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The Australian Processing Tomato Industry (APTI) has observed a decline in yield over recent years and speculates that soil-borne pathogens may be a contributing factor. The decline is characterised by poor stand establishment and the presence of stunted plants sporadically spread throughout the field. In preliminary surveys, Pythium spp. were commonly isolated from the roots of plants showing symptoms of poor growth. The aim of this study was to identify those Pythium species and assess their pathogenicity. Four field surveys were undertaken during the 2016/17 season and plants exhibiting symptoms of putative Pythium disease were collected. Pythium isolates were identified based on morphology and ITS sequences. Eight species of Pythium were identified including some common pathogens and some species which have not been previously reported on tomatoes. The in vitro pathogenicity test showed P. aphanidermatum, P. ultimum var. ultimum and P. irregulare were the most aggressive pathogens. In a glasshouse test P. ultimum var. ultimum and P. recalcitrans significantly reduced plant height 1 month after inoculation. Overall, the pathogenicity results confirmed that pathogens in the genus Pythium were most damaging in the pre-emergence and early seedling phases of tomato plant growth. However, some species also had the capacity to continue to reduce the growth of plants at later stages, potentially leading to yield reduction. Further studies are necessary to better understand the aetiology of these and additional Pythium species in the APTI context, and their ultimate effect on tomato yield.

The aim of this study was to describe the morphology, anatomy and function of underground structures associated with colonies of Solanum centrale J.M.Black (Australian bush tomato), a perennial sub-shrub found in arid areas of Australia and an important traditional staple food for Aboriginal people. It is known that this species forms clonal communities, but there is little understanding of the mechanisms of formation in either natural or cultivated situations. The underground connections within seven clonal communities from Central and South Australia were documented and samples of secondary roots, thick lateral roots and stems were examined under both laboratory and glasshouse conditions. Clonal communities were observed at all sites with individual ramets arising from lateral roots (root-suckers) that ranged from 2–10 mm in diameter growing in a network 5–15 cm below the soil surface. Lateral roots have dicotyledonous root anatomy and rapidly resprout to form new clonal ramets. They also have the capacity to accumulate starch in parenchyma cells. The morphology and root-suckering ability resemble those of weedy Solanum spp. from other parts of the world, as well as species from a variety of genera adapted to arid climates. Methods to capitalise on the ability of lateral roots to form clonal ramets in cultivated situations, particularly given the difficulties in establishing crops from seed, are discussed.

The influence of seedling water potential on infection and colonization of wheat seedlings (Triticum aestivum) by Fusarium graminearum Group 1 was studied using wax partitioning of the soil so that the water potential of the seminal root zone was manipulated independently from the water potential of the infection zone in the subcrown internode region. Eleven days after seeds were sown, water was withheld from the root zone to induce water stress in seedlings, while nonstressed seedlings were watered every 48 h to a soil water content of 0.31 g g -1 , favorable for plant growth (...)

The isolation and taxonomic characterisation of 25 isolates of Fusarium species from a New Zealand farm pasture are described. The ability of these isolates to produce mycotoxins both in liquid culture (MYRO and GYEP) and on rice grain culture was assessed. Toxin production was assessed by a combination of chemical analytical methods and by HeLa cell toxicity tests. The toxins produced included zearalenone (by three isolates), zearalenols (one isolate), butenolide (12 isolates), and various trichothecenes (five isolates). An isolate of F. culmorum (DAOM 193612) produced β-zearalenol (from rice culture) as the major toxin, whereas trichothecene production was greatest in MYRO culture by one isolate of F. crookwellense (DAOM 193611). The major trichothecenes produced by this species were 4, 15-diacetoxynivalenol followed by 8-hydroxy and 7-hydroxyisotrichodermin. Several previously unreported compounds were also isolated. Known trichothecenes produced by other species were deoxynivalenol, 15-acetox...

SUMMARY Using the ‘Cambridge method’, the effect of temperature on the colonization of wheat straw by Fusarium culmorum, Gibberella zeae, Cochliobolus sativus and C. spicifer was studied. Within the range 10–30 °C, saprophytic colonization by the four fungi was favoured by lower temperatures. This could not be attributed to the effect of temperature on the growth of the fungi in pure culture, but was probably caused by increased antagonism at higher temperatures from the general soil microflora. Contrary to previous indications, C. sativus strongly colonized straw under suitable environmental conditions.

Summary A theoretical relationship is developed relating growth of a fungus during one cycle of a diurnal temperature fluctuation to the growth at relevant constant temperatures. The theory involves the assumption that the growth-rate of the fungus at a given temperature in the cycle is unaffected by its previous temperature experience. Growth of Gibberelta zeae, Cochliobolus sativus and C. spicifer was measured at each of sixteen diurnal temperature regimes differing in median temperature and amplitude. The measured growth was compared with the expected growth. In general, the analysis supports the derived theoretical relationship. In some instances, growth at a fluctuating temperature is greater than or less than that at the corresponding median and the difference is anticipated, and explained, by the theory.

Two groups of 4 Hereford steers were housed in a controlled environment room and exposed to simulated high summer temperatures. Both groups were fed a barley grain and hay diet ad libitum. The barley in one diet contained 0.5% w/w ergots of Claviceps purpurea. Within one week of feeding the ergot diet mean rectal temperature was significantly elevated (P less than 0.05) each afternoon (up to 41 degrees C) but returned to normal overnight. Elevated rectal temperature was accompanied by other signs of heat stress, reduced feed intake, body weight loss and depression or serum prolactin concentration. Symptoms disappeared within 1 week of ceasing to feed the ergot diet.