Abstract:

The pathogen of citrus Huanglongbing，Candidatus Liberibacter asiaticus（CLas）was able to multiply in fruit pith. To analyze the proliferation regularity and the distribution pattern of CLas within fruit pith tissue of infected citrus fruit，CLas-infected Wokan（Citrus reticulata Blanco‘Wokan’），Navel orange（C. sinensis），Guanxi pomelo（C. maxima‘Guanxi Miyou’）and Shatian pomelo（C. maxima‘Shatianyou’）were collected for sampling of fruit pith. RT-qPCR was applied to quantify the CLas population in different segments（1.5 cm segment）from the individual fruit pith. The CLas population in different fruit pith from individual fruit of Wokan and Navel orange was also analyzed. The abundance of CLas in different segment of the individual fruit pith and different fruit pith from the individual fruit was statistically compared. Quantitative analyses revealed that CLas population in each of the 1.5 cm segment varied among fruit pith of four citrus varieties. The CLas population in 1.5 cm segments of fruit pith from Wokan and Shatian pomelo fruit was significantly higher than those from Navel orange and Guanxi pomelo fruit. The variable abundance of CLas in four citrus cultivars could be associated with the different substance composition in fruit pith of four citrus cultivars. The reason of CLas tended to multiply in the middle region or stylar region of the individual fruit pith was mainly due to the distribution of nutrients in fruit pith.

Key words: citrus, citrus Huanglongbing, Candidatus Liberibacter asiaticus, fruit, pith, pathogen distribution