here is a simulation model that predicts the overall incidence of disease in a bin of stored fruit as a function of initial infection levels and the fruit's susceptibility to fungal attack. Uninfected fruit tissue, infected fruit tissue, and fungal growth are modelled by a system of three ordinary differential equations. Simulations of the growth and spread of the pathogen in storage were conducted, with disease incidence measured monthly. The model provides insight into the dynamics of postharvest fungal disease, and forms the basis of a predictive model that could be used by packinghouses to determine how long a given crop of fruit can be stored before the infection risk rises above a predetermined tolerable level.     

秋水仙素处理对黑麦根尖细胞有丝分裂的影响

为了解秋水仙素对黑麦根尖细胞有丝分裂的影响，以黑麦根尖为材料，在不同浓度秋水仙素（0．01％、0．05％、0．10％、0．15％、0．20％）和不同处理时间（12、24、36、48、60、72h）条件下测定了根尖细胞中期分裂指数和细胞加倍指数。结果表明，随着秋水仙素浓度的升高，细胞加倍指数增加，当秋水仙素浓度为0．15％时细胞加倍指数达到最大值（0．0362％），以后迅速下降。随着处理时间的延长，中期分裂指数逐渐下降，而细胞加倍指数在处理36h时达到最大值（0．0208％）。在浓度与时间的互作方面，0．15％的秋水仙素处理24h，细胞的中期分裂指数最高，达到0．202％；而0．15％的秋水仙素处理36h，细胞加倍指数最高，达到0．096％。     

Cork weight prediction at tree level

In spite of the importance of cork and cork oak stands in the Portuguese forest and economic scenarios, little research work has been done with this species over the years. The main objective of this study is to define a system of prediction equations to assess air-dried cork weight using dendrometric variables of the tree as predictors. These equations can be used at an intermediate age of the cork production cycle, which is usually of 9 years, or at the year of the stripping process, with 9 years old cork. Several alternative models were developed, from simpler models, using variables easy to gather in the field, to more complex ones that maximise the prediction ability. The development of the weight prediction equations was based on data gathered on three stands located in a region located in the centre/south Portugal, the Coruche county, with average aptitude regarding cork production.     

Analytical models of soil and litter decomposition: Solutions for mass loss and time-dependent decay rates

Combining decomposition data with process-based biogeochemical models is essential to quantify the turnover of organic carbon (C) in surface litter and soil organic matter (SOM). Long-term decomposition may be suitably analyzed by linear models (i.e., all fluxes defined by first-order kinetics), which allow the derivation of analytical expressions to estimate the loss of C and the overall apparent decay rate (k_app) through time. Here we compare eight linear models (four discrete-compartment models with one or two C pools, two models with a single time-dependent decay rate, and two models based on a continuous distribution of decay rates) and report their analytical solutions for two types of decomposition experiments: i) studies that evaluate the decomposition of a single input of fresh litter (i.e., a single cohort, as in litterbag and C labeling experiments), and ii) studies that evaluate the decomposition of soil samples with compounds of different ages (i.e., multiple cohorts, as in long-term incubations or isotope dilution experiments). We fitted analytical mass loss functions to both types of datasets and evaluated the performance of the models. For single-cohort data, continuous-decay models provide the best balance between accuracy and parsimony (R² = 0.99, lowest Akaike and Bayesian information criteria), while for multiple-cohort data the two-pool models tend to perform better (R² = 0.96), perhaps because of the strong separation of time scales in the decomposition data considered. Differences among some models are marginal, suggesting that decomposition data alone do not point to a single ‘best’ model. All models resulted in apparent decay rates that decreased markedly through time, in contrast with the assumption of constant k adopted in the single-pool exponential decay model. We also show how model parameters estimated from single cohort samples can be used to model multiple cohort decomposition, unifying both types of experimental data in one theory. Based on our results, it is possible to distinguish the temporal changes in C loss that are attributable to initial chemical composition or abiotic factors, from those associated with the presence of multiple ages in the substrate.     

陆地棉抗虫品种不同年份间农艺性状的比较

笔者对3个陆地棉抗虫品种在两年间的农艺性状和纤维品质性状进行了研究。结果表明,3个抗虫棉品种的产量性状年份间表现基本一致,而纤维品质性状差异较大。新棉33B在3个抗虫棉品种中产量性状表现最好。品种与年份的互作极为显著,2002年新棉33B在籽棉产量和皮棉产量上显著高于对照品种中棉所12号,而在2003年则与对照品种产量相当。JS166在单株籽棉产量和单株皮棉产量、单株铃数、单铃重等性状上两年间表现均较好,2003年还有较低的蕾铃脱落率。99035两年间在产量性状上与对照相比略有提高,但差异并不明显。所有3个抗虫棉品种2002年的纤维品质指标与对照相当,而2003年纤维长度和纤维整齐度明显高于对照。