New Records for Pathogenic Fungi on Weedy Or Non-Indigenous Plants

North American Fungi

Volume 4, Number 8, Pages 1-12 Published December 14, 2009

New records for pathogenic fungi on weedy or non-indigenous plants

George Newcombe1, Rhonda Gaylord2, Joseph P. Yenish3, Joy Mastrogiuseppe4, and Frank M. Dugan5

1College of Natural Resources and Center for Research on Invasive Species and Small Populations, University of Idaho, Moscow, Idaho 83844-1133, 2George Fischer Agricultural Sciences Library, 3Department of Crop and Soil Sciences, 4Ownbey Herbarium, and 5USDA-ARS Plant Germplasm Introduction and Testing Research Unit, Washington State University, Pullman, Washington 99164.

Newcombe, G., R. Gaylord, J. P. Yenish, J. Mastrogiuseppe, and F. M. Dugan. 2009. New records for pathogenic fungi on weedy or non-indigenous plants. North American Fungi 4(8): 1-12. doi: 10.2509/naf2009.004.008

Abstract: A rust fungus, Puccinia jaceae, is reported for the first time in the United States on spotted knapweed, Centaurea stoebe. Powdery mildew (Blumeria graminis) of bulbous bluegrass, Poa bulbosa, is reported for the first time in western North America. Ramularia nivosa on Penstemon palmeri, Albugo candida on Lunaria annua, and Pucciniastrum pustulatum on Epilobium brachycarpum, are reported for the first time from Idaho. A Golovinomyces sp. on Verbena bonariensis is reported for the first time from Washington State. The basis for diagnosis for each disease is reported, accompanied by photomicrographs of the fungal pathogens, photographs of some of the diseases, and discussion of the implications of the findings.

Key words: Albugo candida, Blumeria graminis, Centaurea stoebe, Epilobium brachycarpum, Golovinomyces, Lunaria annua, Penstemon palmeri var. palmeri, Poa bulbosa, Puccinia jaceae, Pucciniastrum epilobii, Pucciniastrum pustulatum, Ramularia nivosa, rust, white rust, Verbena bonariensis 2 Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12

Introduction: Non-native (non-indigenous or annua, and Verbena bonariensis) may increase exotic) plants growing in the absence of the co- pathogen control costs. evolved natural enemies of their home ranges are said to be in a state of enemy release; this state is Materials and Methods: Observations of common for non-native plants (Mitchell and microscopic characters were made and Power 2003). Many invasion biologists photographs taken with an Olympus BH-2 hypothesize that enemy release drives non-native research microscope equipped with a DP-11 plant invasions (Keane and Crawley 2002). digital camera, or with a Zeiss Axioskop 2 According to this hypothesis, it is the extent of equipped with a Nikon Coolpix digital camera. enemy release, which can vary from total to Microscopic structures were measured at 100- negligible, that matters. Testing of this 1000X while mounted in distilled water or, for hypothesis has drawn heavily on host-pathogen Puccinia jaceae, Blumeria graminis and records. For example, the hypothesis has been Ramularia nivosa, in lactoglycerol, or for most comprehensively tested with the host- Golovinomyces sp., in 3% KOH, and for Albugo pathogen databases of the USDA Systematic and Pucciniastrum, 85% lactic acid. Free-hand Mycology and Microbiology Laboratory for an sections of ascocarps were made when needed. analysis published in Nature (Mitchell and Power Literature used for determination of identities of 2003). hosts and fungi, and place of deposit of vouchers, are specified in the text of each record.

Enemy release may be steadily eroded over time Inoculations were performed with both the rust as pathogens from the native range of the plant fungus of spotted knapweed, Centaurea stoebe, find their way to their host’s invaded range. This and with the fungus associated with leaf spots of outcome has been described as enemy reunion Penstemon palmeri var. palmeri. For the former, (Newcombe and Dugan, in press). Enemy release seedlings were raised from seed of C. stoebe that may also be eroded by pathogens that shift or had been collected in Moscow, Idaho, and from jump from native plants (Shipunov et al. 2008). seed of Centaurea diffusa, diffuse knapweed, These changes in the extent of enemy release can collected from four sites: Tygh Valley, Oregon; affect the extent of plant invasions and thus their Portland, Oregon; Douglas County, Colorado; annual cost to the U.S. economy, estimated to be and Kittitas County, Washington. Forty seedlings close to $35 billion (Pimentel et al. 2005). Host- of each species were grown; in the case of C. fungus records documenting new hosts or diffusa there were ten seedlings from each of the expanded ranges of pathogens also are useful for four sites. The eighty seedlings were grown diagnosticians and other plant health outdoors in pots until they had developed full professionals. Herein we focus on new records of rosettes. Then they were misted with water and pathogens of plants that are either non-native inoculated by wiping rust inoculum onto leaf (Poa bulbosa, Centaurea stoebe, Penstemon surfaces with cotton swabs. At the time of this palmeri var. palmeri, Lunaria annua, and inoculation (29 September 2008), only Verbena bonariensis) or native but weedy teliospores appeared to be present on the (Epilobium brachycarpum) in Idaho and naturally infected plants from Lapwai, Idaho (46 Washington. Whereas new pathogens on 20 30.20 N. 116 36 39.60 W) that were used as invasive Poa bulbosa and Centaurea stoebe can the source of inoculum. Trays of the inoculated potentially reduce weed control costs, new plants were inserted into large plastic bags to pathogens on plants with ornamental value maintain leaf wetness overnight. The trays of (Penstemon palmeri var. palmeri, Lunaria inoculated plants were then placed near Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12 3 uninoculated plants of C. stoebe that served as developed on C. stoebe than on C. diffusa and on controls. C. stoebe telia were initially associated with less chlorosis and necrosis, indicating a more With respect to the leaf spot of Penstemon susceptible infection type. Chlorotic areas were palmeri var. palmeri, potato dextrose agar (PDA) sometimes bordered by a purpling of leaf tissues. cultures of the fungus that sporulated freely on Teliospores from the potted C. stoebe plants were the leaf spots were first obtained from conidia of then used during the subsequent winter to the fungus. Seeds of Penstemon palmeri var. periodically inoculate seedlings of C. stoebe in a palmeri were obtained from Seeds Trust (PO Box greenhouse. In early spring 2009, uredinia were 596, Cornville, AZ 86325) and germinated to finally produced from an inoculation with produce greenhouse plants. An aqueous teliospores, suggesting that an aecial state is suspension of fragmented mycelia from one- unnecessary for this fungus. The greenhouse month-old PDA cultures (Ganley et al. 2008) was urediniospores were identical to those produced used to inoculate the three most basal perfoliate on collections from naturally infected plants in leaves of these plants. The suspension was spring (Fig. 3). simply poured into the cup formed by perfoliate leaves and allowed to remain there until it dried. The foremost students of the rusts of Centaurea The leaves of five plants were inoculated; another and the Cardueae to date have undoubtedly been five plants were inoculated with sterile water D.B.O. Savile and A.L. Guyot (Guyot 1965; Savile alone. 1970). Both were candid about the manner in which the difficulty of their research problem was Results: Puccinia jaceae Otth on “compounded by the chaotic taxonomy of the Centaurea stoebe L. s. lat. (= C. maculosa, hosts” (Savile 1970). Centaurea may comprise C. pseudomaculosa, C. biebersteinii, C. between 400 and 700 species and has long been micrantha, spotted knapweed), 12 miles one of the largest and most difficult genera of the south of Lapwai along U.S. Highway 95, Asteraceae (Garcia-Jacas et al. 2001), so Savile’s Nez Perce County, Idaho, 2 October 2007, caution seems justified. With that caveat in 28 September 2008, and again 22 May mind, we considered the fact that Guyot 2009, collector G. Newcombe. Fall recognized two species of Puccinia on C. stoebe: collections yielded dark-brown telia on stems and P. centaureae-vallesiacae Hasler (related to P. leaves (Fig. 1). Teliospores were 30-43 x 21-29 centaureae), and P. jaceae Otth. Savile followed μm, often somewhat constricted at septum, with suit and stated that P. centaureae and its hyaline pedicels, warty and orange-brown walls varieties are characterized by urediniospores with when spores were observed singly with three germ pores, whereas P. jaceae and its transmitted light (Fig. 2). A spring 2009 varieties possess urediniospores with two germ collection yielded uredinia only. Urediniospores pores. According to Savile, the teliospores of P. were nearly spherical (Fig. 3), 25-33 μm x 23-31 centaureae and P. jaceae are “easily confused”, μm, and echinulate except for smooth areas so the urediniospore distinction is key. associated with germ pores. There were always two germ pores. A specimen was deposited in the The only report of any rust on C. stoebe in North U.S. National Fungus Collections (BPI 879147). America was from 1989 in British Columbia, Canada (Mortensen et al. 1991), where the rust The inoculation of plants of C. stoebe and C. was identified as P. jaceae var. diffusae. This diffusa with teliospores in fall 2008 produced variety specializes on C. diffusa and it was telia on leaves and stems 30 days later. Controls subsequently reported on this host in the United remained free of rust. A greater density of telia States (Dugan and Carris 1992; Palm et al. 1992). 4 Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12

However, P. jaceae var. diffusae also possesses asexual state of B. graminis was present on the limited virulence on C. stoebe (Mortensen et al. leaves of both collections, and was largely as 1991). No variety of P. jaceae has been described reported previously from Festuca idahoensis to date that specializes on C. stoebe. (Dugan and Newcombe 2007). Conidia were somewhat longer (Fig. 4), ranging from 26-36 As the Lapwai rust fungus produced μm. However, included in the second collection urediniospores with two germ pores, it would were chasmothecia in various stages of appear to be P. jaceae by Savile’s criterion. maturation (Fig. 5). A secondary mycelium However, the urediniospores of the Lapwai rust including hyaline, thick-walled setae appear to be more nearly circular in outline (Fig. accompanied them (Fig. 6). Immature, clavate 3) than the broadly ellipsoid urediniospores of P. asci with short stalks were present in some jaceae var. diffusae, P. jaceae var. jaceae, and P. chasmothecia. Specimens from the two jaceae var. solstitialis (Mortensen et al. 1989; collections were deposited in the U.S. National Savile 1970). And, although our results are Fungus Collections (BPI 879148 and BPI 879151). preliminary, it would appear that the rust of spotted knapweed in Lapwai is more virulent on To our knowledge, B. graminis has only been C. stoebe than on C. diffusa. With further study, found once on Poa bulbosa in North America a new variety may be warranted for the fungus (Farr et al. n.d.). A single specimen, BPI 563092, that we are reporting here. For now, however, we was collected in Washington, D.C., in 1916. In are reporting this rust of C. stoebe simply as P. contrast, B. graminis appears to be common on jaceae. Our collections from three successive Poa bulbosa throughout its native range in years show that this rust is capable of successful Eurasia, with records from many countries (Farr overwintering in the region. et al. n.d.). In western North America, where Poa bulbosa subsp. vivipara is invasive, B. graminis If managed effectively, P. jaceae might contribute may have been present for some time at low significantly to the biological control of C. stoebe, levels, but this is the first report of its presence as just as Puccinia chondrillina has to the control of far as we know. Many uninfected plants were Chondrilla juncea L., or rush skeleton weed, in observed near infected plants, and the powdery Australia (Hanley and Groves 2002). Centaurea mildew of the latter was inconspicuous as it was stoebe is such a serious invader in western North mostly confined to leaves, particularly their America that twelve insect species have been adaxial surfaces. If reports of powdery mildew on deliberately introduced for the purposes of Poa bulbosa are any indication, in its invaded classical biological control (Story et al. 2006). range in North America this plant may still be Increasing the number of enemies should benefiting from enemy release with respect to decrease the invasiveness of the target plant, this pathogen. It is possible that relatively few according to the enemy release hypothesis virulent pathotypes of B. graminis have been (Mitchell and Power 2003). introduced in the invaded range of Poa bulbosa, and that this fact explains the low infection Blumeria graminis (D.C.) Speer on Poa frequency that we observed. bulbosa L. subsp. vivipara (Koel.) Arcang. (bulbous bluegrass), along Fall Creek Ramularia nivosa (Ellis & Everh.) W.B. above the middle fork of the Weiser River, Cooke & C.G. Shaw on Penstemon palmeri Valley County, Idaho, 2 June 2008. A var. palmeri (scented penstemon), the second collection was made in Moscow, collector’s garden, Moscow, Latah County, Latah County, Idaho, 26 May 2009. Idaho, 26 May 2009. Collector G. Collector in both cases G. Newcombe. The Newcombe. Produced on leaf spots (Fig. 7), Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12 5 conidia were hyaline, catenulate, and minutely introduced seedlings into his garden in Moscow echinulate (Fig. 8) with single, medial septa. which is farther north than the just-mentioned, Conidia varied in length from 19 to 32 μm, and naturalized populations of southern Idaho. The were produced on conidiophores from 32 to 80 reason for the introduction was the beauty of the μm in length, with several conidiogenous loci flowers (Fig. 10) and their scent. For three years (Fig. 9). This fungus fit the description of these plants and their seedlings grew without Ramularia nivosa (Savile 1968; Braun 1998). Ramularia leaf spot. For the past five years The leaf spots have been described previously (including 2009), however, R. nivosa has (Braun 1998); each lesion was typically necrotic, appeared each year in mid-May on new leaves concentric, and bounded by a darker periphery. (Fig. 7). Ramularia leaf spot appears to be Savile noted that conidia and conidiophores of R. limiting the local naturalization of P. palmeri in nivosa can vary considerably in length. this garden; plants are short-lived and new Specimens were deposited in the U.S. National seedlings frequently die before flowering. Fungus Collections (BPI 879149). Inoculations of greenhouse seedlings of P. palmeri var. palmeri Oddly, leaf lesions have not been seen in the with mycelium from the culture made from garden on P. digitalis, P. strictus, and P. conidia of R. nivosa produced leaf spots like albertinus, all of which have been recorded those seen in the field (Fig. 7) on all fifteen before as hosts of R. nivosa (Farr et al. n.d.). P. leaves; all control leaves remained free of spots. davidsonii var. menziesii is also present and When moist-incubated these leaf spots supported unaffected in the garden; however, this species characteristic sporulation of R. nivosa from has never been recorded as a host of R. nivosa. which a new culture was obtained that was very The source of the initial inoculum is unknown but similar to the culture from conidia from the four species of Penstemon grow wild on nearby garden. This appears to be the first successful Moscow Mountain, and three of them have been completion of Koch’s Postulates for R. nivosa. recorded as hosts of R. nivosa: P. confertus, P. fruticosus, and P. wilcoxii (Farr et al. n.d.). This single species of Ramularia, R. nivosa, and no other, specializes on species of Penstemon Albugo candida (Pers.) Roussel on (Farr et al. n.d.; Savile 1968; Braun 1998). But Lunaria annua L. (annual honesty, money not all species of Penstemon have been recorded plant), Moscow, Latah County, Idaho, 20 as hosts. Braun (1998) does list P. palmeri in August 2008, collector R. Gaylord. Utah as a host but does not state which of the two Sporangia (sporangiospores) (Fig. 11) were varieties of P. palmeri there, var. palmeri or var. subglobose, hyaline, thin-walled, smooth to eglandulosus (USDA n.d.), hosted R. nivosa. slightly punctate, 15.5-18 x 13.5-17.5 μm, borne Thus, it is possible that this is the first report of on smooth, hyaline, typically straight R. nivosa on P. palmeri var. palmeri. But it is sporangiophores, 22-31 x 11-14 μm. Dimensions equally possible that we are only reporting R. of sporangia differed slightly from, but were nivosa on P. palmeri var. palmeri for the first overlapping with, dimensions from Glawe et al. time in Idaho, and it is this more cautious (2004) and Mukerji (1975); sporangiophores alternative that is presented in the Abstract. from our specimens and those of Glawe et al. (2004) were shorter than those described in The three varieties of P. palmeri are all native to Mukerji (1975). Sori were as described and the American Southwest, although some illustrated in Glawe et al. (2004) from disease introduced populations of P. palmeri var. incidents in Willamette Valley, Oregon, and palmeri are naturalized in southern Idaho Seattle and Tacoma, Washington. Albugo spp. (Cronquist et al. 1984). In 2002, the first author (Albuginaceae, Peronosporales) are often called 6 Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12

"white rusts" because of the appearance of the Hitchcock and Cronquist (1973). The collection sori, which in our instance were conspicuous, is represented by WSP 71639. often in semi-concentric patterns, becoming quite dense and numerous. Plants with larger The life cycle of the rust, including alternate hosts numbers of sori were stunted relative to those (Abies species) and other host species of with fewer sori. The collection is represented by Epilobium, is discussed in Arthur (1962), Hotson WSP 71638. Albugo candida has been recorded (1934) and Ziller (1974). Ziller referenced the on numerous hosts, mostly in the Brassicaceae opinions of several prominent uredinologists (Choi et al. 2009; Farr et al. n.d.). (J.C. Arthur, G.B. Cummins, Y. Hiratsuka, W. Tranzschel and others) that P. pustulatum and P. Lunaria annua is not indigenous to North epilobii were conspecific, but accepted D.B.O. America, but is widely cultivated as an Savile's opinion that the species were distinct, ornamental annual and recognizable by its with P. pustulatum occuring on Epilobium distinctive, coin-shaped silicles (Hitchcock and species in section Lysimachion. Epilobium Cronquist 1973). It can be weedy in disturbed brachycarpum (as E. paniculatum) had been areas (DiTomaso and Healy 2007), but is also a traditionally placed in this section (Just 1891; candidate crop for oilseed (e.g., Walker et al. Trelease 1891), although Ziller (1974) did not 2003). Albugo candida had not been reported on specify this species in a short list of other species L. annua in North America prior to Glawe et al. in Lysimachion. Faull (1938) failed to obtain (2004), and, to our knowledge, this is the first infection in cross inoculations when using report of A. candida on L. annua in Idaho. Pucciniastrum isolates from Epilobium species then classified in Lysimachion or Chamaenerion. Pucciniastrum pustulatum Dietel (= Epilobium paniculatum was later made the type Pucciniastrum epilobii G.H. Otth) on of a new section in Epilobium, Xerolobium Epilobium brachycarpum C. Presl (= (Raven 1976). Index Fungorum Epilobium paniculatum Nutt. ex Torr. & (www.indexfungorum.org) treats P. pustulatum A. Gray, tall annual willowherb, panicle and P. epilobii as conspecific, and provides willowweed), University of Idaho additional synonyms. We infer that knowledge of Arboretum, Moscow, Latah County, Idaho, the taxonomy and host ranges of the rusts 14 July 2008, collector F.M. Dugan. infecting Epilobium spp. is incomplete. Urediniospores (Figs. 12, 13) were somewhat irregularly obovate or oval, with orange-yellow Numerous Epilobium spp. are listed as hosts of P. contents; colorless wall ca. 1.5 μm thick, epilobii and/or P. pustulatum (Farr et al. n.d.). In echinulate (spines ca. 0.2 μm tall, separated by addition to records from North America, there ca. 1.5 μm); 17-22.5 x 13-16.5 μm. Uredinia were are numerous reports of Pucciniastrum (Fig. 14) spherical, orange, mostly hypophyllous, pustulatum on Abies spp. and/or Epilobium spp. ca. (80-)110-240 μm, opening by an apical pore, in Eurasia (Azbukina 1974; Kuprevich and densely to sparsely distributed, and accompanied Tranzschel 1957). Pucciniastrum pustulatum by varying degrees of leaf chlorosis, being more and/or E. epilobii are recorded in Idaho from intense with greater numbers of uredinia at time other species of Epilobium and from Abies spp. of collection. Urediniospores of our specimens (Farr et al. n.d.), but to our knowledge this is the were slightly wider and with a slightly larger first report for infection of P. brachycarpum in minimum length than those of Arthur (1962), and Idaho. closer to dimensions in Ziller (1974). The host, a "ruderal native" that "can be weedy" (DiTomaso Golovinomyces sp. on Verbena and Healy 2007), was identified by the keys in bonariensis L. (purpletop vervain, tall Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12 7 vervain), Lawson Gardens, Pullman, The dimensions of conidia in our specimen are Whitman County, Washington, 27 more congruent with those of G. verbenae than September 2007, 14 October 2008, with those of G. orontii in Braun (1987), wherein collector F.M. Dugan. Conidia were hyaline, both species have Verbena listed as a host. in chains of up to four, oval to ellipsoid (more GenBank has numerous sequence records for G. rarely cylindrical-ellipsoid), 25-33.5 (-37.5) x orontii, but none for G. verbenae, and 12.5-18 μm, lacking fibrosin bodies, on descriptions of the latter that might complement conidiophores with straight foot-cells generally Braun (1987) were not located. We therefore 39-67 x 10-13 μm and followed by (1-)2-3(-4) refrain from applying a specific epithet for our shorter cells (Figs. 15-17). Appressoria were specimen, but note that this appears to be the papillate (Fig. 18). Conidia germinated sub- first formal report of any Golovinomyces sp. on apically. Chasmothecia were not seen. Colonies Verbena bonariensis in Washington State. on leaves (primarily abaxial) and stems were spreading, off-white, becoming gray, without any Acknowledgements: We thank Amy Blair for conspicuous chlorosis at the time. The collections seed collections of Centaurea diffusa, Anil are represented by WSP 71640 and 71641. Raghavendra for seed of Centaurea stoebe, and Shari Lupien for technical assistance. Steve Verbena bonariensis, a South American plant, is Koike and Melodie Putnam made constructive planted in gardens in North America, often comments on the manuscript. escapes into moist habitats, and apparently is expanding in range (DiTomaso and Healy 2007). Literature cited Powdery mildews on various Verbena species are Arthur, J.C. 1962. Manual of the Rusts in United documented in Farr et al. (n.d.), including States and Canada, with Illustrations and a New records of Erysiphe cichoracearum auct. on V. Supplement by G.B. Cummins. Hafner, New bonariensis in Australia, and "Oidium sp." on York. numerous Verbena spp., including V. bonariensis from Argentina, Australia, Brazil and Japan. Azbukina, Z.M. 1974. Rust Fungi of the Soviet Far Erysiphe cichoracearum D.C. sensu stricto is East. Akad. Nauk., Moscow (in Russian). presently considered confined to Asteraceae (Braun 1987). Specimens of E. cichoracearum on Braun, U. 1987. A monograph of the Erysiphales Verbena are considered under Golovinomyces (powdery mildews). Beihefte zur Nova Hedwigia orontii (Castagne) V.P. Heluta (= Erysiphe 89: 1-700. orontii Castagne) in Braun (1987). Other powdery mildews commonly reported on Braun, U. 1998. 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Figs. 1-6. Fungi on Centaurea stoebe or Poa bulbosa. Fig. 1. Telia of Puccinia jaceae on Centaurea stoebe. Fig. 2. Teliospore of Puccinia jaceae. Bar = 15 μm. Fig. 3. Urediniospores of Puccinia jaceae. Bar = 25 μm. Fig. 4. Conidia of Blumeria graminis. Bar = 20 μm. Fig. 5. Chasmothecia of Blumeria graminis in varying stages of maturation on Poa bulbosa subsp. vivipara. Bar = 450 μm. Fig. 6. Transverse section of chasmothecia of Blumeria graminis, including surrounding mycelium and thick-walled setae. Bar = 200 μm. Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12 11

Figs. 7-11. Fungi on Penstemon palmeri or Lunaria annua, and flowers of P. palmeri. Fig. 7. Leaf spots induced by Ramularia nivosa on Penstemon palmeri. Fig. 8. Conidia of Ramularia nivosa. Bar = 20 μm. Fig. 9. Conidiogenesis in Ramaria nivosa. Bar = 15 μm. Fig. 10. Penstemon palmeri var. palmeri in flower, Moscow, ID. Fig. 11. Sporangia of Albugo candida on leaf of Lunaria annua. Differential interference contrast. Bar = 30 μm. 12 Newcombe et al. New records of pathogenic fungi. North America. North American Fungi 4(8):1-12

Figs. 12-18. Fungi on Epilobium brachycarpum or Verbena bonariensis. Figs. 12,13. Urediniospores of Pucciniastrum pustulatum from E. brachycarpum. Differential interference contrast. Fig. 12. Optical section. Bar = 10 μm. Fig. 13. Surface view. Bar = 10 μm. Fig. 14. Uredinia of Pucciniastrum pustulatum, showing release of urediniospores from apical pores. Bar = 230 μm. Fig. 15 . Conidia, conidiophore and foot cell of Golovinomyces sp. on Verbena bonariensis. Differential interference contrast. Bar = 45 μm. Figs. 16, 17. Conidia of Golovinomyces sp. on Verbena bonariensis. Differential interference contrast. Fig. 16. Terminal conidium. Bar = 12 μm. Fig. 17. Intercalary conidium. Bar = 15 μm. Fig. 18. Appressoria (arrows) of Golovinomyces sp. on Verbena bonariensis. Phase contrast. Bar = 13 μm.