Analysis of Defense-Related Gene Expression in New Citrus Hybrids Resistant to Citrus Variegated Chlorosis and eQTL Mapping

Brazil is the largest producer of sweet orange, but the productivity is not the highest due to disease problems. A major problem is the Citrus Variegated Chlorosis (CVC) caused by the bacterium Xylella fastidiosa, which promotes obstruction of the xylem, causing physiological disorders in plant and in advanced cases, affecting fruits, leading to production losses. In this study, hybrids obtained from controlled crosses between Murcott tangor [Citrus reticulata Blanco x Citrus sinensis (L.) Osbeck] and Pera sweet orange [Citrus sinensis (L.) Osbeck] were evaluated by analysis of symptoms and by diagnosis through conventional and real time PCR (Polymerase Chain Reaction), showing seven resistant hybrids, twenty-four tolerant hybrids and six susceptible hybrids. The expressions of thirteen genes associated with resistance [NBS-LRR - RGH1, Abscisic Acid (ABA), Thaumatin, Chitinase, Xa21 Kinase, Kinase CHRK1, Isoflavone Synthase, Protein Defense-Related Resistance - DRRP, No Product Set - SPD, Isoflavone Reductase, HCr2-0A, Ankyrin, and Glutathione GST-22] were evaluated, and it was possible to relate the resistance to X. fastidiosa with gene expression. QTL (Quantitative Trait Loci) were mapped through the quantification of symptoms and bacterial concentration, thus expression QTL (eQTL) of genes were carried out with the evaluation of thirty-seven hybrids.