ANÁLISIS HISTOLÓGICO FOLIAR DE CÍTRICOS AGRIOS Y NARANJA DULCE CON SÍNTOMAS OCASIONADOS POR Candidatus Liberibacter asiaticus HISTOLOGICAL ANALYSIS OF SOUR CITRUS AND SWEET ORANGE LEAVES WITH SYMPTOMS CAUSED BY Candidatus Liberibacter asiaticus

2 INIFAP. 100. Santiago Ixcuintla Naya- rit. 3 INIFAP. 2810. Tecoman, Colima. 4 INIFAP. 67413. General Teran. AbstRAct In Mexico Huanglongbing disease (HLB), caused by Candidatus Liberibacter asiaticus, was reported for the first time in 2009 and has mainly prevailed in sour citrus. There are no formal reports of histological response associated to foliar symptom expression in sour citrus. The objective of this study was to characterize the anatomical and histochemical changes related to HLB symptoms in leaves of Persian lime (Lp) (Citrus latifolia), Mexican lemon (Lm) (C. aurantifolia), and sweet orange (Nd) (C. sinensis). Symptomatic and asymptomatic trees were selected in orchards of Nayarit, Colima, and Yucatan, Mexico, in July 2010, and the progress of the disease was assessed during six months in one sprout per tree. Area and phloem width, area of vascular system and the mesophyll tissue with starch and proteins were analyzed by split plots. Macroscopic symptoms appeared more rapidly in Lm, starting with chlorotic spots unto yellowing of leaves and foliar abscission. The phloem of the central nervure in symptomatic leaves of Lm showed major hyperplasia (p£0.05) and the three species presented increase of protein deposits. The parenchyma palisade layer and the symptomatic spongy tissue of Lm had higher starch content than Lp and Nd. Indices of asymptomatic-symptomatic relation with respect to phloem area and width, and starch accumulation suggested that Lm (1: 63.8, 1:2.5, and 1: 1.9) is more susceptible. This is the first histological study in sour citrus with HLB symptoms in Mexico indicating the production risk facing the recent entrance of the disease into the country.