Range of winter cereal reactions to root and crown rot pathogens

Range of winter cereal reactions to root and crown rot pathogens

Winter cereals can be colonised by a number of different soil-borne organisms, including crown rot and common root rot pathogens which can have a devastating economic impact on associated industries. These diseases damage the tissues of the sub-crown internode (SCI) and the stem, and result in subsequent yield losses. In Australia, crown rot disease is predominantly caused by Fusarium pseudograminearum and Fusarium culmorum. In different parts of the world, such as the United States of America (USA), Fusarium graminearum has also been associated with crown rot. In Australia, Bipolaris sorokiniana is the soil-borne pathogen causing common root rot. The current study aims to examine the ability of these four pathogens to induce crown rot and common root rot symptoms in five winter cereals in the glasshouse and field.

Seedling inoculation tests were conducted, in the glasshouse, to examine disease severity on leaf sheaths and SCIs, specifically the impacts on shoot length and shoot dry weight. Two strains each of F. pseudograminearum, F. culmorum, F. graminearum, and B. sorokiniana were inoculated across a single cultivar of a range of winter cereals: barley (Hordeum vulgare), bread wheat (Triticum aestivum), durum wheat (Triticum durum), oat (Avena sativa), and triticale (xTriticasecale). A significant variation in disease severity (p < 0.05) among the four crown rot and common root rot pathogens was observed, including variation between pathogen strains. Significant differences amongst the cereal cultivars were observed in the disease severity of the leaf sheaths and SCIs. Furthermore, a significant reduction in the shoot length of all cultivars was observed when inoculated with F. pseudograminearum (p < 0.05), while dry shoot weight was only significantly reduced (p < 0.05) in the barley variety Grimmett.

Field inoculation trials using three strains of crown rot pathogens and one strain of common root rot pathogen were conducted to compare the visual disease symptoms on the stems and SCIs of all five winter cereals at three harvest stages (tillering, flowering, and maturity). Significant differences in the disease severities on the SCI (p < 0.001) and stems were observed (p = 0.002) for the crown rot and common root rot pathogens across the five winter cereals. Variation in disease severity was observed among the cultivars depending on the pathogen inoculum. There was a significant effect for pathogens on plant height (p < 0.001) for both years. A significant difference was observed in plant weight between harvest time and pathogen for 2016 trial (p < 0.05), and significant impact between the pathogens in plant weight for 2017 experiment (p < 0.001). Fusarium pseudograminearum and F. culmorum DNA were most frequently detected in all cereal cultivars, while F. graminearum and B. sorokiniana DNA were detected the least. Oat had low or no disease severity, although the DNA of each pathogen was detected.

Oat is a potential host to crown rot pathogens and is considered an asymptomatic crop. The reaction of forage oat cultivars to inoculation with a range of F. culmorum strains has not previously been examined in Australia. The virulence of eight strains of F. culmorum collected from different regions of Australia (northern, southern, and western) across five forage oat cultivars and one bread wheat cultivar were tested. A positive control of mixed inoculum of F. pseudograminearum was included in this experiment, along with a negative/non-inoculated control for each cultivar. A significant interaction between strains and cultivars (p < 0.001) was observed for the disease severity on the leaf sheaths. One F. culmorum strain caused greater disease severity on forage oat cultivars Coolabah, Genie, and Drover compared to the other strains.

Yield losses of bread wheat due to crown rot can be more severe when drought conditions occur during grain fill. Studies have shown that drought alters the root architecture of bread wheat resulting in changes to the root system including root angle, length and biomass which have a negative impact on crop yield. The impact of crown rot infection on the root architecture of bread wheat has not been investigated. Root angle, length, number, fresh weight, and root dry weight of a bread wheat cultivar inoculated with the crown rot pathogens F. pseudograminearum and F. culmorum were examined in a controlled environment. Fresh shoot and dry weight, leaf area of the oldest and the youngest fully-formed leaf, leaf number, and disease severity of the first leaf sheath were recorded. All aspects of the root system were reduced when inoculated with F. pseudograminearum, excluding root angle which exhibited no difference between the inoculated and non-inoculated treatments. In contrast, no impact was observed on the root characteristics of bread wheat when inoculated with F. culmorum.
In conclusion, this research explored the host reaction of different winter cereals species inoculated with four crown rot and common root rot pathogens at different stages of development. In this study, F. pseudograminearum was generally more pathogenic on barley, bread wheat, durum wheat and triticale cultivars than on oat. Whilst oat was considered to be more tolerant to crown rot and common root rot pathogens, some F. culmorum strains caused infection on a range of oat cultivars. This suggests that oats may not be suitable in a crop rotation system to reduce crown rot pathogens in the field. This study has led to a better understanding of the infection potential of some crown rot and common root rot pathogens across a range of winter cereal species. The results of this study will provide valuable information for management strategies targeting crown rot and common root rot diseases in crop rotations.