Effects of yellow spot on wheat: Comparison of epidemics at different stages of crop development

Effects of yellow spot (Pyrenophoua tuitici-repentis) on two cultivars (Banks and Olympic) of wheat have been examined in a field experiment where distinctly different epidemics were produced in various treatments. Severe yellow spot before jointing reduced production of both tillers and dry matter, and substantially lowered leaf area index at jointing. Severe disease after jointing reduced leaf area index at flowering, dry weight of plants at maturity and harvest index. Crop phenology was also modified, with flowering being delayed by early disease and crop maturity hastened by late disease. Where yellow spot was severe throughout, the grain-filling period was greatly reduced. Grain yield of Banks was reduced by c. 13 % by early disease, c. 35 % by late disease, and c. 48 % by disease throughout the crop season. Most of the loss was in reduced grain size. Although yield loss in Olympic was less than in Banks, the resistance of Olympic was shown to be inadequate

Spot Form of Net Blotch Resistance in a Diverse Set of Barley Lines in Australia and Canada.

The responses of 95 barley lines and cultivars to spot form of net blotch (SFNB) caused by Pyrenophora teres f. maculata were analyzed as seedlings and adults in Australia and Canada. Cluster analyses revealed complex reaction responses. Only 2 lines (Esperance Orge 289 and TR3189) were resistant to all isolates at the seedling stage, whereas 15 lines and cultivars (81-82/033, Arimont, BYDV-018, CBSS97M00855T-B2-M1-Y1-M2-Y-1M-0Y, C19776, Keel, Sloop, Torrens, TR326, VB0111, Yarra, VB0229, WI-2477, WI2553, and Wisconsin Pedigree) were resistant toward the two Canadian isolates and mixture of Australian isolates at the adult stages. In Australian field experiments, the effectiveness of SFNB resistance in three barley cultivars (Barque. Cowabbie, and Schooner) and one breeding line (VB9104) with a different source of resistance was tested. Barque, which possessed a resistance gene that provided complete resistance to SFNB, was the most effective and showed no effect on grain yield or quality in the presence of inoculum. Generally, cultivars with seedling or adult resistance had less disease and better grain quality than the susceptible control. Dash, but they were not as effective as Barque. A preliminary differential set of 19 barley lines and cultivars for P teres I. maculata is proposed

Flag smut resistance in selected wheat cultivars and lines

Thirteen wheat cultivars and breeders' lines were evaluated in the field at Toowoomba for resistance to flag smut (Urocystis agropyri). The cultivars Spica, Kite and Gatcher proved highly resistant while Hopps, Songlen, Oxley, Timgalen, Cook and Timson had good levels of resistance. Gamut, Mendos and Tarsa, however were very susceptible

Sustained genetic control of wheat rust diseases in north-eastern Australia

Control of wheat rusts in north-eastern Australia has been based on resistance breeding since the early 1920s. It has been an enduring journey of discovery, disappointment, and achievement, which has culminated in a pool of knowledge and expertise upon which today's plant breeders can efficiently target durable resistance to the major rust diseases. This paper outlines significant advances in genetic control of rusts in the region, with particular emphasis on the invaluable role played by the University of Sydney rust control program and its influence on wheat breeding in the region and throughout Australia. This paper is part of ‘Global Landscapes in Cereal Rust Control’, see Aust. J. Agric. Res. Vol. 58, no. 6

Pathotypes of Cochliobolus sativus on barley in Australia

Pathotypes of Cochliobolus sativus have been reported overseas but variation in the Australian population has not been investigated nor have the optimum conditions for the identification of variation been established. Preliminary experiments showed that maximum separation of infection responses of seedlings to infection by C. sativus conidia was obtained at 21°C using inocula containing 104 conidia/mL and a dew period of 40 h. Under these conditions, the existence of pathotypes in the Australian population of C. sativus was demonstrated. Using 20 lines, six pathotypes were identified among 34 isolates of the fungus. A differential set consisting of 12 barley cultivars is proposed

Fungicidal control of Pyrenophora tritici-repentis in wheat

The use of fungicides to control yellow spot in wheat, caused by Pyrenophora tritici-repentis, in the northern wheat region of Australia, was examined in three field experiments. Field conditions were conducive to disease development. This was aided by spreading stubble infested with P. tritici-repentis and by regular spray irrigations, and moderate yellow spot epidemics resulted in all 3 years. Within the three experiments, 12 fungicides were evaluated for their ability to reduce the impact of yellow spot on grain yield. Single spray applications of the fungicides, some at varying rates, were made at 90% flag leaf emergence. Treated controls had 3-4 applications of propiconazole at 62 mL a.i./ha or tebuconazole at 72.5 ml a.i./ha throughout the season. Grain yield losses of up to 59% were recorded in the untreated plots. A reduction in grain size rather than a decrease in the number of grains was responsible for the yield losses. Yield losses were significantly lower following application of flusilazol, prochloraz, propiconazole and tebuconazole in cvv. Hartog and Banks, in the first experiment. Application of azoxystrobin at 125 and 250 g a.i./ha, difenoconazole at 125 mL a.i./ha, epoxyconizole at 72 mL a.i./ha, propiconazole at 125 mL a.i./ha, tebuconazole at 125 mL a.i./ha or trifloxystrolin at 150g a.i./ha significantly reduced losses in the third experiment, sown with cv. Sunstate. This work has demonstrated that fungicidal control of yellow spot in wheat in the northern region can be a viable control option in years of high yield potential and high disease pressure

Pathotypes of Cochliobolus sativus on barley in Australia

Pathotypes of Cochliobolus sativus have been reported overseas but variation in the Australian population has not been investigated nor have the optimum conditions for the identification of variation been established. Preliminary experiments showed that maximum separation of infection responses of seedlings to infection by C. sativus conidia was obtained at 21°C using inocula containing 104 conidia/mL and a dew period of 40 h. Under these conditions, the existence of pathotypes in the Australian population of C. sativus was demonstrated. Using 20 lines, six pathotypes were identified among 34 isolates of the fungus. A differential set consisting of 12 barley cultivars is proposed