Biological soil crust distribution is related to patterns of fragmentation and landuse in a dryland agricultural landscape of southern Australia

The dryland agricultural landscape of north-west Victoria, Australia, includes isolated remnants of eucalypt woodland that are exposed to ongoing disturbance from sheep grazing and cropping activity. Biological soil crusts are a functionally important feature of these woodland communities. We used a modern form of regression (boosted regression tree (BRT) models) to investigate relationships between crust abundance and environmental and landscape variables. We also investigated whether the use of broad morphological groups of crust organisms is more informative than simply measuring total crust cover. Remnant size was the single most influential variable for crust abundance, with negligible crust cover in small patches (<5 ha). The BRT model also identified relationships between crust abundance and available P, soil C and perennial grass. We argue that disturbance from stock grazing and camping is the mechanism driving these relationships. Other variables related to crust abundance were proximity to the windward edge, litter cover and tree cover. Morphological groups showed a differential response to some variables, suggesting assessment of total cover may mask important patterns in community structure. Crust disturbance represents a serious issue for maintenance of ecosystem function in the study region, particularly loss of crusts from small remnants because the majority of remnants are small.     

Stolon Development and Cultural Production Practices of Winter-Grown Strawberries

ABSTRACT

The four experiments described here are part of a 5-year program focused on determining whether day-neutral and short-day strawberries would be suitable for commercial off-season/winter (temperate climate) production in greenhouses. All research was performed using container-grown plants fertigated through a capillary mat production system with heat supplied under the benches. The first experiment focused on stolon development. The second experiment investigated the influence of stolon removal on berry production and included the removal of flowers for the first three weeks. The third and fourth experiments were conducted as a comparison of university research (experiment 3) versus a commercial operation (experiment 4). In experiment one, of 13 cultivars, ‘AC Wendy’ plants produced significantly more stolons than the other cultivars. In experiment two, stolon production peaked at weeks 12 and 13, with ‘Chandler’ plants producing significantly more stolons (starting at week 9) than the other cultivars. At week 13, ‘Seascape’ plants produced more total berry weight than the other cultivars. The influence of stolon removal on total berry weight varied, with ‘Evie-2+’ plants (large crowns) producing higher total berry weight with the stolons on as compared to ‘Evie-2’ plants, which produced higher total berry weight with the stolons removed. In experiment 2, fruit production was low and was probably a result of deflowering for three weeks. Consequently, it may not be advisable to deflower during the ‘off-season’ for greenhouse-grown strawberries. In the final two experiments, which involved a commercial cooperator as well as the university greenhouse, it was found that of the five cultivars trialed, the same cultivars at both sites produced the maximum total berry weight. Stolon production differed at the two locations, but the optimal time for stolon removal was similar. Thus, it is recommended that for winter greenhouse production, stolons be removed initially at week 8 and then at weeks 11–12 of the production cycle.     

Bovine post-parturient haemoglobinuria: two distinct entities in New Zealand

Haematological and biochemical features of sixteen cases of post-parturient haemoglobinuria (PPH) from 15 farms in the Waikato and Bay of Plenty regions are described. Characteristically there was a marked regenerative anaemia as well as spherocytosis and haemoglobinaemia. Heinz body formation occurred in 140% of erythrocytes depending on the case. Nine of 11 cases examined had subnormal serum inorganic phosphorus concentrations. On two of eight farms there was widespread anaemia in clinically healthy herd mates and in one of these the anaemia was associated with large numbers of Heinz bodies. Hypophosphataemia was widespread in four of ten herds and individual cows were hypophosphataemic in all ten. Six of eight herds had a low selenium status as determined by glutathione peroxidase activity in whole blood. Hypocupraemia and hypomagnesaemia were not consistent findings. It is concluded that there are two distinct entities of PPH in the region. On one farm the disease was typical of that seen in Northland, New Zealand. The clinical case was a young cow and there was widespread subclinical Heinz body anaemia in herd mates. All but one of the cows sampled in that herd had normal serum inorganic phosphorus levels. On most other farms PPH closely resembled that described from North America. Affected cases were miltiparous, high producing and had low serum inorganic phosphorus levels. The possible pathogenesis of these two entities is discussed.     

Influence of Gonadotrophin‐Induced First Oestrus on Gilt Fertility

The aim of this study was to determine the association between the oestrous response of pre‐pubertal gilts to gonadotrophin injection or boar exposure and their subsequent farrowing rate and litter size. At 154 days of age, randomly selected pre‐pubertal gilts received an intramuscular injection of 400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600^®; Merck Animal Health; n = 181). From the remaining pool of animals not treated with hormones, the first gilts showing signs of oestrus were selected to act as controls (n = 201). Boar exposure began at 155 days of age for both groups, and gilts were bred at a weight of approximately 130 kg. Comparisons were made between PG600^®‐treated gilts exhibiting oestrus or not within 7 days post‐injection (early and late responders, respectively) and control gilts exhibiting oestrus or not within 30 days after beginning of boar exposure (select and non‐select control gilts, respectively). By 162 days, oestrus was detected in 67.5% of PG600^®‐treated gilts compared with 5.7% of control gilts (p < 0.0001). The proportion of animals observed in oestrus at least three times before breeding was greater for select control gilts compared with early and late responder PG600^®‐treated gilts (p ≤ 0.001). There were no significant differences in farrowing rate and litter size between the four treatment groups. These data indicate that PG600^® is an effective tool to induce an earlier oestrus in gilts, that subsequent farrowing rate and born alive litter size compare favourably to that of select gilts and that gilts failing to respond promptly to hormonal stimulation do not exhibit compromised fertility.     

Experimental infection with BCG as a model of tuberculosis in the brushtail possum (Trichosurus vulpecula)

AIMS: To study the development and progression of lesions produced following experimental inoculations of possums with Bacille Calmette-Guérin (BCG) Pasteur Strain 1173P2 and to compare these with lesions that occurred following natural Mycobacterium bovis infection.

METHODS: Possums were inoculated with 5 x 10⁶ colony forming units (cfu) of BCG via the intra-dermal (I/D) route into the dorsum of the neck (n=38) or the left brachium (n=7), orally (n=10), via the endo-bronchial (E/B) route (n=12), or intravenously (I/V) (n=10, half of which received 5 x 10⁶ cfu and half of which received 5 x 10⁷ cfu of BCG). The possums were humanely killed between 1–4 weeks post inoculation (p.i.), and the nature and distribution of lesions examined grossly and histopathologically.

RESULTS: The distribution of lesions following I/D inoculation via either route was similar to that of the natural disease, but there were few lesions in the lung. Endo-bronchial inoculation resulted in pulmonary disease but produced few lesions outside the respiratory tract. Lesions produced by I/V inoculation were similar in distribution to those seen in terminally ill tuberculous possums. No lesions were produced following oral inoculation. Regression of lesions commenced after 3 weeks p.i.

CONCLUSIONS: Although the phenomenon of lesion resolution restricts the use of BCG to the study of early lesion development, it avoids the overwhelming disease induced using M. bovis and thus allows the early phases of the development and progression of tuberculosis in this species to be observed. Intra-dermal inoculation produced evidence that infection through the skin is associated with lesions in superficial lymph nodes, whereas pulmonary disease was associated with E/B inoculation. The results are consistent with the hypothesis that both percutaneous and respiratory routes are important in natural infection of possums with M. bovis.     

Crypt abscesses in the caeca of feral rabbits in a rabbit haemorrhagic disease endemic region of New Zealand

AIM: To describe the pathology of crypt abscesses in the caeca of feral rabbits in the Manawatu region of New Zealand, and to examine the possible relationship between their prevalence and rabbit haemorrhagic disease (RHD) virus (RHDV) infection.

METHODS: During the course of a 3-year study of RHD, 173 wild rabbits (Oryctolagus cuniculus) were shot on three pastoral livestock farms in the Manawatu region of New Zealand. All rabbits were necropsied, and tissue samples of the caeca were examined histologically. The age of each animal was determined, and blood samples collected for the detection of RHDV antibodies. Logistic regression was used to model the odds of rabbits having crypt abscesses.

RESULTS: At necropsy, 63/173 (36.4%) rabbits were found to have small circular black nodules on the mucosal surface of their appendix caecum and/or sacculus rotundus. Microscopically, these were identified as small crypt abscesses composed of dilated sacs at the base of the mucosa that were often lined by a thin layer of attenuated epithelial cells. They usually contained large amounts of concentrically-laminated mucopolysaccharide material that was sometimes pigmented, inflammatory debris, and were often the site of a moderate multifocal appendicitis. Although RHDV was active in the study area, no association was found between RHDV antibodies in serum and the presence of lesions. The lesions were more common in older individuals and those born in summer or autumn.

CONCLUSIONS: This is the first report of crypt abscesses with inflammation and necrotic debris in the caeca of rabbits. No association between the occurrence of crypt abscesses and RHDV infection was identified. Wild rabbits born in a particular season were presumably exposed very early in life to conditions that caused the crypt abscesses to develop. Alternatively, association with season of birth may represent rabbits that were of similar age in a later stage of their lives, when they became exposed to the cause of the lesions, which remains unidentified.     

Spatial variation of ammonia volatilization from soil and its scale‐dependent correlation with soil properties

Quantitative predictions of ammonia volatilization from soil are useful to environmental managers and policy makers and empirical models have been used with some success. Spatial analysis of the soil properties and their relationship to the ammonia volatilization process is important as predictions will be required at disparate scales from the field to the catchment and beyond. These relationships are known to change across scales and this may affect the performance of an empirical model. This study is concerned with the variation of ammonia volatilization and some controlling soil properties: bulk density, volumetric water content, pH, CEC, soil pH buffer power, and urease activity, over distances of 2, 50, 500, and >2000 m. We sampled a 16 km × 16 km region in eastern England and analyzed the results by a nested analysis of (co)variance, from which variance components and correlations for each scale were obtained. The overall correlations between ammonia volatilization and the soil properties were generally weak: –0.09 for bulk density, 0.04 for volumetric water content, –0.22 for CEC, –0.08 for urease activity, –0.22 for pH and 0.18 for the soil pH buffer power. Variation in ammonia volatilization was scale‐dependent, with substantial variance components at the 2‐ and 500‐m scales. The results from the analysis of covariance show that the relationships between ammonia volatilization and soil properties are complex. At the >2000 m scale, ammonia volatilization was strongly correlated with pH (–0.82) and CEC (–0.55), which is probably the result of differences in parent material. We also observed weaker correlations at the 500‐m scale with bulk density (–0.61), volumetric water content (0.48), urease activity (–0.42), pH (–0.55) and soil pH buffer power (0.38). Nested analysis showed that overall correlations may mask relationships at scales of interest and the effect of soil variables on these soil processes is scale‐dependent.     

Effects of silver scurf (Helminthosporium solani) on seed potatoes

Summary Seed tubers with severe (80–100% of surface affected) or slight (less than 20% of surface affected) silver scurf were selected from commercial stocks and planted at Rothamsted in 1979–81. Severely affected seed lost more weight (13%) than slightly affected seed (8%) during storage on trays, and produced more but smaller sprouts. Ground cover, leaf area and tuber yields were decreased by severe infection for up to 7 weeks after planting but thereafter effects of seed infection were non-significant. In two years, tubers produced from seed with severe silver scurf had less infection than those from slightly affected seed, but in 1980 most disease developed on tubers from seed with severe infection.

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Zusammenfassung In Rothamsted wurden in den drei Jahren zwischen 1979 und 1981 Pflanzkartoffeln mit starkem (80–100% Oberfl?chenbefall) oder schwachem (Weniger als 20%) Silberschorfbesatz gepflanzt, die aus Konsumanbau stammten. 1979 wurden auch Knollen mit mittlerem Befall (40–60%) einbezogen. Die verwendeten Sorten zeigt Tabelle 1: Ulster Sceptre und King Edward (1979), Désirée (1980), Wilja und King Edward (1981). In allen Jahren war der Gewichtsverlust w?hrend der Keimung bei den stark befallenen Pflanzknollen gr?sser als bei den wenig befallenen, und in drei von fünf Versuchen hatten die stark befallenen Knollen auch kürzere Keime. Das Gesamtgewicht der Keime wurde durch die Befallsst?rke nicht beeinflusst, stark befallene Knollen bildeten mehr Keime als schwach befallene (Tab. 2). Im Jahr 1979 war 4 Wochen nach der Pflanzung die Bodenbedeckung nach stark befallenem Pflanzgut gesichert schw?cher (Tab. 3), und in 1980 und 1981 waren sieben Wochen nach der Pflanzung die Blattfl?chenindizes von stark befallenem Pflanzgut geringer als von schwach befallenem. Die Einflüsse der Pflanzgutinfektion auf die Stengelzahl waren schwankend (Tab. 4): eine starke Infektion erh?hte die Stengelzahl in 1981 bei Wilja und verminderte sie in 1979 bei Ulster Sceptre und in 1981 bei King Edward. Im Jahr 1979 war sieben Wochen nach der Pflanzung von stark infiziertem Pflanzgut der Sorte Ulster Sceptre das Stengelgewicht gesichert niedriger, aber bei sp?teren Probennahmen anderer Jahre und Sorten ergaben sich keine gesicherten Unterschiede. In 1979 waren auch die Zahl der Knollen und deren Gewicht bei der Sorte Ulster Sceptre nach starker Pflanzgutinfektion bis zu sieben Wochen nach der Pflanzung reduziert (Tab. 5), bei sp?teren Probennahmen und bei anderen Sorten zeigten sich keine gesicherten Differenzen. Im Jahre 1979 hatten Knollen der Sorten King Edward und Ulster Sceptre nach stark infiziertem Pflanzgut weniger Befall als nach schwach infiziertem Pflanzgut (Tab. 6), und bei der Ernte und nach der Lagerung war in 1981 auf Knollen der Sorte Wilja und King Edward mehr Silberschorf nach schwach befallenem Pflanzgut als nach stark befallenem. Im Jahr 1980 war jedoch der Silberschorfbesatz bei der Ernte auf Knollen nach stark befallenem Pflanzgut am h?chsten.

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Résumé Au cours des années 1979 à 81, des tubercules de semence destinés à la commercialisation et atteints de gale argentée ont été prélevés et différenciés selon l'importance de la maladie: tubercules sévèrement atteints (80 à 100% de la surface couverte), tubercules légèrement atteints (moins de 20%). Les échantillons ont été plantés à la station de Rothamsted, ainsi que des lots moyennement atteints en 1979 (40 à 60% de la surface couverte). Les variétés Ulster Sceptre et King Edward ont été cultivées en 1979, Désirée en 1980, et Wilja et King Edward en 1981 (tableau 1). Tous les ans des pertes de poids plus importants pendant la germination sont observés pour les tubercules sévèrement atteints, donnant des germes plus courts dans trois cas sur cinq. La gravité de l'infection n'a pas d'incidence sur le poids sec total de germes, les tubercules sévèrement atteints donnant un nombre de germes plus élevé (tableau 2). En 1979, la couverture du sol 4 semaines après plantation est significativement plus faible pour le plant sévèrement atteint (tableau 3), et en 1980 et 1981 l'indice foliaire, 7 semaines après plantation, est inférieur pour les plantes provenant de semences fortement contaminées. L'effet de l'infection de la semence sur le nombre de tiges est controversé (tableau 4). Les plants sévèrement atteints ont donné en 1981 davantage de tiges pour Wilja et pert de tiges en 1979 et en 1981 pour respectivement Ulster Sceptre et King Edward. En 1979 le poids des fanes de la variété Ulster Sceptre est significativement plus faible 7 semaines après plantation dans le cas d'une infection grave, mais les poids ne sont pas significativement différents pour les autres conditions. En 1979, les nombres et les poids de tubercules de la variété Ulster Sceptre sont plus faibles dans le cas d'une infection grave durant les sept premières semaines après plantation (tableau 5), alors q'aucune différence significative n'est observée par ailleurs. En 1979, les tubercules issus de semences gravement atteints des variétés King Edward et Ulster Sceptre, sont moins infectés que ceux provenant de semences légèrement contaminées (tableau 6) tandis qu'à la récolte et après conservation en 1981, pour les variétés Wilja et King Edward, la gale argentée se rencontrait plus communément sur des tubercules issus de semences faiblement contaminées. Toutefois, en 1980, il a été observé plus de gale argentée sur des tubercules gravement atteints (tableau 7).