Independent Preharvest Applications of Methyl Jasmonate and Chitosan Elicit Differential Upregulation of Defense-Related Genes with Reduced Incidence of Gray Mold Decay during Postharvest Storage of Fragaria chiloensis Fruit.

The Chilean strawberry (Fragaria chiloensis) fruit has interesting organoleptic properties, but its postharvest life is affected by gray mold decay caused by Botrytis cinerea. The effect of preharvest applications of methyl jasmonate (MeJA) or chitosan on the molecular defense-related responses and protection against gray mold decay were investigated in Chilean strawberry fruit during postharvest storage. Specifically, we inoculated harvested fruit with B. cinerea spores and studied the expression of genes encoding for the pathogenesis-related (PR) proteins ß-1,3-glucanases (FcBG2-1, FcBG2-2 and FcBG2-3) and chitinases (FcCHI2-2 and FcCHI3-1), and for polygalacturonase inhibiting proteins (FcPGIP1 and FcPGIP2) at 0, 2, 24, 48, and 72 h post inoculation (hpi). Remarkably, MeJA- and chitosan-treated fruit exhibited a lower incidence of B. cinerea infection than the control-treated at 48 and 72 hpi. At the molecular level, both are efficient elicitors for priming in F. chiloensis fruit since we observed an upregulation of the FcBG2-1, FcBG2-3, FcPGIP1, and FcPGIP2 at 0 hpi. Moreover, a chitosan-mediated upregulation of FcPGIPs at early times post inoculation (2-24 hpi) and MeJA upregulated FcBGs (24-72 hpi) and FcPGIP1 at later times could contribute to reduce B. cinerea incidence by differential upregulation of defense genes. We concluded that preharvest applications of MeJA or chitosan had a long-lasting effect on the reduction of B. cinerea incidence during postharvest as well as an enhancer effect on the induction of PR and PGIP gene expression.

[Characterization of growth-promoting rhizobacteria in Eucalyptus nitens seedlings]. / Caracterización de rizobacterias promotoras de crecimiento en plántulas de Eucalyptus nitens.

Rhizospheric and endophytic bacteria were isolated from the rizosphere and root tissue of Eucalyptus nitens. The objective of this work was to evaluate their capacity to promote growth in seedlings of the same species under greenhouse conditions. The isolates that improved seedling growth were identified and characterized by their capacity to produce indoleacetic acid (IAA), solubilize phosphates and increase 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. One hundred and five morphologically different strains were isolated, 15 of which promoted E. nitens seedling growth, significantly increasing the height (50%), root length (45%) as well as the aerial and root dry weight (142% and 135% respectively) of the plants. Bacteria belonged to the genus Arthrobacter, Lysinibacillus, Rahnella and Bacillus. Isolates A. phenanthrenivorans 21 and B. cereus 113 improved 3.15 times the emergence of E. nitens after 12 days, compared to control samples. Among isolated R. aquatilis, 78 showed the highest production of IAA (97.5±2.87 µg/ml) in the presence of tryptophan and the highest solubilizer index (2.4) for phosphorus, while B. amyloliquefaciens 60 isolate was positive for ACC deaminase activity. Our results reveal the potential of the studied rhizobacteria as promoters of emergence and seedling growth of E. nitens, and their possible use as PGPR inoculants, since they have more than one mechanism associated with plant growth promotion.

Production of phytohormones, siderophores and population fluctuation of two root-promoting rhizobacteria in Eucalyptus globulus cuttings.

Vegetative propagation by stem cuttings and mini-cuttings has been used worldwide for growing Eucalyptus plants. However, clones and hybrids of this plant present a great variability in their rooting capacity, apart from a gradual decrease in the rooting potential due to the ontogenetic age of the mother plant. Several studies have demonstrated that some bacteria promote plant growth and rooting through the action of direct and indirect mechanisms that are not still completely clear. Considering this, the objective of this study was to assess the production of auxins, abscisic acid and siderophores in Bacillus subtilis and Stenotrophomona maltophilia, which in previous studies increased rooting of E. globulus cuttings. Additionally, the population of these bacteria in the rhizosphere, superficial tissues of the stem-base and callus of the mini-cuttings was identified, and quantified by real-time PCR. Only S. maltophilia produced IAA in the presence of tryptophan; none of the bacterial strains produced ABA, but both produced siderophores. A comparative analysis of the separation profiles showed that there is a diverse microbial community in the rhizosphere, and only S. maltophilia was capable of keeping its population at a density of 2.03 × 10(7) cells/mg in different tissues of the mini-cuttings. The results would indicate that the rooting stimulus in E. globulus could be related to the action of one or several mechanisms such as the production of auxins and siderophores, and it could also be associated with the ability of bacteria to stay in the rhizosphere or in plant callus tissues.

Biocontrol of Sirex noctilio by the parasitic nematode Deladenus siricidicola: A five season field study in southern Chile.

In 2001, the woodwasp Sirex noctilio was detected in Pinus radiata plantations in the Biobio region of southern Chile. Subsequently, an intense biological control program using the female sterilizing nematode Deladenus siricidicola was implemented in 2010. During five seasons between 2012 and 2017, we studied the parasitism of D. siricidicola nematode and its effect on woodwasp populations and infestation of P. radiata in different locations within the Biobio region. Parasitism was assessed by dissecting adult females of S. noctilio obtained from infested P. radiata logs. The total population of S. noctilio was determined by the emergence of individuals from the same logs. The level of damage caused by the S. noctilio pest was determined by establishing plots in stands of P. radiata at an intensity of 1 plot every 5 ha-1. During the study period, parasitism of S. noctilio by the nematode D. siricidicola increased from 29.6% in 2012 to 93.1% in 2016, while pest population decreased 3.4% in the same time period. Infestation increased from 0.3 to 11,6% of trees between 2012 and 2015, but subsequently decreased to 5.9% by 2017. We confirmed establishment of the nematode in the region under study and its natural dispersion to non-inoculated areas. Finally, we determined that the effect of inoculation age (antiquity) on parasitism levels reached 90% after three years of inoculation.

Caracterización de rizobacterias promotoras de crecimiento en plántulas de Eucalyptus nitens / Characterization of growth-promoting rhizobacteria in Eucalyptus nitens seedlings

Se aislaron bacterias rizosféricas y endófitas a partir de rizósfera y tejidos de raíz de árboles de Eucalyptus nitens con el objetivo de evaluar su capacidad de promover el crecimiento en plántulas de la misma especie en condiciones de invernadero. Los aislamientos que incrementaron el crecimiento de las plántulas fueron identificados y caracterizados por su capacidad de producir ácido indolacético (AIA), solubilizar fosfato y expresar la 1-aminociclopropano-1-carboxilato (ACC) desaminasa. Los 105 aislamientos obtenidos fueron morfológicamente diferentes y solo 15 promovieron significativamente el crecimiento de plántulas de E. nitens. Los máximos incrementos observados fueron en el peso seco aéreo (142 %) y de la raíz (135 %); también aumentaron la altura de las plantas (50 %) y el largo de raíces (45 %) de las mismas. Las rizobacterias pertenecieron a los géneros Arthrobacter, Lysinibacillus, Rahnella y Bacillus. Los aislados identificados como A. phenanthrenivorans 21 y B. cereus 113 incrementaron la emergencia de E. nitens a los 12 días en un valor promedio de 3,15 veces con relación al control. R. aquatilis aislado 78 presentó la mayor producción de AIA (97,5 ± 2,87 μg/ml) en presencia de triptófano y el mayor índice de solubilización de fósforo (2,4). B. amyloliquefaciens aislado 60 fue positivo para la actividad ACC desaminasa. Los resultados obtenidos indican el potencial de las rizobacterias estudiadas como promotoras de emergencia y crecimiento de plántulas de E. nitens y su posible uso como inoculantes, ya que presentan más de un mecanismo de acción asociado a la promoción del crecimiento.

Rhizospheric and endophytic bacteria were isolated from the rizosphere and root tissue of Eucalyptus nitens. The objective of this work was to evaluate their capacity to promote growth in seedlings of the same species under greenhouse conditions. The isolates that improved seedling growth were identified and characterized by their capacity to produce indoleacetic acid (IAA), solubilize phosphates and increase 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. One hundred and five morphologically different strains were isolated, 15 of which promoted E. nitens seedling growth, significantly increasing the height (50%), root length (45%) as well as the aerial and root dry weight (142% and 135% respectively) of the plants. Bacteria belonged to the genus Arthrobacter, Lysinibacillus, Rahnella and Bacillus. Isolates A. phenanthrenivorans 21 and B. cereus 113 improved 3.15 times the emergence of E. nitens after 12 days, compared to control samples. Among isolated R. aquatilis, 78 showed the highest production of IAA (97.5±2.87 μg/ml) in the presence of tryptophan and the highest solubilizer index (2.4) for phosphorus, while B. amyloliquefaciens 60 isolate was positive for ACC deaminase activity. Our results reveal the potential of the studied rhizobacteria as promoters of emergence and seedling growth of E. nitens, and their possible use as PGPR inoculants, since they have more than one mechanism associated with plant growth promotion.