Correlation of lesion size with percent lesion coverage on camellia and rhododendron leaves inoculated with Phytophthora ramorum

• Published in: Phytopathology Vol. 96; no. 6; pp. S114 - S115
• Main Authors: Tjosvold, SA, Chambers, D L
• Format: Journal Article
• Language: English
• Published: 01.06.2006
• Subjects: Camellia; Phytophthora; Rhododendron
• ISSN: 0031-949X

Assess: Image Analysis Software for Plant Disease Quantification (American Phytopathological Society) can be used to determine lesion size and percent lesion coverage on diseased leaves. Lesion size analysis requires that an area-standard be present within the digital leaf image and extra steps during analysis, while percent lesion coverage analysis does not. Since the latter parameter is simpler to obtain, it would be desirable to use it for certain uses if it correlated adequately with lesion size. As part of our field experiments to determine lesion growth rates on leaves infected with Phytophthora ramorum in different seasons, we digitally analyzed lesions of infected leaves using these two parameters. Beginning with uniformly-inoculated leaves, we digitally photographed the lesion on each leaf at 1,2, 4, 8, 12, and 16 weeks after inoculation or until the leaves abscised due to the infection. Lesion size was measured using a 1 cm super(2) standard within the image. Currently, three seasons have been evaluated and there is a very strong linear model (R super(2) = 91.2) equating lesion size with percent lesion coverage. Given that reasonably uniform leaves are selected for analysis, we conclude that using percent lesion coverage of a leaf could be a suitable - and simpler - method for lesion growth analysis with rhododendron and camellia.