Although there is substantial diversity among cultivated sweet oranges genotypes with respect to morphological, physiological, and agronomic traits, very little variation at DNA level has been observed. It is possible that this low DNA molecular variability is due to a narrow genetic basis commonly observed in this citrus group. The most different morphological characters observed were originated through mutations, which are maintained by vegetative propagation. Despite all molecular tools available for discrimination between these different accessions, in general, low polymorphism has been observed in all groups of sweet oranges and they may not be identified by molecular markers. In this context, this paper describes the results obtained by using laser-induced fluorescent spectroscopy (LIFS) as a tool to discriminate sweet orange accessions ( Citrus sinensis L. Osbeck) including common, low acidity, pigmented, and navel orange groups, with very little variation at DNA level. The findings showed that LIFS combined with statistical methods is capable to discriminate different accessions. The basic idea is that citrus leaves have multiple fluorophores and concentration depends on their genetics and metabolism. Thus, we consider that the optical properties of citrus leaves may be different, depending on variety. The results have shown that the developed method, for the best classification rate, reaches an average sensitivity and specificity of 95% and 97.5%, respectively. An interesting application of this study is the development of an economically viable tool for early identification in seedling certification, in citrus breeding programs, in cultivar protection, or in germplasm core collection.
Keywords: LIFS; Laser-induced fluorescence spectroscopy; citrus leaf fluorophores; differentiation of very close orange varieties; instrumentation; sweet orange accession.