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On Pines: 'flagged' branches (with dead foliage) or tops distal to swollen, rough-barked branches or stems producing resin flow from an orange-margined canker. Young trees may be stunted and discoloured prior to death. Younger cankers are elongated and spindle-shaped on branches and diamond-shaped on stems within the orange margin. Conspicuous, orange, aecia develop in spring, followed by oozing pycnia.
On Ribes: orange-yellow spots appear on leaves in early summer; mycelia are visible from the under surface. In late summer, leaves show more-developed spots and necrotic areas, and may be curled. Telial columns are visible to the eye in brownish spots on the under surface.
Where the alternate hosts exist, control is necessary. Control measures differ to protect the most-important hosts.
Genetic resistance and species selection can be used as a means to control some rusts, and infected branches can be eliminated by pruning. Site hazard ratings based on habitat type and elevation are available. Ongoing research is evaluating ways to manage rust diseases in ways that maximize their benefit to forest ecosystems while limiting their detrimental effects on forest resources (Parks and Flanagan, 2001).
Because resistant individuals in all these species are rare, genetic variation may be reduced to the point where future populations may not be viable without active management (Sniezko, 2004).
Understanding host-pathogen interactions is important in managing yield loss and can aid in the identification of disease-resistant trees. Several resistance mechanisms to C. ribicola have been identified in pine. At the molecular level, several defence responsive proteins and their genes have been characterized. Some of these are identified to be potential candidates for markers associated with resistance or susceptibility (Ekramoddoullah and Hunt, 2002).
Programmes of screening and genetic improvement of pines are active in Canada (Corriveau and Lamontagne, 1977; Meagher and Hunt, 1985; Zsuffa, 1985; Hunt, 1999), the USA (Miller,1973; Hoff and McDonald, 1980; Murphy, 1982; Samman, 1982; Franc, 1988; Eramian, 1999; Kitzmiller and Samman, 1999; Sniezko, 1999; Meier, 2000), Romania (Blada, 1994) and Korea (Hyun and Koo, 1981). Field testing of second-generation Pinus monticola seedlings has begun (McDonald et al., 1994). North American trials of species from Asia and Europe indicated potential gain in rust resistance (Heimburger, 1972), but eventual problems with adaptation to climatic differences. Rust resistance generally was higher in species closer to the Asian centre of the rust and least in North American species (Bingham, 1972), whether conducted in Europe (Søegaard, 1972) or North America (Bingham, 1972). Most activity now is in North America, mainly in P. strobus, P. monticola and P. lambertiana.
Heritability and gain estimates have been developed: for example, "spots only" (McDonald and Hoff, 1971), reduced needle-lesion frequency (Meagher and Hunt, 1996), leaf shed (of infected leaves) (Hoff and McDonald, 1971), bark reaction (Hoff, 1986b), and tolerance (Hoff, 1986a; Hunt, 1997) in Pinus monticola. Rust-resistance heritability estimates have been determined for Pinus wallichiana in Romania (Blada, 1994). Dominant genes stopping rust in pine foliage are identified (Kinloch et al., 1999; Kinloch, 2000) and a linkage map is constructed to facilitate cloning (Harkins et al., 1998). Laboratory techniques have identified a protein associated with defence in pines (Ekramoddoullah et al., 1998), and cloned a resistance gene analogue (Kim and Brunsfeld, 2000). Peptides with a potential for use in genetic engineering have affected spore germination and morphology (Jacobi et al., 2000; Rioux et al., 2000).
The aim of the pine genetic improvement programmes is generally to reduce the impact of the disease so that commercially-useful wood can be obtained without exerting such selective pressure on the rust's gene pool that would increase the frequency of rare alleles (Samman, 1982; Meagher and Hunt, 1985).
Ribes hybrids and cultivars are being screened in Russia (Ravkin and Litvinova, 1976), Siberia (Kuminova, 1980), Ukraine (Sherengovyi, 1979), Slovakia (Kozmenko and Invanicka, 1994), Poland (Tylus et al., 1981; Zurawicz et al., 1996; Pluta and Broniarek-Niemiec, 2000), Denmark (Pedersen, 1998) and the USA (Keep et al., 1975; Hummer, 1997; Dorrance and Bergdahl, 1990). Some estimates of genetic resistance are determined for R. nigrum in Poland (Pluta et al., 1993, Zurawicz et al., 1996). Canada has produced immune and highly-resistant clones that produced too little fruit (Luffman, 2000).
Picton (2002) has used marker-assisted selection to screen cultivated or wild currants for rust-immunity. Ribes improvement programmes usually combine rust resistance with resistance to other pests, such as powdery mildew and leaf spot (Zurawicz et al., 1996; Dale, 2000). During the last half of the 20th century, development of genetic resistance superseded other direct control measures such as, Ribes spp. eradication and antibiotics, which proved either ineffective or unfeasible, in large areas of the white pine range (Kinloch, 2003a).
The distribution and frequency of the Cr2 gene for resistance to C. ribicola in western white pine (P. monticola) was surveyed in natural populations of the host. Because Cr2 is dominant and results in a conspicuous hypersensitive reaction (HR) in pine needles, the phenotype can readily be detected in offspring of susceptible seed parents fertilized by unknown Cr2 donors in the ambient pollen cloud. The diminishing frequency of Cr2 from the southern and central Sierra Nevada, USA, northward mirrors that of Cr1 in sugar pine (P. lambertiana) and points to this region as the origin of both genes (Kinloch, 2003b).
Cultural Control and Sanitary Methods
Eradication of Ribes to reduce infection of pines has been successful in some cases (van Ardsel, 1980; Ostrofsky et al., 1988), but not in Pennsylvania, USA (Hall, 2000), and generally not in the Pinus monticola zone, where there are more native species of Ribes (Toko et al., 1967; Carlson, 1978; Maloy et al., 1994; Maloy, 1997). Europe mainly eliminated cultivation of susceptible pines to protect the more-valuable Ribes fruit crops (Laundon and Rainbow, 1971), whereas some US states banned Ribes cultivation to protect pines (McKay, 2000). Pruning and scribing stem cankers in pine stands can reduce rust successfully if started early (Hungerford et al., 1982; Lehrer, 1982; Lavallée, 1991; Schwandt et al., 1994; Hunt, 1998), although thinning of pines can increase rust by facilitating spore travel (Hunt, 1998). Integration of Ribes control and other options have been developed (Hagle et al., 1989). Silvicultural control of rust on pines is outlined by Yi (1982).
Analysis of rust presence and severity has permitted the definition of hazard zones (Hunt, 1983; Lavallée, 1986) to aid allocation of the most-suited pine stock (Goddard et al., 1985) because predictions of field performance of improved stock have been incorrect in some cases (Hunt and Meagher, 1989; Hunt, 1994). Integrated control using the most-appropriate resistance level is being developed (McDonald, 1979). Model-based predictions of rust hazard and pine stock type have been developed (Rust, 1988; Geils et al., 1999).
Labour-intensive efforts were conducted in the Rocky Mountains, USA, to restore the habitat of whitebark pine (P. albicaulis) by using controlled burning and silvicultural treatments. These measures were used to counteract forest decline due to C. ribicola, and a native mountain pine beetle (Dendroctonus ponderosae) (Keane, 2001).
Hunt (2002) experimented with solid deer protectors to prevent blister rust from attacking white pines, and found that rust prevention using barriers is promising and warrants further testing.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
The identification of C. ribicola as the same rust as that infecting cultivated Ribes virtually eliminated cultivation of Pinus strobus in Europe after 150 years (Laundon and Rainbow, 1971). In North America, its impact on all susceptible pine species has been severe The identification of C. ribicola as the same rust as that infecting cultivated Ribes virtually eliminated cultivation of Pinus strobus in Europe after 150 years (Laundon and Rainbow, 1971). In North America, its impact on all susceptible pine species has been severe (Boyce, 1961; Kliejunas, 1985; Hummer, 2000; Smith and Hoffman, 2000). Bega and Scharpf (1993) declared that white pine blister rust caused more damage and cost more to control than any other conifer disease in North America. The epidemic on Pinus monticola (Neuenschwander et al., 1999) was described as 'the world's most spectacular epiphytotic' (Bingham, 1983), causing a reduction of the gene pool of P. monticola (Hunt et al., 1985) and decimating regeneration of the threatened P. albicaulis (Tomback et al., 1995). However, Harvey (1967) found that branch cankers on P. lambertiana grew slower and died earlier, creating a lesser threat to survival, than similar cankers on P. monticola. Its impact on P. albicaulis and P. strobiformis is under recent study (Brown, 1978; Keane and Arno, 1993; Smith and Hoffman, 1998; Campbell and Antos, 2000; Zeglen, 2000). However, in mid-1980s C. ribicola caused trunk cankers in a sugar pine (P. lambertiana) plantation in the mid-Sierra Nevada mountains, killing 95% of the total number of trees (Chen, 2004). Susceptible Ribes species, especially R. nigrum, suffer reduced vigour and fruit yields.