Non-Chemical Treatments for the Pre- and Post-Harvest Elicitation of Defense Mechanisms in the Fungi-Avocado Pathosystem

Exogenous priming of chitosan induces resistance in Chinese prickly ash against stem canker caused by Fusarium zanthoxyli

Stem canker is a highly destructive disease that threatens prickly ash plantations in China. This study demonstrated the effective control of stem canker in prickly ash using chitosan priming, reducing lesion areas by 46.77 % to 75.13 % across all chitosan treatments. The mechanisms underlying chitosan-induced systemic acquired resistance (SAR) in prickly ash were further investigated. Chitosan increased H2O2 levels and enhanced peroxidase and catalase enzyme activities. A well-constructed regulatory network depicting the genes involved in the SAR and their corresponding expression levels in prickly ash plants primed with chitosan was established based on transcriptomic analysis. Additionally, 224 ZbWRKYs were identified based on the whole genome of prickly ash, and their phylogenetic evolution, conserved motifs, domains and expression patterns of ZbWRKYs were comprehensively illustrated. The expression of 12 key genes related to the SAR was significantly increased by chitosan, as determined using reverse transcription-quantitative polymerase chain reaction. Furthermore, the activities of defensive enzymes and the accumulation of lignin and flavonoids in prickly ash were significantly enhanced by chitosan treatment. Taken together, this study provides valuable insights into the chitosan-mediated activation of the immune system in prickly ash, offering a promising eco-friendly approach for forest stem canker control.

Assessing Copper-Alternative Products for the Control of Pre- and Postharvest Citrus Anthracnose

Citrus production is worldwide threatened by Colletotrichum spp., causal agents of pre- and postharvest anthracnose. The recent limitation on the use of copper-based antimicrobials, due to its demonstrated noxious effect on the environment, makes the control of this pathogen difficult. Thus, alternative products able to reduce/phase out copper in organic citrus farming are needed. In this study, the efficacy of 11 commercial alternative products were evaluated in vitro, in growth chamber, in open field and in postharvest environments. In vitro, mineral fertilizers, basic substances, essential oils, plant defense stimulators and biological control agents were able to inhibit the mycelial growth with variable efficacy. On artificially infected citrus fruit, almost all tested products significantly reduced disease incidence and severity, but with lower efficacy than copper. The efficacy of mineral fertilizers-based Kiram and Vitibiosap 458 Plus, citrus essential oil-based Prev-Am Plus and chitosan-based Biorend was confirmed in open field trials, in naturally infected citrus fruits. In these trials Biorend was the best alternative product, significantly reducing disease incidence (71% DI reduction) with better results than copper (47.5%). Field treatments reduced the incidence and severity of the disease in postharvest conditions, especially in fruits field-treated three times. Overall, selected products tested in open field can represent a good alternative to copper compounds in the view of future limitation of its use.

Anthracnose Disease Control and Postharvest Quality of Hass Avocado Stored in Biobased PLA/PBAT/Pine Essential Oil/Chitosan Active Packaging Nets

For sale in the domestic market, Hass avocados are kept in non-biodegradable plastic nets and stored at an ambient temperature. The fungus Colletotrichum gloeosporioides can cause important losses at this stage. Consequently, formulations based on polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) 60/40 biodegradable blends added with pine essential oil (PEO) at 10, 12, 14, and 20% and coated with 1% chitosan (CH) were used for the elaboration of nets, which were evaluated on C. gloeosporioides and Rhizopus stolonifer on nutrient media and fruit and on the ripening behavior of Hass avocados at ambient temperature. The spore germination stage of C. gloeosporioides was the most extensively damaged (78% inhibition). The incidence of anthracnose was notably reduced by almost 80% in the avocados stored in the 60/40 PLA/PBAT nets coated with 1% CH. The overall values regarding weight loss, °Brix, and dry matter were c.a. 23.5%, 7.5, and 24.5%, respectively. The changes in firmness, color, and CO₂ production were particularly associated with the initial harvest index and storage temperature rather than with the nets. In future research, essays on nets should include evaluations at the commercial levels.