Review of diagnosis techniques for Brenneria spp in walnut (Juglans regia)

Abstract

Brenneria nigrifluens and B. rubrifaciens cause superficial and deep canker in walnut bark, respectively. B. nigrifluen causes necrosis in the outer bark and scattered dark brown exudate spots. The symptoms of Brenneria nigrifluens involve holes in the wood, deep longitudinal cracking in the trunk; dark brown bacterial exudate flowing through branch cracks, and eventually the two diseases can cause loss of vigor and death of the trees. Walnut canker caused by Brenneria species has been reported in USA, France, Spain, Italy, Hungary, Persia and Iran. These symptoms have not been reported in Mexico; however, SENASICA (National Service of Health, Food Safety and Food Quality) has developed risk maps to prevent Brenneria, since walnut in Mexico is a profitable crop that reached 125 758.45 tons in 2014, equivalent to more than 6 173 538 million pesos. Due to Brenneria’s bacterial pathogenicity timely diagnosis is crucial to achieve good disease management. The main diagnosis methods for Brenneria genera are: Traditional techniques, biochemical test (API system, Biolog and fatty-acid cell analysis); the serological technique; molecular methods such as end-point PCR and real-time PCR; as well as chromatographic techniques (HPLC, CCD) for the detection of specific metabolites like rubrifacine. The purpose of this work is to provide an outlook of domestic and global walnut canker, as well as reviewing the diagnosis techniques for this disease.