The antimetabolite mangotoxin is a key factor in virulence of Pseudomonas syringae pv. syringae strains which cause apical necrosis of mango trees. Previous studies showed that mangotoxin biosynthesis is governed by the mbo operon. Random mutagenesis led to the identification of two other gene clusters that affect mangotoxin biosynthesis. These are the gacS/gacA genes and mgo operon which harbors the four genes mgoBCAD.

Pseudomonas chlororaphis PCL1606 (PcPCL1606) is a rhizobacterium isolated from avocado roots, which is a favourable niche for its development. This strain extensively interacts with plant roots and surrounding microbes and is considered a biocontrol rhizobacterium. Genome sequencing has shown the presence of thirty-one potential methyl-accepting chemotaxis proteins (MCPs). Among these MCPs, two candidates are putative functional aerotaxis receptors, encoded at locus PCL1606_41090 (aer1-1) and locus PLC1606_20530 (aer1-2), that are homologous to the Aer receptor of Pseudomonas aeruginosa strain PaO1. Single- and double-deletion mutants in one or both genes have led to motility deficiencies in oxygen-rich areas, particularly reduced swimming motility compared with that of wildtype PcPCL1606. No differences in swarming tests were detected, and less adhesion by the aer double mutant was observed. However, the single and double mutants on avocado plant roots showed delayed biocontrol ability. During the first days of the biocontrol experiment, the aer-defective mutants also showed delayed root colonization. The current research characterizes the presence of aer transductors on P. chlororaphis. Thus, the functions of the PCL1606_41090 and PCL1606_20530 loci, corresponding to genes aer1-1 and aer1-2, respectively, are elucidated.

Mango is one of the main subtropical crops growing in southern Spain. Spanish mango fruit production can be efficiently transported to the rest of Europe, and these mangoes are very appreciated for their quality and flavour. However, postharvest rots have been detected in stored mango fruits, making their commercialization difficult. The causal agents associated with such rot symptoms have been isolated and identified. Because the mango crops used to share the same growing area with avocado crops, fungal presence on surrounding asymptomatic avocado fruits was also analysed to detect potential cross infections. Artificial inoculation with Neofusicoccum parvum and N. mediterraneum was able to reproduce rot symptoms in mango but was also able to induce rots in avocado fruits. To approach a biological control strategy against these rot-producing fungi, two very well-known antagonistic biocontrol bacteria, Pseudomonas chlororaphis PCL1606, and Bacillus velezensis UMAF6639, were tested. The obtained results revealed that both bacteria can control the fungal rots on stored mango and avocado fruits under controlled conditions. Additionally, the strain B. velezensis UMAF6639 showed the ability to persist on the fruit surface of adult commercial trees in experiments under open field conditions, helping to prevent the appearance of these postharvest diseases.

The biocontrol rhizobacterium Pseudomonas chlororaphis is one of the bacterial species of the P. fluorescens group where insecticide fit genes have been found. Fit toxin, supported with other antimicrobial compounds, gives the bacterial the ability to repel and to fight against eukaryotic organisms, such as nematodes and insect larvae, thus protecting the plant host and itself. Pseudomonas chlororaphis PCL1606 is an antagonistic rhizobacterium isolated from avocado roots and show efficient biocontrol against fungal soil-borne disease. The main antimicrobial compound produced by P. chlororaphis PCL606 is 2-hexyl-5-propyl resorcinol (HPR), which plays a crucial role in effective biocontrol against fungal pathogens. Further analysis of the P. chlororaphis PCL1606 genome showed the presence of hydrogen cyanide (HCN), pyrrolnitrin (PRN), and homologous fit genes. To test the insecticidal activity and to determine the bases for such activity, single and double mutants on the biosynthetic genes of these four compounds were tested in a Galleria mellonella larval model using inoculation by injection. The results revealed that Fit toxin and HPR in combination are involved in the insecticide phenotype of P. chlororaphis PCL1606, and additional compounds such as HCN and PRN could be considered supporting compounds.

Avocado ( Persea americana ) has become one of the most important subtropical crops in southern Spain. In recent years, the scarcity of irrigation water has made this crop susceptible to opportunistic diseases. This sensitivity has been associated with a series of symptoms characterised by the death of branches, mummification of fruits, cankers and reddening of the vascular bundles. To identify the aetiology of the disease, surveys have been carried out on avocado farms in the most affected areas, including Málaga and Granada (southern Spain). The surveys were conducted from 2019 to 2022. A total of 252 fungal isolates were recovered from trees with symptoms of dieback disease. Of these isolates, 172 were initially identified by sequencing the rDNA internal transcribed spacer (ITS) region to identify potential pathogens compatible with the symptoms. Based on the number of isolates, the most prevalent were Neofusicoccum spp. (110 isolates) and Lasiodiplodia sp. (15 isolates), although some isolates of Diaporthe sp. (four isolates) and Colletotrichum sp. (eight isolates) were also identified. Pathogenicity experiments in plants, branches and fruits confirmed these fungi as possible causal agents as they reproduced the symptoms found in diseased avocado crops. The frequency of isolates associated with dieback symptoms, along with greater severity in the reproduced symptoms, shows Botryosphaeriaceae species as the main cause of dieback in avocado in southern Spain. The main objective of the present study is to elucidate the aetiology of the disease to establish the infection time and thereby lay the groundwork for designing control studies.

Avocado (Persea americana Mill.) is gaining economic relevance in Mediterranean regions such as southern Spain. In recent years, production has been severely affected by dieback caused by Botryosphaeriaceae species, a problem intensified under drought conditions. Conventional chemical control has shown limited effectiveness due to the scarce availability of fungicides and the difficulty of targeting pathogens colonizing lignified tissues. This study therefore evaluated eco-friendly control strategies comparing their performance with conventional fungicides and complementary cultural practices within an integrated management framework. Varietal tolerance significantly influenced symptom development and yield, with younger trees (1–2 years old) being more susceptible. Among the tested treatments, potassium silicate (K-Link) was associated with moderate reduction in disease intensity, with decreases in disease index ranging from 5–10%. Other products, including the biostimulant Brotolom^® SOILFORCE (BTL) and the disinfectant Huwa San^® TR50, also showed reductions in disease severity (approximately 5% and up to 14%, respectively), although their effects varied depending on cultivar and season. Cultural practices such as autumn pruning reduced symptoms and improved yield but required greater economic and labor inputs. In contrast, gibberellic acid was highly effective, reducing flowering, improving canopy balance, decreasing dieback incidence by 28%, and increasing yield by 34%. Integrating eco-friendly products, particularly potassium silicate, with targeted cultural practices and gibberellic acid application provides effective and sustainable tools to mitigate avocado dieback under Mediterranean conditions.