Assessing the effect of Fusarium graminearum inoculation on the root structure of Swedish winter wheat cultivars (Triticum aestivum

Sammanfattning: Several diseases attack the wheat crop and reduce the yield, such as root disease, which causes a tremendous loss in wheat production. Root rot has a variety of causal agents, such as nematodes, viruses, and bacteria, but the most common pathogens causing wheat root rot are oomycetes and fungi. The subject of this study is one of the fungus species from the Fusarium genus, Fusarium graminearum. This thesis aimed to evaluate the susceptibility of several wheat genotypes to root rot caused by F. graminearum under two concentrations of nutrients. This study assessed five winter wheat cultivars - Julius, Brons, Reform, Informer, and Ceylon - in their development with Fusarium root rot. The study consisted of 80 pots of un-inoculated seedlings, 80 pots inoculated with a conidium suspension (62500 conidia/ml), and 40 pots inoculated with a hypha agar plug. In addition, an application of a single nutrient concentration was added to half of the pot numbers of inoculated and uninoculated samples. Then, a double nutrient concentration was added to another half of the pot numbers of inoculated and uninoculated samples. High seedling death was noted with the agar plug treatment, so seedling survival was measured to compare between genotypes—the conidia suspension allowed us to observe the interaction between the genotypes and different nutrient levels. The seedling can grow and use nutrients to support the immune system in the initial stages of development, while the conidial solution needs time to germinate and grow. Three variables were examined to compare these factors, i.e., visual shoot traits, visual root architectural traits, and microscopic root structural traits. Differences in the inoculation method could be due to the difference in hypha development and, thus, the time before the F. graminearum hypha can launch its aggressive offensive against the seedling. With the mycelium growing, the agar plug method represents the living soil-borne pathogen growing on crop debris, with its grown mycelium ready to attach to the young seedlings at germination. The conidia suspension means transferring conidia to new soil (e.g., dispersed by wind or rain). These conidia will need time to germinate before infecting the more advanced seedlings. Then these seedlings will have had more time to use the nutrients and build defences against the pathogen. The shoot traits include fresh and dry shoot biomass and leaf numbers. The plants were provided with two levels of nutrient doses to assist them in tolerating the pathogen. The results showed significantly more leaves developed in Ceylon than other cultivars under the conidia suspension inoculation method. On the other hand, many leaves were developed in Brons under agar plug mycelium inoculation. The essential cellular structure traits, such as xylem number and diameter, are believed to create a kind of elasticity for transporting water and nutrients to other plant tissues. The xylem case was preserved in Julius and Reform cultivars despite the F. graminearum inoculations. In addition, Reform's live cortex cells percentage was higher than the other genotypes, suggesting higher nutrient storage ready to help the plant immune system. The germination survival ratio suggests Brons and Julius are less susceptible to F. graminearum at the germination stage. The three groups of studied traits play a role in understanding the genotypes' susceptibility to F. graminearum, helping to recognize tolerant genotypes. The most distinguished cultivar in this experiment was Reform, showing a high germination survival ratio with the agar plug method compared to other cultivars. This high germination suggests that Reform can be a candidate to establish a molecular insight to study the resistance mechanism. The traits associated with the high germination ratio of Reform are high root and shoot fresh biomass weight. The quantification results of the traits, for instance, dry root and shoot biomass, xylem number, and the most recognized trait, the roots living cortex cells percentage, will support selecting the candidate cultivar and then implement this information in developing a breeding program for sustainable resistance.