Ржавчинный гриб Cronartium ribicola и болезнь белой сосны

Species of rust fungus

Cronartium ribicola is a species of rust fungus in the family Cronartiaceae that causes the disease white pine blister rust. Other names include: Rouille vésiculeuse du pin blanc (French), white pine Blasenrost (German), moho ampolla del pino blanco (Spanish). It was first seen on White pine specifically on imported seedlings from European nurseries in 1909. TOC

Cronartium ribicola has two obligate hosts: Pinus spp and Ribes spp. Five needle pines (Pinus spp.) are infected in the fall by basidiospores that have spread under cool, moist conditions from the alternate host, currants and gooseberries (Ribes spp. ), and germinated on needles to enter with germ tubes through open stomata. Young pines are most susceptible and will die at faster rates following infection. Once spermatia have fertilized receptive hyphae in the Pinus spp. host, aecia are formed within a year, appearing as white blisters before rupture reveals the orange or yellow aeciospores within. The wind blown aeciospores infect Ribes spp. and the fungus quickly develops uredia in less than a few weeks. Uredospores produced in this stage spread to infect other parts of the same host or other Ribes spp. hosts in the area. On the other hand, the telial host, Ribes, can contract yellowish chlorotic leaf spots, but is otherwise not significantly impacted. The signs of C. ribicola on Ribes, come in the form of the pathogen itself as orange pustules on the underside of the leaf.

Environmentally, Cronartium ribicola prefers cooler temperatures coupled with moist conditions in low lying areas, especially during the late summer and early fall. The low temperatures and humidity are an essential part of the pathogen's spore germination and dispersal requirements. The combination of cooler temperatures and a high humidity create an environment at which dew can easily form. The free water helps loosen spores adhered to a leaf's surface and promotes spore germination. At a microclimate scale, lower trees hidden below the canopy exist in a lower temperature and moister environment, and as a result, these young trees are more susceptible to C. ribicola than the older, taller trees that create the canopy, which consequently have more access to the warm, dry sun. This collection of environmental characteristics are common in the Northern Hemisphere, causing many areas in the United States to be labeled at hazard zones for the genus Pinus.

Historically, tactics such as alternate host removal and planting restrictions in hazard zones, as well as quarantines made legal by the 1912 Plant Quarantine Act. Removal of Ribes used to be practiced in full force, which heavily affected blackcurrant production in the United States, however through a combination of the pathogen's hardiness and ability to travel airborne for nine hundred feet, as well as the Ribes ability to regrow from an extremely small root portion, researchers have focused their efforts on creating new cultural practices to lower the abundance of C. ribicola. Since then researchers have come up with multiple new methods to curb the spread of the infection. (In some European countries and Canada, the fruits from currants and gooseberry were more valuable than White pine trees, which did not allow them to do the eradication programs of Ribes.) For example, careful topological selection of plot sites for the white pine would greatly reduce the germination of spores. These plots would include land with characteristics such as well drained soil such as that on a high sloped area, spots that are well aerated, and face the south for dryness and warmth. This would remove the wet, damp environment that is crucial for the germination of the spores on the Pinus. Once plantation spots have been chosen, pruning and inspection practices have been adapted as a monitored cultural practice. Inspections for blister rusts begin in May about six years after the trees are planted. This time period is when obvious symptoms of C. ribicola begin to appear, such as red needles. Infected branches will be pruned to a certain height that is dependent on a rate of infection determined by researchers; generally pruning is required for Pinus trees up to anywhere between nine and eighteen feet. Pathological pruning, in which all lower branches are pruned regardless of signs or symptoms of infection, may reduce disease instance in white pine tree stands. Furthermore, genetic hybridization testing has been conducted for more than half a century in order to find resistance among strains of the species, and have since successfully introduced resistance into the eastern white pine Of the five needle pines, sugar pine (Pinus lambertiana), eastern white pine (Pinus strobus), and western white pine (Pinus monticola) are the most economically important for timber harvest and nursery stock. In fact, forests of these species represent some of the most valuable land for timber harvest in the US, as they fetch a premium price over related species. Today, although some state and local bans remain in place,

Cronartium ribicola is a heteroecious, macrocyclic pathogen on Pinus spp and Ribes spp. The means of resistance in rust resistant five needle pine varieties involve various mechanisms, such as abortion of infected leaves and slow development of canker symptoms. It is likely that varieties exhibiting the latter mechanism act against the pathogen's ability to modify cell walls and avoid plant recognition. In some species of North American pine, hypersensitive responses to C. ribicola have been observed, which suggests a gene for gene interaction that may indicate that C. ribicola is not so ecologically foreign to North American pines as previously assumed.