Publications

4482

The potato/tomato psyllid, Bactericera cockerelli transmits the bacterium ‘Candidatus Liberibacter solanacearum’, also known as ‘Ca. L. psyllaurous’, which causes zebra chip disease in solanaceous crops. There have been no studies addressing the effect of the bacterial plant pathogen on the biology of its insect vector. We examined several life-history traits, including 7-day fecundity, hatching percentage, incubation time, nymphal survival percentage, nymphal development time, total development time, and sex-ratio of ‘Ca. L. solanacearum’-positive and -negative psyllid isofemale lines on tomato, as well as adult mortality index of ‘Ca. L. solanacearum’-positive and -negative insects. The only two life-history traits that differed between the ‘Ca. L. solanacearum’-positive and –negative psyllid isofemale lines were 7-day fecundity and nymphal survival percentage, which were significantly lower in ‘Ca. L. solanacearum’- positive lines. The symbiotic bacteria associated with both psyllid isofemale lines were similar, with the exception of ‘Ca. L. solanacearum’, which showed 100% infection in the ‘Ca. L. solanacearum’-positive lines and was not detected in the negative psyllid lines. These results suggest that ‘Ca. L. solanacearum' has a negative effect on population growth rate of its insect vector on tomato.

Temperature has been shown to have a significant effect on development of liberibacter species associated with citrus Huanglongbing disease. ‘Candidatus Liberibacter africanus’ and ‘Ca. L. americanus’ are both heat sensitive, whereas ‘Ca. L. asiaticus’ is heat tolerant. The recently described ‘Ca. L. solanacearum’ is associated with zebra chip (ZC), a newly emerging and economically important disease of potato worldwide. This psyllid-transmitted liberibacter species severely affects several other solanaceous crops and carrot. Experiments were conducted to evaluate effects of temperature on development of ‘Ca. L. solanacearum’ and ZC disease. Potato plants were inoculated with ‘Ca. L. solanacearum’ by briefly exposing them to liberibacter-infective potato psyllids at various temperatures under laboratory conditions. Following insect exposure, the plants were maintained at selected temperature regimes in growth chambers, monitored for ZC symptom development, and later tested for liberibacter by polymerase chain reaction to confirm infection. Results indicated that temperatures below 17°C appear to slow development of ‘Ca. L. solanacearum’ and ZC symptoms, whereas temperatures above 32°C are detrimental to this liberibacter. Compared to Huanglongbing liberibacters, ‘Ca. L. solanacearum’ appears heat sensitive. The sensitivity of this bacterium and its insect vector to temperature may partially explain incidence, severity, and distribution of ZC in affected regions.