Prolific production of sclerotia in soil by Rhizoctonia solani anastomosis group (AG) 11 pathogenic on lupin

Rhizoctonia solani anastomosis group (AG) 11 causes serious damping‐off and hypocotyl rot of narrow‐leafed lupins (Lupinus angustifolius) in the northern grain‐belt of Western Australia. R. solani AG‐11 produced abundant sclerotia in sand overlaid on potato dextrose agar. Sclerotia were produced in larger numbers in natural Lancelin sand than in Geraldton loamy sand collected from the northern grain‐belt of Western Australia. The majority of the sclerotia produced were in >250 to <500 μam size range. The germination levels of sclerotia in the first two cycles of drying and germination were not significantly different. Sclerotia still retained 50% germination after four such cycles, indicating that they may have the ability to withstand the climatic cycles of the Mediterranean environment of southwestern Western Australia. The radial growth of the mycelium from sclerotia, however, declined with each drying and germination cycle. Inoculum potential of the pathogen increased with the size of sclerotia resulting in more severe lupin hypocotyl rot with larger sclerotia. The number of sclerotia produced in soil increased with increasing density of lupin seedlings. The results also indicate that R. solani AG‐11 can produce sclerotia on infected plant tissues as well as in soil. This is the first report of the prolific production of sclerotia by AG‐11 and their significant role in infection of lupins in soil in Western Australia.     

Pectic Zymograms and Water Stress Tolerance of Endophytic Fungi Isolated from Western Australian Heaths (Epacridaceae)

Forty-nine isolates of root-inhabiting fungi were obtained fromthirteen species of eleven genera of native Epacridaceae andcompared in relation to host taxonomy and habitat of origin.Pectic zymograms of extracts of the cultured endophytes showeda marked degree of homogeneity of banding patterns amongst isolatesfrom a mesic wetland site, whereas those from dryland habitatdisplayed more heterogenous banding. It is speculated that hostspecies can operate with only a limited number of fungal associatesunder mesic conditions but require a higher degree of endophytevariation when combating dry and impoverished environments.Considerable distinction between the geographically diverseendophytes isolated from the common hostLysinema ciliatum suggestedthat selection of endophytes was not driven primarily by hosttaxonomy. Ascribing functional significance to the observed differencesbetween endophytes was studied by examining responses of culturedisolates to polyethylene glycol induced-water stress coveringa range of potentials from -0.16 to -2.96MPa. Three responsetypes were observed: (a) the isolate produced minimal radialgrowth at all water potentials tested, (b) maximum growth ofthe isolate occurred under least water stress, with progressivesuppression of radial extension with decreasing water potentialand (c) maximum growth of the isolate occurred under a degreeof water stress. The broad range of responses to water stressobserved was suggested to reflect the diverse habitat tolerancedisplayed by epacrids and their endophytic partners in southwest Australia. ericoid mycorrhizas; pectic zymogram; water stress; Epacridaceae     

Root responses to cereal cyst nematode (Heterodera avenae) in hosts with different resistance genes

The development of cereal cyst nematode (CCN; Heterodera avenae ) induced syncytia in the host roots of infected resistant bread wheat ( Triticum aestivum cv. AUS10894), diploid wheat ( Aegilops tauschii ), barley ( Hordeum vulgare cv. Chebec and cv. Galleon) and in the susceptible wheat cv. Meering and barley cv. Clipper were studied over a period of 13 d. The resistance to CCN in these cereal plants is conferred by the resistance genes Cre1 in the wheat cv. AUS10894, Cre3 in A. tauschii , Ha2 in barley cv. Chebec and Ha4 in barley cv. Galleon. Anatomical observations were made on the development of the syncytia in CCN-infected wheat and barley roots, which carry each of these four sources of resistance genes. Accelerated development of the syncytia in resistant plants, especially in the barley cultivars, was observed. The sites of syncytia development in susceptible wheat and barley were also closely associated with the vascular tissues in the stele, but less so in the resistant plants. The syncytia in the infected susceptible wheat and barley were also metabolically active at day 13. By contrast, the syncytia of resistant wheat plants carrying the Cre1 or Cre3 genes remained extensively vacuolated and less metabolically active. In barley plants with the Ha2 or Ha4 genes, the syncytia appeared non-functional and in early stages of degeneration by day 13 after inoculation.     

Determining the effectiveness of grazing and trampling by livestock in transmitting white clover mosaic and subterranean clover mottle viruses

Glasshouse and mini-sward experiments were done to determine the relative roles of grazing and trampling by livestock in transmitting white clover mosaic (WC1MV) and subterranean clover mottle (SCMoV) viruses between clover plants in pastures. Wounding due to grazing was simulated by repeatedly cutting plants with serrated scissors (glasshouse) or mowing (mini-swards), while wounding due to trampling was simulated by repeatedly bashing plants with the flat end of a wooden hammer handle (glasshouse) or rolling (mini-swards). In glasshouse experiments, cutting was more effective than bashing in transmitting WC1MV to white clover (Trifolium repens) plants but cutting and bashing transmitted it to subterranean clover (T. subterraneum) plants at similar rates. In an experiment with white clover mini-swards, mowing was more effective than rolling in transmitting WC1MV, and when both were combined, initially spread exceeded that obtained when the spread from mowing and rolling alone was added together. In glasshouse experiments, bashing was more effective than cutting in transmitting SCMoV to subterranean clover plants. In one experiment, neither mowing nor rolling spread SCMoV in mini-swards of subterranean clover. When transmission to subterranean clover cultivars which were ‘susceptible’ or ‘moderately susceptible’ to SCMoV was compared in glasshouse experiments, repeated bashing spread the virus more slowly to the ‘moderately susceptible’ cultivars. When mixed with ruminant saliva, infective sap containing WC1MV or SCMoV was still infective to clover plants after 4 wk storage at room temperature. When infective sap was allowed to dry naturally on a metal surface, SCMoV still infected clover plants when the dried sap was taken up in tap water after 4 but not 14 days, while WC1MV was infective after 24 h but not 4 days. These results suggest that grazing and mowing are more effective than trampling at transmitting WC1MV to white clover plants in pastures, while trampling is more effective at spreading SCMoV to subterranean clover. However, both transmitted WC1MV to subterranean clover at similar rates. Possible reasons for these differences are discussed in relation to differences in clover plant morphology and virus-specific factors.     

Comparative effects of different smoke treatments on germination of Australian native plants

Abstract This study consists of a series of investigations designed to determine the potential of concentrated smoke products to stimulate seed germination and assist in the rehabilitation of degraded landscapes. Aerosol smoke and conventional smoke water products are not practical for use in broad‐scale seed bank regeneration programmes due to infrastructure limitations and the high rate of application required for their use. Concentrated smoke products have been found to be effective in stimulating soil seed banks and are suitable for broad‐scale use due to the lower rate of application required to elicit germination within smoke‐responsive species. The use of concentrated smoke products on undisturbed soil seed banks at 50 and 100 mL m^‐2 increased total seedling numbers 10‐fold, while species richness more than doubled over untreated controls. Although aerosol smoke applied directly to soil promoted 10 times more seedlings compared to concentrated smoke products, species richness levels in each treatment were similar. Concentrated smoke products cause leaf scorch when applied directly over plants in active growth, with limited to nil damage when plants are not actively growing. The affected plants generally recovered following application of concentrated smoke products as a foliar spray.