Identification and biological characterization of a new pathogen that causes potato scab in Gansu Province, China

Identification and Chemical Control of Stem Canker Pathogen of Idesia polycarpa

Idesia polycarpa is an important woody oilseed tree crucial for ensuring China's grain and oil security. The expansion of I. polycarpa plantations has been accompanied by an increase in pests and diseases, with canker disease recently observed in two forests in Henan Province. Field surveys revealed a disease incidence of 70.12% among 328 surveyed trees, indicating a substantial threat to plantation health. The most virulent pathogen, strain SQ5, was identified as Botryosphaeria dothidea through molecular sequencing and morphological analyses. Strain SQ5 showed an optimum growth temperature of 25 °C and a mycelial lethal temperature of 60 °C. The pathogen thrives in acidic conditions and is promoted by light, with the ability to utilize various carbon and nitrogen sources. In vitro toxicity assessments identified four effective fungicides: 70% thiophanate-methyl (EC50 = 0.0169 µg/mL), 43% tebuconazole (EC50 = 0.0219 µg/mL), 20% octylamine acetate (EC50 = 0.0271 µg/mL), and 40% difenoconazole (EC50 = 0.0954 µg/mL). Field trials demonstrated that 43% tebuconazole (average efficacy = 35.29%) and 40% difenoconazole (average efficacy = 23.53%) exhibited superior control of I. polycarpa canker. This study represents the first systematic analysis of I. polycarpa canker and its control measures, laying a foundation for further research and field management strategies. Given the significance of I. polycarpa in Chinese forestry, this underscores the need for effective management strategies to sustain its productivity and mitigate risks associated with expanding plantations.

Identification, characterization, and sensitivity to phytochemicals of a novel Curvularia species associated with leaf spot disease on Curcuma kwangsiensis

A leaf spot disease affecting Curcuma kwangsiensis (Zingiberaceae) has been observed in Qinzhou City, Guangxi Province. Infected leaves exhibit yellow-brown spots that progressively expand and eventually lead to leaf death. Curvularia isolates were obtained from the diseased leaves with tissue isolation and single spore purification methods. To accurately identify these isolates, we analyzed their morphological characteristics and phylogenetic relationships using combinations of ITS, GAPDH, and EF-1α gene sequences. Phylogenetic analysis showed that the investigated strains formed a distinct clade separate from other recognized Curvularia species. Furthermore, the strains exhibited differences in conidiophore size and conidia shape/size. Based on phylogenetic studies, morphology, and pathogenicity tests, the pathogen was identified as a new species named Curvularia qinzhouensis. Optimal conditions for mycelial growth were observed at 30 °C and pH 8. The sensitivity of the pathogen to various phytochemicals was also examined. Honokiol, thymol, and citral demonstrated effective antifungal effects, with EC50 values of 6.72 ± 1.75, 25.74 ± 4.30, and 54.24 ± 4.69 µg/ml, respectively. The present investigation provides the first report of leaf spot disease on C. kwangsiensis caused by C. qinzhouensis, and valuable insights for the prevention and control of this disease.

Characterization and Fungicide Sensitivity of Phaeosphaeriopsis obtusispora That Causes Marginal Leaf Blight in Agave hybrid H.11648

Sisal is an important tropical cash crop in southern China. Unfortunately, it is threatened by various diseases. In 2022, a new disease tentatively named marginal leaf blight disease (MLBD) was first observed in sisal fields across Guangxi and Guangdong provinces, with an incidence rate ranging from 13% to 30%. In this work, to isolate and identify the pathogens causing MLBD, sisal leaves exhibiting the typical MLBD symptoms were collected, and nine strains were obtained. Pathogenicity tests, morphological observations, and phylogenetic analyses confirmed that two strains, namely 22GX1-3 and 22GD1-4, identified as Phaeosphaeriopsis obtusispora, were the causative pathogens of MLBD. Further investigations into the biological characteristics of P. obtusispora showed that its mycelia exhibited optimal growth on PDA medium, with the most favourable temperature and pH being 25 °C and 7.0, respectively. The mycelia could grow in temperatures ranging from 10 °C to 32 °C but ceased at 35 °C. Lactose and yeast extract powder were also identified as the optimal carbon and nitrogen sources, respectively. Additionally, the effectiveness of various control agents was assessed on a single strain, 22GX1-3. Among the twelve fungicides tested, difenoconazole was proven the most effective, with an EC50 value of 0.5045 µg/mL. To our knowledge, this is the first report for sisal MLBD caused by P. obtusispora. Our results provide crucial pieces of information for the development of effective management strategies to control sisal MLBD caused by P. obtusispora.

Insights into the Isolation, Identification, and Biological Characterization Analysis of and Novel Control Strategies for Diaporthe passiflorae in Postharvest Passion Fruit

Postharvest diseases seriously restrict developments in the passion fruit industry. In this study, we aimed to identify the postharvest pathogen affecting passion fruit, investigate its pathogenicity, and explore relevant control methods. The pathogen was isolated from rotting passion fruit and identified using morphological characteristics, ITS sequences, and phylogenetic tree analyses. Additionally, preliminary studies were conducted to assess the biological characteristics of the pathogen and evaluate the efficacy of various treatments for disease control. The fungus on the passion fruit called B4 was identified as Diaporthe passiflorae. Optimal conditions for mycelial growth were observed at 25-30 °C and pH 5-6, with starch as the carbon source and peptone as the nitrogen source. Infection by D. passiflorae accelerated fruit decay, reduced the h° value of the peel, and increased the peel cell membrane permeability when compared to the control. Notably, treatments with appropriate concentrations of ɛ-poly-l-lysine, salicylic acid, and melatonin showed inhibitory effects on the pathogen's growth in vitro and may thus be potential postharvest treatments for controlling brown rot caused by D. passiflorae in passion fruit. The results provide a scientific basis for the development of strategies to control postharvest decay and extend the storage period of passion fruit.

Potential of an endophytic bacteria Bacillus amyloliquefaciens 3-5 as biocontrol agent against potato scab

To obtain a potential biocontrol agent for potato scab, 75 endophytic bacteria were isolated from the healthy potato tubers and strain 3-5 was selected as an optimal antagonistic bacterium against Streptomyces griseoplanus (Streptacidiphilus griseoplanus) causing potato scab. Strain 3-5 was identified as Bacillus amyloliquefaciens based on its morphological characteristics, 16S rDNA and gyrB gene sequence analysis. B. amyloliquefaciens 3-5 has biological functions of indole-3-acetic acid (IAA) production and nitrogen fixation. Polymerase chain reaction (PCR) detection revealed that B. amyloliquefaciens 3-5 had 6 diverse antibacterial substance synthesis genes, named bacD, bacAB, ituD, ituC, sfP and albF, which resulted in the production of bacilysin, iturin, surfactin and subtilosin. Field efficacy evaluation revealed that B. amyloliquefaciens 3-5 (solid fermentation) was successful in controlling potato scab with a 38.90 ± 3.2140% efficiency which is higher than other chemical bactericides except zhongshengmycin·oligosaccharins and kasugamycin·zhongshengmycin. The endophytic bacterium B. amyloliquefaciens 3-5 could be used as a biocontrol agent against potato scab due its control efficacy and environmental safety.