Title: A new detached-leaf assay method to test the inoculativity of psyllids with Candidatus Liberibacter asiaticus associated with huanglongbing disease Authors
Submitted to: International Research Conference on Huanglongbing
Publication Type: Proceedings
Publication Acceptance Date: December 2, 2010
Publication Date: January 10, 2011
Citation: Ammar, E., Hall, D.G., Walter, A.J. 2011. A new detached-leaf assay method to test the inoculativity of psyllids with Candidatus Liberibacter asiaticus associated with huanglongbing disease. 2nd International Research Conference on Huanglongbing. January 10-14, 2011, Orlando, Florida, Abstract No. 3.9. Technical Abstract: Nymphs of the Asian citrus psyllid Diaphorina citri can acquire Candidatus Liberibacter asiaticus (LAS) from huanglongbing (HLB)-infected plants, and both nymphs and adults can transmit HLB to healthy citrus. Normally, however, the proportion of LAS-infected psyllid individuals, based on PCR assays, is much higher than the proportion of psyllids that are capable of inoculating/transmitting HLB to healthy plants. To test their inoculativity with LAS, psyllids are usually fed singly or in small groups on citrus seedlings and the latter assayed by PCR at least 3-12 months later. Here, we have developed a new detached-leaf assay method that can potentially speed up LAS-inoculativity tests on psyllids considerably by shortening this period to 2-3 weeks. To test this method, adults of D. citri that had been reared as nymphs on HLB-diseased citrus were placed on young detached citrus leaves whose petioles were immersed in water, and each leaf was caged in a 50 ml clear plastic tube for one week. Following this inoculation access feeding period, the midribs of these assay leaves were processed for quantitative PCR using LAS primers 1-2 weeks later. Our results indicate that after feeding 10, 5 or 1 adult(s)/leaf/wk the percentages of LAS-positive leaves were 40, 20 and 4.4 percent, respectively. These results are largely similar to those reported earlier, on transmission/inoculativity tests of LAS-infected psyllids, using citrus seedlings. However, we are now comparing these two inoculativity assay methods more directly to make sure that their results are comparable which would greatly enhance various studies on HLB-vector relations.