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

Resumen

Objective: To determine the bacterial diversity in the rhizosphere of coffee (Coffea arabica L.) in coffee plantations in Oaxaca, Mexico.

Design/methodology/approach: Soil samples collected from organic arabian coffee plantations in the Loxicha region of Oaxaca were analyzed to isolate and characterize bacterial populations associated with the rhizosphere of those plantations. Samples were collected from six sites in three altitude ranges (two sampling sites per each range): low (≥1,200, ≤1,400 masl), medium (≥1,700, ≤1,800 masl), and high (≥1,900 masl). Tukey’s test was used to compare the bacteria population distribution per altitude range.

A multivariate analysis (Principal Component Analysis and Hierarchical Cluster Analysis) was performed considering four morphological —shape, surface, border, and color— and two microscopic —type and Gram— characteristics of the colonies.

Results: Forty-three bacterial colonies were isolated and purified; their population distribution showed a significant difference (Tukey α = 0.5) with respect to the altitude range in which they were collected. The Principal Components Analysis showed that the first three principal components accounted for 74.19% of the total variation of the 43 bacterial colonies, indicating that the evaluated characteristics were widely distributed. The Hierarchical Cluster Analysis determined eight groups and divided them into subgroups, based on the semi partial correlation coefficient (0.05).

Study limitations/implications: The environmental conditions where bacteria grow allow changes in the interspecific variation of each species.

Findings/conclusions: The morphological and microscopic characterization of the bacterial colonies shows a high variability that is expressed in characteristics, indicating a high diversity of bacterial species in organically-managed coffee soils in Oaxaca