GiESCO 2019 banner
IVES 9 IVES Conference Series 9 GiESCO 9 GiESCO 2019 9 Disease‐induced alterations in the reflectance spectrum of grape leaves

Disease‐induced alterations in the reflectance spectrum of grape leaves

Abstract

Context and purpose of the study ‐ Phytopathogenic diseases impact the development and yield of grapevines, resulting in economical, social and environmental losses. Sick plants have their metabolism changed, leading to alterations in their reflectance spectra. Little is known on these alterations, and a better knowledge could be used in the development of sensors able to detect diseases through fast, non‐ destructive techniques. The present study was aimed at detecting spectral changes on the reflectance spectra of vines of cv. Cabernet Sauvignon, with early symptoms of downy mildew, powdery mildew, black‐ foot and Petri disease, describing the spectral domains where alterations are measurable with respect to healthy control vines. This information can be used to the development of low‐cost devices which can perform real‐time field measurements to early assessment of vineyard health status.

Material and methods ‐ Plants of Cabernet Sauvignon grown in pots and kept in a greenhouse were inoculated with the pathogens causing mildew, powdery mildew, black‐foot and Petri disease. In early stages of disease development, reflectance measurements were performed using a FieldSpec 3 spectroradiometer, which were compared with data from healthy plants. The investigation began with discriminant analysis, which revealed that symptomatic plants are indeed separated from the control ones. Reflectance spectra were therefore further investigated and alterations on the shape of the spectra, characteristic of each disease, were looked for. The disease descriptors were based on ratios between spectral features internal to a spectrum, a procedure which allowed the derivation of parameters intrinsic to each disease.

Results ‐ A set of thresholds, which are the intensity ratios of reflectance at selected wavelengths, was derived for the studied diseases. The selected wavelength ratios were 443/496, 443/573, 443/695, 443/1900, 496/573, 496/695, 516/1900, and 1900/2435 (values in nanometers), for which the spectra from symptomatic plants present shape changes of as much as 20% in reflectance with respect to healthy plants. The observed spectral deformations are larger for black‐foot and powdery mildew, but some wavelength ratios are also indicators of downy mildew and Petri disease. Data from near‐infrared are in general more useful, compared with measurements at 1900 and 2435nm.

DOI:

Publication date: June 22, 2020

Issue: GiESCO 2019

Type: Article

Authors

Pâmela PITHAN (1), Lucas GARRIDO (3), Diniz ARRUDA (1), Adriane THUM (1,2), Rosemary HOFF (3), Jorge DUCATI (1)

(1) Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, 91501-970 Porto Alegre, Brazil
(2) Universidade do Vale do Rio dos Sinos, Av. Unisinos 950, 93020-190 São Leopoldo, Brazil
(3) Empresa Brasileira de Pesquisa Agropecuária, R. Livramento 515, 95701-008 Bento Gonçalves, Brazil

Contact the author

Keywords

Grapevine diseases, leaf reflectance, spectroradiometry, disease detection

Tags

GiESCO 2019 | IVES Conference Series

Citation

Related articles…

Determination of selected phenolics, carotenoids and norisoprenoids in Riesling grapes after treatment against sunburn damage

Riesling represents the most widely cultivated grape variety in Germany and is therefore of particular economic interest. During recent years an increase in the petrol-note as well as in undesirable bitter and adstringent notes has been reported. These changes are most likely linked to increasing temperature and sunlight exposure of grapes due to climate changes.
The “petrol note” is caused by the formation of the C13-norisoprenoid 1,1,6-trimethyl-1,2-dihydronaphthalin (TDN), which originates from acid-labile precursors formed by the carotenoid degradation in the grape.

Evaluation of the impact of different amelioration techniques on the chemical composition and sensory characteristics of smoke impacted wines

AIM: The increasing incidences of wildfires in wine grape growing regions pose a significant risk. Persistent exposure to smoke can compromise the quality and value of wine grapes and adversely affect wines made from smoke exposed grapes.

Development and validation of a standardized oxidation assay for the accurate measurement of the ability of different wines to form “de novo” oxidation-related aldehydes

From the standpoint of wine aroma oxidation there are two effects observed: aroma degradation of oxygen sensitive compounds (polyfunctional mercaptans) and the appearance of new substances with high aromatic power (acetaldehyde, methional, phenylacetaldehyde, sotolon, alkenals, isobutanal and 2, 3-metylbutanals) (1-5). According to our experience, Strecker aldehydes are compounds with highest sensory relevance in the oxidative degradation of many wines (5-7).

The influence of the soil on the phenolic composition of both grapes and wines : “the Grenache observatory”

La composition fine des raisins de Grenache noir est mal connue. Il est généralement admis une certaine variabilité de comportement de ce cépage qui se manifeste principalement sur la couleur des vins. De nombreux facteurs peuvent être à l’origine de cette variabilité : matériel végétal, pratiques culturales, types de vinification et terroir. Un travail de recherche concernant ce cépage a été engagé dans la Vallée du Rhône.

Effets de l’application d’acide gibbérellique (GA3) sur la qualité de raisins et de vins produits en climat tropical au Nord-Est du Brésil

The honeydew moth Cryptoblabes gnidiella is the main problem for the wineries in the Northeast of the Brazil, because it attacks the bunch and reduces the quality of the grapes and the wines. In order to stretch out the bunch to facilitate the penetration of the insecticides, it was used gibberellic acid. Six treatments with different concentrations and different dates of application, and the control were compared.