Interactive effects of high CO2 and SO2 on growth and antioxidant levels in wheat

The impact of elevated CO2 and/or SO2 on the growth and antioxidant levels of wheat {Triticum aestivum L. cv. Urban) plants has been studied. High CO2 (0.7 ml I-1) significantly enhanced shoot biomass and photosynthetic capacity, while exposure to SO2 (0.14 ul I-1) resulted in a decreased shoot biomass and in an injured photosynthetic aparatus, illustrated by a loss of chlorophyll and a decreased ratio of variable to maximal fluorescence (Fv/Fm) and Amax. However, combined exposure of plants to high CO2 and SO2 eliminated the negative effects of SO2. Sulfate accumulation was almost equal in plants exposed to SO2 and, high CO2 and SO2. A significant increase in ascorbate, glutathione and their redox state was observed in plants exposed to high CO2 and SO2, compared to that of plants exposed to solely SO2. The absence of the negative effects of SO2 in the presence of high CO2 might be related to a high redox state of ascorbate and glutathione

The significance of glucosinolates for sulfur storage in Brassicaceae seedlings

Brassica juncea seedlings contained a twofold higher glucosinolate content than B. rapa and these secondary sulfur compounds accounted for up to 30% of the organic sulfur fraction. The glucosinolate content was not affected by H2S and SO2 exposure, demonstrating that these sulfur compounds did not form a sink for excessive atmospheric supplied sulfur. Upon sulfate deprivation, the foliarly absorbed H2S and SO2 replaced sulfate as the sulfur source for growth of B. juncea and B. rapa seedlings. The glucosinolate content was decreased in sulfate-deprived plants, though its proportion of organic sulfur fraction was higher than that of sulfate-sufficient plants, both in absence and presence of H2S and SO2. The significance of myrosinase in the in situ turnover in these secondary sulfur compounds needs to be questioned, since there was no direct co-regulation between the content of glucosinolates and the transcript level and activity of myrosinase. Evidently, glucosinolates cannot be considered as sulfur storage compounds upon exposure to excessive atmospheric sulfur and are unlikely to be involved in the re-distribution of sulfur in B. juncea and B. rapa seedlings upon sulfate deprivation

Attachment preferences of Hyalomma truncatum and Hyalomma marginatum rufipes ticks (Acari: Ixodidae) on two sheep breeds

Hyalomma ticks were collected from Merino and black-headed Dorper sheep and their attachment preferences determined. The preferred site of attachment for Hyalomma marginatum rufipes on both Dorper and Merino sheep was the anogenital and inguinal areas (75-76%). On Dorper sheep, H. Truncatum attached predominantly to the anogenital and inguinal areas (67,7%). On Merino sheep, most adults of this species attached to the feet (26%). Almost equal percentages also attached to the anogenital/inguinal and brisket areas (21,6 and 22,9%, respectively). These differences should be considered when pour-on acaricides are applied to different breeds of sheep.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Seasonal dynamics of the Karoo paralysis tick (Ixodes rubicundus): a comparative study on Merino and Dorper sheep

Karoo paralysis in South Africa is induced in livestock by feeding female Ixodes rubicundus ticks when infestation densities on hosts exceed certain critical levels. It has been shown previously that Angora goats are at a higher risk of being paralysed than Merino sheep, and such differences have been related to differences in feeding behaviour and spatial distribution of the two small-stock breeds. We hypothesized that differences in infestation densities with Karoo paralysis ticks would also occur between Merino and Dorper sheep breeds. A study was conducted under natural conditions in the south-western Free State, to compare infestation burdens of the two sheep breeds and also to investigate seasonal patterns and annual variations in terms of rainfall and temperature. Ten animals of each breed ran free in an area with a known history of Karoo paralysis and were examined on an approximately fortnightly basis, from March 1992 to December 1995, to determine tick abundance. Differences between the two breeds were significant (P < 0,05) during 1992 and 1993, but not during 1994. During the first two years, peak abundance of ticks was reached earlier in Dorper than in Merino sheep, and it also reached higher levels in Dorper than in Merino sheep (mean= 17,9 and 7,3, respectively). ln 1993, two Dorper, but no Merino sheep, were paralysed. Dorper sheep are clearly at a higher risk of being paralysed than are Merino sheep, and as such, they can serve as indicators of adult tick activity and hence of the time to commence prophylactic treatment. Differences between the two breeds are probably related to differences in grazing patterns. Marked variation in abundance and the time of onset of peak activity of I. rubicundus occurred over the years. Tick numbers were high in 1993 and 1995, but very low in 1992. In 1993, peak activity occurred earlier (April) than during the other years (June or July). These differences are related to differences in prevailing environmental conditions that influence tick activity in a complex manner. Heightened humidity and lower temperatures during the early stages of seasonal activity of the tick (April or May), normally result in peak abundance of ticks on hosts at that time.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Foundation for Research Development. University of the Orange Free State.mn201

The role of Hyalomma ticks in foot infestations and temporary lameness of sheep in a semi-arid region of South Africa

An outbreak of lameness amongst Merino lambs, associated with the presence of Hyalomma ticks, was investigated on a farm in the south-western Free State, South Africa. The purpose was to follow the progress of the condition and to determine the extent of involvement of the two Hyalomma species which occur in the region. The flock of experimental sheep (n = 460) ranged free in natural veld under extensive farming conditions. During September and October 1993, adult ewes and lambs in this flock were examined at weekly intervals to determine tick identity, abundance and attachment-site preferences on lame and unaffected animals. Lameness occurred only among lambs, of which 68 were affected during the 8-week period. Hyalomma ticks tended to aggregate and mean numbers of ticks/aggregation were significantly higher on lame lambs (mean = 11,3) than on either the unaffected lambs (mean = 6,9) or the ewes (mean = 7,1). Most tick aggregations (72,4%) on the lame lambs occurred on the lower legs and feet, 34 out of 55 of these on the fetlocks or interdigital clefts. Hyalomma truncatum dominated (> 97%) on all animals examined. Only 15,8% of the Hyalomma marginatum rufipes recovered from the lame animals were attached to the legs. At two other localities at which H. marginatum rufipes was more abundant, or even dominant, few ticks attached to the lower legs or feet. Those that did were mostly H. truncatum (> 90%). Both H. marginatum rufipes and H. truncatum may attach to the same ventral and anogenital body regions, but H. truncatum has a tendency to attach also to the feet and lower legs. Although attachment of one or a few ticks in the axillar region or upper legs may cause lameness in sheep, the attachment of ticks to the interdigital clefts and fetlocks almost always causes lameness. The latter condition is more likely to occur in regions where H. truncatum dominates.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.University of the Orange Free State. Foundation for Research Development. Poliomyelitis Research Foundation.mn201

Factors affecting the seasonal movements of Cape mountain zebras in the Mountain Zebra National Park

Factors underlying the movement of mountain zebras from a plateau in the summer to hill slopes and ravines in the winter were investigated. The movement was associated with a relative change in diet quality (as indicated by crude protein contents of preferred food plants and of the faeces) between the summer and winter habitats. In summer faecal and grass protein contents were higher in samples collected on the plateau than in those collected on the hill slopes. In the winter the reverse was the case. On the plateau the cover of grasses in the height range favoured by zebras changed only slightly from summer to winter. It thus seemed unlikely that the movement of zebras was caused by a seasonal change in the height structure of the grass sward. The diet comprised mostly grasses but traces of dicotyledons in the faeces were found more frequently during winter than summer

Tick diversity, abundance and seasonal dynamics in a resource-poor urban environment in the Free State Province

The objectives of this study were to determine the diversity, seasonal dynamics and abundance of ticks infesting cattle in urban, small-scale farming communities in and around Botshabelo and Thaba Nchu in the eastern Free State Province, South Africa. A total of ten cattle, ear-tagged for individual identification, were investigated monthly at each of five localities. Adult ticks were removed from the right hand side of each animal and placed in containers filled with 70% ethanol. They were subsequently identified and their numbers quantified. Immature Otobius megnini were counted but not removed. A total of 244 538 adult ticks of ten different species were collected over the 12-month study period. The tick species, in decreasing order of relative abundance, were: Boophilus decoloratus (87,26%), Rhipicephalus evertsi evertsi (6,86%), Hyalomma marginatum rufipes (2,42%), Otobius megnini (1,85%) Rhipicephalus follis (0,76%), Rhipicephalus gertrudae (0,54%), Rhipicephalus sp. (0,21 %), Ixodes rubicundus (0,08%), Hyalomma truncatum (0,01 %) and Margaropus winthemi (0,004 %). The three most abundant species, namely B. decoloratus, R. evertsi evertsi and H. marginatum rufipes, occurred at all localities but with significant differences in abundance. M. winthemi ticks occurred only in the Thaba Nchu area and were not found at any of the three localities in Botshabelo. Significant differences in tick burdens between the six warm months (September to February) and the six cooler months (March to August) were found for most of the species recorded. Boophilus decoloratus occurred in significantly higher numbers in autumn (March to May) and winter (June to August) compared to spring (September to November) and summer (December to February), with 76,8% of the total B. decoloratus burden occurring during the cooler months.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Foundation for Research Development. University of the Free State

Individual host variations in tick infestations of cattle in a resource-poor community

Relative resistance levels of cattle against tick infestations in the communal grazing area of Botshabelo in the south-eastern Free State were determined. The objective was to establish whether differences in resistance can be exploited to contribute to tick control methods used by small-scale farmers in resource-poor environments. Ten cows (Bos taurus crosses) between the ages of 18 months and four years were used and tick counts were conducted once a month over a period of 12 months to compare their total tick burdens. Tick burdens of the various animals were compared mutually as well as with the mean tick burden of the group as a whole. Tick numbers varied throughout the year on all individuals but some animals consistently tended to have either higher or lower numbers than the mean of the group. Tick burdens on cattle classified as having a relatively low resistance to tick infestations increased eleven-fold from January to June 1996 compared to a six-fold increase on cattle categorized as belonging to the high resistance group. Twenty-eight percent of the cattle in the total study group carried 50% of the ticks collected (60 079). It is recommended that farmers in the region visually assess B. decoloratus burdens, the most abundant tick species, and sell or cull the most susceptible animals first in their normal program of utilization of the animals. This should eventually result in the direct improvement of the overall tick resistance of their cattle herds.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Foundation for Research Development. University of the Free State