qPCR-based detection of Candidatus Liberibacter asiaticus in symptomatic citrus plants from Veracruz, Mexico Detección de Candidatus Liberibacter asiaticus mediante qPCR

Veracruz, one of Mexico’s main citrus-producing regions, faces a major phytosanitary threat from huanglongbing (HLB) because of its rapid spread and atypical symptom expression. Symptom variability limits the reliability of field diagnosis and highlights the need to correlate visible symptoms with molecular detection of Candidatus Liberibacter asiaticus (CLas). This study aimed to evaluate the qPCR positivity rate for CLas in symptomatic citrus samples collected from seven citrus-producing municipalities in Veracruz. Branch dieback was the most frequent symptom (67.5 %), followed by generalized yellowing (20.4 %). The qPCR positivity rate in symptomatic CLas samples ranged from 94 % in Chicontepec to 98.7 % in Ixhuatlán de Madero and Castillo de Teayo. Fruit ripening, asymmetric fruit development, and irregular spots on orange leaves cannot be considered classic symptoms of HLB in northern Veracruz because they do not occur recurrently. Logistic regression analysis (odds ratios [OR]) showed no significant association between qPCR positivity and municipality, cultivar, or rootstock. In contrast, generalized yellowing was significantly associated with higher odds of CLas qPCR positivity (OR = 2.29, p = 0.001) (an OR > 1 indicates a higher risk). These results indicate that generalized yellowing is the most strongly associated symptom with CLas infection in citrus trees in northern Veracruz.