Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2011
Publication Date: 10/1/2011
Citation: Hilf, M.E. 2011. Colonization of Citrus Seed Coats by 'Candidatus Liberibacter asiaticus' the bacterium associated with citrus Huanglongbing; Implications for seed transmission of the bacterium. Phytopathology. 101:1242-1250. Interpretive Summary: We studied whether Liberibacter asiaticus, the bacterium associated with the huanglongbing disease of citrus, is transmitted through seed to the seedling which germinates from the seed. We found that even though the bacterium is found at high levels in the seed coats of grapefruit seeds and sweet orange seeds the bacterium does not appear to infect the new seedling. Our study was designed differently but agrees with previous studies which found no evidence of seed transmission.
Technical Abstract: We detected pathogen DNA in nucleic acid extracts of 35% of peduncles from ‘Sanguenelli’ sweet orange fruits and in 100% of peduncles from ‘Conners’ grapefruit fruits. We detected pathogen DNA in extracts of 37% and in 98% of seed coats peeled from mature seeds of ‘Sanguenelli’ and ‘Conners’, respectively, and in 1.6% (2/128) and 4% (5/120) of extracts from the corresponding seeds (cotyledons and embryos). We detected small amounts of pathogen DNA in extracts of 10% of ‘Sanguenelli’ seedlings grown in the greenhouse, but no pathogen DNA was detected in extracts of 204 ‘Conners’ seedlings germinated in the greenhouse. Pathogen DNA was detected in 4.9% and in 89% of seed coats peeled from seeds of ‘Sanguenelli’ and ‘Conners’ germinated on agar under sterile conditions, but only small amounts of pathogen DNA were detected in 5% of ‘Sanguenelli’ seedlings and no pathogen DNA was detected in any of 164 ‘Conners’ seedlings. Grafting of pathogen-free ‘Ridge Pineapple’ sweet orange budwood to greenhouse-grown ‘Sanguenelli’ seedlings saw no appearance of pathogen DNA in the ‘Ridge Pineapple’ grafted tissue at approximately three months post-grafting, even when the graft was on a ‘Sanguenelli’ seedling in which pathogen DNA had been detected initially.