Orbits of the small satellites of saturn

Orbital parameter values and associated uncertainties determined from Voyager 1 imaging data for the satellites 1980S1, 1980S3, 1980S6, 1980S26, 1980S27, and 1980S28 are presented.     

Pseudomonas syringae pv. maculicola in Australia: pathogenic, phenotypic and genetic diversity

Pseudomonas syringae pv. maculicola causes bacterial leaf spot on cruciferous plants in Australia. This is the first record confirming the identity of seven isolates currently stored as P. syringae pv. maculicola in the herbarium of the Department of Agriculture, Orange, Australia (Herb. DAR). The isolates were identified using pathogenicity testing on cauliflower and fatty acid methyl ester analysis. They clustered together using repetitive sequence-based polymerase chain reaction (rep-PCR) and PCR-restriction fragment-length polymorphism (RFLP) of the 16S−23S internal transcribed spacer region (ITS) using seven restriction enzymes. Identification was confirmed by comparison of these isolates with known overseas isolates of P. syringae pv. maculicola , but there was significant variation in their pathogenicity and genetic structure.     

Localization of potato leafroll virus in leaves of secondarily-infected potato plants

Potato leafroll virus (PLRV) antigen was localized by immunogold labelling in semi-thin leaf sections of secondarily-infected potato plants cv. Bintje. Viral antigen was present in all cell types of the phloem tissue. but occurred most abundantly in the companion cells. Detectable amounts of PLRV antigen were found only in the sieve elements in veins with a large number of infected companion cells. Occasionally, parenchyma cells were also found to be infected. PLRV was not exclusively limited to the phloem tissue in the infected potato plants, but was also found in mesophyll cells neighbouring minor phloem vessles. Spread of virus from cell to cell in the mesophyll was not observed. The distribution of PLRV in the potato leaf tissue has implication on its availability, for acquisition by aphids.     

Metalaxyl sensitivity of isolates of Phytophthora erythroseptica in Prince Edward Island

Isolates of Phytophthora erythroseptica , causal agent of pink rot of potato, were obtained from diseased tubers collected in Prince Edward Island (PEI), Canada. In an in vitro assay of field and single-zoospore isolates, all isolates of the pathogen from PEI were sensitive to metalaxyl (EC₅₀ < 0·5  µ g mL⁻¹), unlike moderately or highly resistant reference isolates obtained from Maine, USA. Allozyme-banding patterns at the glucose-6-phosphate isomerase ( Gpi ) locus were identical (91/91) for all isolates of P. erythroseptica examined from PEI and Maine, but could be used to distinguish isolates of P. erythroseptica from local isolates of Phytophthora infestans . Inoculation of potato tubers from plants treated with foliar applications of metalaxyl in the field indicated that compounds inhibitory to metalaxyl-sensitive isolates of P. erythroseptica were present in the periderm, even after 4 months' storage. By contrast, moderately or highly resistant isolates of the pathogen caused significantly ( P  ≤ 0·05) more disease than sensitive isolates in tubers from plants treated with metalaxyl. The effectiveness of metalaxyl in controlling pink rot in a particular region will depend on resistance levels of local populations of P. erythroseptica . Preventing the development and spread of resistant strains of P. erythroseptica will be critical in maintaining metalaxyl as an effective chemical for control of this pathogen.     

Retrospective estimation of the data of infection with beet yellowing viruses in sugar-beet under field conditions

Sugar-beet plants, infected with beet yellows virus (BYV, closterovirus group) or beet mild yellowing virus (BMYV, luteovirus group) develop symptoms on the inoculated leaves on which aphids infected the plant. Symptoms develop also on the systemically-infected leaves to which virus has been transported via the phloem. Systemic infection occurs in the leaves which have just, or not yet appeared at the moment of infection of the plant. All other, older leaves remain uninfected. The infection-date can be estimated by assessing the date of appearance of the oldest systemicallyinfected leaf of a plant. This approach was tested in the field and gave good results.Samenvatting Suikerbieteplanten die besmet zijn met het bietevergelingsvirus, BYV, of met het zwakke vergelingsvirus, BMYV, ontwikkelen symptomen op de geïnoculeerde bladeren, waarop infectieuze bladluizen virus hebben overgedragen, én op de systemisch besmette bladeren waarheen het virus vanuit de geïnoculeerde bladeren is getransporteerd via het vaatsysteem. Bladeren die op het moment van infectie nog niet verschenen zijn of vlak ervóór zijn verschenen, worden systemisch besmet, terwijl oudere bladeren gezond blijven. De infectiedatum kan worden bepaald door aan de hand van temperatuursommen de verschijningsdatum van het oudste systemisch besmette blad te berekenen. Deze methode bleek bij toetsing in het veld goed te voldoen.     

Influence of canopy position, needle age and season on the foliar gas exchange of Pinus canariensis

We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability.     

Epidemiology of tomato yellow leaf curl begomovirus in the Fayium area, Egypt

Tomato yellow leaf curl begomovirus (TYLCV) severely invaded tomato plantations in Egypt (Lower and Middle Egypt) in 1989. This study aimed to discover the relationship between TYLCV and other epidemic-associated factors in the Fayium area. The rate of TYLCV infection was inspected visually for three successive years (1994/1996) in the Fayium area. During the same period, whiteflies were collected for virus detection using bait-plant and DNA hybridization techniques. DAS-ELISA was used to detect mixed virus infections in tomato plants. TYLCV infection was prevalent (60–68%) and severe (2.1–3.0) in the Fayium fields. Cucumber mosaic cucumovirus (CMV) was found in some fields (5–28%) with moderate severity (1.0–20). Potato Y potyvirus (PVY) and potato leaf roll polerovirus (PLRV) were found in few fields (5–19% and 5% respectively) at very low severity. There was a negative correlation between TYLCV occurrence and distance from the source of infection, and a positive correlation (98%) between TYLCV intensity and percentage of viruliferous whiteflies in 1994 and 1995. There was no positive correlation between TYLCV and the total population of whiteflies caught during the same period. Five percent of viruliferous whiteflies, as proved by cDNA hybridization, led to 46% TYLCV infection. The same percentage of whiteflies, as shown by bioassay, led to 68% TYLCV infection. Monitoring of viruliferous whiteflies could be used for early prediction of TYLCV infection.