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Crown rot (CR; Fusarium pseudograminearum) is a serious disease in winter cereals. Soil type, temperature, nutrients, water availability and stubble‐borne inoculum levels play major roles in determining disease severity. This paper reports the impact of two different watering regimes on the disease severity and gas exchange of F. pseudograminearum infected bread wheat for the first time. Fusarium pseudograminearum inoculated and noninoculated genotypes with different susceptibility to CR were watered to either field capacity or a reduced watering regime in three controlled environment experiments. Rate of photosynthesis, stomatal conductance, internal CO2 concentration and transpiration rate were measured using a portable photosynthesis system, together with disease severity of leaf sheaths at 28 days after planting. Significant differences in disease severity were reported between watering treatments with reduction in CR symptoms in the partially resistant genotypes in the reduced water treatment. Photosynthesis, stomatal conductance and transpiration rate were significantly decreased across most genotypes when inoculated with F. pseudograminearum. Differences in gas exchange between inoculum treatments were more evident in plants watered to field capacity. Water availability has been reported to be one of the crucial factors for initiating F. pseudograminearum infection and subsequent development of CR disease. This research demonstrates significant variation in genotype‐related responses to the complex interactions of F. pseudograminearum infection and water treatment, with a negative impact of both limited soil water availability and CR disease severity on plant gas exchange in bread wheat. [ABSTRACT FROM AUTHOR]

Yield losses of bread wheat due to crown rot can be more severe when drought conditions occur during the grain-filling period. Root architecture characteristics are important for soil exploration and belowground resource acquisition and are essential for adaptation to water-limited environments. Traits such as root angle, length and density have been strongly associated with acquisition efficiency and contribute to yield stability of the crop. The impact of crown rot pathogens on wheat root architecture is poorly understood. We examined differences in root angle, length and number, as well as dry root weight of the crown rot-susceptible bread wheat cultivar, Livingston inoculated with one of two crown rot pathogens Fusarium culmorum or Fusarium pseudograminearum in a transparent-sided root observation chamber. Significant adverse impacts on plant health and growth were revealed by visual discolouration of the leaf sheaths; fresh and dry shoot weight; leaf area of the oldest and the youngest fully expanded leaf and leaf number. Values of most recorded root system measurements were reduced when inoculated with either F. culmorum or F. pseudograminearum. In contrast, root angle was increased in the presence of F. culmorum but was not significantly changed by F. pseudograminearum. The development of whiteheads and grain losses in bread wheat caused by crown rot have previously been associated with blockages of the vascular systems. The method employed here was able to identify differences in the pathogen impacts on roots, which were not detected using previous systems. This research indicates that in the presence of F. culmorum and F. pseudograminearum infection, not only reductions in the size and biomass of the shoot system but also changes in the length, biomass and architecture of the root system could play an important role in yield loss. [ABSTRACT FROM AUTHOR]

The development of commercial varieties that are resistant or tolerant to crown rot caused by Fusarium species is an important goal for cereal breeding programs internationally. Ideally, this research requires experimental sites that are initially free from Fusarium in order to establish treatment plots that compare growth in the presence and absence of these soil- and stubble-borne pathogens. Specifically, the assessment of tolerance requires control plots free of disease to determine the reduction in crop yield in plots where the disease is present. The ability of soil solarisation to reduce the background Fusarium pseudograminearum level occurring at experimental sites in comparison to current stubble management techniques was investigated across three field trials at Wellcamp in Queensland. Stubble from a susceptible durum (Triticum turgidum ssp. durum) cultivar inoculated with F. pseudograminearum was incorporated by cultivation into the trial sites to establish a significant background level of inoculum prior to the application of all subsequent treatment plots. In these trials, solarisation over a period of twelve weeks reduced the presence of F. pseudograminearum to low detection levels when compared to the traditional crown rot management techniques of cultivation or growth of the non-host cover crops mungbean (Vigna radiata) and soybean (Glycine max). No negative effects of solarisation were observed on a subsequent crop of bread wheat (Triticum aestivum), with significantly higher yields observed in the solarised treatments. Solarisation has the potential to deliver near zero level crown rot reference sites for experimental purposes in one short application between cropping seasons. • Solarisation decreased Fp levels in both the soil and remaining stubble. • Solarisation reduced Fp to a greater degree than both cultivation and cover crops. • Solarisation increased levels of soil moisture for the following crop. • Solarisation increased yields in the following wheat crop. [ABSTRACT FROM AUTHOR]

Achieving genetic gain when selecting for genotypes with favourable grain production traits in the presence of the fungal pathogen Fusarium pseudograminearum can involve potentially competitive objectives of breeding for tolerance and breeding for resistance. A method for the selection of genotypes for both tolerance and resistance to crown rot in wheat, caused by this fungal pathogen, is presented through a combined analysis of grain yield and symptoms of disease severity across inoculated and uninoculated treatments. The symptoms of disease severity are measured as basal stem browning in the plant, and this trait provides a measure of resistance in this study. The measurement of grain yield in uninoculated and inoculated treatments provides a measure of yield potential and yield in the presence of disease, respectively. Interpretation of analysis results through the regression inherent in the statistical model allows us to derive and select for three traits of interest. Firstly, yield retention can be derived from a random regression of yield of genotypes in inoculated versus uninoculated treatments, independently of yield potential in that environment. Secondly, severity of disease symptoms in inoculated treatments can be used to select genotypes with superior resistance. Finally, a tolerance measure can be derived from the yield retention, when it is assessed independently of the disease severity measured as stem browning. In theory, this method is superior to traditional approaches of forming a yield difference or a percentage yield loss calculation. In practice, genetic gain can be made for tolerance through accurate phenotyping of the trait, independently of resistance in that environment. [ABSTRACT FROM AUTHOR]

In Australia, crown rot of cereals is predominantly caused by Fusarium pseudograminearum and Fusarium culmorum, and common root rot by Bipolaris sorokiniana. Fusarium graminearum is an important pathogen causing Fusarium head blight worldwide and has also been reported to cause crown rot of wheat. The comparative ability of F. pseudograminearum, F. culmorum, F. graminearum and B. sorokiniana to cause crown rot and common root rot across a range of winter cereal species requires investigation. In glasshouse trials, we inoculated one cultivar each of barley, bread wheat, durum wheat, oat and triticale with two strains of each of the four pathogens. At 21 days after inoculation, the sub-crown internode and leaf sheaths of each plant were visually rated for brown discoloration. Shoot length and dry weight of inoculated plants were compared with those of non-inoculated controls. Barley and bread wheat had the highest disease severity ratings on leaf sheaths and sub-crown internode (64.7-99.6%), whereas oat had the lowest disease severity ratings across all pathogens (<5%). The shoot length of all cultivars was significantly reduced (by 12.2-55%, P < 0.05) when exposed to F. pseudograminearum. This study provides a comparison of pathogenicity of crown rot and common root rot pathogens and demonstrates significant variation in visual discoloration and host response across a range of winter cereals. [ABSTRACT FROM AUTHOR]

Summary: An emerging experimental framework suggests that plants under biotic stress may actively seek help from soil microbes, but empirical evidence underlying such a 'cry for help' strategy is limited.We used integrated microbial community profiling, pathogen and plant transcriptive gene quantification and culture‐based methods to systematically investigate a three‐way interaction between the wheat plant, wheat‐associated microbiomes and Fusarium pseudograminearum (Fp).A clear enrichment of a dominant bacterium, Stenotrophomonas rhizophila (SR80), was observed in both the rhizosphere and root endosphere of Fp‐infected wheat. SR80 reached 3.7 × 107 cells g−1 in the rhizosphere and accounted for up to 11.4% of the microbes in the root endosphere. Its abundance had a positive linear correlation with the pathogen load at base stems and expression of multiple defence genes in top leaves. Upon re‐introduction in soils, SR80 enhanced plant growth, both the below‐ground and above‐ground, and induced strong disease resistance by boosting plant defence in the above‐ground plant parts, but only when the pathogen was present.Together, the bacterium SR80 seems to have acted as an early warning system for plant defence. This work provides novel evidence for the potential protection of plants against pathogens by an enriched beneficial microbe via modulation of the plant immune system. [ABSTRACT FROM AUTHOR]