Climatic variations influence the dynamic of epiphyte bacteria of baby lettuce

Abstract

The objective of the present work was to study the relationship between the dynamic of epiphyte bacteria and the climatic variations in three varieties of pigmented baby lettuce (Lactuca sativa) harvested during 16 consecutive weeks, between February and May, which corresponded with the most important growing period for this crop in the south of Spain. Bacterial counts of the main groups (aerobic bacteria, Pseudomonas and coliforms) were enumerated by plating on the appropriate culture media. Concurrently, characterization of the culturable bacterial community present on the leaf surface was performed by partial sequence analysis of the 16S rRNA gene. To relate bacteria counts with weather variation first the main weather modes by principal component analysis (PCA) of climatic variables were characterized. Then, multiple linear regression models, with bacteria count as the dependent variable and the PCA factors as the independent variables, were built. The results obtained showed that the diversity and abundance of the epiphytic community of baby lettuce were affected by the climate variations. However, other factors such as the environment and the agricultural practices may play a role because the R2 obtained was relatively low. Thus, the harvest week as well as the variations in radiation, rainfall and relative humidity (RH) explained part of the observed differences. Pseudomonas growth was influenced by the variations in radiation, rainfall, wind and temperature, the latter being the most relevant variable. Coliform growth was influenced by variations in temperature and RH. Bacillus and Pseudomonas were the most predominant genera identified among the isolates, their growth showing a negative correlation (P<0.01) through the weeks of the study in two of the three lettuce varieties evaluated. Given the diverse functions of phyllospheric microbes, understanding the variations of specific communities such as Pseudomonas spp. due to the climate change could help to understand the different susceptibilities of crops to be affected by spoilage or pathogenic bacteria.