Janna Beckerman, Extension Plant Pathologist
A key symptom of WPBR is the characteristic "flags"(orange branches) that identify infected branches. Photo credit: Bob Blanchette "…in this place it takes all the running you can do, to keep in the same place." Lewis Carroll, Alice in Wonderland
The Red Queen Principle was developed by evolutionary biologist L. van Valen in 1973 as a way to explain what has been described as a "co-evolutionary arms race" between plant and pathogen, predator and prey. Like Alice's visit with the Red Queen, she runs and runs, but ends up going nowhere. This same phenomenon happens in the wild world of plant pathology, right under our noses and involves a fungus, white pine, currants and gooseberries.
When did this "co-evolutionary arms race" begin? At some point, the ancient ancestors to the white pine and Ribes spp (currants and gooseberries) had a feud and went their separate ways. The continent of Asia wasn't big enough for the two of them! Some ended up in North America, the rest remained in Asia. The Asian white pines and Ribes spp. met a fungus named Cronartium ribicola, the causal agent of white pine blister rust (WPBR). While hardly affecting the Asian Ribes spp., WPBR probably killed many of white pines. Over time, natural selection favored the resistant white pines and resistance became an established trait in the population. C. ribicola became a minor nuisance of the Asian white pines, currants and gooseberries. North America was still "undiscovered," and the Ribes spp and white pines reproduced without having to worry about resistance to C. ribicola. The sign of WPBR is the buff to orange fungus that sporulates in late April through May. Photo credit: Bob Blanchette
In the 1700s, when Europeans "discovered" North America, they fell in love with the exotic vegetation. Numerous plants were brought back to Europe, including the North American version of the white pine, which often reached diameters as large as 6 feet across and heights of up to 220 feet! Lord Weymouth brought the white pine to Britain (where it was renamed 'Weymouth pine' to obscure its lowly, colonial origin) and it spread throughout Europe. In 1856, white pine blister rust was first reported in Russia.
At this point, C. ribicola had found a more accommodating host that had never evolved resistance. Unfortunately, the story doesn't end here, or end up being about an introduced host being destroyed by a native pathogen. Timber companies who had over-harvested Eastern forests were looking for fast-growing pines to re-plant and quickly harvest. The growing timber industry lobbied Congress to remove tariffs on imported plant material. Weymouth pines (a.k.a. Eastern white pine) were shipped back to the US, with its new "friend" C. ribicola. The blister rust also found its other "new best friends" that were the native currants and gooseberries who also never evolved resistance to C. ribicola The stage was set for an epidemic.
And epidemic it was. The Red Queen was no longer standing still but was now off and running! Ten years after the Chestnut blight epidemic starting killing all the chestnuts in North America, white pine forests valued in the millions of dollars appeared threatened. In 1912, the Federal Quarantine Act was passed to prevent additional plant products into the country. To control the problem that had already started, an eradication program began with zero tolerance for white pine blister rust. The government went after infected trees with little to no success.
They then implemented a tactic that was only marginally successful with wheat stem rust: Eliminate the alternate host. Thus began the eradication of all European currants within 1000 feet of a white pine in North America. Unfortunately, spores from the Ribes host are believed to travel up to 350 miles to white pine…Not only that, but the native currants were just as susceptible as their European counterparts. Thus, the Ribes Eradication Program against all native currants and gooseberries began from New York to British Columbia (Canada never subscribed to the Ribes Eradication Program). During the Depression, 11,000 men were paid to uproot or poison Ribes . Have you ever tried to pull up a gooseberry or currant? Think deep roots and heavy, sharp prickers! Add to that the fact that it produces berries that are loved by birds that freely disseminate them in a package of fertilizer, and you can imagine how incredibly unsuccessful the program was. The incidence of WPBR was reduced, but not eliminated. Since 1966, Ribes eradication has been implemented on a state-to state basis (17 states still have bans in place). To this day, many homeowners in other states are unable to import any cultivar of Ribes , or are restricted from planting the more susceptible black currant. Additionally, programs are in place to evaluate and select for WPBR resistance in white pines. These two resistance-breeding programs have played an important role in putting the Red Queen back on the proverbial treadmill for now.
In Minnesota, we don't suffer Ribes restrictions. But, because of the presence of white pine and WPBR, it is important that homeowners carefully consider what varieties of currant and gooseberry that they plant. Remember, WPBR is a problem to white pines; it does not severely affect the Ribes . Below is a list of WPBR resistant currants and gooseberries. This way, WPBR, like the Red Queen, will still be running, but going nowhere!
Currants and Gooseberries to Plant: Most currant and gooseberry varieties are considered hardy to zone three.
Black currants (R. nigrum) are considered the most susceptible to WPBR. Black currant fruit has a characteristic aroma. The scent can also be found in the leaves, which are commonly used in tea to impart the characteristic black currant flavor.
'Consort Crusader', 'Coronet': Considered immune to WPBR, these cultivars were released in Canada. Berries are considered very tart with a musky flavor.
'Titania Large', firm berries are produced on extremely vigorous plants. Resistant to PM and WPBR.
'Ben Alder' and 'Ben Sarek'. Medium to large berries are used for juice and desserts. Plants are moderately resistant to WPBR and very resistant to PM.
'Minaj Smeriou'. A new rust resistant release with a more classic black currant flavor. Performance has not been studied in Minnesota. Early reports are positive for both flavor and disease resistance.
'Viking' was erroneously reported to be resistant but is quite susceptible to WPBR
Red currants (R. sativum) are generally considered moderately resistant to WPBR.
'Red Lake' (developed at the University of Minnesota produces clusters of large, mild flavored red berries. It is considered to be one the best red currant variety.
White/Pink Currants (R. sativum) are considered albino forms of red currants, and as such are considered moderately resistant to WPBR.
'Pink Champagne'. Flavor is more delicate (less acid) than that of black currants and less tart than red currants. Plants have a vigorous, upright growth habit and excellent resistance to PM.
'White Imperial' (Geneva, NY) White fruit with a pink blush. Excellent flavor. Considered by some to be the best tasting of all currants. Moderately susceptible to PM, but resistant to WPBR.
Gooseberries (R. hirsutellum and R. grossularia), like red currants, are considered moderately to completely resistant to WPBR. Care should be taken to keep plants healthy to minimize the possibility of WPBR infection. Powdery mildew is capable of defoliating and killing gooseberries. For this reason, consider PM resistance when purchasing plants.
'Welcome'. WPBR and PM resistant, this cultivar is noted for high fruit yields of tart, red gooseberries.
'Pixwell'. Originated in North Dakota, 'Pixwell' is a heavy yielder of large, delicious berries. Often, it bears the year after planting. Moderately mildew resistant.
'Hinnomake Red', This variety from Finland combines excellent flavor and yield of dark red fruit. As an added bonus, it is considered mildew resistance.
Hybrid: Jostaberry. Considered by many to have the best traits of both parents (black currant and gooseberry); Still, others believe it inherited the worst traits of both parents. Plant and decide for yourself, but plants are resistant to both WPBR and PM.
