PCR-based methods for detection of Erwinia psidii on guava

Abstract

Erwinia psidii causes bacterial blight of guava (Psidium guajava), one of the most important diseases of this crop in Brazil. Control measures are not effective, and dissemination often occurs through contaminated but asymptomatic propagating plant material. Considering the need for a reliable and sensitive method for detecting the pathogen in asymptomatic plant material, E. psidii-specific PCR primers were designed from a 355-bp fragment of the recombinase A gene (recA) amplified from E. psidii type strain. Primer pair Ep2L/2R only amplified DNA from E. psidii and its detection limit was 10−5 ng/μL of purified DNA and 10 CFU (colony forming units) of bacterial cell suspension/mL. Three methods, conventional PCR, IC-PCR, and BIO-PCR were evaluated with the selected primers for their potential to detect E. psidii on guava leaves. BIO-PCR and conventional PCR were more sensitive and less time-consuming than IC-PCR. The detection limits on extracts of macerated guava leaves spiked with bacterial suspensions at different concentrations were 10 and 103 CFU/mL for BIO-PCR and conventional PCR, respectively. The PCR method here described could be useful for developing a protocol for early detection of this pathogen in asymptomatic guava plants.