INTERSTRAIN PSEUDORECOMBINANTS OF COWPEA CHLOROTIC MOTTLE VIRUS - EFFECTS ON SYSTEMIC SPREAD AND SYMPTOM FORMATION IN SOYBEAN AND COWPEA

Full-length complementary DNA (cDNA) copies of genomic RNA1, RNA2, and RNA3 segments of cowpea chlorotic mottle virus (CCMV) strains D, N, a nd S were synthesized using polymerase chain reaction and were cloned downstream of a T7 RNA polymerase promoter. Mixtures of the homologous in vitro-transcribed RNAs produced typical CCMV symptoms when inocula ted on soybean (cv. Bragg) and cowpea (cv. California Blackeye) plants . Using either gel-purified or in vitro-transcribed CCMV RNA component s, the pseudorecombinants SSD, SSN, DDS, and NNS were constructed. The properties of these pseudorecombinants were tested by comparing the i nduced symptoms, virus concentration, and systemic spread. These studi es revealed a direct involvement of RNA3 genetic information in necrot ic lesion formation and in breakage of CCMV resistance in soybean. Exc hanges between RNA1 or RNA2 components further affected the biological features of reasserted CCMV variants. The true nature of the pseudore combinants was confirmed by reconstitution of the parental strains fro m the corresponding pseudorecombinant RNA components.