Molecular Pathogens, 2025, Vol.16, No.5, 217-225 http://microbescipublisher.com/index.php/mp 222 in the rhizosphere to promote phosphorus absorption by wheat. With the improvement of nutritional status and the stimulation of hormones, the chlorophyll content of wheat leaves increases, photosynthesis is enhanced, and more assimilation products are accumulated for growth; at the same time, antioxidant enzyme activity increases, making metabolism more balanced. The above effects are more significant under nutrient deficiency or adverse conditions. 6.3 Resistance interaction effect The existence of PGPR significantly improves the stress resistance of wheat. Under drought stress, PGPR produces ACC deaminase to reduce ethylene levels in plants, delay premature plant senescence caused by drought, promote roots to grow deeper to obtain water, and improve wheat's drought tolerance. In a saline environment, PGPR secretes mucus to form a rhizosphere protective layer to reduce salt intrusion, and induces wheat to accumulate proline and other osmotic-adjusting substances, increase antioxidant enzyme activity, and reduce salt damage (Aasfar et al., 2024). In the face of pathogen infection, PGPR-induced wheat systemic resistance (ISR) allows the plant to enter a defense state in advance, and can initiate a response faster once the pathogen invades (Torabi et al., 2021), thereby effectively reducing disease. 7 Interaction between Wheat Roots and Pathogenic Microorganisms 7.1 Main pathogenic bacteria and hazard characteristics of roots The major soil-borne pathogens affecting wheat roots are primarily fungi and nematodes. Typical fungal diseases include take-all caused by Gaeumannomyces graminis, which leads to blackened and decayed roots and yellowing of plants; Fusarium species that cause root rot and crown rot, resulting in browning of the stem base and premature whitening of the spikes; and sheath blight caused by Rhizoctonia cerealis, which infects the leaf sheath at the stem base, producing yellow-brown lesions and often leading to lodging. In addition, Pythiumspecies can cause seedling damping-off, while cereal cyst nematodes infect the roots, forming cysts that impair root function (Ji et al., 2022). These pathogens all damage the wheat root system’s absorptive capacity, leading to poor plant growth and, in severe cases, substantial yield losses or even total crop failure. 7.2 Rhizosphere defense response To resist pathogen invasion, wheat activates multiple levels of defense mechanisms in the rhizosphere. As a physical barrier, root cells rapidly thicken their cell walls and deposit lignin and other substances, which enhances mechanical strength and slows down the invasion and expansion of pathogenic bacteria. For chemical defense, the root system synthesizes and releases a variety of antibacterial substances (such as phenolic acids, phytoalexins) after being stimulated by infection, inhibiting pathogenic spore germination and hyphae growth (Figure 3) (Upadhyay et al., 2022). Biological mutual assistance, the infected roots change the composition of secretions and release specific signals to recruit antagonistic microorganisms such as Actinomycetes and Bacillus to gather in the rhizosphere to jointly fight the pathogen. Finally, there is systemic resistance. Signal molecules (such as salicylic acid and jasmonic acid) produced by local infection are transmitted to other parts of the plant, inducing the entire plant to enter an early warning state and enhancing overall disease resistance. These coordinated defense responses enable wheat to limit root diseases in most cases and prevent the disease from spreading out of control (Chai et al., 2024). 7.3 Ecological functions of microbial communities in disease suppression A healthy wheat rhizosphere microbial community has a natural inhibitory effect on disease. Competition for space and nutrients, a large number of beneficial and neutral microorganisms occupy rhizosphere sites and consume nutrients, making it difficult for pathogenic bacteria to colonize and reproduce. Due to multiple antagonism, microorganisms in the community can secrete a variety of antibacterial metabolites (antibiotics, enzymes, volatiles, etc.) to create a chemical environment that is unfavorable to pathogenic bacteria (Dahiya et al., 2020). For example, in long-term continuous cropping wheat fields, antagonistic bacteria such as Pseudomonas fluorescens and Streptomyces multiply in large numbers and produce antibacterial substances, causing the incidence of total rot disease to decrease year by year (the phenomenon of "total rot disease decline"). In addition,
RkJQdWJsaXNoZXIy MjQ4ODYzNA==