School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemStudies on the etiology and control of parsnip canker, caused by itersonilia pastinacae channon( 1968)In Victoria, parsnip canker is caused chiefly by Itersonilia pastinacae Channon and, less frequently by Phoma sp.. Inoculation of both fungi into parsnip roots produced typical symptoms of the disease. The morphology of the local isolates of I. pastinacae was compared with others described and the taxonomy of the genus discussed. The fungus was shown to be seed-borne, the infection being carried in plant debris contaminating the seed and also externally on the seed itself. An aerated-steam heat treatment was developed to eliminate this seed-borne infection. In field studies I. pastinacae in naturally infected roots survived at least 12 months burial in soil. When the root was mutilated by removing the stem apical meristem, to promote rapid decomposition, the fungus survival period was reduced to 6 months. In laboratory studies the fungus, impregnated in fibre glass mesh, survived 6 months burial in unsterile soil, whereas the survival period in sterile soil was at least 12 months. Survival was shown to be due to the presence of chlamydospores; mycelium and ballistospores being rapidly lysed. Chlamydospores germinated directly to form ballistospores. I. pastinacae, also had a low competitive saprophytic ability. Field and laboratory studies demonstrated that ballistospore discharge was influenced chiefly by high relative humidity, the presence of rain being more effective than dew. Spore discharge followed a diurnal periodicity, the maximum discharge occurring between 08.00 and 10.00 hr.. Low temperature, however, reduced spore discharge even at optimum R.H. Ballistospore germination studies demonstrated soil fungistasis an effect destroyed by sterilization of the soil. Germination of ballistospores was also influenced by nutrients, either diffusates from parsnip roots and leaves or by a 2% glucose solution. Strepstomyces sp. and Bacillus subtilis were isolated from soil and antagonism towards I. pastinacae exhibited. Cell-free culture filtrates of both antagonists lysed I. pastinacae while incorporation of the filtrates into media reduced the growth rate of the fungus. Sterile soil inoculated with the antagonists also lysed I. pastinacae. Foliage applications of fungicides, particularly those containing copper, reduced the incidence of parsnip canker in the field. Control was also achieved in the field by keeping the developing crowns covered with soil during the growth of the crop.
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ItemA study of pathogens associated with stunted patches and deadheads in Victorian wheat crops( 1968)Between 1959-1966 seven species of root-rotting fungi and barley yellow dwarf virus were consistently associated with stunted patches and "deadheads" in Victorian wheat crops. The fungi occurring in order of frequency were: Fusarium culmorum (W.G.Sm) Sacc., Curvularia ramosa (Bainier) Boedijn, Helminthoaporium sativum Pammell, King and Bakke, Pythium ultimum Trow var. ultimum, Rhizoctonia solani Kuhn, Ophiobolus graminis Sacc. and Fusarium graminearum Schwabe. Barley yellow dwarf virus was found each season in the higher rainfall areas of the State; in 1961 and 1965 it occurred in epidemic proportions in all districts. These organisms may be divided into three groups based upon their ability to reduce yield of wheat under controlled glasshouse experiments. (1) MAJOR REDUCTION BY: Barley yellow dwarf virus; Ophiobolus graminis; Helminthosporium sativum. (2) MINOR R RUCTION BY: Fusarium graminearum, Fusarium culmorum; Rhizoctonia solani; Pythium ultimum. (3) NO REDUCTION BY: Curvularia ramosa Ophiobolus graminie and barley yellow dwarf virus are the most important of these pathogens in Victoria. Both caused yield losses of approximately 45-60% in the field. Under controlled glasshouse conditions they caused highly significant yield losses. Five other fungi investigated caused some losses, but during the period 1959-66 were not of great economic importance. The incidence of these pathogens could be related to climatic conditions before and during the wheat growing season. (1) Highest incidence after a dry winter and wet spring: Ophiobolus graminis; Pythium ultimum. (2) Highest incidence after a mild winter and dry spring: Barley yellow dwarf virus; Fusarium graminearum; Fusarium culmorum; Helminthosporlua ; Curvularia ramosa. (3) Highest incidence when crop sown under wet conditions: Rhizoctonia solani; Pahiuta ultimum.