Zebra Chip (A.K.A. Zebra Complex)
Liberibacter & Zebra Complex (ZC; formerly Zebra Chip). ZC, first documented in potato fields around Saltillo, Mexico in 1994, and was first identified in the USA in 2000 in commercial potato fields in the Pearsall, TX. Over the past 8 years, ZC has spread to a number of other states, including NE, CO, KS, NM and CA. This disease was sporadically important economically until the 2004 and 2005 growing seasons when it caused millions of dollars in losses to both potato producers and processors in numerous locations. It also causes serious losses to the fresh market, tablestock potato industry, often causing the abandonment of an entire center-pivot irrigated field. This disease has recently been associated with a new, fourth, pathogenic Candidatus Liberibacter species (called “psyllaurous”) (Hansen et al., in press). Candidatus Liberibacter psyllaurous has also been associated with a similar disease in tomatoes and peppers. In all three cropping systems, the association of this pathogen with disease was originally missed because the traditional diagnostic method, PCR and QRT-PCR, did not amplify DNA from this fourth species. The bacterium is transmitted by the potato psyllid (Bactericera cockerelli), an insect that is prevalent in most growing areas of the US.
ZC & the Potato Psyllid. The causeal agent of ZC was unknown until just a few months ago; however, the potato psyllid’s involvement on the disease was determined a few years ago by three independent labs (Goolsby, Bextine, and Munyaneza) (Goolsby 2007, Munyaneza 2007). It is now suspected that this disease is caused by the presence of Candidatus Liberibacter psyllaurous. When considering the epidemiology of ZC and the association with a potential HLB causal agent, it is important to consider the timeline of ZC history. First, the potato psyllid has been a minor problem in potato and tomato production for years. However, ZC first appeared in Mexico in 1994, and in the USA in 2000. Similarly, tomato and pepper disease pressure accelerated during this same time period. The foliar symptoms that define ZC, including stunting, chlorosis, swollen internodes of the upper growth, proliferation of axillary buds and aerial tubers, browning of the vascular system in belowground portions of stems, leaf scorching, and early plant decline (Munyaneza 2007), all similar to the symptoms in HLB affected citrus.
Dr. Blake Bextine