1a.Objectives (from AD-416)
The goal of this project is to confirm reliability of a newly developed detection method; attempt development of a rapid serological test for tombusviruses causing dieback disease in lettuce (long-term and will depend in part on success of molecular test); determine if it will be possible to monitor levels of tombusviruses in soil using commercial soil nucleic acid testing kits; and develop more cost-effective and reliable methods for greenhouse-based testing for tombusvirus resistance in lettuce.
1b.Approach (from AD-416)
Lettuce will be sampled from a diverse array of dieback infested fields from throughout the Salinas Valley and other regions; we will determine if our new molecular detection method can confirm infection more reliably and timely than previous methods. We will test commercial kits for extracting nucleic acid from soils to determine if it is possible to A) detect TBSV and LNSV from soils, and B) quantify levels from different soils and determine correlation with disease incidence in the fields (multi-year objective). Finally, we plan to test a new method for rapid greenhouse pre-screening of lettuce cultivars/lines for tombusvirus resistance.
This project was initiated during the summer of 2010, and has made significant progress toward the goal of a reliable greenhouse testing method. Previous studies demonstrated that the viruses responsible for lettuce dieback produce different symptoms when lettuce is infected through the soil than when the lettuce is inoculated by rubbing leaves with plant sap. Although root infection results in lettuce dieback symptoms, manually rubbing leaves with virus infected sap at ambient temperature and standard lighting conditions has been shown to produce necrotic local lesions on the inoculated leaf, but no systemic infection (infection of entire plant). However, recent through this project have shown that rub-inoculation of plants maintained at high temperature and 24 hour day length resulted in full systemic infection of nearly all inoculated plants, resembling lettuce dieback symptoms from the field. Further studies are attempting to clarify whether day length or temperature is the primary determinant for the ability of the viruses to infect systemically, and whether these conditions will facilitate selection of resistant materials. Experiments in progress are comparing high and low temperature with 24 hour day length, as well as differential day length at high temperatures previously shown to induce systemic infection, and whether this method will allow effective differentiation of resistant and susceptible genetic materials.