Head smut is a soil-borne fungal disease caused by Sporisorium reilianum that infects maize tassels and ears. This disease poses a tremendous threat to global maize production. A previous study found markedly different and stably heritable tassel symptoms in some maize inbred lines with Sipingtou blood after infection with S. reilianum. In the present study, 55 maize inbred lines with Sipingtou blood were inoculated with S. reilianum and classified into three tassel symptom types (A, B, and C). Three maize inbred lines representing these classes (Huangzao4, Jing7, and Chang7-2, respectively) were used as test materials to investigate the physiological mechanisms of tassel formation in infected plants. Changes in enzyme activity, hormone content, and protein expression were analyzed in all three lines after infection and in control plants. The activities of peroxidase (POD), superoxide dismutase (SOD), and phenylalanine-ammonia-lyase (PAL) were increased in the three typical inbred lines after inoculation. POD and SOD activities showed similar trends between lines, with the increase percentage peaking at the V12 stage (POD: 57.06%, 63.19%, and 70.28% increases in Huangzao4, Jing7, and Chang7-2, respectively; SOD: 27.01%, 29.62%, and 47.07% in Huangzao4, Jing7, and Chang7-2, respectively. These were all higher than in the disease-resistant inbred line Mo17 at the same growth stage); this stage was found to be key in tassel symptom formation. Levels of gibberellic acid (GA₃), indole-3-acetic acid (IAA), and abscisic acid (ABA) were also altered in the three typical maize inbred lines after inoculation, with changes in GA₃ and IAA contents tightly correlated with tassel symptoms after S. reilianum infection. The differentially expressed proteins A5H8G4, P09233, and Q8VXG7 were associated with changes in enzyme activity, whereas P49353, P13689, and P10979 were associated with changes in hormone contents. Fungal infection caused reactive oxygen species (ROS) and nitric oxide (NO) bursts in the three typical inbred lines. This ROS accumulation caused biofilm disruption and altered host signaling pathways, whereas NO signaling triggered strong secondary metabolic responses in the host and altered the activities of defense-related enzymes. These factors together resulted in the formation of varying tassel symptoms. Thus, interactions between S. reilianum and susceptible maize materials were influenced by a variety of signals, enzymes, hormones, and metabolic cycles, encompassing a very complex regulatory network. This study preliminarily identified the physiological mechanisms leading to differences in tassel symptoms, deepening our understanding of S. reilianum-maize interactions.

Background: Maize is an important food crop in cold regions, especially in Northeast China. However, its short growth period and low-temperature stress pose challenges to the breeding of high-yield hybrids. With climate warming, the maize planting area continues to expand to high latitudes. Research on cold-region maize is of great significance to ensure food security and sustainable agricultural development. However, most of the current maize research is concentrated in temperate and tropical regions, and there are few studies on cold-region maize. Methods: Based on this, this study selected some representative cold-region maize materials and materials whose adaptability has not yet been verified, and used a semi-diallel hybrid design for hybridization to determine the general combining ability (GCA) and specific combining ability (SCA) to screen out excellent breeding materials suitable for cold regions. Field experiments were carried out under four different cold environments, and 55 hybrid progenies and their parents were evaluated. The double allele hybridization analysis based on the Griffing method 2 (model 1) showed that the specific combining ability (SCA) and general combining ability (GCA) effects of each trait were significant. Results: The GCA mean square of all traits except yield and number of grains per row was greater than the SCA mean square, indicating that additive gene effects were dominant and genetic improvement through selective breeding was feasible. Hayman plot analysis under four environments showed that yield, ear length, number of grains per row, water content, and plant height were mainly controlled by superdominant genes, while stem thickness, number of nodes, and ear position were controlled by some dominant genes. Conclusions: Parent P1 contained more recessive genes in yield traits, but more dominant genes in number of grains per row, number of nodes, and ear position; P3 contained more dominant genes in yield and water content, but more recessive genes in number of nodes and ear position; P7 contained more recessive genes in most traits; and P9 contained more dominant genes in most traits. P9 and P6 represent excellent parental germplasm, among which the hybrid combinations P1 × P9, P2 × P5, P3 × P10, P4 × P6, P5 × P8, P6 × P9, P7 × P10, and P8 × P10 all show hybrid vigor exceeding that of their parents and have high breeding value.