Identification of Piper yellow mottle virus, a mealybug-transmitted badnavirus infecting Piper spp. in Southeast Asia

A previously undescribed badnavirus was found to be a causal agent of a disease of black pepper (Piper nigrum) in Malaysia, the Philippines, Sri Lanka and Thailand, and was also associated with a disease of betelvine (P. betle) in Thailand. Disease symptoms included chlorotic mottling, chlorosis, vein-clearing, leaf distortion, reduced plant vigor and poor fruit set. The virus, named Piper yellow mottle virus (PYMV), had non-enveloped bacilliform virions averaging 30 x 125 nm in size and containing a double-stranded DNA genome. An isolate of PYMV from Thailand was transmitted by mechanical inoculation and by the citrus mealybug, Planococcus citri, from infected P. nigrum and P betle to healthy P. nigrum seedlings, which developed symptoms similar to those observed in naturally-infected plants. A serological relationship between PYMV and isolates of banana streak (BSV) and sugarcane bacilliform (ScBV) viruses, but not six other badnaviruses, was detected by immunosorbent electron microscopy (ISEM). Genomic PYMV sequences were amplified by polymerase chain reaction (PCR) using badnavirus-specific oligonucleotide primers, and sequence analysis comparisons of the putative reverse transcriptase (RT) domain showed PYMV to be closely related to other mealybug-transmitted badnaviruses. Black pepper infected with PYMV sometimes contained one or more isometric virus-like particles, and PYMV may therefore be only one component of a virus complex infecting black pepper in Southeast Asia.