Abstract
The correct recognition of sweet orange (Citrus sinensis L. Osbeck) variety accessions at the nursery stage of growth is a challenge for the productive sector as they do not show any difference in phenotype traits. Furthermore, there is no DNA marker able to distinguish orange accessions within a variety due to their narrow genetic trace. As different combinations of canopy and rootstock affect the uptake of elements from soil, each accession features a typical elemental concentration in the leaves. Thus, the main aim of this work was to analyze two sets of ten different accessions of very close genetic characters of three varieties of fresh citrus leaves at the nursery stage of growth by measuring the differences in elemental concentration by laser-induced breakdown spectroscopy (LIBS). The accessions were discriminated by both principal component analysis (PCA) and a classifier based on the combination of classification via regression (CVR) and partial least square regression (PLSR) models, which used the elemental concentrations measured by LIBS as input data. A correct classification of 95.1% and 80.96% was achieved, respectively, for set 1 and set 2. These results showed that LIBS is a valuable technique to discriminate among citrus accessions, which can be applied in the productive sector as an excellent cost–benefit tool in citrus breeding programs.
Highlights
Accessions of sweet orange varieties result in different combinations of canopy and rootstock and show a wide diversity of morphological/phenotype traits, such as size and shape of the canopy, color and size of the fruit, and ripening time and quantity of seeds per fruit
A typical orange leaf laser-induced breakdown spectroscopy (LIBS) spectrum is shown in Figure 1, where the entire spectral range is split into two consecutive wavelength ranges and the relevant elemental lines identified
The LIBS spectra of leaves were employed to discriminate among genetically close orange accessions based on the amount of each element
Summary
Accessions of sweet orange varieties result in different combinations of canopy and rootstock and show a wide diversity of morphological/phenotype traits, such as size and shape of the canopy, color and size of the fruit, and ripening time and quantity of seeds per fruit. These features can be identified by visual inspection of adult plants and are widely used to discriminate accessions in the period of fruit production, whereas in other phenological stages the plants do not show any difference in these traits and are not distinguishable. Different combinations of rootstock and canopy may result in different chemical and biological properties of the plants, including the concentration of elements in leaves
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