Nuclear DNA from uninfected or potato spindle tuber viroid-infected tomato plants contains no detectable sequences complementary to cloned double-stranded viroid cDNA.

High molecular weight tomato nuclear DNA was isolated from uninfected and potato spindle tuber viroid (PSTV)-infected tomato leaves. Restriction digests were fractionated on agarose gels, denatured and transferred to diazobenzyloxymethylpaper, and hybridized to 32P-labeled cloned double-stranded PSTV cDNA. No hybridization to DNA from either uninfected or infected tissue could be detected under conditions that permitted detection of cloned double-stranded PSTV cDNA at a concentration equivalent to one-fifth copy of PSTV-related DNA per haploid tomato genome. Hybridization of tomato DNA to 32P-labeled cloned soybean 18S and 28S ribosomal DNA sequences showed that the restricted nuclear DNA was suitable for hybridization to probes containing homologous sequences. Our results indicate that neither PSTV nor its complementary strand is transcribed from nuclear DNA but do not rule out the possibility of sequence homology between host DNA and a small portion of PSTV or its complement.