Comportamiento espectral y espacial de lima tahiti (citrus latifolia tanaka) afectada por phytophthora spp en Corpoica La Libertad-Meta

Abstract

Foot and root rot are two recognized problems of infectious diseases in citrus, which are caused by the transmission of the soil fungus Phythopthora spp, when there is damage to the cambium and inside the bark, the lesions can spread around of the circumference of the trunk and ring the cambium causing the death of the tree, the canopy of the affected trees exhibit leaf yellowing, defoliation, twig dieback and short grow flushes. This work aims to determine the spectral and spatial behavior of Phytophthora spp for its detection and management in Lima Tahiti, through the evaluation of 4 severity scales (0-healthy, 1-initial lesions, 2-light lesions, 3- serious injuries). A batch of Lima Tahiti with an area of 0.7 hectares was selected, which showed symptoms of Phythopthora spp associated with foot rot, located at the La Libertad Corpoica Villavicencio Research Center, Meta department located at 04º03'N, 73º29'W and at an altitude of 336 m.a.s.l. A field evaluation was carried out where the incidence and severity of Phythopthora spp was determined, later multispectral images were obtained through MicaSense RedEdge camera which was mounted on a hexacopter multirotor, (unmanned aerial vehicle), the sensor can capture the Red (R), Green (G), blue (B), Rededge (Re), Near Infrared (NIR) simultaneously. According to the spatial analysis of Phytophthora spp performed with the nearest neighbor function, it is found that the incidence and severity have a scattered pattern with a p-value significance <0.05, whereas with the K-ripley function it is distributed from randomized in both incidence and severity with a significance of p-value <0.01. With Kernel density, the distribution of Phytophthora spp can be observed, which describes patterns of disease propagation from the center of the area to the lateral sides. When analyzing the spectral profiles with reflectance values and digital levels, significant differences are found with a p-value <0.05 between healthy and infected trees scale 3 with the NIR band, which allows the detection of Phythopthora spp, the infected trees show a darker coloration while healthy ones have a brighter coloration in different combinations with the NIR band, since the affected trees show a greater degree of defoliation, which reflects the relationship of the density of the foliage and the response of the NIR. In scale 1 no significant differences were found with any band, but you can find trees with or without defoliation, which suggests that there are different levels of internal damage in the cambium, causing different degrees of defoliation, for this reason there are trees that can have damage to the stem but still do not express symptoms in the canopy. In scale 2, no trees were found, in the case of vegetation indexes NDVI, GNDVI, SAVI and RE-NDVI significant differences were found with a p-value of 0.05 between healthy trees and scale 3, while with the scale 1 There are no differences, this is due to the low degree of involvement of the vascular bundles in this stage of the disease. Regarding the classification with support vector machine (SVM) with the values of digital levels and reflectance of the NIR band are low (60%) with respect to other studies carried out for other diseases in citrus such as HLB (80%), since There are significant differences in scales 1, which makes separation between healthy and infected trees difficult.