Objective Screening and identification of pathogenic Fusarium solani, and investigating its differential infectivity towards the resistant cultivar ‘Ningqi-1’ and the susceptible cultivar ‘Ningqi-5’, aims to clarify the characteristics and advantages of these two cultivated Lycium barbarum cultivars in resisting pathogen invasion. This study is expected to provide theoretical clues for in-depth elucidation of the interaction mechanism between L. barbarum and F. solani and further lay a foundation for breeding of disease-resistant L. barbarum and the control of root rot.
Methods Initially, a preliminary classification and screening of 22 strains of F. solani preserved in the laboratory was conducted based on morphological characteristics. Subsequently, 6 strains were selected and inoculated into potted plants. Pathogenic strains were identified based on the severity of root rot, plant growth status, and results of fungal re-isolation from the roots. Based on the internal transcribed spacer (ITS) region and gene fragments of TEF, RPB1, and CaM, phylogenetic trees were constructed to clarify the phylogenetic position of the pathogenic strain. The identified pathogenic strain was used to infect the resistant cultivar ‘Ningqi-1’ and the susceptible cultivar ‘Ningqi-5’. Plants growth phenotypes were recorded, and both the disease incidence and disease index were calculated. Scanning electron microscopy (SEM) was employed to observe pathogen invasion and distribution. Additionally, by measuring photosynthetic parameters, root activity, and stress resistance indicators of the plants, to evaluate the differential responses of the resistant and susceptible cultivars to the pathogen.
Results (1) Compared to the other five strains inoculated into L. barbarum, strain QT113 exhibited the strongest pathogenicity and was identified as F. solani based on multi-gene sequence analysis. (2) After inoculation with QT113, both the ‘Ningqi-1’ and ‘Ningqi-5’ plants showed yellowing leaves, massive leaf abscission, and progressive wilting. The root systems showed colonization by white hyphae, accompanied by tissue softening, blackening, and decay, as well as cortical sloughing or easy detachment. (3) Compared to the resistant cultivar ‘Ningqi-1’, the susceptible cultivar ‘Ningqi-5’ had a large amount of hyphae proliferating within the phloem parenchyma cells of the roots, loose root cortex tissue, severe structural fragmentation, and abundant granular deposits. Strain QT113 infected two cultivars with 100% disease incidence, with disease indices of 83% and 98%, respectively, indicating a more severe degree of infection by the pathogen in ‘Ningqi-5’. (4) At the physiological and biochemical level, after inoculation with QT113, the photosynthetic parameters and root activity of ‘Ningqi -5’ declined more significantly, accompanied by higher MDA accumulation. Meanwhile, the activities of antioxidant enzymes such as SOD, POD and CAT increased to a lesser extent in both leaves and roots of ‘Ningqi-5’ than in those of ‘Ningqi-1’, indicating a weaker antioxidant response and consequently more severe membrane lipid peroxidation damage.
Conclusion F. solani QT113 exhibits strong pathogenicity toward both Ningqi-1 and Ningqi-5. However, Ningqi-5 demonstrates weaker coordination among photosynthetic parameters, lower antioxidant capacity, poorer physiological status, and reduced defensive responsiveness, making it more susceptible to severe infection and root rot. The findings of this study are expected to provide a reference for breeding resistant cultivars of L. barbarum in Ningxia and furnish a theoretical basis for the precise management of root rot caused by F. solani.
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