Antifungal Activity of Phyllospheric Bacteria Isolated from Coffea arabica against Hemileia vastatrix.

Peru is one of the leading countries that produce and export specialty coffees, favorably positioned in the international markets for its physical and organoleptic cup qualities. In recent years, yellow coffee rust caused by the phytopathogenic fungus Hemileia vastatrix stands out as one of the main phytosanitary diseases that affect coffee culture yields. Many studies have demonstrated bacteria antagonistic activity against a number of phytopathogen fungi. In this context, the aim of this work was to select and characterize phyllospheric bacteria isolated from Coffea arabica with antagonistic features against coffee rust to obtain biocontrollers. For that purpose, a total of 82 phyllospheric bacteria were isolated from two coffee leaf rust-susceptible varieties, typica and caturra roja, and one tolerant variety, catimor. Of all the isolates, 15% were endophytic and 85% were epiphytes. Among all the isolates, 14 were capable of inhibiting the mycelial radial growth of Mycena citricolor, and Colletotrichum sp. 16S rRNA gene sequence-based analysis showed that 9 isolates were related to Achromobacter insuavis, 2 were related to Luteibacter anthropi and 1 was related to Rodococcus ceridiohylli, Achromobacter marplatensis and Pseudomonas parafulva. A total of 7 representative bacteria of each group were selected based on their antagonistic activity and tested in germination inhibition assays of coffee rust uredinospores. The CRRFLT7 and TRFLT8 isolates showed a high inhibition percentage of urediniospores germination (81% and 82%, respectively), similar to that obtained with the chemical control (91%). An experimental field assay showed a good performance of both strains against rust damage too, making them a promising alternative for coffee leaf rust biocontrol.

Effects of Rhizobia Isolated from Coffee Fields in the High Jungle Peruvian Region, Tested on Phaseolus vulgaris L. var. Red Kidney.

Soils in the high jungle region of Peru continuously face erosion due to heavy rain, which leads to significant nutrient losses. Leguminous plants may provide a sustainable solution to this problem due to their ability to fix atmospheric nitrogen with the help of symbiotic rhizospheric microbes that reside in their root nodules and help restore soil fertility. The aim of this study was to isolate native rhizobial strains that can form functional nodules in red kidney beans to help improve their growth, development, and yield in field conditions. Rhizobium strains were isolated from soil samples collected from coffee fields using bean plants as trap hosts. The strain RZC12 was selected because it showed good root nodule promotion and a number of PGPR (plant-growth-promoting rhizobacteria) attributes. In the field, bean plants inoculated with the strain RZC12 and co-cultivated with coffee plants produced approximately 21 nodules per plant, whereas control plants produced an average of 1 nodule each. The inoculation with RZC12 significantly increased plant length (72.7%), number of leaves (58.8%), fresh shoot weight (85.5%), dry shoot weight (78%), fresh root weight (85.7%), and dry root weight (82.5%), compared with the control. The dry pod weight produced by the plants inoculated with RZC12 was 3.8 g, whereas the control plants produced 2.36 g of pods. In conclusion, RZC12 is a promising strain that can be used in field conditions to improve the overall productivity of red kidney beans.

Bioprospection of native psychrotolerant plant-growth-promoting rhizobacteria from Peruvian Andean Plateau soils associated with Chenopodium quinoa.

The Peruvian Andean Plateau, one of the main production areas of native varieties of Chenopodium quinoa, is exposed to abrupt decreases in environmental temperature, affecting crop production. Plant-growth-promoting rhizobacteria that tolerate low temperatures could be used as organic biofertilizers in this region. We aimed to bioprospect the native psychrotolerant bacteria of the quinoa rhizosphere in this region that show plant-growth-promoting traits. Fifty-one strains belonging to the quinoa rhizosphere were characterised; 73% of the total could grow at low temperatures (4, 6, and 15 °C), whose genetic diversity based on DNA amplification of interspersed repetitive elements (BOX) showed 12 different profiles. According to the 16S rRNA sequence, bacterial species belonging to the classes Beta- and Gammaproteobacteria were identified. Only three (6%) isolates identified as nonpathogenic bacteria exhibited plant-growth-promoting activities, like IAA production, phosphate solubilization, growth in a nitrogen-free medium, and ACC deaminase production at 6 and 15 °C. ILQ215 (Pseudomonas silesiensis) and JUQ307 (Pseudomonas plecoglossicida) strains showed significantly positive plant growth effects in aerial length (about 50%), radicular length (112% and 79%, respectively), and aerial and radicular mass (above 170% and 210%, respectively) of quinoa plants compared with the control without bacteria. These results indicate the potential of both psychrotolerant strains to be used as potential organic biofertilizers for quinoa in this region.

Bacteria-Plant interactions: an added value of microbial inoculation / Interacciones bacteria-planta: un valor añadido de la inoculación microbiana

Abstract High world population and the increase in global food demands results in an indiscriminate use of chemical fertilizers by farmers, causing soil deterioration and other environmental problems. In recent years there has been a collective concern to preserve the environment through sustainable and environmentally friendly techniques. Plant growth-promoting bacteria (PGPB) are widely known to benefit plants in a sustainable manner, reducing chemical fertilizers application. Many studies have shown that these bacteria not only improve crop yields but also its quality, increasing certain nutrients and molecules that are important for human health such as aminoacids, proteins, vitamins, flavonoids, antioxidants, essential oils, among others. This work compiles recent information of PGPB as an alternative of chemical fertilizer for improving crop yields and plant metabolites production.

El incremento acelerado de la población mundial que conlleva al aumento en la demanda de alimentos; ha ocasionado el uso indiscriminado de fertilizantes químicos por parte de los agricultores, provocando así el deterioro del suelo y con ello los subsecuentes problemas ambientales. En los últimos años ha surgido la preocupación colectiva de preservar el medioambiente a través del uso de técnicas sostenibles y ambientalmente amigables. Las bacterias promotoras de crecimiento vegetal (PGPB) son ampliamente conocidas por incrementar el crecimiento y desarrollo de las plantas de manera sostenible permitiendo así la reducción de la aplicación de fertilizantes químicos. Muchos estudios han demostrado que estas bacterias no solo mejoran el rendimiento de los cultivos sino también la calidad de estos, aumentando ciertos nutrientes y moléculas que son importantes para la salud del ser humano que los consume como aminoácidos, proteínas, vitaminas, flavonoides, antioxidantes, aceites esenciales, entre otros. Este trabajo recopila información reciente de las PGPB como alternativa a los fertilizantes químicos para la mejora en el rendimiento de los cultivos y la producción de metabolitos en las plantas.

Characterization and potential of plant growth promoting rhizobacteria isolated from native Andean crops.

Bacteria isolated from soil and rhizosphere samples collected in Peru from Andean crops were tested in vitro and in vivo to determine their potential as plant growth promoters and their ability to induce systemic resistance to Alternaria alternata in tomato plants. The isolates were identified by sequencing their 16S ribosomal RNA gene. Test for phosphate solubilization, and indolacetic acid were also carried out, together with in vitro antagonism assays in dual cultures towards the plant pathogens Fusarium solani, A. alternata and Curvularia lunata. The three most promising isolates (Pa15, Ps155, Ps168) belonged to the genus Pseudomonas. Further assays were carried out with tomato plants to assess their plant protection effect towards A. alternata and as growth promoters. Inoculation of tomato seeds with all isolates significantly enhanced seed germination, plantlets emergence and plant development. Bacterial inoculation also reduce damage level caused by A. alternata. The expression levels of three tomato genes involved in the jasmonate (AOS), ethylene responsive (ERF-2) and pathogenesis related (PR-P2) pathways were determined in plants challenged with A. alternata, alone or with each bacterial isolate, respectively. Results showed that at 24 h after infection, in absence of the pathogen, the expression level of the tested genes was very low. The presence of A. alternata alone and in combination with bacteria increased the transcripts of all genes. Data showed a potential of best performing isolate Ps168 to sustain tomato plants nutrition and activate defense-related genes for protection by pathogenic fungi.

Evaluation of plant growth promoting activity and heavy metal tolerance of psychrotrophic bacteria associated with maca (Lepidium meyenii Walp.) rhizosphere.

The high Andean plateau of Peru is known to suffer harsh environmental conditions. Acidic soils containing high amount of heavy metals due to mining activities and withstanding very low temperatures affect agricultural activities by diminishing crop quality and yield. In this context, plant growth promoting rhizobacteria (PGPR) adapted to low temperatures and tolerant to heavy metals can be considered as an environment-friendly biological alternative for andean crop management. The aim of this work was to select and characterize psychrotrophic PGPR isolated from the rhizosphere of maca (Lepidium meyenii Walp.) a traditional andean food crop. A total of 44 psychrotrophic strains isolated from 3 areas located in the Bombon plateu of Junin-Peru were tested for their PGPR characteristics like indole acetic acid (IAA) production, phosphate solubilization and for their ability to improve seed germination. In addition, their capacity to grow in the presence of heavy metals like cadmium (Cd), lead (Pb), cobalt (Co) and mercury (Hg) was tested. Of the total number of strains tested, 12 were positive for IAA production at 22 °C, 8 at 12 °C and 16 at 6 °C. Phosphate solubilization activities were higher at 12 °C and 6 °C than at 22 °C. Red clover plant assays showed that 16 strains were capable to improve seed germination at 22 °C and 4 at 12 °C. Moreover, 11 strains showed tolerance to Cd and Pb at varying concentrations. This study highlight the importance of obtaining PGPRs to be used in high andean plateu crops that are exposed to low temperatures and presence of heavy metals on soil.