Expression of genes for resistance to potato virus Y in potato plants and protoplasts

Plants of several potato clones with major gene resistance to potato virus Y (PVY) developed necrotic local lesions and systemic necrosis after manual inoculation with common (PVY_o) or veinal necrosis (PVY_N) strains of the virus. The clones reacted similarly, although their resistance genes are thought to be derived from four different wild species of Solarium. Mesophyll protoplasts from each clone became infected when inoculated with RNA of PVY_o by the polyethylene glycol method. The proportion of protoplasts infected, assessed by staining with fluorescent antibody to virus particles, was similar to that of protoplasts of susceptible potato cultivars. In contrast, plants of potato cultivars Corine and Pirola, which possess gene Ry from S. stoloniferum, developed few or no symptoms when manually inoculated or grafted with PVY_o. Moreover, only very few protoplasts of these cultivars produced virus particle antigen after inoculation with PVY_o RNA. The extreme resistance to PVY of cvs Corine and Pirola was therefore expressed by inoculated protoplasts whereas the resistance of the necrotic-reacting potato clones was not.     

Sterilisation of the potato moth, Phthorimaea operculella (Lepidoptera: Gelechiidae) by fumigation with thiotepa

The chemosterilant thiotepa was used in fumigation chambers for sterilisation of male and female potato moths. Its effectiveness was registered by recording egg production, egg hatch, longevity of moths, and mating frequency. Also studied was the effect on the persistence of the chemical of temperature, exposure time and concentration. The tests showed that it was possible to sterilise fully male and female moths with thiotepa without adverse effects on mating and longevity. Generally, males were more susceptible to sterilisation than females. No definite relationship was found between dosage and egg production, longevity and mating frequency of moths. The compound did not lose its sterilising activity when used successively up to five times during the same day or once weekly for a total of 4 wk. The sterilising activity was related to temperature, exposure time, concentration and rates of airflow of the circulatory fumigation chambers. Some reduction of fertility occurred when F, adults paired with untreated moths.     

Studies on the mechanisms of barley seed deterioration

The type of chemical treatment used to control regrowth from hardwood stumps affects their colonization by fungi. Since such stumps often act as sources of infection for Armillaria mellea this may have important consequences. Ammonium sulphamate generally favours growth of species causing rapid decay, some of which compete well with A. mellea, whereas 2,4,5-trichlorophenoxyacetic acid tends to promote growth of Chondro-stereum purpureum which is replaced by A. mellea. The former treatment is recommended for situations where serious damage from A. mellea seems likely to occur, because the best hope of control is to ensure rapid killing of stump roots. Prompt colonization of stumps was obtained by inoculating the cut surface with spores of a wood-rotting fungus and then treating it with 40% ammonium sulphamate. In birch stumps jointly inoculated with Coriolus versicolor and A. mellea the amount of wood occupied by the latter after 4 yr was greatly reduced by comparison with controls inoculated with A. mellea alone. Stump inoculation might be worth developing for use in valuable plantations and other intensively managed areas such as parks and gardens, especially where measures such as stump excavation are impracticable.     

Ventilatory Mechanism and Control in Grasshoppers

SYNOPSIS. Grasshoppers exhibit a diversity of ventilatory patternsdepending on activity status. For each pattern, the mechanismand control of gas exchange is analyzed in terms of a two-stepmodel, consisting of tracheolar and trans-spiracular steps inseries. During the intermittent gas exchange that characterizesthe most quiescent grasshoppers, spiracles open and close inresponse to changing carbon dioxide, and trans-spiracular resistancecontrols gas exchange. In resting but alert grasshoppers, abdominalpumping occurs, and gas exchange is controlled equally by tracheolarand trans-spiracular resistances; tracheal oxygen and carbondioxide are regulated by variation in abdominal pumping andspiracular opening. During hopping, abdominal pumping does notoccur, and bulk gas flow is driven by cuticular deformationsassociated with locomotion. Increased cellular oxygen consumptiondepends on use of internal oxygen stores and increased partialpressure gradients. After hopping ceases, abdominal pumpingincreases dramatically and restores tracheal gas composition;however, the rise in abdominal pumping after hopping is notaffected by tracheal gas levels. During flight, bulk flow tothe flight muscles is driven by tidal thoracic auto-ventilation,while the remainder of the body is ventilated by abdominal pumping.During both hopping and flight, the greatest resistances togas transport exist in the tracheolar rather than the trans-spiracularstep.     

Winter Habitat Selection by Canada Lynx in Maine: Prey Abundance or Accessibility?

Abstract: We related winter habitat selection by Canada lynx (Lynx canadensis), relative abundance of snowshoe hares (Lepus americanus), and understory stem densities to evaluate whether lynx select stands with the greatest snowshoe hare densities or the greatest prey accessibility. Lynx (3 F, 3 M) selected tall (4.4-7.3 m) regenerating clear-cuts (11-26 yr postharvest) and established partially harvested stands (11-21 yr postharvest) and selected against short (3.4-4.3 m) regenerating clear-cuts, recent partially harvested stands (1-10 yr), mature second-growth stands (>40 yr), and roads and their edges (30 m on either side of roads). Lynx selected stands that provided intermediate to high hare density and intermediate cover for hares (i.e., prey access) but exhibited lower relative preference for stand types with highest hare densities where coniferous saplings exceeded 14,000 stems/ha.     

Cytochemical Observations of Gemmule Development in Eunapius fragilis (Leidy): Porifera; Spongillidae

The cytology and cytochemistry of gemule formation in the freshwater sponge Eunapius fragilis (Leidy) is investigated. The aggregation of ameboid cells which initiates gemmulation is composed of three distinct cell types, two of these fitting the morphological criteria of the archeocyte class. The third cell type, the granular cell, is a differentiated cell type which undergoes cytolysis during gem-mule coat synthesis. Following early polarisation of the aggregate into an internal reproductive area and a peripheral coat region, a structurally and chemically heterogeneous gemmule coat is synthesis-ed. The coat is formed through secretory activities involving several cell types including, possibly, the internal endothelium. The coat is composed of "collagenous" fibers embedded in a matrix of varying degrees of density–showing close structural and cytochemical similarities to vertebrate chondroid tissue. Vitelline platelets of thesocytes of E. fragilis do not cytochemically resemble any previously reported vitelline inclusions from other sponges. Outer valves of the platelets contain components stained by basic dyes at acidic pH which are not extracted by RNase. Distinct differences in developmental processes and morphological–including cytochemical–characteristics of gemmules of different spongillid species are apparent.     

Climate and CO2 controls on global vegetation distribution at the last glacial maximum: analysis based on palaeovegetation data, biome modelling and palaeoclimate simulations

The global vegetation response to climate and atmospheric CO₂ changes between the last glacial maximum and recent times is examined using an equilibrium vegetation model (BIOME4), driven by output from 17 climate simulations from the Palaeoclimate Modelling Intercomparison Project. Features common to all of the simulations include expansion of treeless vegetation in high northern latitudes; southward displacement and fragmentation of boreal and temperate forests; and expansion of drought‐tolerant biomes in the tropics. These features are broadly consistent with pollen‐based reconstructions of vegetation distribution at the last glacial maximum. Glacial vegetation in high latitudes reflects cold and dry conditions due to the low CO₂ concentration and the presence of large continental ice sheets. The extent of drought‐tolerant vegetation in tropical and subtropical latitudes reflects a generally drier low‐latitude climate. Comparisons of the observations with BIOME4 simulations, with and without consideration of the direct physiological effect of CO₂ concentration on C₃ photosynthesis, suggest an important additional role of low CO₂ concentration in restricting the extent of forests, especially in the tropics. Global forest cover was overestimated by all models when climate change alone was used to drive BIOME4, and estimated more accurately when physiological effects of CO₂ concentration were included. This result suggests that both CO₂ effects and climate effects were important in determining glacial‐interglacial changes in vegetation. More realistic simulations of glacial vegetation and climate will need to take into account the feedback effects of these structural and physiological changes on the climate.     

16S rRNA interoperon sequence heterogeneity distinguishes strain populations of palm lethal yellowing phytoplasma in the Caribbean region

DNA of phytoplasmas in lethal yellowing (LY)‐diseased palms was detected by a nested polymerase chain reaction (PCR) assay employing rRNA primer pair P1/P7 followed by primer pair LY16Sf/ LY16‐23Sr. Polymorphisms revealed by Hinfl endonuclease digestion of rDNA products differentiated coconut‐infecting phytoplasmas in Jamaica from those detected in palms in Florida, Honduras and Mexico. A three fragment profile was generated for rDNA from phytoplasmas infecting all 21 Jamaican palms whereas a five fragment profile was evident for phytoplasmas infecting the majority of Florida (20 of 21), Honduran (13 of 14) and Mexican (5 of 5) palms. The RFLP profile indicative of Florida LY phytoplasma was resolved by cloning into two patterns, one of three bands and the other of four bands, that together constituted the five fragment profile. The two patterns were attributed to presence of two sequence heterogeneous rRNA operons, rrnA and rrnB, in most phytoplasmas composing Florida, Honduran and Mexican LY strain populations. Unique three and four fragment RFLP profiles indicative of LY phytoplasmas infecting Howea forsteriana and coconut palm in Florida and Honduras, respectively, were also observed. By comparison, the Jamaican LY phytoplasma population uniformly contained one or possibly two identical rRNA operons. No correlation between rRNA interoperon heterogeneity and strain variation in virulence of the LY agent was evident from this study.