Seed of tomato fruit affected by bacterial speck was examined for Pseudomonas tomato. The bacterium was isolated from seed taken directly from fruit, but not from seed extracted by the fermentation process. Acid and fermentation extraction processes appeared to eliminate P. tomato. Pulp containing natural and/or added populations of the bacterium was non-infective at 1 hr and 48 hr after commencement of the acid and fermentation processes respectively. Studies on the perennation of P. tomato showed that the bacterium survived in plant debris either on or 2 cm below the soil surface for the test period of 30 weeks; it also survived on Nylon mesh in soil for 25 weeks. The incidence of bacterial speck in seedlings was reduced significantly (P = 0.01) by cupric hydroxide sprays, two sprays per week being more effective (P = 0.05) than one. No heat-tolerant strain of P. tomato was detected, and thermal death points for isolates from green and ripe fruit were 48 and 49°C respectively.

SummaryIsolates of an oat-attacking strain of OphioboIu8 gram~nt8 from Western Australia were differentiated from other isolates by comprehensive pathogenicity tests. Differential criteria for the two recognized varieties of O. gramini8 indicated that the Western Australian oat isolates were similar to var. avenae; South Australian isolates from oats were pathogenically similar to the type variety although some resembled var. avenae in their tolerance of oat extract. Pathogenicity on oats was the most reliable differential criterion and size of asci and ascospores the least; ascospore size was influenced by substrate, being generally greater in culture than on host tissue. Nuclear distribution in mycelia of wheat-and oat-attacking strains was similar but attempts to induce hyphal anastomosis between the two were unsuccessful.A relation was observed between virulence of isolates and perithecial production on host tissue and in culture.

Wheat roots and seeds were examined for Fusarium species during surveys in 1970 and 1971. Fusarium spp. were commonly isolated from root lesions, especially those on older plants, but seldom from seed. However, frequency of isolation from seed was increased by using a selective medium containing pentachloro-nitrobenaene. Fourteen species, including eleven not previously recorded on wheat in Victoria, were identified, Previously recorded species were: F. culmorum, F. equiseti and F. graminearum. Previously unrecorded species were : F. arthrosporioides, F. avenaceum, F. camptoceras, F. chlamydosporum, F. concolor, F. oxysporum, F. poae, F. sambucinum var. coeruleum, F. semitectum, F. sporotrichioides and F. trichothecioides. The commonest were the weakly pathogenic species F. avenaceum, F. equseti and F. oxysporum. The strongly pathogenic species F. graminearum, was seldo isolated and the other strongly pathogenic species, F. culmorum, was common only in the Southern cereal district.

The microflora of 568 samples of surface sterilized wheat grains, harvested in 1963-64 and 1964-65 in Western Australia, were examined. Alternaria spp, were the most commonly isolated organisms, being present in 17.7 per cent of all grain and 98.7 per cent of all samples over the two years. The frequency of occurrence was not related to grain discolouration. Of the remaining organisms, Helminthosporium sativum, Fusarium spp., Podosporiella vertillata, and Septoria nodorum are known to be pathogenic to wheat. H. sativum and Fusarium spp. were isolated only in trace amounts in the grain and in few samples, whereas P. verticillata and S. nodorum occurred in 1.86 and 3.40 per cent respectively of all grain and 39.92 and 70.57 per cent respectively of all samples. Pithomyes chartarum, the organism causing facial eczema in animals, was isolated once from each of two grain samples.

SummaryVariations were studied in the monosporous Fl progeny ot an isolate of Ophiobolus graminis from wheat. All Fl ascospores from perithecia on living host tissue were strongly pathogenic, but half from a perithecium in culture were weakly pathogenic. Perithecia were formed in culture and on host tissue only by strongly pathogenic progeny. Strongly pathogenic progeny survived well on artificially infected wheat straw buried in unsterilized soil, but weakly pathogenic progeny did not. Survival of all isolates was increased by nitrate enrichment of soil.