Interactions between the soilborne root pathogenPhytophthora nicotianae var.parasitica and the arbuscular mycorrhizal fungusGlomus mosseae in tomato plants

In order to study the influence of Arbuscular Mycorrhiza (AM) on the development of root rot infection, tomato plants were raised with or withoutGlomus mosseae and/orPhytophthora nicotianae var.parasitica in a sand culture system. All plants were fed with a nutrient solution containing one of two phosphorus (P) levels, 32µM (I P) or 96µM (II P), to test the consequence of enhanced P nutrition by the AM fungus on disease dynamics. Mycorrhizal plants had a similar development to that of control plants. Treatment withPhytophthora nicotianae var.parasitica resulted in a visible reduction in plant weight and in a widespread root necrosis in plants without mycorrhiza. The presence of the AM fungus decreased both weight reduction and root necrosis. The percentage reduction of adventitious root necrosis and of necrotic root apices ranged between 63 and 89% The enhancement of P nutrition increased plant development, but did not appreciably decrease disease spread. In our system, mycorrhiza increased plant resistance toP. nicotianae var.parasitica infection. Although a contribution of P nutrition by mycorrhiza cannot be excluded, other mechanisms appear to play a crucial role.     

Effects of an African grass invasion on Hawaiian shrubland nitrogen biogeochemistry

African perennial C₄ grasses are highly successful invaders in Hawaiian ecosystems. We examined the effects of African molasses grass (Melinis minutiflora Beauv.) on Hawaiian shrubland nitrogen (N) dynamics without the influence of fire disturbance. Vegetation tissue carbon and nitrogen chemistry, soil inorganic N pools, net N mineralization rates, and total soil N were studied in three adjacent areas: a monospecificMelinis grassland, a mixed grass/shrubland mosaic, and an un-invaded shrubland.Melinis plots within the mosaic area exhibited the largest inorganic N pools and fastest net N mineralization rates, but were temporally variable with grass phenology. Un-invaded shrubland plots contained the smallest inorganic N pools and lowest net N mineralization rates. Grass foliar C:N and litter C:N were lower than those of common shrubland species, providing one possible link between species and ecosystem N dynamics at this site. The combined effects of N cycle modification, successful light competition, and fire-cycle enhancement make the invasion ofMelinis a significant perturbation to Hawaiian shrubland ecosystem function and successional dynamics. ei]Section editor H Lambers     

Identification and characterization of bacterial endophytes of rice

We isolated seven different bacteria from rice seedlings grown from surface sterilized seeds. Three were associated with the rice seed husk and the other four were growing endophytically within the seed. Microscopic studies revealed that the endophytes were concentrated in the root stele region. Some of the bacteria exhibited strong anti-fungal activity against Rhizoctonia solani, Pythium myriotylum, Guamannomyces graminis and Heterobasidium annosum.     

Keratinolytic fungi in sewage sludge

Sewage sludge from the Upper Silesia Region of Poland were surveyed for keratinolytic fungi. Out of 100 Petri dishes examined, 89 were positive for these micro-organisms. Altogether, 185 fungal appearances belonging to 10 species were observed. Trichophyton terrestre with its teleomorph Arthroderma quadrifidum, T. ajelloi with A. uncinatum, Microsporum gypseum with Arthroderma sp., and Chrysosporium keratinophilum with Aphanoascus keratinophilus prevailed in the sludges. The sewage treatment technologies together with the sludge structure, humidity and pH were found to be critical factors determining the occurrence of keratinolytic fungi in the sludge environment. The qualitative and quantitative composition of keratinolytic fungi could be a useful tool in evaluation of sludge treatment processes.     

Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae)

Abstract. The native flora of tropical oceanic islands is known to be particularly susceptible both to displacement and extinction, following the invasion of alien organisms. Miconia calvescens DC. (Melastomataceae), first introduced to Tahiti (French Polynesia, South Pacific Ocean) in 1937 as an ornamental plant, now covers over two-thirds of the Island. As it forms dense monotypic stands which have progressively overwhelmed the native forests, this plant pest is a direct threat to the rich Tahitian indigenous flora. Between 40 and 50 species of the 107 species endemic to Tahiti are thought to be on the verge of extinction. M. calvescens was finally declared a'noxious species in French Polynesia'in 1990. Without efficient control efforts and effective endangered plant conservation and protection legislation, M. calvescens could cause Tahiti and all the high islands of French Polynesia to become ecological deserts.     

Response of adult parasitoids ofBemisia tabaci (Hom.: Aleyrodidae) to leaf residues of selected cotton insecticides

The contact toxicity of eight insecticides to adults of four parasitoids of the sweetpotato whiteflyBemisia tabaci was evaluated in the laboratory. Two common Texas species,Eretmocerus sp. andEncarsia pergandiella Howard, and two exotic species,Eretmocerus mundus Mercet from Spain andEncarsia formosa Gahan from Greece were tested. Insecticides, applied as sprays to greenhouse-grown cotton plants at recommended rates were amitraz (Ovasyn^®), azinphosmethyl (Guthion^®), bifenthrin (Capture^®), buprofezin (Applaud^®), cypermethrin (Ammo^®), methyl parathion and thiodicarb (Larvin^®), with a water control. Parasitoid adults were confined on discs cut from leaves (1) sprayed the same day and (2) sprayed two days previously. Survival in both treatments was measured two and four days following exposure. Significant differences in toxicity were detected among the insecticides. Buprofezin was not toxic to any of the four parasitoids. When caged on leaves sprayed two days previously, only amitraz of the remaining compounds allowed significant general parasitoid survival after two days.E. mundus exhibited the greatest overall tolerance to insecticides, with 40% or more surviving 48 hr after confinement on leaves sprayed with amitraz, thiodicarb and cypermethrin. Survival was generally much reduced after 96 hr. In a separate test, fresh residues of endosulfan (Thiodan^®) were highly toxic at the two rates tested, but two day old residues at the lower rate allowed 76.7% survival ofE. mundus and 35% survival ofE. pergandiella after 48 hrs.     

Biology ofTrichogramma ostriniae (Hym.: trichogrammatidae) reared onOstrinia nubilalis (Lep.: pyralidae) and survey for additional hosts

Trichogramma ostriniae has been identified as a candidate for biological control ofOstrinia nubilalis. As little was known about the biology of this parasitoid when reared onO. nubilalis, we undertook experiments to quantify biological parameters important to mass-rearing and ase ofT. ostriniae. When reared continuously onO. nubilalis, femaleT. ostriniae on average lived 2.7 days and produced 24 progeny. Continuous access to honey resulted in a four-fold increase in longevity and fecundity and a significant increase in the percentage of females parasitizing eggs. Rates of fecundity and parasitism decreased with age of female. Likewise, emergence rates and percentage of female progeny decreased with age of parental female.T. ostriniae successfully parasitizedO. nubilalis eggs until the blackhead stage. Most parasitism of eggs and eclosion of adults occurred during the first half of photophase. Eggs of 13 Lepidopterans were parasitized byT. ostriniae. Eggs of the Noctuidae, Pyralidae, and Plutellidae experienced higher levels of parasitism than others tested.T. ostriniae appears to be similar to other species ofTrichogramma in several respects and does not possess any characteristics that limit its potential for mass rearing and use for augmentative biological control ofO. nubilalis.     

Detection of mining impacts on aquatic macroinvertebrate communities: Results of a disturbance experiment and the design of a multivariate BACIP monitoring programme at Coronation Hill,Northern Territory

Abstract Multivariate methods for the detection of impacts on communities are: (i) explored in the context of a disturbance experiment at a site of previous uranium mining in Kakadu National Park, Northern Territory; and (ii) applied to the design of a monitoring programme for a proposed mining development at nearby Coronation Hill. The disturbance experiment in Rockhole Mine Creek used a gravity-fed redirection of polluted water from the mine adit to create a point-source pollutant. Weekly samples of the macroinvertebrate communities were taken both before and after disturbance at the control and‘impact’ site, as part of a multivariate BACIP (Before-After-Control-Impact-Pairs) design. The results of the experiment show that the multivariate approach provided high sensitivity in detecting impacts on the community, with little difference in sensitivity between species and family level analyses. A simple procedure for deleting those taxa that show poor discrimination between pristine and presently disturbed areas further increased the sensitivity of the tests. In addition to the BACIP analyses, robust ordination of the community data suggested a time/treatment interaction effect. Application of the multivariate BACIP approach also was explored using baseline data for benthic communities from the South Alligator River near Coronation Hill. The method provides high statistical power for monitoring; a relatively small change in community dissimilarity would be detectable in a programme with 5 years of observations before and after commencement of mining. A robust ordination of the yearly samples for the control and potential-impact sites showed that, although samples varied along identifiable gradients over time, the two areas changed in parallel so that the difference between the areas was approximately constant over years. This result demonstrates that the multivariate BACIP approach can provide relative constancy of pre-impact difference values, a key requirement of BACIP designs that is difficult to satisfy using abundance data for a single species.     

THE LASER TOMOGRAPHICAL METHOD USINGMINIMUM OF PROJECTION FOR BIOLOGICAL OBJECT STRUCTURE STUDY

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中国特有植物台湾杉的生物学特性及其保护

本文全面地综述了我国一级国家重点保护植物台湾杉的生物学特性,其中有外部形态特征,内部结构包括苗端、叶片、树皮及木材结构,雌雄配子体与胚胎发育,花粉和染色体。此外还有台湾杉的组织培养、地理分布,生态学与群落学特性等。最后,本文作者还初步分析了台湾杉的濒危原因,并提出了具体保护措施。