Identification of Small Single- and Double-Stranded RNAs Associated with Severe Symptoms in Beet Western Yellows Virus-InfectedCapsella bursa-pastoris

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Abstract
An isolate (ST9) of beet western yellows virus (BWYV) that caused severe stunting symptoms in infected plants of C. bursa-pastoris was compared with 2 isolates (ST1 and STFL) that caused typical symptoms. Yields of purified virions were 10 times greater from C. bursa-pastoris infected with ST9 than with ST1 or STFL. Purified ST9 virions contained 2 single-stranded (ss-) RNA of 1.9 and 0.93 .times. 106 MW; ST1 and STFL virions each had only 1 ss-RNA of 1.9 .times. 106 MW. The ST9-infected plants also contained 2 prominent double-stranded RNA (ds-RNA) that were not found in ST1- or STFL-infected plants. These RNA were 2.2 .times. 106 MW and smaller than 4.6 .times. 105 MW. Both new ds-RNA were present in much higher concentrations than were the other ds-RNA from the ST9- or STFL-infected plants. No differences in proteins or densities were detected between the ST9 and the STFL or ST1 virions. The association of the extra RNA with the ST9 isolate and the resulting severe symptom development on C. bursa-pastoris is discussed.