School of Agriculture, Food and Ecosystem Sciences - Theses

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    An ecological comparison of California red scale (Aonidiella aurantii (Mask.)) and yellow scale (Aonidiella citrina Coq.) on citrus
    McLaren, Ian William. (University of Melbourne, 1970)
    Red scale (Aonidiella aurantii (Maskell)) and yellow scale (Aonidiella citrina Coquillet ) have been compared by constructing age-specific life and fecundity tables over a range of temperatures and humidities. Using; the data from these tables the values were calculated for rm The Intrinsic Rate of Natural Increase, rc The Capacity for Increase, Ro The Nett Reproductive Rate, and LAMBDA The Finite Rate of Increase. A study of these parameters showed that: (1) The upper thermal deathpoint was similar for both species. (2) A. citrina multiplied more rapidly than A. aurantii over the median range of temperatures. (3) The threshold of population growth was about 13�C for A. aurantii and 18�C for A. citrina. A study was made of the settling behaviour of crawlers on leaves, and it was found that: (1) Crawlers of A. aurantii were negatively geotropic, and because of this they tended to settle on the upper tissues of the host plant. (2) Crawlers of A. citrina demonstrated negative phototaxis, and as a result they tended to settle on the shaded undersurface of leaves. Correlations were found between the fecundity of red scale females on leaves, and: (1) Size of the adult (+ve). (2) Increase in size from 2nd instar to adult (+ve). (3) Initial natality (+ve). (4) The feeding site w.r.t. distance from vascular tissue in the leaf (-ve). A further correlation (+ve) was found between delayed mating and initial natality. This was thought to result from continued ovulation in the unfertilized female, a postulate which was verified by examining the intreabdominal eggs in virgin females of various ages. These results have been used to discuss the relative abundance and distribution of both scale species in Sunraysia, the dispersai and invasiveness of each species, and the present limitations on biological control of red scale. On the basis of this project it has been possible to formulate a revised approach for regulating red scale populations in Sunraysia.
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    A study of blue mould (Peronospora tabacina Adam) of tobacco in Victoria : including a review of the history of the disease, its epidemiology and control, with some comparisons between Australian and overseas experiences
    Paddick, Richard Gordon ( 1970)
    A brief resume of tobacco culture in Victoria and descriptions of the more important types of tobacco derived from Nicotiana tabacum are given. The symptomatology, history and distribution, nomenclature and economic importance of blue mould (Peronospora tabacina) site are discussed. Epidemiology of blue mould was studied with particular reference to the relationship between disease occurrence in tobacco fields, diseased transplants and weather, especially rainfall. Surveys showed that the first appearance of blue mould was not related to a particular plant growth stages or time of year. An increase in the percentage of diseased plants could be related to rain on two of three consecutive days. There was an interval of 2 - 5 weeks from first appearance to maximum percentage of diseased plants, the shorter period occurred when more than 25% of plants were diseased at the first record. Soil conditions that produced lush growth, combined with weather which favoured sporulation and infection early in the season were the main factors that influenced disease severity. Although the disease could be be destructive on leaves, basal stem infection caused the greatest Ioses. A relationship between benzol vapour concentration in covered seed beds, temperature and wind speed was established. Higher concentrations of benzol vapour were maintained under wet covers than under dry. Zineb and maneb were found to be the most effective fungicides of a wide range tested for control of blue mould in the field. Neither had any adverse effect on quality at the concentration and frequency at which they were used. Weekly spraying with fungicides gave better control of blue mould than did application according to four spray warning systems.
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    Studies on brown rot of stone fruits, with particular reference to the causal fungi, dispersal and longevity of conidia
    Jenkins, Peter Thomas ( 1970)
    Brown rot of stone fruits was studied with particular reference to causal fungi, and dispersal and longevity of conidia. Surveys showed that brown rot was caused by Sclerotinia fructicola, throughout Victoria, and also by Sclerotinia laxa in Southern Victoria. In studies with S. fructicola, conidia, but not ascospores, were inoculum for new infections. Dispersal of conidia was studied in detail. In the field, large numbers were dispersed by rain falling on to sporulating blossoms, but only little aerial dispersal was detected. In laboratory experiments, both water splash and aerial dispersal was demonstrated, aerial dispersal being greatest at minimum humidities and maximum temperatures. Longevity of conidia was studied in an orchard environment. Viability and virulence was reduced by exposure within tree canopies, and on unsterilized soil; and was further reduced by prior wetting. A species of Bacillus antagonistic to S. fructicola in plate cultures and on surfaces of mature fruits was associated with exposed conidia. Cell free filtrates of Bacillus cultures prevented germination of conidia, or caused germ tube abberations. A technique was developed to isolate airborne bacteria antagonistic to S. fructicola. The mode of dispersal, longevity and virulence of conidia are discussed in relation to spore load and infection.
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