Assessment of the sample size to estimate the weed seedbank in soil

It was found that, in order to estimate the number of weed seeds in soil with a desirable degree of accuracy and confidence level. the sample size depends to large extent on the spatial distribution pattern of the seeds in the soil. The seeds of most weeds found in cultivated soils are distributed according to one of two statistical distributions: Poisson or Negative Binomial. For an acceptable degree of accuracy in estimating the number of seeds in the soil, the sample size must be large, Taking this into account, in this study a practical solution based on a theoretical approach is proposed for the problem of establishing the sample size for a species distributed according to either statistical pattern. In addition, given the sample size, it was possible to determine the estimation error to be expected. This theoretical approach is compared with that proposed in previous studies. Two abaci, based on simple expressions, are provided to determine the sample size, according to the Poisson or the Negative Binormal distribution of the weed species. For Poisson distribution, the sample size is determined (given the desired maximum relative error estimation and the confidence level) as a function of only one parameter: the expected number of seeds per sampling unit m (estimaied by the sample mean). For Negative Binomial distribution, the sample size is determined as a function of two parameters: m and p (estimated according to the relationship between the sample mean and the sample variance). A sample size n nol very different from those given in previous studies is obtained, but the lower limit found for the n -values is lower than that found in these studies.     

Dose response of weeds to methyl iodide and methyl bromide

Labonuory bioassay and field experiments were conducted to characterize the dose response of weeds to methyl iodide and methyl bromide as soil fumigants. The patterns in potency of both fumigants and in sensitivity of diffcretit weed species to the fumigants were distinguished with the use of logistic dose-response models. Similar to its response to methyl hromide fumigation. Amaranthus retrofleus L. was the most sensitive to methyl iodide fumigation. Cyperus rotundtis L. was the least sensitive to methyl iodide fumigation, whereas Portuloca oleracea L. was the least sensitive to methyl hromide. Lolium multiflorum Lam. Abutilon theophrasti Medik. Chenopodium album L. P. ateracea . Brassica kaber (D.C.) L.C. Wheeler and Cyperus escuden-tus L. were similar in sensitivity to methyl iodide. Methyl iodide was as potent as methyl bromide for A. retroflexus but more potent than methyl bromide for L. multiflorum , A. theophrasti. C. album. P. oleracea. B. kaber, C. esculentus and C. rotundus. The dose response for weeds in the field was similar to that obtained in laboratory bioassays. Under fieid conditions. 280 kg ha^-1 methyl iodide killed all species tested except Solanum nigrum L Methyl iodide appears to be a suitable replacement for meihyl bromide because it can be used in situations simitar to methyl bromide fumigation, has superior efficacy against a broad spectrum of pests and has a low potential for degrading the earth's ozone lavers.     

Biological and molecular characterization of Tomato spotted wilt Virus in Israel

Received April 24, 1997; received in final form June 29, 1997. Symptoms resembling tomato spotted wilt virus (TSWV) infections were documented among ornamental and vegetable crops in commercial greenhouses and open fields in Israel. Plants exhibiting these symptoms were collected from January 1992 to December 1996. Among cultivated plants analyzed for TSWV by enzyme-linked immunosorbent assay (ELISA), 19 species representing five families were found to be infected; natural infection was also recorded in six plant species of weeds. Virus identity was characterized by host range, serology and electron microscopy. Serological reaction with the isolates, found in Israel, using antisera from different sources as well as the sequence analysis of the nucleocapsid gene, demonstrated that the Israeli isolates of TSWV are a member of tospovirus serogroup I, type I (BR-01 strain). No virus transmission was found in seeds collected from virus-infected vegetable and ornamental crops. A non-radioactive molecular probe derived from the cloned nucleocapsid isolate enables specific detection of the virus in crude sap from infected plants. The detection of TSWV in Israel constitutes a severe potential threat to the ornamental and vegetable industry.     

Changes in the content of steroidal glycoalkaloids in potato tubers grown in the field and in the greenhouse under different conditions of light, temperature and daylength

Differences in the content of steroid glycoalkaloids (SGA) were noted in the peels of potato tubers cultivars Alpha, Cara, Désirée and LT-7. Cultivar LT-7 had always the highest SGA content, Désirée was intermediate and Alpha and Cara had the lowest SGA content, regardless of growing conditions, tuber ageing and tuber treatments. Tubers grown during the summer developed the highest SGA content as compared to those grown in the spring and winter seasons, respectively. Tubers grown during winter showed an increase in SGA toward the end of the storage period. Similar results were obtained with tubers of LT-7 grown in a greenhouse under cool temperatures in combination with short days (which imitate the winter conditions in Israel). A decrease in SGA content was observed in tuber slices treated with a fungal cell-wall preparation fromPhytophthora citrophthora. This decrease was much stronger in the pith than in the peel, indicating a possible role for SGA in the defence mechanism because peels are the first part of the tuber to be invaded by pathogens. The above results were observed in tubers of all cultivars regardless of the growing season or tuber ageing.     

Effects of the host, the pathogen, the environment and their interactions, on fusarium wilt in carnation

Fusarium oxysporum f.sp.dianthi causes severe wilting in carnation (Dianthus caryophyllus L.) worldwide. The pathogen is present in the soil profile in which carnation roots are distributed and may infect the plants at any time during the growing season. To minimize the losses induced by Fusarium wilt, growers use carnation cuttings free ofFusarium spp. and fumigate the soil with methyl bromide prior to planting. The severity of epidemics and the resulting losses are governed by the main and interacting effects of the three components of the disease syndrome: the host, the pathogen and the environment. Host variables include the type and the degree of cultivar resistance (i.e., complete, partial or tolerance); pathogen variables include the race, its virulence and infectivity, and the amount of initial inoculum; environmental variables include solar radiation intensity, photoperiod, temperature and the growth substrate. In the present review the information available on the effect of the host, the pathogen and the environment, and their interactions, on Fusarium wilt in carnation is summarized.     

魔芋新品种———清江花魔芋

 ‘清江花魔芋’是恩施州魔芋研究中心从武陵山区地方魔芋种质资源中通过系统选择育成, 产量324115 kg/ hm² , 干魔芋含葡甘露聚糖5114 % , 鲜魔芋含干物质1714 % , 全生育期125 d 左右, 较抗白绢病和抗软腐病, 比目前主栽品种增产10212 % , 成为了恩施州及武陵山区魔芋产业发展的主导品种。     

Clone identification and genetic relationship among vine cacti from the genera Hylocereus and Selenicereus based on RAPD analysis

Clones of Hylocereus and of Selenicereus species were distinguished from each other by the banding pattern generated by one to nine 10-mer oligonucleotide primers in the random amplified polymorphic DNA (RAPD) reaction. RAPD analysis was also applied to estimate the genetic relationship among five Hylocereus and nine Selenicereus species. A dendrogram was constructed based on a data matrix of 173 polymorphic bands originated by nine primers. Two groups were identified, one consisting of Hylocereus species and the other consisting of Selenicereus species. These results are consistent with the accepted taxonomic classification of the genera studied. The principal coordinate analysis (PCO), i.e. the plot drawn on the basis of the RAPD data, clearly distinguished between three groups, namely, Hylocereus species, S. megalanthus and the rest of the Selenicereus species studied. PCO thus strongly support the notion that the tetraploid S. megalanthus is an exception among the Selenicereus group. The RAPD results support our hypothesis regarding the allopolyploid (rather than autopolyploid) origin of this species.     

Quantifying patch distribution at multiple spatial scales: Applications to wildlife-habitat models

Multiscale analyses are widely employed for wildlife-habitat studies. In most cases, however, each scale is considered discrete and little emphasis is placed on incorporating or measuring the responses of wildlife to resources across multiple scales. We modeled the responses of three Arctic wildlife species to vegetative resources distributed at two spatial scales: patches and collections of patches aggregated across a regional area. We defined a patch as a single or homogeneous collection of pixels representing 1 of 10 unique vegetation types. We employed a spatial pattern technique, three-term local quadrat variance, to quantify the distribution of patches at a larger regional scale. We used the distance at which the variance for each of 10 vegetation types peaked to define a moving window for calculating the density of patches. When measures of vegetation patch and density were applied to resource selection functions, the most parsimonious models for wolves and grizzly bears included covariates recorded at both scales. Seasonal resource selection by caribou was best described using a model consisting of only regional scale covariates. Our results suggest that for some species and environments simple patch-scale models may not capture the full range of spatial variation in resources to which wildlife may respond. For mobile animals that range across heterogeneous areas we recommend selection models that integrate resources occurring at a number of spatial scales. Patch density is a simple technique for representing such higher-order spatial patterns.     

Karambole (Averrhoa carambola L.)

The carambola (Averrhoa carambola L., family Oxalidaceae) is believed to have originated in Sri Lanka and the Moluccas but it has been cultivated in southeast Asia and Malaysia for many centuries. The evergreen tree is slow-growing, has a rounded crown and reaches 6 to 9 m in height. The 5- to 6-angled fruits (6 to 15 cm long and up to 9 cm wide) have thin, waxy, orange-yellow skin and juicy, yellow flesh. The fruit has a more or less pronounced oxalic acid odor and the flavor ranges from very sour to middle sweetish. The carambola is a tropical and subtropical tree, it can tolerate freezing temperature (?2°C) for short periods and sustain little damage. Trees can be propagated by seed, grafting, budding, and air layering. Tissue culture propagation has met only limited success. Plant spacing varies with growing region and cultural practices. Tree training is practiced intensively in different countries. Harvest timing and postharvest handling are critical to successful marketing of fresh fruit. Carambola is a nonclimateric fruit. Growers carefully harvest fruit by hand at color break — light green fruit with yellow color. The storage conditions should be 5 to 10°C and 85 to 95% relative humidity. Most carambola fruit is eaten fresh, used in salads, desserts, and cooked as star-shaped slices; fruit can also be dried, canned and frozen. The leaves have been eaten as a substitute for sorrel. Commercial production occurs in Taiwan, Malaysia, southern China, the Philippines, Australia, USA (Florida, Hawaii), Brazil, Suriname and Guyana. Production and consumption appears on the rise throughout the world and will most likely increase as selection and breeding for superior tasting cultivars with improved handling characteristics and storage conditions are found.