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Title: Assessment of Canopy Porosity in Avocado Trees as a Surrogate for Restricted Transpiration Emanating from Phytophthora Root Rot
Contributor(s): Salgadoe, Arachchige Surantha Ashan  (author); Robson, Andrew James  (author)orcid ; Lamb, David William  (author); Dann, Elizabeth Kathryn (author)
Publication Date: 2019-12-02
Open Access: Yes
DOI: 10.3390/rs11242972
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Abstract: Phytophthora root rot (PRR) disease is a major threat in avocado orchards, causing extensive production loss and tree death if left unmanaged. Regular assessment of tree health is required to enable implementation of the best agronomic management practices. Visual canopy appraisal methods such as the scoring of defoliation are subjective and subject to human error and inconsistency. Quantifying canopy porosity using red, green and blue (RGB) colour imagery offers an objective alternative. However, canopy defoliation, and porosity is considered a 'lag indicator' of PRR disease, which, through root damage, incurs water stress. Restricted transpiration is considered a 'lead indicator', and this study sought to compare measured canopy porosity with the restricted transpiration resulting from PRR disease, as indicated by canopy temperature. Canopy porosity was calculated from RGB imagery acquired by a smartphone and the restricted transpiration was estimated using thermal imagery acquired by a FLIR B250 hand-held thermal camera. A sample of 85 randomly selected trees were used to obtain RGB imagery from the shaded side of the canopy and thermal imagery from both shaded and sunlit segments of the canopy; the latter were used to derive the differential values of mean canopy temperature (Delta T-mean), crop water stress index (Delta CWSI), and stomatal conductance index (Delta I-g). Canopy porosity was observed to be exponentially, inversely correlated with Delta CWSI and Delta I-g (R-2 > 90%). The nature of the relationship also points to the use of canopy porosity at early stages of canopy decline, where defoliation has only just commenced and detection is often beyond the capability of subjective human assessment.
Publication Type: Journal Article
Source of Publication: Remote Sensing, 11(24), p. 1-12
Publisher: MDPI AG
Place of Publication: Switzerland
ISSN: 2072-4292
Fields of Research (FoR) 2008: 070104 Agricultural Spatial Analysis and Modelling
070508 Tree Nutrition and Physiology
Fields of Research (FoR) 2020: 300710 Tree nutrition and physiology
300206 Agricultural spatial analysis and modelling
Socio-Economic Objective (SEO) 2008: 820299 Horticultural Crops not elsewhere classified
Socio-Economic Objective (SEO) 2020: 260599 Horticultural crops not elsewhere classified
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
Appears in Collections:Journal Article
School of Science and Technology

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