Jingwei Chen

Stem nematode disease, the most prevalent of three major diseases in northern China, causes huge sweet potato production losses. In this study, the resistant (Zhenghong22) and sensitive (Longshu9) parents, and the F₁ segregating population mixed pools (Resistant- and Sensitive-Mixed) having extreme resistance traits, were used for BSA-Seq, BSR-Seq, and transcriptomic analyses to locate stem nematode disease resistance-conferring genes in sweet potato. Transcriptome results indicated that ethylene and ABA were the main hormones involved in disease resistance regulation, with secondary metabolic pathways playing crucial roles. In total, 7 and 17 candidate regions, which contained 743 candidate genes, were identified in the BSA-Seq and BSR-Seq analyses, respectively. Eight candidate genes were identified using a combined analysis. The protein phosphatase 2C gene itf15g20460, the signal transduction-related gene itf00g76200, and an unknown functional gene itf00g75950, were identified as key resistance gene candidates through RT-qPCR validation in mixed pools and individuals. These results will be beneficial to the cultivation of nematode-resistant sweet potato cultivars.

Background/Objectives: Sweetpotato black rot, caused by Ceratocystis fimbriata, is a severe fungal disease in sweetpotato production. Biological control strategies represent a promising, environmentally sustainable approach to managing this disease. This study investigates the biocontrol potential of Bacillus amyloliquefaciens SFB-1 against C. fimbriata. Methods: The antagonistic activities of strain SFB-1 on C. fimbriata were assessed through in vitro assays, including evaluations of mycelial inhibition, spore germination, and mycelial morphology. Pathogenicity assays on harvested sweetpotato roots assessed lesion diameter and depth. A transcriptomic analysis of C. fimbriata exposed to strain SFB-1 was performed to explore the underlying antifungal mechanism of SFB-1 on C. fimbriata. The qRT-PCR was employed to validate the RNA-seq results. Results: In vitro assays demonstrated that strain SFB-1 inhibited C. fimbriata mycelial growth by up to 81.01%, caused mycelial swelling, and completely suppressed spore germination at 10⁸ CFU/mL. The cell-free supernatant of strain SFB-1 also suppressed C. fimbriata growth. Pathogenicity assays revealed that strain SFB-1 treatments reduced lesion diameter and depth on harvested sweetpotato roots by over 50% compared to untreated controls. Transcriptomic analysis of C. fimbriata treated with strain SFB-1 identified 1164 differentially expressed genes, with significant alterations in genes associated with cell wall integrity, cell membrane stability, spore germination, detoxification, and antioxidant responses. The qRT-PCR validation of 16 genes confirmed the consistency with the RNA-seq results. Conclusions: B. amyloliquefaciens SFB-1 demonstrates significant biocontrol efficacy against C. fimbriata through multiple mechanisms, positioning it as a promising solution for the sustainable management of sweetpotato black rot.

Black rot disease, caused by Ceratocystis fimbriata Ellis & Halsted, severely affects both plant growth and post-harvest storage of sweet potatoes. Invertase (INV) enzymes play essential roles in hydrolyzing sucrose into glucose and fructose and participate in the regulation of plant defense responses. However, little is known about the functions of INV in the growth and responses to black rot disease in sweet potato. In this study, we identified and characterized an INV-like gene, named IbINV, from sweet potato. IbINV contained a pectin methylesterase-conserved domain. IbINV transcripts were most abundant in the stem and were significantly induced in response to C. fimbriata, salicylic acid, and jasmonic acid treatments. Overexpressing IbINV in sweet potato (OEV plants) led to vigorous growth and high resistance to black rot disease, while the down-regulation of IbINV by RNA interference (RiV plants) resulted in reduced plant growth and high sensitivity to black rot disease. Furthermore, OEV plants contained a decreased sucrose content and increased hexoses content, which might be responsible for the increased INV activities; not surprisingly, RiV plants showed the opposite effects. Taken together, these results indicate that IbINV positively regulates plant growth and black rot disease resistance in sweet potato, mainly by modulating sugar metabolism.

Stem nematode disease can seriously reduce the yield of sweet potato (Ipomoea batatas (L.) Lam). To explore resistance mechanism to stem nematode in sweet potato, transcriptomes and metabolomes were sequenced and compared between two sweet potato cultivars, the resistant Zhenghong 22 and susceptible Longshu 9, at different times after stem nematode infection. In the transcriptional regulatory pathway, mitogen-activated protein kinase signaling was initiated in Zhenghong 22 at the early stage of infection to activate genes related to ethylene production. Stem nematode infection in Zhenghong 22 also triggered fatty acid metabolism and the activity of respiratory burst oxidase in the metabolic pathway, which further stimulated the glycolytic and shikimic pathways to provide raw materials for secondary metabolite biosynthesis. An integrated analysis of the secondary metabolic regulation pathway in the resistant cultivar Zhenghong 22 revealed the accumulation of tryptophan, phenylalanine, and tyrosine, leading to increased biosynthesis of phenylpropanoids and salicylic acid and enhanced activity of the alkaloid pathway. Stem nematode infection also activated the biosynthesis of terpenoids, abscisic acid, zeatin, indole, and brassinosteroid, resulting in improved resistance to stem nematode. Finally, analyses of the resistance regulation pathway and a weighted gene co-expression network analysis highlighted the importance of the genes itf14g17940 and itf12g18840, encoding a leucine-rich receptor-like protein and 1-aminocyclopropane-1-carboxylate synthase, respectively. These are candidate target genes for increasing the strength of the defense response. These results provide new ideas and a theoretical basis for understanding the mechanism of resistance to stem nematode in sweet potato.

Sweetpotato (Ipomoea batatas) is an important root crop that is infected by Fusarium solani in both seedling and root stages, causing irregular black or brown disease spots and root rot and canker. This study aims to use RNA sequencing technology to investigate the dynamic changes in root transcriptome profiles between control check and roots at 6 h, 24 h, 3 days, and 5 days post-inoculation (hpi/dpi) with F. solani. The results showed that the defense reaction of sweetpotato could be divided into an early step (6 and 24 hpi) without symptoms and a late step to respond to F. solani infection (3 and 5 dpi). The differentially expressed genes (DEGs) in response to F. solani infection were enriched in the cellular component, biological process, and molecular function, with more DEGs in the biological process and molecular function than in the cellular component. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the main pathways were metabolic pathways, the biosynthesis of secondary metabolites, and carbon metabolism. More downregulated genes were identified than upregulated genes in the plant–pathogen interaction and transcription factors, which might be related to the degree of host resistance to F. solani. The findings of this study provide an important basis to further characterize the complex mechanisms of sweetpotato resistance against biotic stress and identify new candidate genes for increasing the resistance of sweetpotato.