The genetic variability and aggressiveness of Brazilian Erwinia psidii isolates from Eucalyptus spp. was studied and compared with reference isolates from guava (Psidium guajava). Repetitive element sequence (rep)‐based PCR markers of 101 isolates from Eucalyptus spp. and five from guava showed that the populations of E. psidii displayed a relatively low genetic variability. No correlation of genetic clustering based on rep‐PCR analysis with geographic origin or host of origin was observed, indicating that genome rearrangements associated with adaptation to a particular host were not detected by these molecular markers. A higher genotypic richness was detected in the Mato Grosso do Sul population, probably reflecting a pathogen dissemination associated with the recent expansion in eucalypt plantations. Wilcoxon and ANOVA tests of disease severity data indicated differences in aggressiveness among isolates and an isolate × clone interaction. The area under the disease progress curve (AUDPC) and disease severity for some isolates were significantly different between two susceptible clones tested. Notably, isolate LPF681 from guava was not able to cause disease on a susceptible Eucalyptus urophylla clone, suggesting that some co‐evolution between pathogen and host has taken place. The variability in aggressiveness and virulence among isolates of E. psidii observed in this study will be important for the establishment of appropriate screening approaches to select for disease resistance.

Dieback, caused by Erwinia psidii is currently one of the most severe emerging diseases of Eucalyptus spp. in Brazil. Because of its recent report, little is known about the mechanisms underlying bacterial infection. We studied the colonization and movement of E. psidii in host tissue using a strain labeled with green fluorescent protein. We were able to transform E. psidii with pGreen-TIR and to demonstrate plasmid stability in the absence of antibiotic selection both in vitro and in vivo. We demonstrate that tissue colonization by E. psidii is not restricted to the inoculation point (leaf axil). E. psidii colonizes the xylem vessels, sclerenchyma and parenchyma of leaves and stems of eucalypt. At 35 days after inoculation, the bacterium was found at 5 cm above the inoculation point, indicating that it colonizes the plant acropetally. Confocal microscopy analysis revealed that when rootinoculated the bacterium penetrates the primary and secondary roots and reaches the xylem, but it was never found in the root crown or stem, irrespective of the evaluation time. Our results provide insights into the biology of the E. psidii-eucalypt interaction, which requires a better understanding in order to design efficient strategies for pathogen control and disease management.

BACKGROUND Corn grains are commonly contaminated with mycotoxins and fungi. The purpose of this study was to evaluate the reduction of aflatoxins B1, B2, G1, and G2 and the inhibition of Aspergillus niger in corn grains using ultrasound, ultraviolet (UV) radiation, electrolyzed water, and sodium bicarbonate. The determination of aflatoxins was performed by high‐performance liquid chromatography with fluorescence detection and postcolumn derivatization, and analysis of A. niger was performed by evaluating mycelial growth in potato dextrose agar. The best treatment for reducing aflatoxins and inhibiting mycelial growth was evaluated in corn contaminated with A. niger. RESULTS The results show a significant reduction in aflatoxins in the following order: sodium bicarbonate > ultrasound > UV > electrolyzed water for aflatoxins B1, B2, and G2. For aflatoxin G1, the order of reduction was sodium bicarbonate > ultrasound > electrolyzed water > UV, with maximum values between 70.50% and 87.03% reached with sodium bicarbonate; for the other treatments, the reduction was between 51.51% and 65.44%. Regarding the fungus, the order of inhibition in the control of mycelial growth was sodium bicarbonate > ultrasound > electrolyzed water > UV in corn grains, and inhibition of mycelial growth was obtained at a sodium bicarbonate concentration of 3.0 g L−1. CONCLUSION Sodium bicarbonate, electrolyzed water, ultrasound, and UV radiation inhibited the growth of A. niger on potato dextrose agar and reduced the contents of aflatoxins B1, B2, G1, and G2 in vitro. Sodium bicarbonate showed an ability to inhibit mycelial growth in corn grains. © 2020 Society of Chemical Industry

Ultraviolet radiation and generally recognized as safe (GRAS) preservatives for inactivation of Aspergillus niger in vitro and corn dough.

Dieback and wilt, caused by Erwinia psidii (Ep), is one of the most important emergent diseases of Eucalyptus spp. in Brazil. Currently, pathogen detection relies on isolation of bacteria from infected plant tissue and either identification based on morphological, physiological and biochemical tests or DNA amplification using the polymerase chain reaction (PCR), which in many cases is laborious and cumbersome. Considering the need for a simpler and more rapid, yet reliable, method for detecting the pathogen, we obtained a polyclonal antibody (anti‐Ep) and developed an agglutination test for specific detection of E. psidii. The antiserum was produced against the E. psidii strain LPF534 and tested against 101 E. psidii isolates from Eucalyptus spp.; three E. psidii isolates from Psidium guajava; 23 Ralstonia solanacearum and 18 Xanthomonas axonopodis isolates pathogenic to Eucalyptus spp.; and seven endophytic isolates from Eucalyptus spp., three of which are phylogenetically related to the genus Erwinia. Results of direct ELISA indicated that a concentration as low as 3.5 µg/ml of the anti‐Ep antibody was able to detect the E. psidii antigen and that the antibody did not cross‐reacted with other bacteria pathogenic and non‐pathogenic to Eucalyptus spp. In the agglutination test, the anti‐Ep antibody showed positive reaction with all strains of E. psidii tested whereas cross‐reaction with none of the strains that belong to other taxonomic groups was observed. The agglutination test showed a detection limit of 105 colony‐forming units (CFU)/ml, and its specificity was the same as that obtained by PCR amplification using E. psidii‐specific primers. These results demonstrate that the agglutination test developed here is a useful tool for specific, fast and inexpensive detection of E. psidii although only operational on pure bacterial suspensions and not yet directly from infected tissues.

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