无融合生殖：它的证实及其在植物育种中的应用

无融合生殖是一种通过种子进行的无性繁殖方式,它为未来的作物优良品种选育提供了独特的机遇。在一些栽培物种及与其有关的近缘野生植物中,无融合生殖发生的频率较低。本文的目的在于帮助植物育种工作者和遗传学家认识无融合生殖并提出在植物改良中的可能利用方法。无融合生殖向主要作物上的转育可以不需要细胞质雄性不育系而进行纯杂种的培育和商品化生产,可省工节支。由于专性无融合生殖的杂种产生杂合而整齐一致的后代,因而提供了一个将杂合基因带进新的遗传型的有效方法。优良的专性无融合生殖的杂种可不必进行稳定性试验而直接进行产量比较。无融合生殖杂种的利用可以简化商品杂种的生产过程。几种无融合生殖的机制都是遗传控制的,因此植物育种计划中的遗传操作将是一个主要问题,诸如以下的现象都应该作为无融合生殖的特性而加以调查:(1)杂种F_1或开放授精的杂本后代的一致性:(2)杂交后代中的母性类型;(3)不稳定基因型的高结实率;(4)多胚或一胚多苗现象。     

喷灌评价的简化方法

作为干、支管上喷头间距的函数的灌水均匀度和灌水深度的计算机模拟结果,用来作为研究无风条件下固定、半固定喷灌系统性能评价的简化方法。传统的在整个有效控制面积上格形布置的全套雨量筒设备可减少为等间距地布置于同一支管上两喷头间的10个雨量筒设备。根据模拟的结果,在干管间距小于0.65倍的湿润直径(0.65D)的情况下,简化法能取代精确法。这个间距值不超过詹森1980年提出的无风条件下,干管间距为0.65D的标准。同时,由于建改支管间距不超过干管间距的一半的规定,那么支管的最大适用间距为(0.65/2)D。而且,对于支管间距大于此限值的情形,简化法与精确法的应用结果也是一致的。尽管简化法已显示出可用于测估均匀度,然而对于估测灌水深度却不怎么行。平均灌水深度可通过喷嘴流量和喷头间距的测定值计算得到。     

喷灌工程常用经济指标的适用条件及内在联系

关于喷灌工程经济效益的评价标准,规范中推荐采用效益费用比(或称益本比)、净现值、内部回收率以及投资回收年限等指标。就方法上讲,效益费用比、内部回收率和投资回收年限都属于比值法,即以求得的不同指标反映工程项目所花社会劳动的效率或有效性。而净现值属差值法,以指标大小直接反映工程项目可为社会提供的效益。近几年的实     

Predicting behavioral changes associated with age-related cognitive impairment in dogs

OBJECTIVE: To monitor the progression of age-related behavioral changes in dogs during a period of 6 to 18 months and to determine whether signs of dysfunction in any of 4 behavioral categories can be used to predict further impairment. DESIGN: Age-stratified cohort study. ANIMALS: 63 spayed female and 47 castrated male dogs 11 to 14 years of age. PROCEDURE: Data were collected from randomly selected dog owners who were interviewed by telephone twice at a 12- to 18-month interval; data were included if the dog had lived > or = 6 months between interviews. The interview focused on signs of impairment in the following behavioral categories: orientation in the home and yard, social interactions with human family members, house training, and the sleep-wake cycle. Dogs were determined to have impairment in 0 behavioral categories (on the basis of < or = 1 sign for each category), impairment in 1 category (> or = 2 signs of dysfunction in that category), or impairment in > or = 2 categories. RESULTS: Between interviews, 22% (16/73) of dogs that did not have impairment in a category at the time of the first interview developed impairment in that category by the time of the second interview. Forty-eight percent (13/27) of dogs that had impairment in 1 category at the time of the first interview developed impairment in > or = 2 categories by the time of the second interview and were significantly more likely to develop impairment in > or = 2 categories, compared with dogs that initially had impairment in 0 categories. Dogs with 1 sign of dysfunction in orientation were significantly more likely to develop impairment in that category, compared with dogs that had 0 signs of dysfunction in orientation. CONCLUSIONS AND CLINICAL RELEVANCE: Age-related behavioral changes in dogs are progressive. Clinicians should consider trying to predict which dogs are most likely to become progressively impaired during the subsequent 6 to 18 months.     

Sequential sampling for incidence of phomopsis leaf blight of strawberry

ABSTRACT Sequential sampling models for estimation and classification were developed for the incidence of strawberry leaflets infected by Phomopsis obscurans. Sampling protocols were based on a binary power law analysis of the spatial heterogeneity of Phomopsis leaf blight in commercial fields in Ohio. For sequential estimation, samples were collected until mean disease incidence could be estimated with a preselected coefficient of variation of the mean (C). For sequential classification, samples were collected until there was sufficient evidence to classify mean incidence as being below or above a threshold (p(t)) based on the sequential probability ratio test. Monte-Carlo simulations were used to determine the theoretical average sample number (ASN) and probability of classifying mean incidence as less than p(t) (operating characteristic) for any true value of incidence. Estimation and classification sampling models were both tested with bootstrap simulations of randomly selected data sets and validated by data sets from another year that were not utilized in developing the models. In general, achieved (or calculated) C after sequentially sampling for estimation was close to the preselected C of 0.2, and mean incidence was estimated with little bias. Achieving a C of 0.1 with less than 75 sampling units (the nominal value for many original data sets) was more problematical, especially with true incidence less than 0.2. ASN for classification was only 9 to 18 at disease incidence values near p(t), and approximately five or less at incidence values far from p(t). Correct classification decisions were made in over 88% of the validation data sets. Results indicated that it is possible to estimate Phomopsis leaf blight with high precision and with high correct classification probabilities.