Changes in symptoms, disease incidence and virus level during the development of papaya ringspot virus (PRSV) infection in papaya (Carica papaya L.)

Issue Date

12-2009

Abstract

The dynamics of Papaya ringspot virus (PRSV) infection including the conditions affecting disease development in a susceptible papaya variety and the resulting changes in symptoms, incidence of infection and virus level through time were determined in order to establish a standard and reliable method for assessing PRSV resistance in papaya. 'Solo' papaya seedlings of different ages were mechanically inoculated under different disease pressure (virus inoculum dilution). Two-month old seedlings inoculated with 1:5 inoculum dilution had disease onset at 7 days post inoculation (dpi) when 70% of the plants had symptoms, and were confirmed positive to PRSV in enzyme-linked immunosorbent assay (ELISA). Symptoms appeared on the newly emerged leaves above the point of inoculation where the first youngest fully-developed leaf had early symptoms of mottling. The mottling symptom developed into mosaic at 15 dpi; then the mosaic became severe and vein banding appeared on the youngest fully-developed leaf at 20 dpi;. At 25 dpi, most of the leaves had severe mosaic and became deformed with shoe stringing symptom at 30 dpi. The incidence of infection became 100% starting at 10 dpi and did not change until 30 dpi. Based on ELISA absorbance value, virus accumulated in a cyclic-like manner resulting to changes in virus levels through time after inoculation. Absorbance value increased from 5 to 10 dpi, peaked at 15 dpi, then decreased at 20 dpi until 25 dpi, and increased again at 30 dpi. Higher inoculum dilution and older seedling at inoculation could reduce incidence of infection. Four-and 6 month old seedlings inoculated with 1:5 inoculum dilution had lower disease incidence of 45 and 20%, respectively, compared with 100% infection in the inoculated 2-month old seedlings. Incidence was further reduced with higher inoculum dilutions of 1:25 and 1:50. The PRSV was detected by reverse transcription-polymerase chain reaction (RT-PCR) but not by ELISA in asymptomatic samples collected at 5 dpi when virus level was presumably low. The expected 850 bp fragment of PRSV coat protein gene was amplified in total RNA from asymptomatic samples. There was no close association found between virus level and symptom severity.

Source or Periodical Title

Philippine Journal of Crop Science

ISSN

0115-463x

Volume

34

Issue

3

Page

11-20

Document Type

Article

Frequency

tri-quarterly

Physical Description

tables, graphs, pictures

Language

English

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