Evaluation of Biological Control Agents for the Protection of Almond Pruning Wounds Against Infection by Fungal Canker Pathogens

The Sweet Cherry Tree Genotype Restricts the Aggressiveness of the Wood Decay Fungi Cytospora sorbicola and Calosphaeria pulchella

The wood decay fungi Cytospora sorbicola and Calosphaeria pulchella severely threaten the worldwide cultivation of sweet cherry trees (Prunus avium L.). Both fungi cause similar symptoms, including vascular necrosis, which leads to branch and twig dieback. In advanced stages of the disease, cankers are visible on tree branches and trunks. The sweet cherry is the most widely planted fruit tree in Chile, with 74,000 hectares in 2023. According to the planted surface, the predominant sweet cherry varieties are Lapins, Santina, Regina, and Bing. Variety-dependent susceptibility studies on Cyt. sorbicola and Cal. pulchella are lacking. The main entry points for wood necrosis-causing fungi are pruning wounds; therefore, we evaluated the aggressiveness of Cyt. sorbicola and Cal. pulchella in one-year-old sweet cherry plants. Santina and Lapins showed the lowest necrotic lesion caused by Cyt. sorbicola (13.6 and 14.31 mm, respectively), followed by Bing (19.51 mm) and Regina (26.14 mm). All plants infected by Cyt. sorbicola showed shoot blight regardless of the variety. In addition, there was a varying susceptibility to Cal. pulchella, with Lapins (21.6 mm), Bing (22.83 mm), Santina (27.62 mm), and Regina (30.8 mm) showing increasing levels of observed necrosis. The lesion caused by Cal. pulchella was more significant than that observed for Cyt. sorbicola, regardless of the cherry tree genotype. We identified each fungal growth from the wood necrosis progression area using two independent novel PCR-HRM strategies based on the ITS fungal region, which allowed us to differentiate each pathogen of interest individually or simultaneously. This study demonstrates different levels of susceptibility of sweet cherry tree genotypes to wood-degrading pathogens, emphasizing the need to include these factors in phytosanitary management programs.

Biocontrol of almond canker diseases caused by Botryosphaeriaceae fungi

BACKGROUND

Botryosphaeria dieback is a canker disease caused by fungal species of the Botryosphaeriaceae family that threatens almond productivity. The most common control measure to prevent canker development is the application of fungicides which are being phased out by European Union regulations. In the present study, two sets of bacterial strains were evaluated for their antifungal activity against pathogenic Botryosphaeriaceae species through in vitro and in vivo antagonism assays.

RESULTS

The rhizospheric bacteria Pseudomonas aeruginosa AC17 and Bacillus velezensis ACH16, as well as the endophytic bacteria Bacillus mobilis Sol 1-2, respectively inhibited 87, 95, and 63% of the mycelial growth of Neofusicoccum parvum, Botryosphaeria dothidea, Diplodia seriata, and Macrophomina phaseolina. Additionally, they significantly reduced the length of lesions caused by N. parvum and B. dothidea in artificially inoculated detached almond twigs. All these bacterial strains produce hydrolytic enzymes that are able to degrade the fungal cell wall. P. aeruginosa AC17 also produces toxic volatile compounds, such as hydrogen cyanide. This strain was the most effective in controlling Botryosphaeria dieback in planta under controlled conditions at a level similar to the biocontrol agent Trichoderma atroviride and standard chemical fungicide treatments.

CONCLUSION

Pseudomonas aeruginosa AC17 is the best candidate to be considered as a potential biocontrol agent against Botryosphaeriaceae fungi affecting almond. © 2023 Society of Chemical Industry.

Plant-Associated Neoscytalidium dimidiatum-Taxonomy, Host Range, Epidemiology, Virulence, and Management Strategies: A Comprehensive Review

Neoscytalidium dimidiatum, a plant- and human-associated fungus, has emerged as a substantial global ecological and agricultural threat aggravated by global warming. It inflicts various diseases, including canker, blight, dieback, leaf spot, root rot, and fruit rot, across a wide spectrum of fruit trees, field crops, shrubs, and arboreal species, with a host range spanning 46 plant families, 84 genera, and 126 species, primarily affecting eudicot angiosperms. Six genera are asymptomatic hosts. Neoscytalidium dimidiatum exhibits worldwide distribution, with the highest prevalence observed in Asia and North America, notably in Iran, Turkey, and California. Rising disease prevalence and severity, aggravated by climate change, particularly impact tropical arid places across 37 countries spanning all 7 continents. This comprehensive review encapsulates recent advancements in the understanding of N. dimidiatum, encompassing alterations in its taxonomic classification, host range, symptoms, geographic distribution, epidemiology, virulence, and strategies for effective management. This study also concentrates on comprehending the taxonomic relationships and intraspecific variations within N. dimidiatum, with a particular emphasis on N. oculus and N. hylocereum, proposing to consider these two species as synonymous with N. dimidiatum. Furthermore, this review identifies prospective research directions aimed at augmenting our fundamental understanding of host-N. dimidiatum interaction.