Determination of bacteria morphotypes associated with the rhizosphere of organic coffee plantations

Abstract

Objective: To determine bacterial diversity associated with the coffee rhizosphere on coffee plantations on Oaxaca, Mexico.

Design/methodology/approach: Soil samples collected from organic arabic coffee plantations in the Loxicha region of Oaxaca were analyzed to isolate and characterize populations of bacteria associated with the rhizosphere of the plantations. Six sites were sampled in three altitudinal ranges; low (≥1200, ≤1400 masl), medium (≥1700, ≤1800 masl) and high (≥1900 masl); two sites per rank. The population distribution of the bacteria by altitudinal range was compared using the Tukey test. A multivariate analysis (Principal Component Analysis and Hierarchical Cluster Analysis) was performed considering four morphological characters of the colonies: Shape, Surface, Border and Color, and two microscopic characters: Type and Gram.

Results: 43 bacterial colonies were isolated and purified, whose population distribution showed a significant difference (Tukey α = 0.5) with respect to the altitudinal range of collection. The Principal Component Analysis showed that the first three principal components expressed 74.19% of the total variation of the 43 bacterial colonies, indicating a wide distribution of the bacterial colonies from the evaluated characters. The Hierarchical Cluster Analysis determined eight groups divided into subgroups based on the semipartial correlation coefficient of 0.05.

Limitations on study/implications: The environmental conditions where bacteria grow allow the interspecific variation of each species to change.

Findings/conclusions: The morphological and microscopic characterization of the bacterial colonies shows the existence of a high variability that is expressed in characters that indicate high diversity of bacterial species in organically managed coffee soils in Oaxaca.