Early Detection and Quantification of Almond Red Leaf Blotch Using High-Resolution Hyperspectral and Thermal Imagery

Manuel López-López,Victoria González-Dugo,Pablo Zarco-Tejada,Rocío Calderón,Elías Fereres

doi:10.3390/rs8040276

Abstract

Red leaf blotch is one of the major fungal foliar diseases affecting almond orchards. High-resolution thermal and hyperspectral airborne imagery was acquired from two flights and compared with concurrent field visual evaluations for disease incidence and severity. Canopy temperature and vegetation indices were calculated from thermal and hyperspectral imagery and analyzed for their ability to detect the disease at early stages. The classification methods linear discriminant analysis and support vector machine, using linear and radial basis kernels, were applied to a combination of these vegetation indices in order to quantify and discriminate between red leaf blotch severity levels. Chlorophyll and carotenoid indices and chlorophyll fluorescence were effective in detecting red leaf blotch at the early stages of disease development. Linear models showed higher power to separate between asymptomatic trees and those affected by advanced stages of disease development while the non-linear model was better in discriminating asymptomatic plants from those at early stages of red leaf blotch development. Leaf-level measurements of stomatal conductance, chlorophyll content, chlorophyll fluorescence, photochemical reflectance index, and spectral reflectance showed no significant differences between healthy leaves and the green areas of symptomatic leaves. This study demonstrated the feasibility of early detecting and quantifying red leaf blotch using high-resolution hyperspectral imagery.

Highlights

Red leaf blotch of almond (Prunus amigdalus) is a fungal foliar disease widely extended throughout almond production regions of Europe and Asia and it is considered of high economic importance [1,2,3].Nowadays, the spread of almond red leaf blotch is increasing in importance in Spain [4] due to the intensification of production in recently-planted almond orchards, i.e., incorporation of new varieties, irrigation, higher tree density, light pruning, and occupation of sites with temperate climate that could be advantageous for the disease development [5]
The spread of almond red leaf blotch is increasing in importance in Spain [4] due to the intensification of production in recently-planted almond orchards, i.e., incorporation of new varieties, irrigation, higher tree density, light pruning, and occupation of sites with temperate climate that could be advantageous for the disease development [5]
Red leaf blotch disease is caused by the fungus Polystigma amygdalinum PF Cannon (Phyllachoraceae), formerly known as Polystigma ochraceum [2], which is mainly present in the Mediterranean Basin [2]

Summary

Introduction

Red leaf blotch of almond (Prunus amigdalus) is a fungal foliar disease widely extended throughout almond production regions of Europe and Asia and it is considered of high economic importance [1,2,3].Nowadays, the spread of almond red leaf blotch is increasing in importance in Spain [4] due to the intensification of production in recently-planted almond orchards, i.e., incorporation of new varieties, irrigation, higher tree density, light pruning, and occupation of sites with temperate climate that could be advantageous for the disease development [5]. Red leaf blotch of almond (Prunus amigdalus) is a fungal foliar disease widely extended throughout almond production regions of Europe and Asia and it is considered of high economic importance [1,2,3]. There are noticeable cultivar differences in genetic resistance to the disease, this being a crucial factor determining its potential impact on almond production. Some varieties such as Guara and Tarraco are considered very susceptible, while Vayro and Constantí have shown high resistance [5]. Red leaf blotch disease is caused by the fungus Polystigma amygdalinum PF Cannon (Phyllachoraceae), formerly known as Polystigma ochraceum [2], which is mainly present in the Mediterranean Basin [2].

Objectives

Methods

Results

Discussion

Conclusion