M.Sc. / Please refer to full text to view abstract

The importance of the cichlid teleost Tilapia mossambica as a protein source, coupled with its remarkable adaptability, has resulted in its introduction into many water systems throughout the tropical, sub-tropical and even temperate regions of the world. However, its successful exploitation of these waters is dependent very largely upon the value of minimum temperatures and their duration. For e.g. Long et al (1961) has drawn attention to the tremendous mortalities of T. mossambica that occur in shallow water bodies during the precipitous temperature decreases that accompany the winter monsoons in Vietnam and other eastern countries, even at temperatures as high as 14 or 16º C. Coehe (1967) does not recommend stocking with T. mossambica where temperatures are not above 14º C all the time. Ailanson et al (1962) conclude, after an experimental study, that low temperatures (13º C or lower) in South African highveld dams in winter are certainly an important factor in the extensive mortalities of T. mossambica that have been reported from these dams. Jubb (1961) also reports that this species is often killed during a severe winter in Rhodesia. Intro., p.1.

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This report contains an analysis of the factors responsible for the 1949-50 winter injury to cherry, peach and apricot trees in the Okanagan Valley of British Columbia, Canada. Included in the report are sections dealing with the history of winter injury, various theories of the causes of winter injury, and a description of the many forms of injury. The non-climatic and climatic factors affecting the intensity of injury are discussed in detail. Recommendations for minimizing the susceptibility of trees to winter injury under Okanagan Valley conditions are included, together with recommendations for the care of trees after injury has occurred. Reports on the relative hardiness of specific stone-fruits are presented in some detail. The report is liberally supplied with tables indicating the extent of crop damage and tree damage in each district of the Okanagan Valley. These tables are based on observations made in over two thousand orchards. The statistical analyses are based on detailed observations carried out in over four hundred orchards. The published literature dealing with winter injury has been freely consulted, and reference is made to many of the important papers dealing with the winter injury complex. A complete bibliography is included. / Land and Food Systems, Faculty of / Graduate

It is desirable to develop tomato varieties which have the character of being able to set fruit at relatively cool temperature between 10°C to 15.5°C for commercial production in Canada. The tomato varieties Puck, Bonny Best, Immur, Prior Beta, Cold Set and some of their reciprocal Fl hybrids were grown both in greenhouses and in growth chambers under two different temperature levels, experiments were carried out to study fruit, set and the effects of self and cross-pollination on fruit development in four varieties and the Fl hybrids of PxBB, BBxP, IPBxBB, BBxIPB, CSxBB, and BBxCS. Under both cool and warm temperatures, the percentage of fruit set and also size of fruit were increased when cross-pollination was used in contrast to self-pollination. Under cool temperature, all Fl hybrid lines had a higher percentage of fruit set than their two parents, but in warm temperature the Fl hybrid lines had a intermediate percentage between those of the two parents. Under both temperature regimes there were distinct differences among lines in the time intervals for different component stages in the life cycle. Cool temperatures increased lengths of these intervals, but relative difference in lengths of interval was clearly evident. Among the ten lines, IPB was notably the earliest variety to ripe first fruit. In the first component interval from seeding to flower opening, IPB was the earliest and Bonny Best the latest; however, for the two succeeding intervals, namely flowering to fruit set and fruit set to ripening, IPB did not have the shortest intervals or most rapid growth. In fact Puck variety was better than IPB for the second component interval, and in the third interval, (BBxIPB) Fl and the reciprocal cross were the earliest. This sort of variability suggests recombination to put the earliest component stages together to synthesize a very early line. / Land and Food Systems, Faculty of / Graduate

Effects of day/night temperature regimes ranging from 45/40 to 90/75°F on growth and development of Dark Skin Perfection peas were studied in controlled-environment cabinets. Light intensity was about 1500 foot-candles and the photoperiod was 16 hours. Rate of plant development, in terms of nodes produced per day, increased steadily as the average temperature increased. Rate of stem elongation, however, was most rapid at 70/55°F; and plant height was greatest at 60/50°F. On a dry matter accumulation per day basis, vine growth decreased above and below a temperature optimum which shifted from 70/60 to 60/50°F in the course of plant development. Tillering was most prolific at the lower temperatures and was absent at 90°F. Pea yield decreased as temperature increased above 60/50°F, due mainly to a reduction in the number of pods per plant. The number of peas per pod was decreased by high day/high night-temperature treatments and by high day temperature treatments imposed prior to full bloom. The combination of high day and high night temperatures caused an increase in the number of nodes to the first flower, whereas number of nodes to the first flower was decreased at the very low temperatures. Percent dry matter of plants was markedly increased at 45/40°F. / Land and Food Systems, Faculty of / Graduate

Low, non-freezing temperatures can cause both, harmful and beneficial effects on plants, and this research was carried out to survey some effects on starch and pigment accumulation. Four species were selected on the basis of photosynthetic biochemistry and major systematic grouping. Zea and Gomphrena possess the C₄-dicarboxylic acid pathway typical of certain families of tropical origin, while Triticum and Phaseolus contain the Calvin cycle alone which is typical of plants originating in temperate regions. Zea and Triticum are Monocotyledoneae while Gomphrena and Phaseolus are members of the Dicotyledoneae. Plants of each species were subjected to 10 days of cold treatment starting when they were 10, 21 or 35 days old (15, 26 and 40 days old for Gomphrena), and spectrophotometry measurements of starch, chlorophylls a and b, and carotenoids were carried out during the treatments. The effects of cold temperature depended on species, age, and duration of treatment. All of the species exhibited a significantly higher level of starch in the cold temperature for at least two of the three ages tested. The most dramatic effect of low temperature occurred in Gomphrena when the starch concentration increased to over 2000 per cent of the concentration attained at the warm temperature. Variations in the effect of cold treatment between the different ages tested were more pronounced in the monocots used than in the dicot species studied and variations due to the duration of cold treatment were observed in Gomphrena and Triticum. Cold treatment also caused significant reduction in total chlorophylls, chlorophyll a and chlorophyll b in all the species except Triticum. In Zea, the response to cold decreased as the plants aged, and the duration of cold treatment had a significant effect in Zea and Gomphrena. When the youngest plants only are considered, the response of starch and chlorophyll levels to cold treatment was well correlated with the typical photosynthetic pathway of the species tested. Low temperature had no significant effect on total carotenoid concentration .The effect of low temperature on light transmission by young Zea leaves during the first 48 hours of greening was also examined. Chlorophyll a concentration and leaf light transmission were highly correlated and the more convenient transmission measurements can therefore be used to predict leaf chlorophyll concentration. At the warm temperature used, there was a linear increase in chlorophyll concentration after a 2 hour lag period. Preceding cold treatment caused a longer lag period before chlorophyll began to accumulate at the warm temperature. Also, no chlorophyll accumulated, or there was net chlorophyll breakdown at low temperature. Kinetin treatment did not prevent the decrease in chlorophyll concentration at the low temperature. / Land and Food Systems, Faculty of / Graduate

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M. Tech. Civil Engineering / Climatic data is one of the most important inputs required in any road design. The historical information being currently relied upon for pavement design may soon lose its significance due to the expected global climate change. The broad objective of the study was to determine and simulate future climate change for road sub-grades in the southern African region, with a view to developing new pavement design parameters in order to protect the pavement infrastructure.

No description available.