Spatial distribution of weeds in arable crops: are current sampling and analytical methods appropriate?

This paper reviews the literature concerning the spatial distribution of weeds; highlighting the limitations of our current sampling and analytical methodologies, and suggesting how these inadequacies can be addressed. Most research studies have used discrete sampling, i.e. weeds are counted within a quadrat, on a grid basis. Few have mapped weeds at a whole-field scale, either with a resolution appropriate to spraying operations or key ecological processes. Statistical analyses used to describe the data can be divided into two main types, spatially implicit (also at the scale of the sampling unit) or spatially explicit, in which the location of individuals is included in the analyses. Spatially implicit methods can be strongly affected by quadrat size and mean density and are of doubtful benefit. More attention is required to address sampling resolution issues for spatially explicit methods. Our understanding of the formation and dynamics of spatial pattern, as well as predicting the consequences of site-specific management, can be improved with models. Unfortunately, most models consider only newly expanding patches and appear incapable of predicting spatial distributions when an area has been fully invaded. More detailed biological information is required if models are to become more realistic and informative. We also need to ensure that we understand the spatial processes in the context of the whole field environment, to optimize the success of site-specific weed management in the longer term.     

Early detection of Neophysopella tropicalis in grapevine leaves and on spore traps by qPCR

Neophysopella tropicalis, one of the causal agents of Asian grapevine leaf rust (AGLR), can cause severe epidemics in Brazil that lead to yield losses in commercial vineyards. An early detection of the pathogen by air sampling of urediniospores on spore traps or in symptomless leaves would be valuable to multiple studies, such as epidemics modelling, risk forecasting, monitoring of pathogen introductions in rust-free areas, and predicting the beginning of epidemics. This study developed a quantitative PCR (qPCR) protocol to quantify N. tropicalis urediniospores attached to adhesive tapes and in grapevine leaves before symptom appearance. A specific primer pair was designed based on the internal transcribed spacer (ITS) sequence region of the AGLR pathogen. Standard amplification curves using genomic DNA from urediniospores of N. tropicalis and from urediniospores attached to adhesive tapes were established. Grapevine leaves inoculated with N. tropicalis were collected at 2, 5, and 7 days postinoculation (dpi). One primer pair (580F/720R) amplified a 140 bp product in all AGLR isolates but did not amplify products of other rust genera, such as Phakopsora, Puccinia, Hemileia, Tranzschelia, Cerotelium, and Coleosporium. As little as 0.1 pg DNA and 10 urediniospores of N. tropicalis attached to adhesive tapes could be detected. qPCR enabled the detection of the pathogen as early as 2 dpi, before symptom appearance. This method can be used to monitor N. tropicalis inoculum in grapevine-growing areas and to quantify symptomless infections of the AGLR pathogen.     

Antibody-mediated response of pigeons to Argas polonicus larval feeding and characterization of larval antigen

Circulating antibodies to larval Argas polonicus antigen detected in the blood of pigeons by means of ELISA reach their highest level 3-6 days post-tick attachment. During 6-8 days post infestation when most larvae detach from their host, there is an abrupt drop of the antibody level in blood followed by second peak at day 10-15. During the secondary and subsequent infestations the dynamics of the antibody production is analogous, but the maximum absorbance values found are higher with each following infestation. This is in direct correlation with the growth of immune resistance of hosts. The transfer of immunoglobulins of resistant pigeons produces in naive hosts a partial resistance in a statistically significant (P less than 0.01) reduction of the number of engorged larvae, in the shortening of larval feeding period and in the decrease of their mean weight after feeding. However this resistance was significantly (P less than 0.01) less expressed than in naturally resistant pigeons during secondary infestation. The protracted effect on the duration of premoulting period and the percentage of moulted larvae manifested in larvae after secondary infestation was not apparent in molecular weight of approximately 19, 21, 23, 27, 45 and 165 kilodaltons, were recognized by serum of resistant pigeons.     

PCR-based detection of Xanthomonas campestris pathovars in Brassica seed

Xanthomonas campestris is a seedborne bacterium that causes black rot of crucifers. Substantial crop losses may result from the rapid spread of the bacteria under favourable conditions, especially those occurring during seedling production. A PCR-based method has been developed for the rapid and sensitive detection of the pathovars of X. campestris that affect crucifers. Primers were designed to specifically amplify a 619 bp fragment of the hrpF gene from X. campestris . Amplification products were not detected from other Xanthomonas species, or from other pathogenic or epiphytic bacteria occurring on these plants. To avoid false-negative results arising from the presence of amplification inhibitors in plant extracts, primers targeting a 360 bp section of the internal transcribed spacer (ITS) region from Brassica spp. were included in a multiplex PCR. The assay readily detected X. campestris pv. campestris infections in diseased plants and from bacterial colonies isolated on growth media, and was more sensitive and specific than traditional plating methods and a commercially available ELISA. A seed-washing protocol was optimized to allow the detection of a single artificially infected seed among 10 000 healthy seeds using the multiplex PCR.     

Plasma aspartate aminotransferase and creatine kinaseactivities in thoroughbred racehorses in relation to age, sex, exercise and training

In order to investigate the effect of age, sex and month on the response of plasma aspartate aminotransferase(AST) and creatine kinase (CK) to exercise, blood samples were collected once a month between March and September from a group of 40 2- and 3-year-old (2yo and 3yo) thoroughbred racehorses (kept under the same managemental regimen) at rest before exercise (PRE) and at 2 (2H) and 24h (24H) post-exercise. The absolute change in activities between the 2H and PRE samples (2HΔ) and the 24H and PRE samples (24HΔ) was also calculated. Age had a significant effect on all measured and calculated parameters for colts (C), apart from 24HΔ CK but showed no effect in the fillies (F). Sex only had a significant effect in the 3yo in the 2HΔ CK. In the 2yo, significant effects of sex were found for both CK and AST in the PRE, 2H and 24H samples. The effect of month varied according to the classification group with only the 2yoC not showing any significant effect on any parameter. Fillies were, in general, more likely than colts to show greater than a twofold increase in CK activity at 2H post-exercise and the number of animals showing such an increase decreased as the season progressed. Very little change in AST activities occurred with exercise.     

Feeding and vigilance behaviour of breeding ostriches (Struthio camelus) in a farming environment in Britain

1. Vigilance and feeding behaviour of male and female adult breeding ostriches were recorded to determine feeding and scanning bout lengths, a time budget and the pattern of vigilance immediately after food was provided. 2. Males were more vigilant and fed for shorter periods than females immediately after concentrate food was delivered but not throughout the whole day. 3. Most interscan periods of males were below 40 s with a maximum of 90 s compared with most interscan periods of females lasting less than 70 s with a maximum of 160 s. 4. Gender differences in behaviour are attributed to increased male vigilance for predators and/or conspecifics, and increased female feeding required for egg production and greater opportunity to feed because of male vigilance.     

Comparison of carcinogenicity studies with aldrin and dieldrin.

Laboratory testing of animals is the principal method used to identify chemical carcinogens. However conflicting results are often obtained. This is emphasized in a cross-comparison of 6 aldrin-dieldrin studies; 3 were positive for tumor induction and 3 were negative. Four components of the assays are examined: husbandry, compound administration, observation, and interpretation of results.     

Agar well technique for antibiotics in animal feeds.

The agar well technique compares favorably with the cylinder plate assay in accuracy, sensitivity, and precision. It is more flexible and more rugged, and growth of seed organism is not inhibited. The wells are precision cut with Grafar gel punch assembly with sets (6) of 10, 7, 5, 4, and 3 mm cutters. The wells are easily and rapidly filled with short, disposable Pasteur pipets fitted with rubber bulbs. The smaller wells are filled with capillary pipets. The diameter of the well (independent of volume) appears to be a function of concentration. For every decrease in the diameter size of the well, concentration can be increased, at least to the next higher level of the standard response line. Extracts of chlortetracycline containing as much as 3.2 mu-g/ml can be analyzed if the 3 mm wells are used and with no sacrifice in accuracy or precision. This works especially well for antibiotic premixes. The technique has been used successfully for penicillin, streptomycin, chlortetracycline, oxytetracycline, oleandomycin, and tylosin.