Quantification of Mirafiori lettuce big‐vein virus and its vector, O lpidium virulentus , from soil using real‐time PCR

Big vein disease of lettuce ( L actuca sativa ) is an economically important disease transmitted through soil by O lpidium virulentus , and has occurred in most production areas worldwide. The disease is assumed to be caused by M irafiori lettuce big‐vein virus ( M i LBVV ). To understand the dynamics of the virus and its vector, M i LBVV and O . virulentus were directly detected in soil. DNA and RNA were extracted from 5 g soil using a bead beating method, followed by purification using adsorption to a column. Detection and quantification were performed using real‐time PCR and a TaqMan probe that was prepared based on the CP region of M i LBVV and the r DNA ‐ ITS region of O . virulentus , respectively. Furthermore, using a visual assessment of the incidence rate of big vein disease on lettuce in agricultural fields, the C t values of M i LBVV and O . virulentus from soil were also determined using real‐time PCR . The results showed that M i LBVV concentrations in the soil were high in the field, as also determined by a visual assessment of the incidence rate of big vein disease on lettuce. However, the amount of O . virulentus in soil was not directly correlated with the incidence of M i LBVV . From these results, it is suggested that the risk of lettuce crops developing big vein disease can be estimated using an index of the amount of M i LBVV in the soil.