Scientia Agropecuaria 11(2): 223 – 231 (2020) SCIENTIA AGROPECUARIA Facultad de Ciencias Scientia Agro pecuaria Agropecuarias Universidad Nacional de Website: http://revistas.unitru.edu.pe/index.php/scientiaagrop Trujillo Rhizospheric actinomycetes from organic crops of native potato (Solanum tuberosum): isolation, phenotypic characterization, molecular identification, and impact on biocontrol of Phytophthora infestans (Mont.) de Bary Astrid Chumpitaz Bermejo1 ; Junior Caro Castro1 ; Wilbert Cruz Hilacondo2 ; Jorge León Quispe1,* 1 Laboratorio de Ecología Microbiana, Facultad de Ciencias Biológicas, Universidad Nacional Mayor de San Marcos, Lima, Peru. 2 Dirección de Desarrollo Tecnológico Agrario. Instituto Nacional de Innovación Agraria (INIA). Av. La Molina 1981, Lima, Lima 15024, Peru. Received February 25, 2020. Accepted May 31, 2020. Abstract Potato (Solanum tuberosum L.) is the fourth most consumed food crop in the world, whose production in Peru is diminished due to phytosanitary problems and high costs of chemical fertilizers. In the present work, 32 actinomycetes isolated from the rhizosphere of organic native potato crops collected in the town of Cabana, Lucanas, Ayacucho, were characterized phenotypically and evaluated for their in vitro antagonistic capacity against Oomycete phytopathogen Phytophthora infestans. The characterization tests showed that 97% of the actinomycetes were able to assimilate glucose, sucrose, and mannitol; as well as producing extracellular enzymes like amylases (100%) and cellulases (50%). Furthermore, the growth in laboratory culture was better in the range of pH 5.5-8.5 and temperature 28-30 °C. From the tests of antagonism in oat agar (71.9%) and rye agar (31.2%), three strains were selected according to the native potato variety were selected as CAB10-J2 (Ccompis), CAB9-CA4 (Cuchipa-akan) and CAB5- F5 (Futis) with pathogen inhibition rates of 80.05, 77.47 and 37.5% respectively. The strains were identified by molecular tests as members of the genus Streptomyces and owners of polyketide synthase (PKS) genes. It is concluded that the rhizospheric actinomycetes of potato are producers of bioactive compounds capable of remarkably inhibiting the pathogen Phytophthora infestans, being able to be considered candidates in biological control programs of the "potato blight". Keywords: actinobacteria; Phytophthora infestans; native potato; biocontrol of pests; antagonism. 1. Introduction Potato cultivation is affected by limiting fac- Potato (Solanum tuberosum L.) is the fourth tors such as low tuber quality, soil impover- most consumed crop in the world after ishment, indiscriminate use of agrochemi- wheat, corn, and rice, which are exceeds in cals, as well as the attack of insects and phy- terms of nutritional value. Among the potato topathogenic organisms, resulting in a de- producing countries, Peru is ranked 19th crease in productivity and profitability of worldwide, being the main producer in Latin this tuber (Rico, 2009). On the other hand, America, producing more than 4.5 million due to exposure to various pests and patho- tons of this tuber and involving the participa- gens, potato cultivation is an activity with tion of approximately 600,000 farmers dis- high use of agrochemicals, substances that tributed in 19 regions; being La Libertad, are toxic and dangerous for the farmer, the Huánuco, Puno, Junín and Ayacucho re- crop itself and the environment (Virmond et gions where ancestral crops are still carried al., 2017). out (Ministerio de Agricultura y Riego, A number of viral, fungal and bacterial 2017). agents, as well as nematodes, viroids and Cite this article: Chumpitaz, A.; Caro, J.; Cruz, W.; León, J. 2020. Rhizospheric actinomycetes from organic crops of native potato (Solanum tuberosum): isolation, phenotypic characterization, molecular identification, and impact on biocontrol of Phytophthora infestans (Mont.) de Bary. Scientia Agropecuaria 11(2): 223-231. --------- * Corresponding author © 2020 All rights reserved E-mail: jleonq@unmsm.edu.pe (J. León). DOI: 10.17268/sci.agropecu.2020.02.09 -223- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) oomycetes cause diseases to the potato Isolation and selection of actinomycetes crop (Bertschinger et al., 2017), highlighting 10 g of soil from each dry sample was among them, the Oomycete Phytophthora weighed, placing them inside a sterile bottle infestans (Mont.) De Bary, causal agent of with 90 mL of 1.5% phenol saline solution the disease "late blight", and the main re- and incubating at 30 °C for 30 minutes. Sub- sponsible for the deficit in yield and produc- sequently, serial dilutions were prepared up tion, being able to cause from slight, moder- to 10-4, sowing 100 µl in plates with Oat Agar ate damages, until the total destruction of (BD DifcoTM, UK), Asparagine Agar (Merck, crops (Cardona-Piedrahita et al., 2016). The Germany), Czapeck Agar (Merck, Germany) main sign of late blight is the burning of the and Casein-Starch Agar (HiMedia, India), all foliage and the dry rot of the tubers supplemented with nystatin (50 μg/mL) and (Steańczyk et al., 2016). nalidixic acid (25 μg/mL) (Sigma-Aldrich, Currently, antagonistic microorganisms are USA), incubating them at 28 °C from 15 to 20 used to control fungi and oomycetos in dif- days (Cisneros, 2016). ferent types of crops, reducing the use of chemical methods that cause a negative en- Morphological characterization of isolated vironmental impact and induce the emer- actinomycetes gence of resistance in the future (Marín et Actinomycetes were characterized macros- al., 2013). Actinomycetes as Streptomyces copically by observation of the colonies. The sp. are capable of synthesizing bioactive microscopic characterization was perfor- compounds that inhibit the development of med using microcultures, comparing the certain phytopathogens, thus providing pro- characteristics with those described in the tection to crops (Sinha et al., 2014). Some Bergey's Manual of Systematic Bacteriology important studies include the control of phy- (Whitman et al., 2012). Selected strains topathogens such as Verticillium dahliae in were processed according to Colona et al. cotton (Xue et al., 2013), Valsa mali in apple (2014) for observation by a scanning elec- TM trees (Tang et al., 2015) and Fusarium tron microscopy Inspect TM S50 (FEI , oxysporum in soybeans (Mariastuti et al., Japan). 2018), Assimilation of sugars and activity of hydro- Some microorganisms such as Pseudomo- lytic enzymes nas aeruginosa (De Vrieze et al., 2019), Glucose, sucrose, and mannitol metabolism Lysobacter capsici (Puopoloet al., 2015), tests were performed in ISP 9 medium with and the fungi Aureobasidium pullulans (Di 1% of carbohydrates (w/v) (Caro, 2016). Li- Francesco et al., 2017) have been previously kewise, the ability to produce amylase and used in the control of Phytophthora in- cellulase were determined in Almidón Agar festans with great results. However, there and Mandels-Reese Agar respectively, are not many studies of the use of actinomy- being evaluated according to Pérez et al. cetes for the control of this pathogen. In this (2015) with Lugol and Congo red solutions. context, the aim of the present study is to In all cases, the tests were evaluated up to contribute to the current knowledge about 15 days. certain native strains of rhizospheric action- mycetes that have antagonistic capacity Growth depending on pH and temperature with potential use as biological controllers The tests were performed according to of Phytophthora infestans that affects po- Calvo and Zúñiga (2010), using Oat Agar, tato crops. evaluating its development at pHs 5.5; 7 and 8.5, and the temperatures of 4, 28, 30 and 45 2. Materials and methods °C, incubating them up to 10 days. The inten- Maintenance of Phytophthora infestans sity of growth was evaluated at the end of Phytophthora infestans, strain PHU-117, the test period, measuring the diameter of was maintained by subcultures of Rye Agar the colonies, and recording the average (HiMedia, India), incubating the plates at 28 size. °C from 5 to 7 days. Actinomycete antagonism against Sampling and transport to the laboratory Phytophthora infestans Sampling took place in potato fields located In vitro antagonism was performed by dual in the town of Cabana, Lucanas, Ayacucho culture (Pérez et al., 2015), sowing a sus- (14° 17' 10" South Latitude; 73° 57'51" West pension of actinomycete spores (105 Longitude). The rhizospheric soil samples CFU/mL-1) in Oat Agar and Rye Agar plates were collected from native potato plants of at 3 equidistant sites, being in the center an Canchán, Futis, Huayro, Cuchipa-akan, inoculum of P. infestans. The plates were in- Ccompis and Chaska varieties, collecting cubated at 28 °C for 10 days. The diameters 200g portions of soil in ziploc bags, and then of the inhibition halos were measured with a sent to the laboratory for processing millimeter ruler. The percent inhibition (PI) -224- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) was calculated according to Ezziyyani et al. performed by PCR amplification of 16S rRNA 𝑅−𝑟 (2004): 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑖𝑛ℎ𝑖𝑏𝑖𝑡𝑖𝑜𝑛 (𝑃𝐼) = 𝑥 100 gene using universal primers 27F and 𝑅 1429R, whose sequences are 5′- Where, R is the major radius (in mm) of the AGAGTTTGATCMTGGCTCAG-3′ and 5′- Oomycete colony (control); r is the smallest GGTTACCTTGTTACGACTT-3′respectively, radius (in mm) of the Oomycete in the dual following the Parada et al. (2017) protocol. culture. In all cases the radius measurement The amplicons were revealed by electro- was the average of triplicate measure- phoresis in agarose gels (1300 bp) and sent ments. to Macrogen Inc. (Korea) for sequencing. The chromatograms were evaluated and PKS gene detection and molecular edited in MEGA7 program, with multiple identification of actinomycetes alignments of 16S rRNA sequences belon- Selected strains which had the best antago- ging to other actinomycetes of GenBank nistic results were seeded in fermentation database, using Bacillus subtillis as an broths and incubated under stirring at 28 oC external group. The phylogenetic tree was for 7 days. Then, they were centrifuged at constructed using Neighbor-Joining method 14,000 rpm for 10 minutes, adding 1 ml of Ly- (Kumar et al., 2016). sozyme (20 mg/ml) (Sigma- Aldrich, USA) to the pellet, keeping in incubation at 56 °C for 1 h. DNA extraction was performed using 3. Results and discussion GeneJET Genomic kit (Thermo Fisher Scien- Characterization of isolated actinomycetes tific, UK). For PCR amplification of PKS A total of 32 strains of rhizospheric acti- genes, primers K1 and M6R were used, nomycetes from five native potato varieties whose sequences are 5′- were isolated, except for the Chaska variety. TSAAGTCSAACATCGGBCA-3′ and 5′- Table 1 shows the macroscopic charac- CGCAGGTTSCSGTACCAGTA-3′respec- teristics of actinomycete colonies, which tively, according to Chen et al. (2019) proto- presented the following characteristics: Dry col, whose detection was revealed by aga- colonies strongly adhered to the medium rose electrophoresis by visualization of the and with a velvety, grainy, or powdery band at 700 bp in a transilluminator (Bi- appearance, with or without pigment oBase, China). Molecular identification was production (Figure 1A and 1B). Table 1 Macroscopic characterization of actinomycete colonies isolated from the native potato rhizosphere grown Colony characteristics Strain Potato variety Shape Pigment Color Edge Elevation CAB3-C1 Canchán Regular Green White Lobate Convex CAB3-C2 Canchán Regular NP White Entire Convex CAB3-C3 Canchán Regular NP Gray Entire Convex CAB4-C1 Canchán irregular NP Gray Entire Convex CAB4-C2 Canchán Irregular NP Gray Entire Convex CAB4-C3 Canchán Regular NP Gray Entire Convex CAB4-C4 Canchán Irregular Green White Entire Convex CAB4-C5 Canchán Irregular Green Gray Lobate Convex CAB4-C6 Canchán Irregular Green Gray Entire Convex CAB5-F1 Futis Regular Red White Lobate Convex CAB5-F2 Futis Regular Green Gray Lobate Convex CAB5-F3 Futis Regular Green Gray Entire Convex CAB5-F4 Futis Irregular Green Gray Entire Convex CAB5-F5 Futis Irregular Green White Entire Convex CAB6-F1 Futis Regular NP Gray Entire Convex CAB7-H1 Huayro Irregular Yellow White Entire Convex CAB7-H2 Huayro Regular Mustard Gray Lobate Convex CAB7-H3 Huayro Regular Mustard Gray Lobate Convex CAB7-H4 Huayro Regular NP Gray Lobate Pulvinate CAB7-H5 Huayro Regular NP Red Lobate Pulvinate CAB8-H1 Huayro Regular NP Gray Entire Convex CAB8-H2 Huayro Regular Green Gray Entire Convex CAB9-CU1 Cuchipa-akan Regular NP White Lobate Acuminate CAB9-CU2 Cuchipa-akan Irregular NP Gray Entire Convex CAB9-CU3 Cuchipa-akan Irregular NP Gray Lobate Convex CAB9-CU4 Cuchipa-akan Regular Green Gray Lobate Convex CAB10-J1 Ccompis Regular Red White Lobate Convex CAB10-J2 Ccompis Irregular Yellow Gray Entire Pulvinate CAB10-J3 Ccompis Irregular Yellow Gray Entire Pulvinate CAB10-J4 Ccompis Regular Mustard White Entire Convex CAB10-J5 Ccompis Regular Red Gray Lobate Convex CAB10-J6 Ccompis Regular NP Gray Lobate Convex NP: No pigment. -225- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) Figure 1. Various colonies of rhizospheric actinomycetes isolated from rhizosphere of native potatoes (A and B); and Gram staining observed under a microscope at 1000X magnification (C). Figure 2. Actinomycetes seen by scanning electron microscope. A: strain CAB9-CA4; B: strain CAB10-J2. Magnification: 6800X and 6000X, respectively. The microscopic characterization by micro- physical-chemical factors of each place that culture showed fragmented mycelia and influence the growth or activity of microor- long spore chains. At Gram staining, Gram ganisms (Li et al., 2018). positive spiral filaments were observed (Fig- Regarding the ability to produce extracellu- ure 1C), typical of the genus Streptomyces. lar enzymes, all strains of actinomycetes Likewise, the observation by scanning elec- showed amylolytic activity (100%); in con- tron microscopy of selected strains allowed trast, only 16 (50%) showed cellulolytic ac- distinguishing branched filaments (Figure tivity. Actinomycetes CAB9-CU4 and 2A) and presence of abundant spores (Fig- CAB10-J2 had the best results of amylolytic ure 2B). and cellulolytic activity, respectively (Figure Oat Agar is not usual for the study of actino- 3). In this regard, Caro (2016) reports similar mycetes; however, it was used in this case results for producers of amylases (89.8%) following the recommendations of Franco- and cellulases (26.5%). Correa et al. (2010), who isolated important native strains of actinomycetes with poten- tial application of Plant Growth Promoting Rhizobacteria (PGPR) from samples of rhi- zospheric soil. Sugar metabolism, hydrolytic activity and growth depending on pH and temperature The results of each test are shown in Table 2. A big number (97%), except for strain CAB7-H5, indicated that they were able to assimilate the three sugars. In contrast, Figure 3. Rhizospheric actinomycetes of potato and its amylolytic (A) and cellulolytic (B) activity. Rico (2009), who also worked with isolated potato actinomycetes, only found that 15% Also, the actinomycetes showed optimal of their isolates could use these sugars. The growth in the pH range from 5.5 to 8.5 and at reason for this difference could be explained the incubation temperature of 28 °C, by the nature of the samples, since they reporting very few strains that could grow at come from different locations, soil types and low temperatures (Table 2). -226- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) Table 2 Metabolic activity on carbohydrates, production of extracellular enzymes and growth based on pH and temperature of rhizospheric actinomycetes isolated from rhizosphere of native potatoes Synthesis of hydrolytic Carbohydrate Assimilation pH Temperature (°C) Strain enzymes Gluc Sac Man Cellulase Amylase 5,5 7,0 8,5 4 28 45 CAB3-C1 + + + - +++ ++ +++ ++ - +++ - CAB3-C2 + + + - +++ ++ ++ ++ - ++ - CAB3-C3 + + + ++ +++ ++ ++ ++ - +++ ++ CAB4-C1 + + + ++ +++ ++ ++ ++ - +++ - CAB4-C2 + + + +++ +++ ++ ++ + - ++ -- CAB4-C3 + + + +++ +++ ++ +++ ++ - +++ - CAB4-C4 + + + - +++ + ++ ++ - ++ - CAB4-C5 + + + - +++ ++ ++ + - ++ - CAB4-C6 + + + - + ++ +++ ++ - +++ - CAB5-F1 + + + ++ +++ ++ +++ ++ - +++ - CAB5-F2 + + + - +++ ++ ++ ++ - ++ - CAB5-F3 + + + - +++ ++ +++ ++ - ++ - CAB5-F4 + + + - ++ ++ +++ ++ - ++ - CAB5-F5 + + + - ++ + ++ ++ - +++ - CAB6-F1 + + + ++ +++ + +++ ++ - ++ - CAB7-H1 + + + - +++ ++ ++ ++ - +++ - CAB7-H2 + + + ++ +++ ++ +++ ++ - +++ - CAB7-H3 + + + + +++ ++ +++ ++ - ++ - CAB7-H4 + + + ++ ++ ++ +++ ++ + +++ - CAB7-H5 - - - + ++ ++ ++ ++ - ++ + CAB8-H1 + + + ++ +++ ++ +++ + - +++ - CAB8-H2 + + + - +++ ++ ++ ++ - ++ - CAB9-CU1 + + + + ++ ++ +++ ++ - +++ - CAB9-CU2 + + + - ++ ++ +++ ++ - ++ - CAB9-CU3 + + + - ++ ++ +++ ++ - ++ - CAB9-CU4 + + + - +++ ++ +++ ++ - +++ - CAB10-J1 + + + - ++ ++ +++ + + +++ - CAB10-J2 + + + - +++ ++ +++ ++ ++ +++ - CAB10-J3 + + + +++ ++ ++ +++ ++ - +++ ++ CAB10-J4 + + + +++ ++ ++ ++ ++ - +++ - CAB10-J5 + + + +++ ++ ++ +++ ++ - ++ - CAB10-J6 + + + +++ ++ ++ +++ ++ + +++ - Carbohydrate Assimilation: positive = +; negative = - Synthesis of hydrolytic enzymes: negative = -; low = +; moderate = ++; good = +++ Growth depending on pH and temperature: negative = -; low = +; moderate = ++; good = +++ -227- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) Table 3 Rhizospheric actinomycetes isolated from native potatoes and their antagonistic activity to Phytophthora infestans in two culture media Percent inhibition (%) Strain Variety Oat Agar Rye Agar CAB3-C1 Canchán 50,0 0 CAB3-C2 Canchán 13,3 0 CAB3-C3 Canchán 0 0 CAB4-C1 Canchán 33,3 0 CAB4-C2 Canchán 26,6 37,5 CAB4-C3 Canchán 16,6 16,6 CAB4-C4 Canchán 33,3 32,8 CAB4-C5 Canchán 57,14 38,0 CAB4-C6 Canchán 11,11 0 CAB5-F1 Futis 16,6 0 CAB5-F2 Futis 44,4 21,05 CAB5-F3 Futis 16,0 0 CAB5-F4 Futis 44,4 0 CAB5-F5 Futis 37,5 0 CAB6-F1 Futis 0 0 CAB7-H1 Huayro 37,3 37,3 CAB7-H2 Huayro 0 0 CAB7-H3 Huayro 0 0 CAB7-H4 Huayro 0 0 CAB7-H5 Huayro 16,6 0 CAB8-H1 Huayro 37,73 0 CAB8-H2 Huayro 33,3 0 CAB9-CU1 Cuchipa-akan 30,43 0 CAB9-CU2 Cuchipa-akan 58,33 0 CAB9-CU3 Cuchipa-akan 0 0 CAB9-CU4 Cuchipa-akan 77,47 30,16 CAB10-J1 Ccompis 39,81 42,31 CAB10-J2 Ccompis 80,05 43,90 CAB10-J3 Ccompis 0 0 CAB10-J4 Ccompis 40,0 0 CAB10-J5 Ccompis 60,0 0 CAB10-J6 Ccompis 60,0 31,07 Figure 4. Anti-Phytophthora infestans activity shown by the actinomycetesCAB9-CA4 (A), CAB10-J2 (B) and CAB5-F5 (C). Rico (2009) reports that, at a pH 5.5 and a actinomycetes (n = 32), 25 (78.1%) showed temperature of 10 °C, 65% of its isolates can activity against P. infestans at least in one of be developed, although with limitations in the two culture media used here. In Oat their development, presenting colonies of Agar, it was possible to observe 25 (78.1%) smaller size than at higher temperatures. On of strains with positive activity, while in the other hand, Cisneros (2016) reports that Centeno Agar only 10 (31.25%) had a none of its isolates could develop at acidic positive result. The percentages of inhibition pHs and low temperatures. These results in- obtained varied in the range from 13.33 to dicate that the physical-chemical character- 80.05%, being strains CAB10-J2 (80.05%), istics of the soil are determinants for the de- CAB9-CU4 (77.47%) and CAB5-F5 (37.5%) velopment of actinomycetes, and that they who pre-sented the highest values of must be taken into consideration when con- inhibition per-centages (Figure 4). ducting tests in field of biological control of Performing a comparative analysis, pests Fonseca et al. (2011) find that, of the total actinomycetes isolated from organic Actinomycete antagonist activity against P. residues of chipaca (Bidens pilosa), only infestans 32% presented antagonistic activity against The results of antagonistic activity tests are P. infestans. It should be noted that these shown in Table 3. From all isolated -228- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) tests were performed on Rye Agar. antagonistic effect wasused directly, which Likewise, Pérez et al. (2015) reported that is not explored in this study, but it is an 42.4% of their isolated actinomycetes from important aspect to consider for future compost showed P. infestans inhibitory researches. activity in Rye Agar. Another similar study PKS gene detection and molecular identifi- was carried out by Caro (2016), indicates cation that 46.9% of actinomycetes isolated from Three of the actinomycetes which had the potato rhizosphere had positive activity best results were selected for the molecular against P. infestans in Rye Agar. In the tests, CAB10-J2, CAB9-CU2 and CAB5-F5, present work, we obtained results of having the 700 bp band of PKS gene (Figure antagonisms superior to those already 5). mentioned; however, it is necessary to specify that these results come from the tests in Oat Agar, which had not been used before for antagonism tests, being a different situation with Rye Agar because it possesses sitosterol, which is necessary for the development of this pathogen (Fonseca et al., 2011). Some other microorganisms with direct anti- Phytophthora activity have been described. Potential biocontrol candidates for which inhibitory activity against P. infestans was demonstrated include Trichoderma sp., Pythium oligandrum, Bacillus sp. and Pseudomonas sp. (Mariastuti et al., 2018; De Vrieze et al., 2019), which could have in vitro inhibition results superior to those obtained in this study; however, it is necessary to Figure 5. PCR electrophoresis gel indicating PKS gene amplification (700 bp). Lane 1: CAB10-J2. Lane 2: CAB9- emphasize that in many of them the CU2. Lane 3: CAB5-F5. MW: Molecular-weight size secondary metabolite that causes the marker. Figure 6. Phylogenetic tree of 16S rDNA gen of actinomycetes isolated from native potato constructed with MEGA7. -229- A. Chumpitaz et al. / Scientia Agropecuaria 11(2): 223 – 231 (2020) These were selected for sequencing of 16S introducciones de tomate silvestre. Revista U.D.C.A rRNA gen, identifying strains CAB10-J2 and Actualidad & Divulgación Científica 19(1): 45-54. Caro, J. 2016. Capacidad antagonista de actinomicetos CAB9-CU2 as Streptomyces luteoverticilla- aislados de la rizósfera de la papa (Solanum tus with 99% of similarity, while strain CAB5- tuberosum sp. andigena) para el control de hongos F5 was identified as Streptomyces sp. with fitopatógenos de importancia agrícola. Tesis de grado, Universidad Nacional Mayor de San Marcos, 99% of similarity (Figure 6). The sequences Lima. Perú. 120 pp. of these three strains were deposited in the Cisneros, J. 2016. Aislamiento y selección de GenBank database (Access numbers: actinomicetos rizosféricos con potencial aplicación MN416404.1, MN416403.1 and MN4164 como bioinoculante en el cultivo de Solanum tuberosum sp. andigena (Papa). Tesis de grado, 12.1). Universidad Nacional Mayor de San Marcos, Lima. About S. luteoverticillatus, it is known as a Perú. 93 pp. major producer of antifungal compounds Chen, P.; Zhang, C.; Ju, X.; et al. 2019. Community Composition and Metabolic Potential of Endophytic like Carbazomycin B (Feng et al., 2019), Actinobacteria From Coastal Salt Marsh Plants in which would explain the positive antago- Jiangsu, China. Front Microbiol. 10: 1063. nistic effect on P. infestans described in this Colona, E.; Galindo, N.; León, J.; et al. 2014. Desarrollo work. de un método para la observación de actinomicetos por microscopía electrónica de barrido. En XXIII Reunión Científica ICBAR, Perú, 12-14 ago, 2014. 4. Conclusions De Vrieze, M.; Gloor, R.; Codina, J.; et al. 2019. Biocontrol Activity of Three Pseudomonas in a Newly The results of this work provide important Assembled Collection of Phytophthora infestans data from in vitro tests, although additional Isolates. Phytopathology 109(9): 1555-1565. studies of Streptomyces and its secondary Di Francesco, A.; Milella, F.; Mari, M.; et al. 2017. A preliminary investigation into Aureobasidium compounds are required that lead to pullulans as a potential biocontrol agent against effective practical formulations for field Phytophthora infestans of tomato. Biological control application. The potential of Streptomyces 114: 144-149. 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Efecto bioinoculants of easy elaboration and low antagónico in vitro de actinomicetos aislados de cost to increase the yield and reduce the purines de chipaca (Bidens pilosa L.) frente a losses by pests of this tuber. Phytophthora infestans (Mont) de Bary. Rev. Fac. Nal. Agr. Medellín 64(2): 6111-6119. Franco-Correa, M. 2009. Utilización de los actinomicetos Acknowledgment en procesos de biofertilización. Revista Peruana de To Vicerrectorado de Investigación y Posgrado Biología 16(2): 239-242. (VRIP) of National University of San Marcos, for its Kumar, S.; Stecher, G.; Tamura, K. 2016. MEGA7: financing through the Undergraduate Thesis Molecular Evolutionary Genetics Analysis Version o 7.0 for Bigger Datasets. Molecular Biology and Promotion Fund (Project: B17100244a) (RR N Evolution 33(7):1870-1874. 06369-R-17) and Alejandro Delgado León, potato Li, L.; Xu, M.; Eyabuk, M.; et al. 2018. 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