Asociación de cepas fijadoras de nitrógeno de vida libre, con recursos genéticos de pastos para zonas áridas

Abstract

Para evaluar microorganismos de la rizosfera de Bouteloua curtipendula (Michx.) Torr., se recolectó suelo de cinco localidades 1) Salinas, San Luis Potosí 2) Ejido, Jacalón, Salinas, San Luis Potosí; 3) Calera, Zacatecas; 4) Santa María del Oro, Durango y 5) Crucero La Zarca, Durango. La población de actinomicetos, bacterias y hongos, se estimó con diluciones seriadas (10-1 a 10-10). Los actinomicetos (AS), bacterias (BS) y hongos (HS) se estimaron con diluciones 10-3 a 10-5; 10-5 a 10-7; 10-2 a 10-4, respectivamente, con cinco repeticiones. Las siembras en placa se incubaron a 30 °C. Las unidades formadoras de colonias de bacterias (ufc) se cuantificaron a 24, 48 y 72 h; mientras que, para actinomicetos y hongos, las ufc se cuantificaron a 7, 8 y 9 d. En dos medios de cultivo, crecieron bacterias fijadoras de nitrógeno, las cuales se caracterizaron morfológicamente. Para determinar el efecto de la inoculación de bacterias sobre recursos forrajeros nativos, se evaluaron los tratamientos: cepa a66 (C1), I27 (C2), I95 (C3), S73 (C4) y ZA40 (C5), consorcio (C6), mezcla de las cepas anteriores y (C7) testigo, sin inoculación de bacteria. Se inocularon semillas, en prueba de germinación, para determinar asociatividad con el pasto; también, se inocularon dos genotipos de pasto (G1, La Zarca) y (G2, genotipo 5) para estimar el rendimiento de materia seca. Se encontraron poblaciones de AS con 4.2, 9.0, 5.1, 2.4 y 8.4 x 104 ufc g-1 suelo seco-1; para BS, de 0.5, 1.8, 1.9, 1.5 y 1.2x105 ufc g-1 suelo seco-1; para HS de 0.1, 0.3, 0.2, 0.4 y 0.5x103 ufc g-1 suelo seco-1 para las localidades 1, 2, 3, 4 y 5, respectivamente. En la inoculación, se observaron diferencias (P<0.01) a 14 días después de la siembra (dds) 43, 34, 32, 33, 35, 39 y 78% de germinación en a66, I27, I95, S73, ZA40, Consorcio y testigo, respectivamente. En inoculación, las alturas para C1, C2, C3, C4, C5, C6 y C7 mostraron promedios de 28.4, 29.7, 32.0, 35.1, 30.9, 38.4 y 31.3cm, respectivamente. El consorcio fue el que presentó los mayores valores en germinación y altura de planta. _______________ FREE LIVING BACTERIAL STRAINS ASSOCIATION CAPABILITY WITH GRASS GENETIC RESOURCES, FOR ARID LANDS. ABSTRACT: In order to evaluate rhizospheric microorganisms to Bouteloua curtipendula (Michx.) Torr., soil was collected from five locations 1) Salinas, San Luis Potosí; 2) Ejido, Jacalón, Salinas, San Luis Potosí; 3) Calera, Zacatecas; 4) Santa María del Oro, Durango; 5) La Zarca, Durango. The population of actinomycetes, bacteria and fungi, was estimated through serial decimal dilutions (10-1 a 10-10). Actinomycetes (AS), bacteria (BS) and fungi (HS) were estimated through 10-3 to 10-5; 10-5 to 10-7; 10-2 to 10-4 dilutions, respectively with five replicates. Plating microorganisms were incubated at 30 °C. Bacterial colony forming units (cfu) were quantified at 24, 48 and 72 h; while actinomycetes and fungi, cfu were quantified 7, 8 and 9 d. Two culture media were used to increase nitrogen fixing bacteria, which were characterized morphologically. In order to define the inoculation effect of bacterial strains on native grasses, several microorganism strains were evaluated: a66 (C1), I27 (C2), I95 (C3), S73 (C4) and ZA40 (C5); consortium (C6), a mixture of all the strains, and (C7) as placebo. In order to define microorganism-plant associativity, germination test were evaluated through seed inoculation and two grass genotypes were inoculated: G1 (La Zarca) and G2 (Genotipo 5) for dry matter production. Populations of AS were detected with 4.2, 9.0, 5.1, 2.4 and 8.4 x 104 cfu g-1 dry soil. For BS, detected levels were 0.5, 1.8, 1.9, 1.5 and 1.2x105 cfu g-1 dry soil; for HS, detected levels were 0.1, 0.3, 0.2, 0.4 and 0.5x103 cfu g-1 dry soil for sites 1, 2, 3, 4 and 5, respectively. Differences were detected for inoculation level (P<0.01) at 14 days after sowing (das) 43, 34, 32, 33, 35, 39 and 78% germination was registered for a66, I27, I95, S73, ZA40, consortium and control, respectively. Plants height was different (P<0.01) strains C1, C2, C3, C4, C5, C6, and C7 showed averages of 28.4, 29.7, 32.0, 35.1, 30.9, 38.4 and 31.3 cm, respectively. The consortium showed the highest values for germination and forage yield.