School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAntagonistic interactions between Colletotrichum graminicola and yeasts on maize leaves( 1986)During the last two decades it has been demonstrated many times that populations of leaf surface micro-organisms are capable of reducing the levels of disease caused by various fungal pathogens. The various mechanisms by which this may be achieved have been studied and reported. In many cases, the disease depressing interactions are effective in depressing germination of spores of pathogens, in causing lysis of germtubes or in hyperparasitising the pathogen. This work is reviewed. The objective of the present study was to determine how the leaf-colonising yeasts, Cryptococcus laurentii var. flavescens and Sporobolomyces roseus reduced the infection of maize by the anthracnose fungus, Colletotrichum graminicola. Initial experiments did not support the hypothesis that the yeasts suppressed germination, nor did they demonstrate an effect of the yeasts on appressorium production. Experiments on attached leaves, however, provided data which showed that maize leaves inoculated with equal inocula in the presence and absence of the yeasts produced many more infection courts than with yeasts. This suggested, since there were equal numbers of appressorium on each set of leaves, that appressorium behaviour was different in the presence of yeasts from in their absence. In further experiments, using different techniques, it was found that in the presence of the yeasts, the proportion of appressoria which germinated was reduced. It is suggested that the effect of the yeasts on appressorium behaviour is similar to fungistasis. It was also found that in the presence of yeasts fewer acervuli developed, and individual acervuli produced fewer setae and conidia. The manner in which the cohabiting yeasts influence the behaviour of C. graminicola during its post-penetration phase was not investigated here, but offers another challenging research topic. The implications of the present findings are discussed in relation to the natural and manipulated control of plant pathogens by biological agents.
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ItemStudies on the ecology and control of some important plant parasitic nematodes in Victoria( 1986)Since 1965 I have been employed as a nematologist by the Victorian Department of Agriculture and Rural Affairs, based at the Plant Research Institute, Burnley. My major responsibilities have included: (1) From 1965-1975, funded exclusively by the Wheat Industry, to conduct research on the biology and ecology of the cereal cyst nematode (Heterodera avenae Woll.), and to advise on methods for controlling the disease it causes in wheat and other cereals. (2) From 1975, in addition to research on H. avenae, to conduct research on nematode diseases of other agricultural and horticultural crops in Victoria. My research has always been directed at achieving methods of control which are both practical, and economic to apply. Prior to 1965, cereal cyst nematode was recognised as a major cause of disease in cereals in the southern wheatbelt of Australia; its distribution was known to be related to well structured soils; knowledge of its biology and ecology under Australian conditions was limited; and, crop rotation was the only recommended method of control. There were no sources of resistance suitable for use in breeding programs; the existence of pathotypes was unknown; and, the extent and magnitude of yield losses had not been determined. My research has culminated in the adoption by cereal growers, of several new control strategies, and the results have lead to the establishment of a new pesticide market (valued at millions of dollars per year), and economic benefits from the use of nematicides are already being obtained by rural communities in Victoria and South Australia. The results of this, and other research on various aspects of the biology and control of nematodes causing disease in grapevines, citrus, pastures, vegetable crops, ornamentals, etc. are presented in the papers which follow.