Bacterial Species as Causative Agents Involved in Pistachios Dieback in Iran

Abstract

Pistachio dieback (DBP) is a significant disease affecting pistachio trees in Iran, and it has emerged as a serious problem in Kerman province in recent years. This study investigates the role of bacteria as causal agents of DBP under laboratory and field conditions. Samples were collected from infected pistachio orchards in Kerman province from 2015 to 2016. The ability of bacterial isolates to induce disease and colonize vascular tissues was studied using various inoculation methods. Identification of isolates was carried out using biochemical and physiological assays, amplification of the 16S rDNA region, and partial analyses of the gyrA gene. A total of 281 bacterial isolates were obtained from infected trees, of which 148 induced a hypersensitivity reaction on tobacco leaves. Among these, 128 isolates were able to colonize vascular tissues in sub-bark inoculations of pistachio branches under laboratory conditions. In field experiments, 24 selected isolates were able to spread in vascular tissues of pistachio branches and twigs using sub-bark and apical inoculation methods, although disease severity varied. Staphylococcus pasteuri, Bacillus pumilus, Bacillus sp., Acinetobacter radioresistens, Xanthomonas sp., Curtobacterium flaccumfaciens, Pseudarthrobacter oxydans, and Pseudomonas koreensis were identified as being involved in the dieback of pistachio trees. This work demonstrates that a wide range of bacterial genera and species may be involved in DBP, and urgent strategies should be considered for managing the disease.

Keywords

• pathogenicity
• pistacia vera
• bacterial pathogens
• crop damage