Etiology of stem rot on Hylocereus spp. cause by Enterobacter hormaechei in Costa Rica.

Abstract

In 2011 infected samples were examined to identify the causal agent of stem rot of Hylocereus costaricensis in Costa Rica. During the rainy season, symptoms associated with the disease included a small yellowish rot that typically started from the edge of the cladodium and extended inward towards the stem. Eventually the whole stem decayed. During the dry season, orange circular spots appeared on the stem, turning dark brown. For determine the causal agent, were collected 25 samples of each type of decay, complete cladodes with different stages of symptom development, from which 15 isolations of each disease were made. A bacterium was obtained consistently from each symptomatology, with which the identification, characterization based on biochemical tests and molecular identification was carried out, as well as the verification of Koch’s postulates. Results indicated that the symptoms were caused by the same bacteria. Based on sequencing of the 16S region, the bacterium showed 99.2% similarity with Enterobacter hormaechei (KJ999997). According to Koch’s postulates, a similar symptomatology was obtained on plants from the field and on inoculated plants. This is the first report of this pathogen causing damage to the stem of Hylocereus costarricensis in American continent.