Garma, Nadia2025-08-222025-08-222025-07-022025-07-03http://hdl.handle.net/1993/39248Wheat (Triticum aestivum) and soybean (Glycine max) are threatened by many diseases caused by bacteria and fungi, in addition to insects. Microbial diseases caused by fungal pathogens are among the most important factors limiting wheat and soybean production. Fusarium graminearum causes Fusarium head blight (FHB) in wheat and has recently been identified as a causal pathogen of Fusarium root rot (FRR) in soybean. Rotation is one of the major components of FHB management in wheat; however, information about the cross-pathogenicity of F. graminearum between wheat and soybean is scarce. Therefore, it was essential to investigate whether the F. graminearum causing FHB in wheat can contribute to disease in soybeans and vice versa, and how much pathogenic F. graminearum isolates were on their original versus their alternative host. Here, we conducted two separate inoculation experiments, under controlled conditions, using twelve F. graminearum isolates collected from wheat, barley, oat, and soybean to inoculate two different hosts: wheat and soybean. For the latter, we used two wheat cultivars (Prosper and Muchmore, moderately resistant and susceptible to FHB, respectively) and three soybean lines (22-60RY, Th32004R2Y, susceptible, and 24-10RY, moderately resistant). All the isolates from wheat, barley, and oat caused FRR in soybeans, and those from soybeans were able to cause FHB in wheat. A high variability was observed among the isolates obtained from both wheat and soybean when inoculated on their respective original hosts as well as on alternative hosts (wheat and soybean). This led us to investigate whether the aggressiveness or saprophytic fitness (growth rate) of F. graminearum is affected by continued infection on original and/or alternative host plants. All the tested isolates, whether from soybean or wheat, successfully completed six passages (ability to cause FRR on soybean and FHB on wheat). The six passages through either alternative or original host significantly influenced the pathogenic fitness on such host and affected the growth rate of most isolates. Although wheat's defensive mechanisms against the FHB agent F. gramineaum have been thoroughly investigated, no such studies have been documented for soybean. In an attempt to gather more of such information on soybean response in its interaction with F. graminearum, the expression levels of ten defense-related genes PR-2, PR-3, PR-4, NPR1, JAR1, OPR3, AOS2, ICS1, ICS2, and PAL2. are generally associated with the salicylic and/or jasmonic acids defense signaling pathways, were evaluated using qRT-PCR during the interaction of two F. graminearum isolates, varying in their host of origin with two soybean susceptible and moderately resistant lines. Gene expression was assessed at 6,12, and 24 hours post inoculation (hpi). Compared to the susceptible cultivar, the moderately resistant cultivar exhibited more expression of the selective genes in this study. working together, ICS and PAL contribute to soybean defense against F. graminearum, indicating a cooperative role in catalyzing the required defense reactions. F. graminearum is a hemibiotrophic pathogen that initially behaves as a biotroph and later transitions to a necrotrophic lifestyle, which involves signaling pathways mediated by both SA and JA.engFusarium graminearumWheatSoybean