Special Issue: “Advances in Disease Diagnostics and Pathogen Biocontrol of Horticulture Crops”

1. Introduction

Horticultural crops play an important role in global food security and the economy [1]. However, they face persistent threats from various pathogens—fungal, bacterial, viral [2], and insect-borne [3]—that impact yield, quality, and sustainability. Traditionally, reliance on chemical pesticides has led to environmental concerns [4] and resistance development in pathogens and pests [5], highlighting an urgent need for eco-friendly and sustainable disease management strategies.

In line with the United Nations’ Zero Hunger goal [6], which aims to end hunger, achieve food security, improve nutrition, and promote sustainable agriculture, this Special Issue compiles research on disease diagnostics and the use of biocontrol agents to manage horticultural crop diseases. By advancing sustainable plant protection, these studies contribute to the development of resilient agricultural systems capable of supporting global food needs.

2. Overview of Published Articles

Carrera et al. (Contribution 1) analyzed the epidemiology of downy mildew (Plasmopara vitícola) in grapevines during a two-year study in northwestern Spain, evaluating two bioclimatic zones. Temperature, humidity, and wind speed were identified as key variables influencing disease dynamics. These findings emphasized the importance of region-specific disease forecasting for improved disease management.

Zheng et al. (Contribution 2) reported the first occurrence of gray mold (Botrytis cinerea) on pecan fruits and leaves in China. Molecular and pathogenicity analyses confirmed its identity and laid the groundwork for future disease control research in nut crops.

Huang et al. (Contribution 3) explored Exiguobacterium acetylicum SI17’s potential as a biocontrol agent against litchi downy blight. Although the bacterium did not antagonize Peronophythora litchii, a genomic analysis revealed several secondary metabolite genes contributing to plant defense, suggesting significant promise for pre-harvest biocontrol.

Expósito-Goás et al. (Contribution 4) focused on bean common mosaic virus (BCMV) in protected geographical indications (PGIs). The PGI “Faba de Lourenzá” faced challenges from BCMV due to uncertified seeds. Field strategies such as virus-free seedlings, rogueing, and intercropping were tested, revealing effective control methods and highlighting the need for farmer education and off-site seed production.

Mrkvová et al. (Contribution 5) used high-throughput sequencing to analyze the virome in Fabaceae species, including red clover, peas, and beans. The genetic characterization of Slovak bean yellow mosaic virus isolates provided insights into host susceptibility and virus–host interactions in pea genotypes.

Liu et al. (Contribution 6) studied strawberry root rot control with Trichoderma asperellum, where the isolate CMT10 controlled Neopestalotiopsis clavispora through multiple biocontrol mechanisms, including competition, hyperparasitism, and metabolite production. It also promoted plant growth, showing potential as a sustainable alternative to fungicides.

Shanmugaraj et al. (Contribution 7) is about collar rot management in tomato. In this study, among 20 T. asperellum isolates, A10 exhibited the strongest antagonism against Agroathelia rolfsii and the highest enzyme activity. In vitro and greenhouse assays confirmed its effectiveness in reducing collar rot and producing antimicrobial compounds.

Tomar et al. (Contribution 8) investigated biological control of the cabbage pest Pieris brassicae (an invasive pest affecting cole crops, with rising resistance to current control methods) using Steinernema carpocapsae and its symbiotic bacterium Xenorhabdus nematophila. Lab tests showed high larval mortality, highlighting the potential of these bacteria for integrated pest management, pending further field trials.

Osman et al. (Contribution 9) studied the biocontrol of onion white rot using the bacteria Stenotrophomonas maltophilia and Serratia liquefaciens which significantly suppressed Stromatinia cepivora infection and enhanced the plant growth and yield, aided by volatile metabolite production and plant defense activation.

Finally, Tyagi et al. (Contribution 10) reviewed the use of biocontrol agents in sustainable horticulture. Their review examined the roles of fungal, bacterial, and viral biocontrol agents, the environmental and genetic factors affecting their performance, and the challenges and opportunities in integrating these agents into mainstream horticultural practices.

3. Conclusions

This Special Issue presents recent advancements in understanding and managing horticultural diseases through innovative diagnostic tools and eco-friendly biocontrol approaches. The studies included emphasize the importance of region-specific strategies, molecular identification, and the integration of biocontrol agents into sustainable agriculture. Collectively, these findings underline the potential of biocontrol methods to reduce the dependency on chemical pesticides, protect biodiversity, and enhance crop productivity. Future efforts should focus on scaling these solutions under field conditions, improving the formulation of biocontrol microorganisms, and integrating them into holistic crop management systems.