1. Fusarium roseum �Graminearum� was the predominant fungus associated with stalk rot of maize in eastern Australia in the 1972, 1973 and 1974 growing seasons. All isolates of this pathogen were of the Group 2 type. Thus Group 2 contrasts with Group I which is normally isolated :Erora crown rot of wheat and grasses. Other fungi isolated in order of frequency were Diplodia maydis, F. rnoniliforme �Subglutinans�, Bipolaris sorokiniana, Nigrospora oryzac, F. roseum �Semitectum�, F. moniliforme, F. roseum �Equiseti�, F. roseum �Concolor�, Macrophomina phaseolina, Rhizoctonia sp., F. roseum �Acuminatum�, F. oxysporum, F. solani, F. tricinctum and F. roseum �Heterosporum�. The relative isolation frequencies of the fungi varied according to the seasonal conditions. Stalk rots were not of major importance in 1973, a relatively dry growing season. However, in 1974, a wet growing season, stalk rot diseases were common in all areas investigated. 2. Isolates of F. roseum �Graminearum�,derived mainly from wheat and maize but also from other sources and from various regions of eastern Australia, were examined for perithecia formation, colony characteristics, fertility, colony growth, conidia production and conidia size. The distribution of the fungus in field colonized maize and wheat plants was also studied. The Group 1 isolates did not produce perithecia, were heterothallic and very infertile, had a mean colony growth of 4.4 cm per 3 days (range, 3.9- 5.1) and produced relatively large numbers of conidia. In contrast, Group 2 isolates were homothallic and produced perithecia readily, had a mean colony growth of 5.4 cm per 3 days (range, 4.7�6.1) and produced relatively low numbers of conidia. Group 1 isolates were found to be commonly associated with crowns and roots of plants and Group 2 isolates were commonly associated with aerial plant parts. 3. The ability of a number of Group 1 and Group 2 isolates to produce the fungal hormone, zearalenone was assessed. Group I isolates produced three to four times more zearalenone than Group 2 isolates. In addition, a. culture which had previously produced perithecia but had lost that ability following numerous transfers, produced no detectable zearalenone. The results provided good evidence that the observed difference in perithecia formation was directly related to the ability to produce zearalenone. 4. The pathogenicity to wheat, maize and carnations of Group 1 isolates from crown rot affected wheat plants and Group 2 isolates from stalk rot affected maize plants was tested. Pathogenicity of 11 other isolates from teosinte, carnations, pearl millet, wheat and barley scab, banana, ginger and common wheat grass was also assessed. The results indicated that pathogenic specialization exists within F. roseum �Graminearum�. Wheat isolates were the most pathogenic to wheat, carnation isolates were the most pathogenic to carnations and all maize isolates were pathogenic to maize while those from wheat and common wheat grass were not as pathogenic to maize. Moreover, Group 2 isolates were more pathogenic when inoculated in aerial plant parts, and the Group I isolates were more pathogenic when inoculated in plant parts in soil. Inoculations on wheat seedlings in sterile field soil demonstrated that the inherent pathogenicity to wheat seedlings of isolates from wheat and maize were similar. 5. Some factors which could contribute to the observed pathogenic differences between isolates from wheat and maize to wheat seedlings in field soil were examined. Conidia volume, germination rate and inherent germinability in the soil were studied. The Group I isolates had the largest volume, the most rapid germination and the highest inherent germinability. Pathogenicity was positively correlated with conidium volume and inherent germinability. In addition, the inherent germinability and conidium volume were positively correlated. Thus, it was established that pathogenic behaviour of conidia of Group 1 and Group 2 reflected differences in conidia morphology.
| Identifer | oai:union.ndltd.org:ADTP/220666 |
| Date | January 1976 |
| Creators | Francis, Rodney Gordon |
| Publisher | University of Sydney. Agriculture |
| Source Sets | Australiasian Digital Theses Program |
| Language | English, en_AU |
| Detected Language | English |
| Rights | Copyright Francis, Rodney Gordon;http://www.library.usyd.edu.au/copyright.html |
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