Pathogenic interactions between variants of cauliflower mosaic virus and Arabidopsis thaliana

Pathogenic interactions between genetic variants of cauliflower mosaic virus (CaMV) and Arabidopsis thaliana were! characterized to identify combinations potentially useful in molecular genetic analysis. Infections of a glabrous mutant (g/1) of Arabidopsis ecotype Columbia (Col-0 g/1) by 30 CaMV isolates were assessed by recording symptom character. Thirteen isolates failed to cause symptoms; the remainder induced symptoms that varied between mild and very severe. Sl,me CaMV isolates produced symptoms in Arabidopsis that differed significantly in severity or character from those produced in a standard host Brassica rapa (turnip). A greater variety of symptom types was observed in a single Arabidopsis ecotype infected with a range of CaMV isolates than was found in a range of Arabidopsis ecotypes infected with a single, typical CaMV isolate (Cabb B-JI). One isolate, Bari-1, that was asymptomatic but accumulated virus in Arabidopsis ecotype Col-0 g/1, caused mild symptoms in ecotype Ler g/1. A hybrid virus constructed from CaMV isolates Cabb B-JI and Bari-1 produced symptoms; in Arabidopsis variants that were more severe than in either parental isolate. From a screen of EMS-mutagenized Arabidopsis, one mutant (Col-0 dv1) with a pale-green, dark-vein phenotype which had an altered symptom response to CaMV, was isolated. From this;, a phenotypically near-normal revertant (Col-0 dv1R) spontaneously arose, but which showed altered responses to CaMV. Infection of Col-0 dv1R by CaMV isc,late Bari-l elicited symptoms unlike the parent Arabidopsis ecotype (Col-0 g/1. Also, Col-0 dv1 and Col-0 dv1R expressed an uncharacteristic necrotic reaction to CaMV.