Bacteria associated with the rhizosphere of manganese-deficient date palms affected by brittle leaf disease.

Abstract

Brittle leaf disease or “Maladie des feuilles cassantes” (MFC) is a disorder affecting date palm (Phoenix dactylifera) orchards in oases of southern Tunisia. No causal pathogen has yet been identified, despite search for nematodes, fungi, bacteria, viruses and viroids. Although the soils of the oases in which affected palms grow have similar contents of total and exchangeable manganese (Mn) compared with oases with no disease, the leaflets of affected palms are deficient in this element. Here, we characterized the bacterial flora in the rhizosphere of three MFC-affected date palms and three non-affected controls. Our results show a high bacterial diversity in the date palm rhizosphere. From 201 clones corresponding to a 16S rDNA PCR fragment, we identified 177 different bacterial phylotypes. Some of them corresponded potentially to Mn-oxidizing bacteria that may be involved in soil Mn oxidation and, consequently, deplete this micronutrient in MFC-affected date palms. More detailed studies are necessary to establish the exact role of these bacteria in the disease syndrome.