Abstract:
Commercial cultivation of passion fruit (Passiflora edulis) is becoming a
growing industry in Hambantota, Galle and Kalutara districts in Sri Lanka
due to increasing demand from industry for processing. Recently, a
previously unreported severe mottling on yellow passion fruit was reported
from the Fruit Research and Development Institute in Horana. Mottling was
observed only on the fruit skin while fruit size appeared normal compared
to symptomless fruits. Objectives of this study were to screen the
symptomatic passion fruit plants for association of any viruses with the
disease and select passion fruit lines exhibiting resistance to the disease.
Crude sap extracted from leaves of symptomatic vines was serologically
tested using enzyme-linked immunosorbent assays (ELISA). ELISA
confirmed that the causal agent belongs to the genus Potyvirus and
serologically related to Sri Lankan passion fruit mottle virus (SLPFMV).
Reverse transcription polymerase chain reaction was conducted using total
RNA extracted from leaf tissues of symptomatic vines. Due to the
unavailability of SLPFMV sequences on the database for primer designing,
a pair of degenerate primers for potyviruses (PNIbF5, PCPR1) which
amplifies a region between coat protein and nuclear inclusion b protein was
used. Sequencing of an amplicon of approximately 500 bp did not match to
any sequence on the NCBI/GenBank. A disease index was prepared by
visual observation of fruits and rating of symptom severity. Comparison of
disease index and ELISA showed that there is no correlation between
symptom severity and virus titer. Passion fruit lines that rated zero
percentage disease index but containing high virus titer were identified as
plant lines that exhibited high resistance for mottling.
