980 resultados para Simultaneous control


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The seed-feeding jewel bug, Agonosoma trilineatum (F.), is an introduced biological control agent for bellyache bush, Jatropha gossypiifolia L. To quantify the damage potential of this agent, shadehouse experiments were conducted with individual bellyache bush plants exposed to a range of jewel bug densities (0, 6 or 24 jewel bugs/plant). The level of abortion of both immature and mature seed capsules and impacts on seed weight and seed viability were recorded in an initial short-term study. The ability of the jewel bug to survive and cause sustained damage was then investigated by measuring seed production, the survival of adults and nymph density across three 6-month cycles. The level of seed capsule abortion caused by the jewel bug was significantly affected by the maturity status of capsules and the density of insects present. Immature capsules were most susceptible and capsule abortion increased with jewel bug density. Similarly, on average, the insects reduced the viability of bellyache bush seeds by 79% and 89% at low and high densities, respectively. However, sustaining jewel bug populations for prolonged periods proved difficult. Adult survival at the end of three 6-month cycles averaged 11% and associated reductions in viable seed production ranged between 55% and 77%. These results suggest that the jewel bug has the potential to reduce the number of viable seeds entering the soil seed bank provided populations can be established and maintained at sufficiently high densities.

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A transformation technique for the introduction of transgenes to control blackheart by particle bombardment has been developed for pineapple cv. Smooth Cayenne. Leaf callus cultures capable of high frequency organogenesis with a short regeneration time were used as explant material. Gus and gfp reporter genes were used to observe and determine transient and stable expression. The ppo gene, isolated from pineapple, was introduced to control blackheart. Co-transformation occurred with constructs containing the nptII gene conferring geneticin resistance. We have recovered 15 independent transgenic gus and gfp lines each from 8 separate experiments and 22 ppo lines from 11 experiments. Gus, gfp, ppo and nptII positive plants have been regenerated, which have been shown by Southern blot analysis to be stable transgenics containing multiple copies of the introduced genes. These results show that biolistic gene delivery in pineapple can be successfully achieved at an acceptable efficiency of 0.21-1.5% for genetic improvement of 'Smooth Cayenne', the industry standard throughout the world.

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In this paper we study two problems in feedback stabilization. The first is the simultaneous stabilization problem, which can be stated as follows. Given plantsG_{0}, G_{1},..., G_{l}, does there exist a single compensatorCthat stabilizes all of them? The second is that of stabilization by a stable compensator, or more generally, a "least unstable" compensator. Given a plantG, we would like to know whether or not there exists a stable compensatorCthat stabilizesG; if not, what is the smallest number of right half-place poles (counted according to their McMillan degree) that any stabilizing compensator must have? We show that the two problems are equivalent in the following sense. The problem of simultaneously stabilizingl + 1plants can be reduced to the problem of simultaneously stabilizinglplants using a stable compensator, which in turn can be stated as the following purely algebraic problem. Given2lmatricesA_{1}, ..., A_{l}, B_{1}, ..., B_{l}, whereA_{i}, B_{i}are right-coprime for alli, does there exist a matrixMsuch thatA_{i} + MB_{i}, is unimodular for alli?Conversely, the problem of simultaneously stabilizinglplants using a stable compensator can be formulated as one of simultaneously stabilizingl + 1plants. The problem of determining whether or not there exists anMsuch thatA + BMis unimodular, given a right-coprime pair (A, B), turns out to be a special case of a question concerning a matrix division algorithm in a proper Euclidean domain. We give an answer to this question, and we believe this result might be of some independent interest. We show that, given twon times mplantsG_{0} and G_{1}we can generically stabilize them simultaneously provided eithernormis greater than one. In contrast, simultaneous stabilizability, of two single-input-single-output plants, g0and g1, is not generic.

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1. Mammalian predators are controlled by poison baiting in many parts of the world, often to alleviate their impacts on agriculture or the environment. Although predator control can have substantial benefits, the poisons used may also be potentially harmful to other wildlife. 2. Impacts on non-target species must be minimized, but can be difficult to predict or quantify. Species and individuals vary in their sensitivity to toxins and their propensity to consume poison baits, while populations vary in their resilience. Wildlife populations can accrue benefits from predator control, which outweigh the occasional deaths of non-target animals. We review recent advances in Australia, providing a framework for assessing non-target effects of poisoning operations and for developing techniques to minimize such effects. We also emphasize that weak or circumstantial evidence of non-target effects can be misleading. 3. Weak evidence that poison baiting presents a potential risk to non-target species comes from measuring the sensitivity of species to the toxin in the laboratory. More convincing evidence may be obtained by quantifying susceptibility in the field. This requires detailed information on the propensity of animals to locate and consume poison baits, as well as the likelihood of mortality if baits are consumed. Still stronger evidence may be obtained if predator baiting causes non-target mortality in the field (with toxin detected by post-mortem examination). Conclusive proof of a negative impact on populations of non-target species can be obtained only if any observed non-target mortality is followed by sustained reductions in population density. 4. Such proof is difficult to obtain and the possibility of a population-level impact cannot be reliably confirmed or dismissed without rigorous trials. In the absence of conclusive evidence, wildlife managers should adopt a precautionary approach which seeks to minimize potential risk to non-target individuals, while clarifying population-level effects through continued research.

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The ribosomal DNA internal transcribed spacer region was amplified and sequenced from a selection of specimens of the Sporobolus smut Ustilago sporoboli-indici. Phylogenetic comparison with other Ustilago and Sporisorium species revealed strong support for an evolutionary radiation of Ustilago species infecting the Chloridoideae and Pooideae, of which U. sporoboli-indici forms a major lineage. Comparisons are made with other groups of plant pathogenic fungi, and it is concluded that phylogenetic analyses of potential biocontrol agents are useful for identifying pathogens that are derived from evolutionary lineages that parasitize a wide range of unrelated plants. Such pathogens are less desirable as biocontrol agents as they may have a greater likelihood of infecting plants outside their normal host ranges.