Modification of native grasses for biofuel production may increase virus susceptibility

Bioenergy production is driving modifications to native plant species for use as novel biofuel crops. Key aims are to increase crop growth rates and to enhance conversion efficiency by reducing biomass recalcitrance to digestion. However, selection for these biofuel‐valuable traits has potential to compromise plant defenses and alter interactions with pests and pathogens. Insect‐vectored plant viruses are of particular concern because perennial crops have potential to serve as virus reservoirs that influence regional disease dynamics. In this study, we examined relationships between growth rates and biomass recalcitrance in five switchgrass (Panicum virgatum) populations, ranging from near‐wildtype to highly selected cultivars, in a common garden trial. We measured biomass accumulation rates and assayed foliage for acid detergent lignin, neutral detergent fiber, in vitro neutral detergent fiber digestibility and in vitro true dry matter digestibility. We then evaluated relationships between these traits and susceptibility to a widely distributed group of aphid‐transmitted Poaceae viruses (Luteoviridae: Barley and cereal yellow dwarf viruses, B/CYDVs). Virus infection rates and prevalence were assayed with RT‐PCR in the common garden, in greenhouse inoculation trials, and in previously established switchgrass stands across a 300‐km transect in Michigan, USA. Aphid host preferences were quantified in a series of arena host choice tests with field‐grown foliage. Contrary to expectations, biomass accumulation rates and foliar digestibility were not strongly linked in switchgrass populations we examined, and largely represented two different trait axes. Natural B/CYDV prevalence in established switchgrass stands ranged from 0% to 28%. In experiments, susceptibility varied notably among switchgrass populations and was more strongly predicted by potential biomass accumulation rates than by foliar digestibility; highly selected, productive cultivars were most virus‐susceptible and most preferred by aphids. Evaluation and mitigation of virus susceptibility of new biofuel crops is recommended to avert possible unintended consequences of biofuel production on regional pathogen dynamics.     

Biofilm development and invertebrate colonization of wood in four New Zealand streams of contrasting pH

1. Biofilm development and activity on wood substrata (Nothofagus menziesii) were examined at four forested sites in a South Island, New Zealand, river catchment over a period of 6 months. Two of the sites had brown waters and mean pH of 3.7 and 4.5, whereas the other two had clear waters and mean pH of 6.3 and 6.8. 2. Fungi and other filamentous heterotrophs were the dominant colonizers of wood at all sites; few algal cells were present. Incorporation of ¹⁴C-glucose by biofilms was greatest in all four streams after 3 months, whereas endocellulase activity fluctuated over time and temporal patterns differed among streams. 3. No clear relationship was found between the incorporation of ¹⁴C-glucose or endocellulase activity of biofilms and pH, although at one near-neutral pH site ¹⁴C-glucose uptake increased in response to nutrient (N + P) additions. 4. After 6 months, incorporation of ¹⁴C-glucose and endocellulase activity of biofilms on Pinus radiata dowels buried vertically in the stream beds did not differ at depths of 3–9 cm and 19–25 cm in each stream. 5. Radiotracer experiments with a grazing amphipod (Paraleptamphopus sp.) demonstrated that biofilms on wood from all four sites could be ingested and at least partially assimilated. Chironomid larvae and harpacricoid copepods were the most abundant invertebrates colonizing wood substrata at all sites. Different chironomid species dominated at acidic and near-neutral pH sites. 6. Overall, our findings provide little support for the hypothesis that microbial activity on organic substrata is necessarily lower in streams of low pH.     

Brachiopod orientation to water movement: functional morphology

Previous work by the author has shown that Laqueus californianus. Terebratulina unguicula , and. to a lesser extent, Hemithyris psittacea will actively reorient to water currents in the laboratory; Terebratalia transversa will not. This active reorientation is effected primarily by the dorsal adjustor muscles; the ventral adjustors function to depress and tilt the shell. The torque around the pedicle generated by drag on the shell is low at moderate current speeds. The dorsal adjustor muscles are competent to resist these torques up to current speeds of 35 cm/s for L. californianus and H. psittacea and 56 cm/s for T. unguicula . Shell shape, gross pedicle form, and form of the pedicle foramen are unreliable indicators of a brachiopod's ability to actively reorient. Shape of the pedicle bulb and position and size of the pedicle connectives are better indicators but. on functional grounds, the dorsal adjustor muscle morphology is the best indicator of active reorientation. An angle α (the maximum possible rotation of the shell that can be produced by contraction of one of the dorsal adjustor muscles) correlates well with both the maximum observed rotations and the exhibition of active reorientation to currents. For fossil material, the existence of dorsal adjustor muscle scars that touch medially should also be a good indicator of active reorientation ability.     

Nitrate Uptake by Manganese-Deficient Lemon Plants

The uptake of nitrate and water was followed in Eureka lemon (Citrus limon (L.) Burm. f.) plants grown in solution culture in a greenhouse under short (3–6 months) and long-term (22–24 months) Mn-nutrition stress. Uptake was determined from depletion in the nutrient solution. Under short-term stress, manganese-deficient plants absorbed 14.5% more nitrate and 3.4% more water than the control plants, on a weight basis. Under long-term stress there was a three-fold increase in nitrate and a two-fold increase in water uptake in the Mn-deficient plants. The intensive nitrate uptake under Mn-deficiency stress was more spectacularly demonstrated in plants which were exposed also to low nitrogen supply. The low-nitrogen Mn-deficient plants absorbed more nitrate, had less stunted growth and developed fewer visible symptoms of both N and Mn deficiencies than high-nitrogen Mn-deficient plants.     

The biology of some Argiope species from New Guinea: predatory behaviour and stabilimentum construction (Araneae: Araneidae)

Three species of Argiope: A. picta, A. aemula and A. reinwardti were studied at Wau, New Guinea. The stabilimenta in 548 webs of these species were classified into 18 categories, and the frequency of occurrence of each category was recorded. The data from this study are compared with previous records on the variation in the form of the devices built by spiders of the genera Argiope and Gasteracantha and related to theories about stabilimentum function.
Studies of the predatory behaviour of the three species show that this is, in general, similar to that of Argiope argentata . Data are cited to show that the spiders discriminate lepidopterans from insects of similar size. Particular attention was paid to the question of whether the species interrupt predatory sequences, after the attack phase, with a stage during which they rest at the hub of the web before transporting the prey. Unlike Argiope argentata these species interrupt a high proportion of predatory sequences that are initiated by bite/wrap attacks. This aspect of their behaviour is evaluated and discussed.     

Cold-Inhibited Phloem Translocation in Sugar Beet: II. CHARACTERIZATION AND LOCALIZATION OF THE SLOW-COOLING RESPONSE

Experiments were undertaken on a simplified sugar beet systemto characterize the phloem translocation response to slow coolingtreatments that were applied to the source leaf petiole. Inthese experiments the temperature was decreased by 4°C every16 min, such that the tissue temperature was lowered from 25°Cto 1°C over a period of 80 min. Our results indicated thatan initial slow cooling treatment, on a given test plant, causedno change in the rate of translocation. However, all subsequentslow cooling regimes that were applied to the same petiole positionelicited a characteristic step-type inhibition. This inhibitionaveraged about 10% of the original translocation rate in allcases with no recovery being observed. The data suggest thatthe initial cooling treatment induced an alteration in the petioletissue which facilitated the inhibition phenomenon during subsequentslow coolings. This alteration was shown to be localized withinthe upstream region of the chilled petiole segment, followingan initial slow cooling, or throughout the chilled petiole segmentafter an initial quick cooling from 25°C to 1°C. Resultsalso show that the alteration is a long-lived phenomenon thathas no detectable influence on the quick-cooling induced transientinhibition of translocation. Key words: Phloem, Translocation, Cooling response, Petiole