Detection of Phytophthora nicotianae from annual vinca and tomato using a species-specific LAMP assay

Phytophthora nicotianae affects many floriculture crops and is an important pathogen of tomato and potato. Foliar symptoms of P. nicotianae on tomato and potato are similar to those caused by P. infestans , the causal agent of late blight. Species-specific detection assays are important for early deployment of appropriate management practices. A previously published LAMP assay specific for P. nicotianae was modified to improve the reaction time and application of the LAMP assay for use on vegetable and floriculture crops. The improved LAMP assay was specific for P. nicotianae , did not detect other Phytophthora species found on tomato, potato, or floriculture crops, and was 100% accurate and precise. The limit of detection was 100 fg/µl. P. nicotianae was detected 100% of the time in mixed samples with P. infestans . The LAMP reaction time was reduced to within 15 min by adding F-loop/B-loop primers. To understand if the presence of systemic fungicides would inhibit detection of P. nicotianae by LAMP assay, leaves of inoculated annual vinca plants treated with or without three systemic fungicides (cyazofamid, mefenoxam, or oxathiapiprolin) were compared to culturing on a semi-selective medium and Agdia ImmunoStrip® Phytophthora tests. P. nicotianae was detected 100% of the time in annual vinca leaves treated with the systemic fungicides. In contrast, detection by ImmunoStrips® and/or culturing ranged from 80 to 100% and 60 to 100%, respectively. The P. nicotianae specific LAMP assay may help diagnosticians detect the pathogen rapidly and differentiate it from P. infestans .