Biological, Physical, and Molecular Properties of a Papaya lethal yellowing virus Isolate

Papaya (Carica papaya) is an important tropical fruit crop in northeastern Brazil. Lethal yellowing is a disease caused by Papaya lethal yellowing virus (PLYV) that occurs only in northeastern Brazil. The symptoms are characterized by progressive leaf yellowing and greenish circular spots on the fruits. The virus has isometric particles (30 nm), genomic single-stranded (ss)RNA (1.6 × 10⁶ Da), and a coat protein with a single component (35 kDa). Although no biological vector has been confirmed, the virus is spreading every year. In the present study, an isolate of the virus was characterized biologically, serologically, physically, and molecularly, and its survival in dried tissue was evaluated. Approximately 309.5 mg of virus was purified per kilogram of infected papaya leaves, and a high-titer polyclonal antiserum (1:1,024,000) was obtained from an immunized rabbit. The virus was detected in dried roots and leaves maintained up to 120 days. Its physical properties were thermal inactivation point (80°C), longevity in vitro (60 days), and dilution end point (10^-6). The virus was inactivated in leaves and roots eradicated from infected plants when they were submitted to a solarization period of 12 days, but maintained its infectivity when leaves and roots were maintained over the soil at natural conditions for 32 days. Among 58 plant species from 13 botanical families, the PLYV isolate infected only C. papaya, Jacaratia heterophylla, J. spinosa, Vasconcella cauliflora, V. quercifolia, and V. monoica, all from the family Caricaceae. A fragment of 1,098 nt of the virus isolate, corresponding to the 3' replicase (RdRp) and 5' coat protein (CP) cistron, was cloned and sequenced. Phylogenetic analysis of the RdRp nucleotide sequences indicated some similarity of PLYV with members of the genus Sobemovirus.