Evaluating White Pine Blister Rust Resistance in Ribes after Artificial Inoculation

Paul J. Zambino

ADDITIONAL INDEX WORDS. black currant, Cronartium ribicola, urediniospore, teliospore, Ribes nigrum, Ribes rubrum.

SUMMARY. Artificially inoculated single-leaf cuttings and small plants consistently differentiated european black currant (Ribes nigrum L.) cultivars susceptible to white pine blister rust (WPBR; Cronartium ribicola J.C. Fisch.) from immune cultivars carrying the Cr resistance gene. Black currant cultivars Consort, Crusader, and Titania showed no signs of infection with any of 21 strains of WPBR, suggesting that strains able to overcome immunity conferred by the Cr resistance gene, if they exist, are uncommon in North America. However, in red currant (Ribes rubrum L.), two sources of material presumed to represent the immune cultivar Viking showed no resistance to infection. All rust strains infected and sporulated as if the cultivar were fully susceptible, casting doubt on the true identity of available sources of ‘Viking’.

hite pine blister rust can cause multiple cycles of urediniospore production and infection on leaves of susceptible currants and gooseberries (Ribes L.) Wduring the growing season, leading to premature leaf drop. Under cool conditions, infected leaves also produce hairlike columns of teliospores. Basid- iospores released from teliospores during cool, moist conditions infect needles of five-needle pines (Pinus L.). The cankers that subsequently form in branches and stems reduce the number of living branches in crowns and girdle trunks, causing widespread mortality. Development and use of resistant currant cultivars in areas where commercial currant production occurs in close proximity to white pine for- ests provide a strategy for minimizing losses in both hosts. The present study de- scribes artificial inoculation of young cuttings non destructively sampled from ac- tively growing plants and inoculation of small plants grown from rooted cuttings as methods of rapidly identifying immune forms of resistance in currants. Materials and methods Ribes used in the study were immune european black currant cultivars Consort, Crusader, and Titania carrying the dominant Cr resistance gene from R. ussuriense Jancz. (Brennan, 1996); susceptible black currant cultivars Boskoop Giant, Ben Alder, and Ben Lomand; two independent sources presumed to represent the im- mune red currant cultivar Viking (syn. ‘Rød Hollandsk Druerips’) which carries an unnamed dominant resistance gene from R. petraeum Wulf. (Hahn, 1943); and susceptible red currant cultivar Red Lake.

USDA Forest Service, Placerville Nursery, 2375 Fruitridge Road, Camino, CA 95709; research conducted at North Central Research Station, Forestry Sciences Laboratory, 5985 Hwy. K, Rhinelander, WI, 54501; e-mail [email protected]. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

544 ● July–September 2000 10(3) Four types of plant materials were Engelm. (ID1.5A); P. flexilis James conditions and in plants exposed to inoculated: softwood cuttings with a (SD1.1B, WY3.1B, WY5.1A); P. natural inoculum in the field (Ander- single young but fully expanded, sub- lambertiana Dougl. (CA2.1B, Happy son, 1939; Hahn, 1935, 1943). The terminal leaf; similar cuttings allowed Camp CA1.1C) and P. strobiformis most advanced signs of infection pre- to mature for 3 weeks after cutting; Engelm. (NM1.1B). The first two let- viously reported have been necrotic rooted plants grown from recent cut- ters of each strain identification num- flecks that developed on very young tings and having at least six leaves; and ber indicates state of origin. leaves, approximately 2 d after artificial similar plants in which shoot growth inoculation (Anderson, 1939). Ability had ceased and all leaves were fully Results and discussion to infect the presumed ‘Viking’ in the hardened. Inoculation of young but fully current studies under all conditions To provide uniformity among expanded leaves on intact plants or as tested and with 21 different strains inoculations, aliquots of WPBR single-leaf stem cuttings successfully eliminates differences in environment urediniospores had been viably stored identified immunity conferred by the and rust strain as causes for the unex- in heat-sealed plastic envelopes at –80 Cr resistance gene in R. nigrum. Abun- pected results. Additional sources of °C (–112 °F) after desiccation to <40% dant infections [13 to 29/cm2 (84 to ‘Viking’ are being sought. The rapid relative humidity (RH) over saturated 187/inch2)] developed within 9 d af- methods of assessing resistance de- calcium chloride for 7 d at 4 °C (39 °F) ter inoculation on fresh and mature scribed in this paper may then be used (Zambino et al., 1997). Spores were cuttings and the topmost leaves of to identify a valid source of the ‘Vi- revived by submerging the envelopes rust-susceptible plants. Infections were king’ gene for immunity. in 40 °C (104 °F) water for 5 min, then not as dense or uniform on lower and removing and rehydrating the spores more mature leaves of intact plants, Literature cited for 4 h at 100% RH and 4 °C. Rehy- and infections were predominantly drated spores were dispersed in 0.25% along veins in older leaves of cultivars Anderson, O.C. 1939. A cytological study Tween 20, pelleted by centrifugation, Ben Lomond and Ben Alder. In con- of resistance of Viking currant to infection resuspended at a concentration of 0.1 trast to susceptible cultivars, all tests of by Cronartium ribicola. Phytopathology 29:26–40. g desiccated spores per 400 mL (13.5 immune black currant cultivars Con- fl oz) 0.07 % water agar, and the sus- sort, Crusader, and Titania showed no Brennan, R.M. 1996. Currants and Goose- pension lightly misted onto the under- signs of infection within 28 d of inocu- berries, III, p. 191–295. In: J. Janick and side of leaves using a perfume atomizer lation. Leaf scorching was noted on J.N. Moore (eds.). Fruit breeding. vol. 2. attached to an air supply. After inocu- some plants and cuttings kept in green- Small fruits and vine crops. Wiley, New lation, plants and cuttings were incu- house conditions, suggesting the need York. bated 24 h at 100% RH and 20 °C (68 for plants to be artificially shaded to Hahn, G.G. 1935. Immunity of Viking, a °F), then placed in a greenhouse in full prevent excessive leaf temperatures. Norwegian red currant, to Cronartium sun (plants and cuttings), or in incuba- Results from red currant inocula- ribicola and Cronartium occidentale under tors and growth chambers with 12 h tions demonstrated the need for rou- greenhouse conditions. USDA Circ. 330. day/night photoperiods at 25/25 °C tine reassessment of resistance during Hahn, G.G. 1943. Blister rust relations of (77 °F) (cuttings only), or 20/15 °C development, propagation, and main- cultivated species of red currants. Phytopa- (68/59 °F) (plants and cuttings). tenance of resistant cultivars. Both of thology 33:341–353. Cuttings were kept before and after the sources presumed to represent the Zambino, P., C. Echt, P. Pijut, and C. inoculation in 5-cm (2-inch) diameter red currant cultivar Viking became Michler. 1997. Desiccation, storage tem- pots of fresh vermiculite within trans- infected, which suggests that an error perature, and heat shock affect germina- parent plastic containers. During in- in propagation or labeling may have tion of Cronartium ribicola urediniospores, fection, containers were covered with been made at some time in the over 60 aeciospores, and teliospores. Inoculum tight-fitting plastic lids; after infec- years since the immunity of this culti- 48:42 (abstr.). tion, a single covering of lab tissue var was first documented. The ‘Vi- provided air circulation and moderate king’ used in this test could not be humidity. Plants were misted and kept differentiated from susceptible red in plastic bags during infection. currant cultivar Red Lake in any set of Most inoculations used Wiscon- inoculations on the basis of onset of sin isolate WI4.1B from eastern white urediniospore production, density of pine (Pinus strobus L.). However, one infections, and onset of teliospore pro- set of mature cuttings incubated at duction at 20/15 °C. Both cultivars 20/15 °C was used to test the effect of also had similar onset of leaf necrosis in WPBR strains from white pine species rust pustules on whole plants kept from across North America on black under greenhouse conditions after in- and red currant immunity to infection. oculation. Strains, listed by host of origin, were as Our results starkly contrast with follows: P. strobus (ME1.1A, ME2.9B, previous reports that indicate the com- MN1.1C, MN4.1A, MN6.1C, plete lack of successful infection and MN7.1C, MN9.1C, NH1.1B, urediniospore production in ‘Viking’ NY4.1A, VT1.4A, WI1.1C, WI4.1B); in plants artificially inoculated with P. monticola Dougl. (Champion Mine either aeciospores and urediniospores OR2.1A, OR2.3B); P. albicaulis and grown under greenhouse or field

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