The chaperones, heat shock proteins (HSPs), stabilize proteins to minimize proteotoxic stress, especially during heat stress (HS) and polyamine (PA) oxidases (PAOs) participate in the modulation of the cellular homeostasis of PAs and reactive oxygen species (ROS). An interesting interaction of HSP90s and PAOs was revealed in Arabidopsis thaliana by using the pLFY:HSP90RNAi line against the four AtHSP90 genes encoding cytosolic proteins, the T-DNA Athsp90-1 and Athsp90-4 insertional mutants, the Atpao3 mutant and pharmacological inhibitors of HSP90s and PAOs. Silencing of all cytosolic HSP90 genes resulted in several-fold higher levels of soluble spermidine (S-Spd), acetylated Spd (N⁸-acetyl-Spd) and acetylated spermine (N¹-acetyl-Spm) in the transgenic Arabidopsis thaliana leaves. Heat shock induced increase of soluble-PAs (S-PAs) and soluble hydrolyzed-PAs (SH-PAs), especially of SH-Spm, and more importantly of acetylated Spd and Spm. The silencing of HSP90 genes or pharmacological inhibition of the HSP90 proteins by the specific inhibitor radicicol, under HS stimulatory conditions, resulted in a further increase of PA titers, N⁸-acetyl-Spd and N¹-acetyl-Spm, and also stimulated the expression of PAO genes. The increased PA titers and PAO enzymatic activity resulted in a profound increase of PAO-derived hydrogen peroxide (H₂O₂) levels, which was terminated by the addition of the PAO-specific inhibitor guazatine. Interestingly, the loss-of-function Atpao3 mutant exhibited increased mRNA levels of selected AtHSP90 genes. Taken together, the results herein reveal a novel function of HSP90 and suggest that HSP90s and PAOs cross-talk to orchestrate PA acetylation, oxidation, and PA/H₂O₂ homeostasis.

In June 2017, a severe vine decline of the netted melon (Cucumis melo L.) hybrids Global F1 and Lavigal was observed in a greenhouse of Messara valley, Heraklion, Crete, Greece. Diseased plants exhibited wilting, leaf chlorosis, yellowing and vine collapse. Root rot and necrosis, foot rot and to a lesser extent vascular tissue discoloration at the lower part of the stem were also observed. Numerous perithecia embedded in the root cortex, containing asci and ascospores typical of Monosporascus cannonballus Pollack & Uecker (1974) were observed. Disease incidence in the greenhouse was estimated at 100 and 78% for Global F1 and Lavigal, respectively. The fungus was isolated from the root lesions and the discolored vessels of the basal part of the stem, previously surface-sterilized with 1.5% sodium hypochlolrite for 1 min, on potato dextrose agar (PDA) amended with 0.5 g/l streptomycin sulfate. To obtain single hyphae isolates, hyphal tips were transferred onto new PDA plates and the growth rate of the fungu...

Tomato bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis (Cmm) (Li et al. 2018), is a common destructive disease worldwide. The bacterium colonizes plant’s vascular system causing characteristic symptoms such as wilting, cankers, brown and black discoloration of vessels, white spots on the fruit and leaves. In the present work, isolates were collected from infected tomato plants of 11 Greek Prefectures during the years 2003-2018, and the genetic variability was investigated. After initial identification, 93 selected Cmm strains were subjected to phylogenetic analyses based on the sequencing of multiple loci (Multi-Locus Sequencing Analysis, MLSA) utilizing four housekeeping genes (atpD, ppk, kdpA and sdhA). MLSA highlighted 4.1% variability in nucleotide sequences and classified the 93 Cmm strains into 38 haplotypes. Nevertheless, the phylogenetic grouping of the strains was not in accordance with the geographical distribution, a fact that probably advocates the introduction of the disease from infected propagating material. However, strains isolated from the same area in a different year were placed in the same group which means that the pathogen can remain active between growing seasons. The study provides important epidemiological information on the disease outbreaks and the spread of Cmm in Greece.

This study highlights the growing concern over copper resistance in Pseudomonas syringae pv. actinidiae (Psa), a significant pathogen threatening kiwifruit cultivation globally. Copper-based treatments, widely used for their broad-spectrum bactericidal properties, have become less effective over time due to the emergence of copper-resistant strains. This study found that 22 strains of Psa, collected from Greek kiwifruit orchards, exhibited significant copper resistance. All strains were capable of growing in copper concentrations of at least 200 µg/mL (0.8 mM), and two strains (9.1%) survived even at higher concentrations of 400 µg/mL (1.6 mM). Additionally, resistant bacterial colonies were observed in four strains (18.2%), suggesting the presence of resistant subpopulations within the broader bacterial community. In addition to studying copper resistance, the research evaluated the effectiveness of several products in controlling Psa through field experiments. The copper products IONIC CONCENTRATED COPPER, MAGNA BLUE, and COPROFIX ULTRA were tested due to their historical effectiveness in managing bacterial diseases in plants. However, these copper products were unable to fully control Psa in this study, likely due to the observed resistance. In addition, the plant defense activator products MICONIC and NUTRI BIOCLEAN, NUTRI BIOCLEAN, BAR, and BION were evaluated and showed promising results in reducing the intensity of symptoms associated with Psa, suggesting that these formulations may enhance the plant’s natural defenses against the pathogen. While these products did not completely eliminate the disease, they significantly reduced symptom severity. The findings highlight the need for alternative strategies to combat Psa, particularly in areas where copper resistance has developed.