Predictive test for take-all; Effect of nitrogen fertalizers on wheat rhizosphere micro-organisms.

Predictive test for take-all. The use of the most probable number technique. Effect of nitrogen fertalizers on wheat rhizosphere micro-organisms, 78LG3, 78E16. 76LG25, 77LG20, 76E6, 77JE4, 78LG3, 78E16

Fungal endophytes and a virus confer drought tolerance to Nicotiana benthamiana plants through modulating osmolytes, antioxidant enzymes and expression of host drought-responsive genes

Microbial symbionts increase plant growth and eco-physiological performance under abiotic stress. In this study, we evaluated how the colonization of two fungal endophytes isolated from wild Nicotiana species from areas of drought-prone northern Australia, and a plant virus, yellowtail flower mild mottle virus (genus Tobamovirus), improved water stress tolerance in N. benthamiana plants. Inoculation with both of the two fungal strains used and the virus significantly increased plants tolerance to water stress as manifested by their significant delay in wilting of shoot tips. The water stress tolerance of fungus-inoculated plants was correlated with increases in plant biomass, relative water content, soluble sugar, soluble protein, proline content, increased activities of the antioxidant enzymes catalase, peroxidase and polyphenol oxidase, decreased production of reactive oxygen species, and decreased electrical conductivity. In addition, there was significant upregulation of several genes previously identified as drought induced. The influence of the virus was similar to the fungi in terms of increasing the plant osmolytes, antioxidant enzyme activity and gene expression. Although separate infection of fungi and virus increased plant water stress tolerance responses, their co-infection in plants did not have an additive effect on water stress responses. These findings show that both fungi and viruses reprogram plant responses to water stress in a similar way

Influence of environmental factors on germination of Plasmopara viticola sporangia sourced from mediterranean Western Australia

Direct germination via the production of a germ tube was demonstrated in the absence of the host for Plasmopara viticola (causal agent of grape downy mildew) sporangia sourced from a major grape production area in mediterranean Western Australia (WA). In general, direct germination was favoured by environmental conditions considered less than optimal for infection by P. viticola. Most notable however was that sporangia had the capacity to germinate in the absence of free water, a factor known to be essential for the production and release of zoospores. The frequency of direct germination was low with only seven among 108 000 sporangia observed producing a germ tube. This is the first study to i) examine the influence of environmental factors viz: temperature, relative humidity (RH) and light, on the direct germination of P. viticola sporangia and ii) establish the frequency of this event. The infectivity of directly germinated P. viticola sporangia however remains unknown. Although rare, the capacity of sporangia to germinate directly and potentially infect the host, most likely when conditions are not conducive for zoospore production or survival, may provide an explanation for the source of the disease during the predominantly hot dry summer months in WA and other climatically similar viticultural areas

Fungal endophytes from salt-adapted plants confer salt tolerance and promote growth in wheat (Triticum aestivum L.) at early seedling stage

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt-sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants’ roots and their ability to withstand in vitro salt stress was evaluated. The fungal endophytes could withstand up to 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt-sensitive wheat seeds/seedlings, several of the endophytes showed a positive impact on germination and biomass-related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolates from dicot plants (identified as Microsphaeropsis arundinis) could successfully colonize wheat and promote its growth under salt and no-salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate and has previously been reported to be an effective biocontrol agent. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for enhancing the salt stress tolerance of wheat crop

Spillover of a tobamovirus from the Australian indigenous flora to invasive weeds

The tobamovirus yellow tailflower mild mottle virus (YTMMV) was previously reported in wild plants of Anthocercis species (family Solanaceae) and other solanaceous indigenous species growing in natural habitats in Western Australia. Here, we undertook a survey of two introduced solanaceous weeds, namely Solanum nigrum (black nightshade) and Physalis peruviana (cape gooseberry) in the Perth metropolitan area and surrounds to determine if YTMMV has spread naturally to these species. At a remnant natural bushland site where both solanaceous weeds and indigenous Anthocercis hosts grew adjacent to one another, a proportion of S. nigrum and P. peruviana plants were asymptomatically-infected with YTMMV, confirming spillover had occurred. Populations of S. nigrum also grow as weeds in parts of the city isolated from remnant bushland and indigenous sources of YTMMV, and some of these populations were also infected with YTMMV. Fruit was harvested from virus-infected wild S. nigrum plants and the seed germinated under controlled conditions. Up to 80% of resultant seedlings derived from infected parent plants were infected with YTMMV, confirming that the virus is vertically-transmitted in S. nigrum, and therefore infection appears to be self-sustaining in this species. This is the first report of spillover of YTMMV to exotic weeds, and of vertical transmission of this tobamovirus. We discuss the roles of vertical and horizontal transmission in this spillover event, and its implications for biosecurity

Factors affecting the production of Trichoderma harzianum secondary metabolites during the interaction with different plant pathogens

Strains of Trichoderma spp. produce numerous bioactive secondary metabolites. The in vitro production and antibiotic activities of the major compounds synthesized by Trichoderma harzianum strains T22 and T39 against Leptosphaeria maculans, Phytophthora cinnamomi and Botrytis cinerea were evaluated. Moreover, the eliciting effect of viable or nonviable biomasses of Rhizoctonia solani, Pythium ultimum or B. cinerea on the in vitro production of these metabolites was also investigated. T22azaphilone, 1-hydroxy-3-methyl-anthraquinone, 1,8-dihydroxy-3-methyl-anthraquinone, T39butenolide, harzianolide, harzianopyridone were purified, characterized and used as standards. In antifungal assays, T22azaphilone and harzianopyridone inhibited the growth of the pathogens tested even at low doses (1-10 mu g per plug), while high concentrations of T39butenolide and harzianolide were needed (> 100 mu g per plug) for inhibition. The in vitro accumulation of these metabolites was quantified by LC/MS. T22azaphilone production was not enhanced by the presence of the tested pathogens, despite its antibiotic activity. On the other hand, the anthraquinones, which showed no pathogen inhibition, were stimulated by the presence of P. ultimum. The production of T39butenolide was significantly enhanced by co-cultivation with R. solani or B. cinerea. Similarly, viable and nonviable biomasses of R. solani or B. cinerea increased the accumulation of harzianopyridone. Finally, harzianolide was not detected in any of the interactions examined. The secondary metabolites analysed in this study showed different levels of antibiotic activity. Their production in vitro varied in relation to: (i) the specific compound; (ii) the phytopathogen used for the elicitation; (iii) the viability of the elicitor; and (iv) the balance between elicited biosynthesis and biotransformation rates. The use of cultures of phytopathogens to enhance yields of Trichoderma metabolites could improve the production and application of novel biopesticides and biofertilizers based on the active compounds instead of the living microbe. This could have a significant beneficial impact on the management of diseases in crop plants

Management of root diseases of annual pasture legumes in Mediterranean ecosystems - a case study of subterranean clover root diseases in the south-west of Western Australia

Subterranean clover (Trifolium subterraneum) is an important component of Mediterranean dryland pasture ecosystems, such as in the south-west of Western Australia, where it is utilised as a winter annual pasture that provides nitrogen as well as disease breaks for rotational crops. Necrotrophic soil-borne fungal pathogens dominate Mediterranean ecosystems because of the ease of survival of these pathogens on infested residues over the dry summer period, and because of low levels of microbial competition in the impoverished and nutrient-defi cient soils characteristic of these regions that predisposes plants to root diseases. In addition to herbage and seed yield losses from soil-borne fungal and nematode pathogens, changes in botanical composition, in the number of regenerating plants, their persistence, and factors affecting feed quality are signifi cantly affected. Further, where the causal organisms of the diseases on subterranean clover are also common on other rotational crops, the impact of these soilborne pathogens appears far wider in Mediterranean ecosystems than previously considered. Under these conditions, soil-borne pathogens pose a serious threat to the productivity of this self-seeding pasture legume, to the extent that reseeding may become necessary. Pathogens such as Phytophthora clandestina, various Pythium species particularly Pythium irregulare, Aphanomyces sp., Rhizoctonia solani, one or more Fusarium species, Phoma medicaginis and Cylindrocarpon didymium are of concern, as are the nematode parasites from the genera Meloidogyne, Heterodera, Pratylenchus, Trichodorus and Radopholus. In this ecosystem, root pathogens operate together as disease complexes and the challenge therefore has been to source host genotypes with resistance to multiple pathogens. In addition to plant nutrition, environmental factors, in particular rainfall (soil moisture) and soil temperature, have a marked effect on both the disease severity caused by individual pathogens and on the interactions that occur between the different root pathogens. Approaches to disease control in this region include a range of management strategies. Cultural control strategies, including manipulation of grazing and rotations, offer some benefi ts. Manipulation of soil fertility also offers scope as this can enhance root physiology related to host resistance, overall plant growth and vigour, and also to improve the effective biological buffering against the pathogens. Fungicide treatments and manipulation of management practices may have a place in an integrated control system incorporating cultivars with useful resistance to root diseases. Clearly, host resistance offers the most cost-effective, long-term control, especially as resistance to several of these soil-borne pathogens has been identifi ed. The Mediterranean Basin, which is the centre of origin of this pasture legume, has proved to be a productive source of resistance to soil-borne necrotrophic pathogens and is likely to be a source of new subterranean clover cultivars

Trichoderma secondary metabolites active on plants and fungal pathogens

Beneficial microbes typically produce bioactive molecules that can affect the interactions of plants with their pathogens. Many secondary metabolites may also have antibiotic properties, which enable the producing microbe to inhibit and/or kill other microorganisms i.e. competing for a nutritional niche. Indeed, some of these compounds have been found to play an important role in the biocontrol of plant diseases by various beneficial microbes used world-wide for crop protection and bio-fertilization. In addition to direct toxic activity against plant pathogens, biocontrol-related metabolites may also increase disease resistance by triggering systemic plant defence activity, and/or enhance root and shoot growth. Fungi belonging to the Trichoderma genus are well known producers of secondary metabolites with a direct activity against phytopathogens and compounds that substantially affect the metabolism of the plant. The widescale application of selected metabolites to induce host resistance and/or to promote crop yield may become a reality in the near future and represents a powerful tool for the implementation of IPM strategies