Environmental and Genetic Factors Influencing Self-Fertility in Phytophthora infestans

ABSTRACT Phytophthora infestans is generally regarded as heterothallic-requiring physical proximity of two individuals of different mating type (A1 and A2) for oosporogenesis. Recent reports of limited selfing in young cultures of this oomycete stimulated us to investigate factors contributing to the phenomenon. The ability to produce oospores rapidly (within 2 weeks) in pure, single individual cultures (self-fertility) was tested in 116 individual isolates. The 116 isolates were from geographically diverse locations (16 countries) and were genetically diverse. Mating type and growth medium were the most prominent factors in determining if an isolate would be self-fertile. The majority of A2 isolates (45 of 47 tested) produced oospores when grown on a 50:50 mixture of V8 and rye B medium. In contrast, the majority of A1 isolates (65 of 69 tested) did not produce oospores on this medium. None of the 116 isolates produced oospores when grown on rye B medium (with no V8 juice). Further tests on representative A1 and A2 isolates revealed that oatmeal agar, tomato juice agar, and V8-juice agar all induced the A2 mating type isolate to produce oospores but did not induce the A1 mating type isolate to produce oospores. Calcium carbonate and pH did not alter the self-fertile oospore production in either A1 or A2 mating type isolates. For in vivo tests, the application of fungicide to potato or tomato leaf tissue either before or after inoculation did not stimulate any individual isolate (one A2 and one A1 isolate) to produce oospores in infected tissue. However, in all of the controls for all experiments (in vivo and in vitro), many oospores were produced rapidly if both strains grew in physical proximity.     

Development of AFLP and RAPD markers linked to a locus associated with twisted growth in corkscrew willow (Salix matsudana 'Tortuosa')

Salix matsudana Koidz. cultivar 'Tortuosa' (corkscrew willow) is characterized by extensive stem bending and curling of leaves. To investigate the genetic basis of this trait, controlled crosses were made between a corkscrew female (S. matsudana 'Tortuosa') and a straight-stemmed, wild-type male (Salix alba L. Clone 99010). Seventy-seven seedlings from this family (ID 99270) were grown in the field for phenotypic observation. Among the progeny, 39 had straight stems and leaves and 38 had bent stems and curled leaves, suggesting that a dominant allele at a single locus controls this phenotype. As a first step in characterizing the locus, we searched for amplified fragment length polymorphism (AFLP) and randomly amplified polymorphic DNA (RAPD) markers linked to the tortuosa allele using bulked segregant analysis. Samples of DNA from 10 corkscrew individuals were combined to produce a corkscrew pool, and DNA from 10 straight progeny was combined to make a wild-type pool. Sixty-four AFLP primer combinations and 640 RAPD primers were screened to identify marker bands amplified from the corkscrew parent and progeny pool, but not from the wild-type parent or progeny pool. An AFLP marker and a RAPD marker linked to and flanking the tortuosa locus were placed on a preliminary linkage map constructed based on segregation among the 77 progeny. Sectioning and analysis of shoot tips revealed that the corkscrew phenotype is associated with vascular cell collapse, smaller cell size in regions near the cambium and less developed phloem fibers than in wild-type progeny. Identification of a gene associated with this trait could lead to greater understanding of the control of normal stem development in woody plants.     

The rural identity and the encroaching city: Governance,policy and development in Northern Virginia's Wine Country

In exurban areas, there are commonly issues and tensions associated with development and rural life. We assess how two counties located approximately one hour west of Washington, DC manage these tensions. Although both have enabled development, they have done so in different ways and neither has simply succumbed to exurban development as a given. Utilizing stakeholder interviews and document analysis, we note the different policy approaches that the two counties have taken and contrast them with the more common imagery of areas that fully acquiesce to suburban style development. Our findings suggest that tensions between the pressures of development and the persistent appeal of the rural identity occupy much time and attention in these two counties. Both counties have adopted observable policy changes driven by development pressures in recent years, underscoring a policy landscape that is in flux and the modern tension between the commercial economy of modernity, and the rural identity that is retained from the past. We observe that rural governance is largely about land, while urban governance is largely about people. As these two cases suggest, exurban governance has to be about both issues and this tension may lead to governance that is inherently unstable.     

Hydroureteronephrosis and fetal mummification secondary to uterine torsion in a Merino ewe

A 6 year old pluriparous Merino ewe was presented for investigation of a large intra-abdominal mass. Post-mortem examination revealed a 360° clockwise uterine torsion was present with a mummifying fetus. The torsion involved the left ureter resulting in a severe hydroureteronephrosis. Uterine torsion is uncommon in the ewe, occurring in less than 0.1% of pregnancies in one report (Mahmoud et al. Livest Res Rural Dev 2018;30), but cases are likely to be undiagnosed, particularly under the extensive management conditions typical of Australia. The chronicity of the condition in this ewe would support this statement. To the authors' knowledge this is the first reported case of hydroureteronephrosis secondary to uterine torsion in any species.     

Leaf litter C and N cycling from a deciduous permanent crop

Our understanding of leaf litter carbon (C) and nitrogen (N) cycling and its effects on N management of deciduous permanent crops is limited. In a 30-day laboratory incubation, we compared soil respiration and changes in mineral N [ammonium (NH₄⁺-N) + nitrate (NO₃^–-N)], microbial biomass nitrogen (MBN), total organic carbon (TOC) and total non-extractable organic nitrogen (TON) between a control soil at ¹⁵N natural abundance (δ¹⁵N = 1.08‰) without leaf litter and a treatment with the same soil, but with almond (Prunus dulcis (Mill.) D.A. Webb) leaf litter that was also enriched in ¹⁵N (δ¹⁵N = 213‰). Furthermore, a two-end member isotope mixing model was used to identify the source of N in mineral N, MBN and TON pools as either soil or leaf litter. Over 30 d, control and treatment TOC pools decreased while the TON pool increased for the treatment and decreased for the control. Greater soil respiration and significantly lower (p < 0.05) mineral N from 3 to 15 d and significantly greater MBN from 10 to 30 d were observed for the treatment compared to the control. After 30 d, soil-sourced mineral N was significantly greater for the treatment compared to the control. Combined mineral N and MBN pools derived from leaf litter followed a positive linear trend (R² = 0.75) at a rate of 1.39 μg N g^?1 soil day^?1. These results suggest early-stage decomposition of leaf litter leads to N immobilization followed by greater N mineralization during later stages of decomposition. Direct observations of leaf litter C and N cycling assists with quantifying soil N retention and availability in orchard N budgets.     

Response of economically important aphids to components of Hemizygia petiolata essential oil

The essential oil of Hemizygia petiolata Ashby (Lamiaceae) contains high levels (>70%) of the sesquiterpene (E)-beta-farnesene, the alarm pheromone for many economically important aphid species. In order to test the suitability of H. petiolata oil as a source of (E)-beta-farnesene for use in new integrated aphid control strategies, behavioural responses of pest aphid species were studied in laboratory and field experiments. In alarm pheromone assays the peach-potato aphid, Myzus persicae Sulzer, and the pea aphid, Acyrthosiphon pisum (Harr), showed a lower level of response to the oil than expected given the high levels of (E)-beta-farnesene. It was shown that minor components in the oil, (+)-bicyclogermacrene and (-)-germacrene D, caused inhibition of the alarm response for M. persicae and A. pisum respectively. Nevertheless, in olfactometer studies the oil was directly repellent to A. pisum and the grain aphid, Sitobion avenae F. Sitobion avenae was not only repelled by (E)-beta-farnesene but also by (-)-germacrene D. Furthermore, although it was not directly repellent to M. persicae, the oil interfered with its attraction to host plant stimuli. In field plot experiments, numbers of A. pisum were significantly reduced in plots treated with a slow release formulation of the oil, when compared with control plots.     

The effect of Hetastarch (670/0.75) in vivo on platelet closure time in the dog

Objective – To evaluate the effect of 6% hydroxyethyl starch (HES) solution in vivo, with an average molecular weight of 670 kDa and degree of substitution of 0.75, on canine platelet function.
Design – Prospective, controlled-experimental study.
Setting – University of California, Davis, Veterinary Medical Teaching Hospital.
Animals – Seven healthy employee-owned dogs.
Interventions – Seven dogs were included in the treatment group. Four of these dogs also served as the control group. Platelet closure time (CT) was measured using a platelet function analyzer and collagen/ADP cartridges. Dogs were given 20 mL/kg of either sodium chloride 0.9% (control group, n =4) or HES (treatment group, n =7) IV over 1 hour. CT was measured before the infusion, and at 1, 3, 5, and 24 hours after the start of the infusion.
Measurements and Main Results – There was a significant change over time from 0 to 24 hours ( P <0.001), a significant difference between groups across time ( P <0.001), and a significant group-by-time interaction ( P =0.007). At 3 hours, mean CT for the treatment group was 122.3±18.1 seconds, which was significantly different ( P <0.001) from the control group (71.0±3.5 s). At 5 hours, mean CT for the treatment group was 142.7±33.9 seconds, which was significantly different ( P =0.001) from the control group (75.0±8.6 s). Mean CT at 24 hours was within the reference interval for both the control and treatment group (66.0±2.9 and 81.8±11.9 s, respectively); however, CT in 3 individual dogs in the treatment group at this time point remained prolonged.
Conclusions – A clinically relevant dose of HES 670/0.75 prolongs CT in dogs for up to 24 hours. This may be due to platelet dysfunction in addition to the effects of hemodilution, and therefore, may increase the risk of bleeding.     

The effect of landscape-scale environmental drivers on the vegetation composition of British woodlands

Assessment of factors influencing woodland vegetation composition across Britain was made using multivariate techniques to analyse data gathered during the 1971 National Woodland Survey. Indirect gradient analysis (unconstrained ordination using detrended correspondence analysis) suggested a gradient strongly associated with nutrient availability and pH. Direct gradient analysis (constrained ordination using canonical correspondence analysis) and variation partitioning were used with over 250 ecophysiologically relevant variables, including climatic, geographical, soil and herbivore data, to model the response of woodland vegetation. Although there was a high degree of multicollinearity between environmental variables, analysis revealed the vegetation composition of surveyed woodlands to be primarily structured by geographical, climatic and soil gradients, in particular rainfall, soil pH and accumulated temperature. The woods have recently been resurveyed. The results of this analysis therefore provide a baseline against which species dynamics can be assessed under a series of conservation threats, such as land use and climate change.