Worldwide forest surveys reveal forty-three new species in Phytophthora major Clade 2 with fundamental implications for the evolution and biogeography of the genus and global plant biosecurity

During 25 surveys of global Phytophthora diversity, conducted between 1998 and 2020, 43 new species were detected in natural ecosystems and, occasionally, in nurseries and outplantings in Europe, Southeast and East Asia and the Americas. Based on a multigene phylogeny of nine nuclear and four mitochondrial gene regions they were assigned to five of the six known subclades, 2a-c, e and f, of Phytophthora major Clade 2 and the new subclade 2g. The evolutionary history of the Clade appears to have involved the pre-Gondwanan divergence of three extant subclades, 2c, 2e and 2f, all having disjunct natural distributions on separate continents and comprising species with a soilborne and aquatic lifestyle and, in addition, a few partially aerial species in Clade 2c; and the post-Gondwanan evolution of subclades 2a and 2g in Southeast/East Asia and 2b in South America, respectively, from their common ancestor. Species in Clade 2g are soilborne whereas Clade 2b comprises both soil-inhabiting and aerial species. Clade 2a has evolved further towards an aerial lifestyle comprising only species which are predominantly or partially airborne. Based on high nuclear heterozygosity levels ca. 38 % of the taxa in Clades 2a and 2b could be some form of hybrid, and the hybridity may be favoured by an A1/A2 breeding system and an aerial life style. Circumstantial evidence suggests the now 93 described species and informally designated taxa in Clade 2 result from both allopatric non-adaptive and sympatric adaptive radiations. They represent most morphological and physiological characters, breeding systems, lifestyles and forms of host specialism found across the Phytophthora clades as a whole, demonstrating the strong biological cohesiveness of the genus. The finding of 43 previously unknown species from a single Phytophthora clade highlight a critical lack of information on the scale of the unknown pathogen threats to forests and natural ecosystems, underlining the risk of basing plant biosecurity protocols mainly on lists of named organisms. More surveys in natural ecosystems of yet unsurveyed regions in Africa, Asia, Central and South America are needed to unveil the full diversity of the clade and the factors driving diversity, speciation and adaptation in Phytophthora. Taxonomic novelties: New species: Phytophthora amamensis T. Jung, K. Kageyama, H. Masuya & S. Uematsu, Phytophthora angustata T. Jung, L. Garcia, B. Mendieta-Araica, & Y. Balci, Phytophthora balkanensis I. Milenković, Ž. Tomić, T. Jung & M. Horta Jung, Phytophthora borneensis T. Jung, A. Durán, M. Tarigan & M. Horta Jung, Phytophthora calidophila T. Jung, Y. Balci, L. Garcia & B. Mendieta-Araica, Phytophthora catenulata T. Jung, T.-T. Chang, N.M. Chi & M. Horta Jung, Phytophthora celeris T. Jung, L. Oliveira, M. Tarigan & I. Milenković, Phytophthora curvata T. Jung, A. Hieno, H. Masuya & M. Horta Jung, Phytophthora distorta T. Jung, A. Durán, E. Sanfuentes von Stowasser & M. Horta Jung, Phytophthora excentrica T. Jung, S. Uematsu, K. Kageyama & C.M. Brasier, Phytophthora falcata T. Jung, K. Kageyama, S. Uematsu & M. Horta Jung, Phytophthora fansipanensis T. Jung, N.M. Chi, T. Corcobado & C.M. Brasier, Phytophthora frigidophila T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora furcata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora inclinata N.M. Chi, T. Jung, M. Horta Jung & I. Milenković, Phytophthora indonesiensis T. Jung, M. Tarigan, L. Oliveira & I. Milenković, Phytophthora japonensis T. Jung, A. Hieno, H. Masuya & J.F. Webber, Phytophthora limosa T. Corcobado, T. Majek, M. Ferreira & T. Jung, Phytophthora macroglobulosa H.-C. Zeng, H.-H. Ho, F.-C. Zheng & T. Jung, Phytophthora montana T. Jung, Y. Balci, K. Broders & M. Horta Jung, Phytophthora multipapillata T. Jung, M. Tarigan, I. Milenković & M. Horta Jung, Phytophthora multiplex T. Jung, Y. Balci, K. Broders & M. Horta Jung, Phytophthora nimia T. Jung, H. Masuya, A. Hieno & C.M. Brasier, Phytophthora oblonga T. Jung, S. Uematsu, K. Kageyama & C.M. Brasier, Phytophthora obovoidea T. Jung, Y. Balci, L. Garcia & B. Mendieta-Araica, Phytophthora obturata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora penetrans T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora platani T. Jung, A. Pérez-Sierra, S.O. Cacciola & M. Horta Jung, Phytophthora proliferata T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora pseudocapensis T. Jung, T.-T. Chang, I. Milenković & M. Horta Jung, Phytophthora pseudocitrophthora T. Jung, S.O. Cacciola, J. Bakonyi & M. Horta Jung, Phytophthora pseudofrigida T. Jung, A. Durán, M. Tarigan & M. Horta Jung, Phytophthora pseudoccultans T. Jung, T.-T. Chang, I. Milenković & M. Horta Jung, Phytophthora pyriformis T. Jung, Y. Balci, K.D. Boders & M. Horta Jung, Phytophthora sumatera T. Jung, M. Tarigan, M. Junaid & A. Durán, Phytophthora transposita T. Jung, K. Kageyama, C.M. Brasier & H. Masuya, Phytophthora vacuola T. Jung, H. Masuya, K. Kageyama & J.F. Webber, Phytophthora valdiviana T. Jung, E. Sanfuentes von Stowasser, A. Durán & M. Horta Jung, Phytophthora variepedicellata T. Jung, Y. Balci, K. Broders & I. Milenković, Phytophthora vietnamensis T. Jung, N.M. Chi, I. Milenković & M. Horta Jung, Phytophthora ×australasiatica T. Jung, N.M. Chi, M. Tarigan & M. Horta Jung, Phytophthora ×lusitanica T. Jung, M. Horta Jung, C. Maia & I. Milenković, Phytophthora ×taiwanensis T. Jung, T.-T. Chang, H.-S. Fu & M. Horta Jung. Citation: Jung T, Milenković I, Balci Y, Janoušek J, Kudláček T, Nagy ZÁ, Baharuddin B, Bakonyi J, Broders KD, Cacciola SO, Chang T-T, Chi NM, Corcobado T, Cravador A, Đorđević B, Durán A, Ferreira M, Fu C-H, Garcia L, Hieno A, Ho H-H, Hong C, Junaid M, Kageyama K, Kuswinanti T, Maia C, Májek T, Masuya H, Magnano di San Lio G, Mendieta-Araica B, Nasri N, Oliveira LSS, Pane A, Pérez-Sierra A, Rosmana A, Sanfuentes von Stowasser E, Scanu B, Singh R, Stanivuković Z, Tarigan M, Thu PQ, Tomić Z, Tomšovský M, Uematsu S, Webber JF, Zeng H-C, Zheng F-C, Brasier CM, Horta Jung M (2024). Worldwide forest surveys reveal forty-three new species in Phytophthora major Clade 2 with fundamental implications for the evolution and biogeography of the genus and global plant biosecurity. Studies in Mycology 107: 251-388. doi: 10.3114/sim.2024.107.04.

First Report of Phytophthora taxon niederhauserii Causing Root and Stem Rot of Mimosa in Italy

Mimosa [Acacia dealbata Link, syn. Acacia decurrens (Wendl. F.) Wild. var. dealbata (Link) F. Muell., Fabaceae] is an evergreen shrub native to southeastern Australia that is cultivated as an ornamental plant in warm temperate regions of the world. In spring 2010, in a commercial nursery in Liguria (northern Italy), 6- to 10-month-old potted plants of A. dealbata showed symptoms of sudden collapse, defoliation, and wilt associated with root and basal stem rot. An abundant gum exudate oozed from the basal stem. A Phytophthora species was consistently isolated from roots and stem on BNPRAH selective medium (4). On V8 agar (V8A), axenic cultures obtained by single hyphal transfers formed stellate to radiate colonies with aerial mycelium whereas on potato dextrose agar (PDA) the colonies grew more slowly than on V8A and showed stoloniform mycelium and irregular margins. Minimum and maximum growth temperatures on PDA were 10 and 35°C, with the optimum at 30°C. In water, all isolates produced catenulate or single fusiform hyphal swellings and ellipsoid, nonpapillate, persistent sporangia. Dimensions of sporangia were 46.1 to 65.4 × 23.1 to 30.8 μm (mean l/b ratio 2.1). All isolates were A1 mating type and produced spherical oogonia with amphyginous antheridia when paired with A2 mating type of P. drechsleri Tucker on V8A plus β-sytosterol (4). Internal transcribed spacer (ITS) regions of rDNA of the representative Phytophthora isolate IMI 500394 from A. dealbata were amplified and sequenced in both directions with primers ITS6/ITS4. The consensus sequence (GenBank Accession No. JF900371) was 99% similar to sequences of several isolates identified as Phytophthora taxon niederhauserii Z.G. Abad and J.A. Abad (e.g., GQ848201 and EU244850). Pathogenicity tests were performed on 1-year-old potted plants of A. dealbata with isolate IMI 500394. Twenty plants were transplanted into pots (12-cm-diameter) filled with soil infested (4% v/v) with the inoculum of IMI500394 produced on kernel seeds. Plants were kept in a greenhouse with natural light at 25 ± 2°C and watered to field capacity weekly. All inoculated plants showed symptoms of wilt, leaf chlorosis, and basal stem rot within 3 to 4 weeks. Twenty control plants transplanted in autoclaved soil mix remained healthy. P. taxon niederhauserii was reisolated solely from inoculated plants, thus fulfilling Koch's postulates. Since 2003, this pathogen has been found on bottlebrush and rock rose grown in a nursery in Sicily (southern Italy), as well as on Banksia in a nursery in Liguria (2,3). To our knowledge, this is the first report of P. taxon niederhauserii on A. dealbata. P. taxon niederhauserii, recently described as P. niederhauserii sp. nov. (1), is a polyphagous pathogen that was originally reported on arborvitae and ivy in North Carolina in 2001. References: (1) Z. G. Abad et al. Mycologia (in press), 2013. (2) S. O. Cacciola et al. Plant Dis. 93:1075, 2009. (3) S. O. Cacciola et al. Plant Dis. 93:1216, 2009. (4) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

Bud and Root Rot of Windmill Palm (Trachycarpus fortunei) Caused by Simultaneous Infections of Phytophthora palmivora and P. nicotianae in Sicily

In June 2009 in a commercial nursery in eastern Sicily (Italy), 3-year-old potted windmill palms (Trachycarpus fortunei (Hooker) H. Wendl.) showed a decline in growth, wilt, droop, and basal rot of the youngest leaves. The rot progressed inward and killed the bud. Initially, older leaves remained green but eventually the entire plant collapsed. Root rot was consistently associated with aboveground symptoms. Two Phytophthora species were consistently isolated from the petiole base, heart, roots, and rhizosphere soil of symptomatic plants on a selective medium (2) and occasionally recovered from roots and rhizosphere soil of asymptomatic plants. Pure cultures were obtained by single-hypha transfers and the two species were identified on the basis of morphological and molecular characters as Phytophthora palmivora and P. nicotianae. Both species were recovered from all symptomatic plants. From multiple tissue samples per plant, we recovered either or both species. On potato dextrose agar (PDA), P. palmivora isolates grew between 10 and 35°C, with the optimum at 27°C. On V8 juice agar, they produced elliptical to ovoid, papillate, caducous sporangia (32 to 78 × 23 to 39 μm) with a mean length/breadth (l/b) ratio of 1.8:1 and a short pedicel (mean pedicel length = 5 μm). Isolates of P. nicotianae produced arachnoid colonies on PDA, grew at 37°C but did not grow at 40°C. Sporangia (29 to 55 × 23 to 45 μm) were spherical to ovoid (l/b ratio 1.3:1), papillate and often bipapillate, and noncaducous. Isolates of both species produced amphigynous antheridia and oogonia only when paired with reference isolates of P. nicotianae of the A2 mating type. The internal transcribed spacer (ITS) region of rDNA of two isolates of P. palmivora (IMI 398987 and IMI 398988) and an isolate of P. nicotianae (IMI 398989) from T. fortunei was amplified with primers ITS6/ITS4 and sequenced (1). Blast analysis of the sequences of isolates IMI 398987 and IMI 398988 (GenBank Accession Nos. HQ596556 and HQ596558) showed 99% homology with the sequence of two reference isolates of P. palmivora (GQ398157.1 and GU258862), while the sequence of isolate IMI 398989 (HQ596557) showed 99% homology with a reference isolate of P. nicotianae (EU331089.1). Pathogenicity of isolates IMI 398987 and IMI 398989 was proved by inoculating separately each isolate on 1-year-old potted plants of T. fortunei (10 plants per isolate). A zoospores suspension (2 × 10⁴ zoospores/ml) was pipetted onto the petiole base of the three central leaves (200 μl per leaf) of each plant. Sterile water was used for control plants. All plants were incubated at 25 ± 2°C with 100% humidity for 48 h and then maintained in a greenhouse at 24 to 28°C. Within 3 weeks, all inoculated plants showed symptoms of bud rot. Control plants remained healthy. P. palmivora and P. nicotianae were reisolated only from inoculated plants. Bud rot of palms caused by P. palmivora was reported previously in Italy (3). However, to our knowledge, this is the first report of simultaneous infections of P. palmivora and P. nicotianae as causal agents of this disease. Outbreak of bud rot may have been favored by overhead sprinkler irrigation. The recovery of P. palmivora and P. nicotianae from rhizosphere soil and roots of asymptomatic plants suggests infested soil was the primary inoculum source. References: (1) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (2) H. Masago et al. Phytopathology 67:425, 1977. (3) A. Pane et al. Plant Dis. 91:1059, 2007.

Root and Basal Stem Rot of Mandevillas Caused by Phytophthora spp. in Eastern Sicily

Approximately 150,000 potted mandevillas (Apocynaceae) are produced each year in the Etna District of eastern Sicily. Since 2004, leaf chlorosis, wilt, and sudden collapse of the entire plant associated with root and basal stem rot of 6- to 12-month-old potted mandevillas, including Mandevilla × amabilis 'Alice du Pont', M. splendens, and M. sanderi 'Alba', 'My Fair Lady', and 'Scarlet Pimpernel', have been observed in six nurseries. Incidence of affected plants varied from 5 to 40%. Four Phytophthora species were consistently isolated from rotted roots and stems on a selective medium (2). Pure cultures of the first species produced colonies with a camellia pattern on potato dextrose agar and grew between 10 and 37°C with an optimum of 27°C. On V8 juice agar they produced ellipsoid to obpyriform (length/breadth [l/b] 1.45:1), nonpapillate sporangia with internal proliferation, coralloid, spherical hyphal swellings and both terminal and intercalary chlamydospores. In dual cultures with A1 and A2 isolates of P. nicotianae, all isolates produced oogonia with amphyginous antheridia only with A2 isolates. Isolates of the second species formed petaloid colonies, had an optimum growth temperature of 25°C, and produced mono- and bipapillate, ovoid to limoniform sporangia (l/b 1.40:1); they did not produce gametangia. Isolates of the third species formed colonies with a slight petaloid pattern and grew between 2 and 30°C with an optimum of 25°C. Sporangia were obpyriform (l/b 1.48:1), nonpapillate, and proliferous. All isolates were A2 mating type. The isolates of the fourth species formed arachnoid colonies, grew between 8 and 38°C with an optimum of 30°C, and produced mono- and bipapillate, ellipsoid, and obpyriform (l/b 1.3:1) sporangia and apical chlamydospores. All isolates were A2 mating type. DNA was extracted from mycelium and amplified by PCR using the ITS 4/ITS 6 primers (1). Blast search of the rDNA-ITS sequence of isolate IMI 397618 (GenBank Accession No. GQ388261) of the first species showed 100% identity with the ITS sequence of an isolate of P. cinnamomi var. parvispora (EU748548). The sequences (GQ463703 and GQ463704) of isolates IMI 397471 and IMI 397472 of the second species showed 99% similarity with the sequences of a P. citrophthora isolate (EU0000631). The sequence of isolate IMI 397473 (GQ463702) of the third species showed 99% similarity with the sequence of a P. cryptogea isolate (AY659443.1), while the sequence of isolate IMI 397474 (GU723474) of the fourth species showed 99% similarity with the sequence of a P. nicotianae isolate (EU331089). The pathogenicity of individual isolates IMI 397618, IMI 397471, IMI 397472, IMI 397473, and IMI 397474 was tested on 3-month-old potted plants (10 plants per isolate) of mandevilla 'Alice du Pont' by applying 10 ml of a suspension (2 × 10⁴ zoospores/ml) to the root crown. Plants were maintained at 25°C and 95 to 100% relative humidity. All inoculated plants wilted after 4 weeks, while noninoculated control plants remained healthy. The four Phytophthora spp. were subsequently reisolated only from symptomatic plants. To our knowledge, this is the first report of P. cinnamomi var. parvispora in Italy and on mandevilla worldwide. In recent years, Phytophthora root and stem rot has become the most serious disease of potted mandevillas in Sicily. References: (1) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (2) H. Masago et al. Phytopathology 67:425, 1977.

Four Phytophthora Species Causing Foot and Root Rot of Apricot in Italy

In the summer of 2006, 1-year-old apricot (Prunus armeniaca L.) trees with leaf chlorosis, wilting, and defoliation associated with root and crown rot were observed in a nursery in Sicily (Italy). Of 3,000 plants, ~2% was affected. Four Phytophthora spp. (45, 25, 20, and 10% of the isolations of the first, second, third, and fourth species, respectively) were isolated from decayed roots and trunk bark on BNPRAH (3). Axenic cultures were obtained by single-hypha transfers. Isolates of the first species formed petaloid colonies on potato dextrose agar (PDA) and had an optimum growth temperature of 25°C. On V8 agar (VA), they produced persistent, papillate (often bipapillate), ovoid to limoniform sporangia (length/breadth ratio 1.4:1). They did not produce gametangia when paired with A1 and A2 isolates of Phytophthora nicotianae. The second species formed arachnoid colonies, had an optimum growth of 30°C, and produced uni- and bipapillate, ellipsoid, ovoid or pyriform sporangia (length/breadth ratio 1.3:1). All isolates were A2. The third species formed rosaceous colonies on PDA, had an optimum temperature of 28 to 30°C, and produced papillate (sometime bipapillate), ellipsoid or limoniform (length/breadth ratio 2:1), caducous sporangia with a tapered base and a long pedicel (as much as 150 μm). All isolates were A1 type. The fourth species formed petaloid-like colonies on PDA and had an optimum growth of 26 to 28°C. On VA, it produced papillate (sometimes bipapillate), ovoid (length/breadth ratio 1.3:1), and decidous sporangia with a short pedicel (<4 μm). The isolates were homothallic and produced oogonia (25 to 31 μm in diameter) with paragynous antheridia and aplerotic oospores. On the basis of morphological and cultural characters, the species were identified as P. citrophthora, P. nicotianae, P. tropicalis and P. cactorum. Identification was confirmed by the electrophoretic analysis of total mycelial proteins and four isozymes (acid and alkaline phosphatases, esterase, and malate dehydrogenase) on polyacrylamide gel (1). Analysis of internal transcribed spacer (ITS) regions of rDNA using the ITS 4 and ITS 6 primers for DNA amplification (2) revealed 99 to 100% similarity between apricot isolates of each species and reference isolates from GenBank (Nos. AF266785, AB367355, DQ118649, and AF266772). The ITS sequence of a P. citrophthora isolate from apricot (IMI 396200) was deposited in GenBank (No. FJ943417). In the summer of 2008, pathogenicity of apricot isolates IMI 396200 (P. citrophthora), IMI 396203 (P. nicotianae), IMI 396201 (P. tropicalis), and IMI 396202 (P. cactorum) was tested on 3-month-old apricot seedlings (10 plants for each isolate) that were transplanted into pots filled with soil prepared by mixing steam-sterilized sandy loam soil (4% vol/vol) with inoculum produced on autoclaved kernel seeds. Ten control seedlings were grown in autoclaved soil. Seedlings were maintained in a screenhouse and watered daily to field capacity. Within 40 days of the transplant, all inoculated seedlings showed leaf chlorosis, wilting, and root rot. Control seedlings remained healthy. All four Phytophthora spp. were reisolated solely from inoculated plants. To our knowledge, this is the first report of Phytophthora root and crown rot of apricot in Italy and of P. tropicalis on this host. References: (1) S. O. Cacciola et al. Plant Dis. 90:680, 2006. (2) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) H. Masago et al. Phytopathology 67:425, 1977.

First Report of Phytophthora spp. as Pathogens of Pandorea jasminoides in Italy

In the summer of 2005, approximately 5% of a nursery stock of 12-month-old potted plants of bower vine (Pandorea jasminoides (Lindl.) K. Schum.) in Sicily (Italy) showed wilt, leaf chlorosis, defoliation, root rot, and collapse of the entire plant. Three Phytophthora spp. (20, 50, and 30% of the isolations of the first, second, and third species, respectively) were isolated from rotted roots on BNPRAH selective medium (2). Single-hypha isolates of the first species formed petaloid colonies on potato dextrose agar (PDA) and had an optimum growth temperature of 25°C (9.3 mm/day); on V8 juice agar, they produced uni- and bipapillate, ovoid to limoniform sporangia with mean dimensions of 45 × 30 μm and a mean length/width (l/w) ratio of 1.4:1. They did not produce gametangia when paired with A₁ and A₂ isolates of Phytophthora nicotianae. The second species formed arachnoides colonies on PDA, had an optimum growth temperature of 30°C (6.9 mm/day) and produced sporangia that were uni- and bipapillate, ellipsoid, ovoid, or pyriform to spherical (dimensions 44 × 34 μm; l/w ratio 1.3:1). All isolates were A₂ mating type and produced amphyginous antheridia and spherical oogonia with smooth walls. The third species formed rosaceous colonies on PDA, had an optimum growth temperature of 28 to 30°C (11.9 mm/day), and produced uni- and bipapillate, ellipsoid or limoniform, caducous sporangia (dimensions 52 × 26 μm; l/w ratio 2.1:1) with a tapered base and a long pedicel (as much as 150 μm). All isolates were A₁ type and produced amphigynous antheridia and spherical oogonia with smooth walls. The three species were identified as P. citrophthora, P. nicotianae, and P. tropicalis, respectively. The electrophoretic analysis of the mycelial proteins and four isozymes (1) confirmed the identification. Blast analysis of the sequence of the internal transcribed spacer region of the rDNA of a P. tropicalis isolate from bower vine (GenBank Accession No. EU076731) showed 99% similarity with the sequence of a P. tropicalis isolate from Cuphea ignea (GenBank Accession No. DQ118649). The pathogenicity of three isolates from bower vine, IMI 395552 (P. citrophthora), IMI 395553 (P. nicotianae), and IMI 395346 (P. tropicalis), was tested on 3-month-old potted bower vine plants (10 plants for each isolate) by applying 10 ml of a suspension (2 × 10⁴ zoospores/ml) to the root crown. The plants were maintained at 24°C and 95 to 100% relative humidity. All inoculated plants wilted after 4 weeks. Noninoculated control plants remained healthy. The three Phytophthora spp. were reisolated from symptomatic plants. To our knowledge, this is the first report of Phytophthora root rot of bower vine in Italy. References: (1) S. O. Cacciola et al. Plant Dis. 90:680, 2006. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

Wilt and Collapse of Cuphea ignea Caused by Phytophthora tropicalis in Italy

The genus Cuphea (Lythraceae) includes approximately 250 species of annual, evergreen perennials and short shrubs native to Central and South America. During the springs of 2003 and 2004, 10% of the nursery stock of approximately 12,000 potted cigar-flowers (C. ignea A. DC) grown in a screenhouse at a commercial ornamental nursery near Piedimonte Etneo, Sicily, had symptoms of wilt, defoliation, and rapid collapse of the entire plant. These foliar symptoms were associated with a reduced root system, browning of the collar, and dark brown discolored roots. A Phytophthora species was consistently recovered by plating small pieces of rotted roots of symptomatic plants onto selective medium (3); pure cultures were obtained by single-hypha transfers. On potato dextrose-agar (PDA), cardinal temperatures for growth were 10 to 35°C and the optimum was 28 to 30°C. Sporangiophores were umbellate or in a close monoclasial sympodium and mean dimensions of sporangia were 52 × 26 mm, with a mean length/width ratio of 2:1. Sporangia produced on V8 juice agar (VJA) were ellipsoid, fusiform, or limoniform with a tapered base. They were papillate, occasionally bipapillate, caducous, with a long pedicel (as much as 150 μm). All isolates were mating type A1 determined by pairing with A2 reference isolates of P. palmivora (Butl.) Butl. and P. nicotianae Breda de Haan. Oogonia with amphigynous antheridia were formed on VJA after 10 to 15 days at 24°C in the dark. Occasionally, 10 of 15 isolates formed small chlamydospores on VJA. Electrophoretic patterns of total mycelial proteins and four isozymes (acid and alkaline phosphatase, esterase, and malate dehydrogenase) on polyacrylamide slab gels (3) of all Cuphea isolates were very similar to those of reference isolates of P. tropicalis M. Aragaki & J. Y. Uchida from Convolvulus cneorum L. (IMI 391714) and Rhamnus alaternus L., respectively. In addition, the Cuphea isolates were clearly distinct from reference isolates of other species including P. capsici Leon., P. citricola Sawada, P. citrophthora (R. E. Smith & E. H. Smith) Leon., P. nicotianae, and P. palmivora. On the basis of morphological cultural characters and the electrophoretic phenotype, the isolates were identified as P. tropicalis. Internal transcribed spacer (ITS) regions of rDNA sequences (2) confirmed the identification. Koch's postulates were fulfilled by testing three cigar-flower isolates, including isolate IMI 391709, on 10 6-month-old potted cuttings of Cuphea inoculated by applying a 10-ml zoospore suspension (2 × 10⁴ zoospores/ml) to the crowns, incubated for 24 h at 100% relative humidity, and maintained in the greenhouse at 20 to 24°C. After 10 days, crowns and stems were brown and all plants wilted within 20 days. Ten control plants treated with water remained healthy. P. tropicalis was reisolated from infected tissues. The test was repeated with similar results. In Europe, P. tropicalis has been reported on Cyclamen persicum Mill. in Germany (4) and C. cneorum and R. alaternus in Italy (1), indicating a broad host range and spreading in ornamental nurseries. References: (1) S. O. Cacciola et al. Boll. Acc. Gioenia Sci. Nat. 31:57, 1999. (2) S. O. Cacciola et al. For. Snow Landsc. Res. 76:387, 2001. (3) D. C. Erwin and O. K. Ribeiro. Pages 39-41, 138-139 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul MN. 1996. (4) W. W. P. Gerlach and A. Schubert. Plant Dis. 85:334, 2001.

First Report of Brown Rot and Wilt of Fennel Caused by Phytophthora megasperma in Italy

Fennel (Foeniculum vulgare Mill. var. azoricum (Mill.) Thell.) in the Apiaceae family is native to southern Europe and southwestern Asia. It is an economically important crop in Italy that produces approximately 85% of all fennel worldwide. The main producing regions are Apulia, Campania, Latium, and Calabria. During the late winter of 2004 in the Crotone Province of the Calabria Region, following heavy rains, patches of fennel plants with symptoms of brown, soft rot of the bulb-like structure formed by the thickened leaf bases, development of yellow leaves, stunting, and wilting of the entire plant were observed in fields. A homothallic Phytophthora sp. was isolated consistently from the brownish tissues of the stout stems and leaf bases of symptomatic plants using a selective medium (3). Pure cultures were obtained by single hyphal tip transfers. On potato dextrose agar (PDA), the diameter of oospores varied from 28 to 42 μm (mean = 36.3 ± 0.4). Antheridia were primarily paragynous. Sporangia were not produced on solid media but were formed in sterile soil extract solution. They were nonpapillate, noncaducous, ovoid and obpyriform (25 to 45 × 35 to 60 μm), and internally proliferating. Optimum and maximum temperatures for radial growth of the colonies on PDA were 25 and 30°C, respectively. At 25°C, radial growth rate was approximately 6 mm per day. On the basis of morphological and cultural characteristics, the isolates were identified as Phytophthora megasperma Drechsler. Electrophoretic patterns of mycelial proteins and four isozymes (acid and alkaline phosphatase, esterase, and malate dehydrogenase) on polyacrylamide gels of the fennel isolates were identical to those of reference isolates of P. megasperma of the BHR (broad host range) group included in P. gonapodyides-P. megasperma Clade 6 (1,3), but distinct from those of the isolates of other nonpapillate species included in Waterhouse's taxonomic group VI. Internal transcribed spacer (ITS) regions of rDNA sequences (2) confirmed that fennel isolates belonged to P. megasperma BHR group. Pathogenicity of a fennel isolate from Calabria (IMI 391711) was confirmed by pouring a zoospore suspension at 2 × 10⁴ zoospores per ml on the soil of 10 3-month-old potted fennel plants. The soil of the inoculated and 10 control seedlings was flooded for 24 h. After 10 days, stems and leaf bases of the seedlings showed a brown rot. Chlorosis and wilting of all seedlings developed after 20 days. Controls inoculated with water did not develop any symptoms. The pathogen was reisolated from typical brown rot and tests were repeated with similar results. To our knowledge, this is the first report of P. megasperma causing disease on fennel. References: (1) S. O. Cacciola et al. For. Snow. Landsc. Res. 76:387, 2001. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (3) H. Masago et al. Phytopathology, 67:425, 1977.

Root and Basal Stem Rot of Scotch Broom Caused by Phytophthora citricola and P. drechsleri in Italy

Scotch broom (Cytisus scoparius (L.) Link, Fabaceae), an evergreen shrub native to Europe, is cultivated as a garden plant. In 2003 and 2004, potted plants with symptoms of leaf chlorosis, defoliation, and eventual wilt and associated with root and collar rot were observed in ornamental nurseries in Sicily. As much as 10% of plants were affected in a single nursery. Two species of Phytophthora were consistently isolated alone or together from the same pot with the selective medium of Masago et al. (2). Pure cultures were obtained by single-hypha transfers and the species were identified as P. citricola Sawada (approximately 40% of isolations) and P. drechsleri Tucker (60% of isolations) on the basis of morphological, cultural characters, and electrophoretic phenotype. The isolates of P. drechsleri grew between 10 and 37°C (optimum 27°C) on potato dextrose agar (PDA). The sporangia produced on V8 juice agar (V8A) were ellipsoid to obpyriform, nonpapillate, persistent with internal proliferation, and often forming in a sympodium. Sizes varied, 30 to 60 × 20 to 40 μm (length/width ratio between 1.4 and 2.2). The hyphal swellings were produced in aqueous culture. All isolates were A₁ mating type and formed plerotic oospores (mean diameter (ф) 25 μm) with amphigynous antheridia when paired with the A₂ reference isolates of P. cryptogea on V8A plus β-sitosterol. The aryl-esterase and malate dehydrogenase isozymes of scotch broom isolates on polyacrylamide slab gels (1) were identical to those of the authentic isolate CBS 292.35 of P. drechsleri and differed from reference cultures of other nonpapillate species. The cardinal temperatures of P. citricola isolates on PDA ranged from 2 to 30°C (optimum 25°C). In liquid culture, the isolates produced irregular-shaped, obovoid to obpyriform sporangia 20 to 70 × 21 to 44 μm that were noncaducous, semipapillate or with inconspicuous papilla, often with two apices. The isolates were homothallic and produced oospores (mean ф 22 μm) with paragynous antheridia. The electrophoretic phenotype of these isolates was identical to the phenotype of P. citricola reference isolates and very different from that of the reference isolates of other semipapillate species. The pathogenicity tests of the representative isolates of P. drechsleri (IMI 391710) and P. citricola (IMI 391715) were carried out in a screenhouse. Twenty 3-month-old scotch broom seedlings were transplanted into pots (12 cm ф) filled with soil infested with the inoculum produced on a mixture of vermiculite and autoclaved oat seeds. The plants were maintained at 20 to 28°C and watered to field capacity once a week. After 30 to 40 days, all inoculated plants showed symptoms of wilting and root rot. The 20 control plants transplanted into pots containing noninfested soil remained healthy. P. citricola and P. drechsleri were reisolated from infected tissues. To our knowledge, this is the first report of P. citricola and P. drechsleri on scotch broom. A root rot of scotch broom caused by P. megasperma has been reported in central Italy (3). References: (1) S. O. Cacciola et al. Plant Dis. 86:327, 2002. (2) D. C Erwin and O. K. Ribeiro. Pages 39-41 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (3) A. M. Vettraino and A. Vannini. Plant Pathol. 53:417, 2003.

Root and Foot Rot of Lantana Caused by Phytophthora cryptogea

Lantana (Lantana camara L.) is an evergreen shrub in the Verbenaceae. In some countries, this plant has been declared a noxious weed. However, a number of sterile or near-sterile forms are cultivated as attractive flowered potted and garden plants. In early spring 2004, ≈4,000 potted, small trees of lantana grown in a screenhouse in a commercial nursery of ornamentals near Giarre, Sicily, showed symptoms of chlorosis, defoliation, and sudden collapse of the entire plant. These aboveground symptoms were associated with a reduced root system, rot of feeder roots, and brown discoloration of the base of the stem. A Phytophthora sp. was isolated consistently from roots and basal stems of symptomatic plants using the selective medium of Masago et al. (3). Cardinal temperatures for radial growth of pure cultures obtained by single hypha transfer were 2°C minimum, 25°C optimum, and 30 to 35°C maximum. Sporangia produced in the saline solution of Chen and Zentmyer (3) were obpyriform, persistent, and nonpapillate. All isolates were A1 mating type and differentiated oospores with amphigynous antheridia in dual cultures with A2 reference isolates of P. cryptogea Pethybr. & Laff. and P. drechsleri Tucker (3). Electrophoretic patterns of total mycelial proteins (3) of the isolates from lantana were very similar to those of reference isolates of P. cryptogea from different hosts, but clearly distinct from those of reference isolates of other species included in Waterhouse's taxonomic group VI (3). Indeed, isolates from lantana were identified as P. cryptogea on the basis of morphological and cultural characters as well as the electrophoretic phenotype. Sequences of internal transcribed spacer (ITS) regions of rDNA (1) confirmed the identification as P. cryptogea. Pathogenicity of a representative isolate from lantana (IMI 392045) was tested in a screenhouse by transplanting 20 6-month-old rooted cuttings of lantana in pots (12 cm in diameter) filled with infested soil; the soil was prepared by mixing steam-sterilized sandy loam soil at a concentration of 4% (vol/vol) with inoculum produced on a mixture of vermiculite and autoclaved oat seeds. Twenty control plants were transplanted in pots containing noninfested soil. The soil was saturated with water by plugging the pots' drainage holes for 48 h and watering. After 40 days, all plants except the controls showed symptoms of root and foot rot, and P. cryptogea was reisolated from infected tissues. To our knowledge, this is the first report of P. cryptogea on lantana. On this host and other species in the verbena family, only P. nicotianae van Breda de Haan (= P. parasitica Dastur) has been previously reported (2,3,4). A possible cause of the high incidence of this disease in the nursery was waterlogging due to heavy rain and excessive irrigation. References: (1) S. O. Cacciola et al. For. Snow Landsc. Res. 76:387, 2001. (2) M. L. Daughtrey et al. Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (3) D. C Erwin and O. K. Ribeiro. Pages 39-41, 84-95, 138-139 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (4) K. H. Lamour et al. Plant Dis. 87:854, 2003.

First Report of Phytophthora palmivora on Grevillea spp. in Italy

The genus Grevillea (family Proteaceae) comprises over 300 species and is a popular and widely cultivated group of Australian plants. In the last 3 years, numerous potted grevilleas with symptoms of decline associated with a rot of feeder roots were found in ornamental nurseries in Sicily. Aboveground symptoms were reduced growth, yellowing of foliage, wilt, dieback, and death of the entire plant. The disease was observed on many commercial cultivars and was especially severe on G. alpina (mountain grevillea), G. juniperina (juniper-leaf grevillea), G. lavandulacea (lavender grevillea), and G. rosmarinifolia (rosemary grevillea) as well as the hybrid cultivars Clearview David (G. lavandulacea × rosmarinifolia) and Poorinda Rondeau (G. baueri × lavandulacea), while G. lanigera (woolly grevillea) cv. Mount Tamboritha and G. thelemanniana subsp. obtusifolia appeared resistant. A species of Phytophthora was consistently isolated from rotted roots of symptomatic plants using a selective medium (4), and pure cultures were obtained by single-hypha transfers. The species was identified as P. palmivora (E.I. Butler) E.I. Butler on the basis of morphological and cultural characters. On solid media, all isolates produced elliptical to ovoid, papillate sporangia with a mean length/width ratio of 1.8. Sporangia were caducous with a short pedicel (5 μm) and a conspicuous basal plug. All isolates were heterothallic (mating type A1) and produced oogonia and oospores only when paired with A2 mating type reference isolates of P. nicotianae and P. palmivora. Antheridia were amphyginous. Identification was confirmed by electrophoresis of mycelial proteins in polyacrylamide slab gels (1). The electrophoretic patterns of total soluble proteins and six isozymes (alkaline phosphatase, esterase, fumarase, NAD-glucose dehydrogenase, malate dehydrogenase, and superoxide dismutase) of isolates from grevillea were identical to those of a reference isolate of P. palmivora from Coronilla valentina subsp. glauca (2) but distinct from those of reference strains of eight other papillate species of Phytophthora included in Waterhouse's taxonomic group VI. Koch's postulates were fulfilled using 6-month-old rosemary grevillea plants that were transplanted into pots filled with soil that was artificially infested with chlamydospores (50 per gram of soil) produced in submerged cultures (3) by grevillea isolate IMI 390579. Plants were maintained in a glasshouse at 20 to 28°C and watered to field capacity once a week. One month after transplanting, infected plants showed decline symptoms similar to those of naturally infected plants. Control plants grown in pots containing noninfested soil remained healthy. P. palmivora was reisolated from roots of symptomatic plants. It appears that P. palmivora has become a widespread root pathogen in commercial ornamental nurseries in Italy (2). References: (1) S. O. Cacciola et al. EPPO Bull. 20:47, 1990.D. (2) S. O. Cacciola et al. Plant Dis. 86:327, 2002. (3) J. Y. Kadooka and W. H. Ko. Phytopathology 63:559, 1973. (4) H. Masago et al. Phytopathology 67:425, 1977.

Collar and Root Rot of Olive Trees Caused by Phytophthora megasperma in Sicily

Olive (Olea europea L.) is grown on about 154,000 ha in Sicily (southern Italy). In the summer of 1999, a few 3-year-old olive trees with decline symptoms were observed in a recently planted commercial orchard in the Enna province (Sicily). The trees were propagated on wild olive (O. europea L. var. sylvestris Brot.) rootstock. Aerial symptoms, consisting of leaf chlorosis, wilting, defoliation, and twig dieback followed in most cases by plant death, were associated with root rot and basal stem cankers. A Phytophthora sp. was consistently isolated from rotted rootlets and trunk cankers using the BNPRAH (benomyl, nystatin, pentachloronitrobenzene, rifampicin, ampicillin, and hymexazol) selective medium. Pure cultures were obtained by single-hypha transfers. The species isolated from symptomatic olive trees was identified as P. megasperma Drechsler on the basis of morphological and cultural characteristics. All isolates were homothallic, with paragynous antheridia. The diameter of oospores varied from 28 to 42 μm (mean ± SE = 36.3 ± 0.4) when they were produced on potato-dextrose agar (PDA) and from 30 to 43 μm (mean ± SE = 37.8 ± 0.4) when they were produced in saline solution. Sporangia were non-papillate. Optimum and maximum temperatures for radial growth of the colonies on PDA were 25 and 30°C, respectively. At 25°C, radial growth rate was about 6 mm per day. The identification was confirmed by the electrophoresis of mycelial proteins on a polyacrylamide slab gel. The electrophoretic banding patterns of total soluble proteins and three isozymes (esterase, fumarase, and malate dehydrogenase) of the isolate from olive were identical to those of two isolates of P. megasperma obtained from cherry and from carrot in Italy and characterized previously (1). Conversely, they were clearly distinct from the electrophoretic patterns of four isolates of P. megasperma var. sojae Hildebr. from soybean (= P. sojae Kauf. & Ger.), from those of three isolates from asparagus tentatively identified as P. megasperma sensu lato (1) and from those of reference isolates of various species producing non-papillate sporangia, including P. cambivora (Petri) Buisman, P. cinnamomi Rands, P. cryptogea Pethybr. & Laff., P. drechsleri Tucker, and P. erythroseptica Pethybr. Pathogenicity of the isolate from olive was tested in the greenhouse at 18 to 25°C using 18-month-old rooted cuttings of olive cv. Biancolilla. Cuttings were inoculated on the lower stem by inserting a 3-mm plug taken from actively growing colonies on PDA into an incision made with a sterile scalpel. The wound was sealed with waterproof tape. Agar plugs with no mycelium were placed into the stem of cuttings used as a control. The bark was stripped and lesion areas were traced and measured 60 days after inoculation. The isolate from olive produced a brown necrotic lesion (mean size = 500 mm²) around the inoculation wound and was reisolated from the lesion. Conversely, the wound healed up on control plants. P. megasperma has previously been recognized as a pathogen of olive in Greece and Spain (3). However, this is the first report of P. megasperma causing root and collar rot of olive in Italy. References: (1) S. O. Cacciola et al. Inf. Fitopatol. 46:33, 1996. (2) D. C. Erwin and O. K. Ribeiro, 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN. (3) M. E. Sánchez-Hernádez et al. Plant Dis. 81:1216, 1997.

Race 1,2y of Fusarium oxysporum f. sp. melonis on Muskmelon in Sicily

Muskmelon (Cucumis melo L.) is very important economically to agriculture in Italy. The Sicily area accounts for ≈40% of the total muskmelon production. Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Leach & Currence) W.C. Snyder & H.N. Hans. is the most prevalent and damaging disease of muskmelon in Sicily. Use of cultivars with major resistance genes, Fom 1 and Fom 2, is the most effective control measure for combating the disease. During March 1999, severe infections of Fusarium wilt were noted in a commercial muskmelon crop, cv. Firmo F1, grown in plastic tunnels in Syracuse Province (eastern Sicily). The muskmelon seedlings had been transplanted into the tunnels during January 20 days after soil fumigation with methyl bromide. Firmo F1 possesses both Fom 1 and Fom 2 genes. Of 18,000 Firmo F1 plants, ≈6,500 showed symptoms consisting of stunting, vein clearing; leaf yellowing, wilting, and dying; brown necrotic streak; and gummy exudates on the basal portion of vines. A pinkish white mold developed on dead tissues when infected plants were kept at high relative humidity. The pathogenicity of both a single-conidium isolate of F. oxysporum f. sp. melonis from a symptomatic Firmo F1 plant and two isolates of races 0 and 1, recovered previously from other cultivars in Sicily and used as references, was tested with three differential muskmelon cultivars, Charentais T, Doublon, and CM 17187 (1), as well as three commercial cultivars, Ramon, Cassella, and Geamar (possessing Fom 1, Fom 2, and both Fom 1 and Fom 2 resistance genes, respectively). Muskmelon seedlings were inoculated by the root-dip method (3), using a suspension of 5 × 10⁵ conidia per ml. Inoculated seedlings were transplanted to plastic pots filled with sterilized soil and placed in a greenhouse (25 to 30°C). Symptoms were scored 7 to 10 days after inoculation. The isolate from Firmo F1 was pathogenic to all cultivars tested, the race 0 isolate was pathogenic only to cv. Charentais T, and the race 1 isolate was pathogenic only to cvs. Charentais T, Doublon, and Ramon. F. oxysporum was reisolated from symptomatic plants. Based on its pathogenicity and symptomology, the isolate from Firmo F1 was classified as race 1,2y (yellows), according to the nomenclature proposed by Risser et al. (1). Race 1,2 poses a serious threat to muskmelon production in Sicily, because all currently used cultivars are susceptible to the race, and other control measures, such as preplant soil fumigation with methyl bromide and solarization, are not as effective as use of resistant cultivars. Further study is needed to establish which is the prevalent race of F. oxysporum f. sp. melonis in Sicily. This report confirms that race 1,2 occurs in all major muskmelon-production areas in Italy (2). References: (1) G. Risser et al. Phytopathology 66:1105, 1976. (2) G. Tamietti et al. Petria 4:103, 1994. (3) F. L. Wellman. Phytopathology 29:945, 1939.

First Report of Root Rot Caused by Phytophthora cinnamomi on Avocado in Italy

Root rot caused by Phytophthora cinnamomi Rands is generally recognized to be the most important disease of avocado (Persea americana Miller) wherever this tropical fruit tree is grown (3). The disease was first found in Italy in the spring of 1998. Eight-year-old trees, with symptoms ranging from initial to severe, were observed in an experimental field near Rocca di Caprileone, in Sicily. Few trees showed symptoms of both root rot and collar rot. Infected trees were of 13 commercial cultivars. Trees were grafted on two different rootstocks: Hass seedlings and G6 seedlings. G6 is a selection reported to have some field resistance to P. cinnamomi infections (2). However, no correlation was observed between symptom severity and rootstock. P. cinnamomi was isolated on BNPRAH selective medium (4) from trunk bark, feeder roots, and rhizosphere soil of diseased trees, and from roots of symptomless trees. The isolates, identified primarily on the basis of morphological and cultural characteristics, formed rosaceous colonies on potato dextrose agar (PDA) and on corn meal agar (CMA) coralloid-type mycelium, with abundant hyphal swellings, which were typically spherical and in clusters. Chlamydospores were either terminal or intercalary, and often occurred in characteristic grapelike clusters. Sporangia, which were produced in saline solution (1), were broadly ellipsoidal or ovoid, persistent, non-papillate and proliferous. The identification was confirmed by the electrophoresis of mycelial proteins on polyacrylamide slab gel. The electrophoretic patterns of total soluble proteins and eight isozymes (AKP [alkaline phosphatase], EST [esterase], FUM [fumarase], GLC [NAD-glucose dehydrogenase], G6PD [glucose-6-phosphate dehydrogenase], LDH [lactate dehydrogenase], MDH [malate dehydrogenase], and SOD [superoxide dismutase]) of the isolates from avocado were identical to those of two strains of P. cinnamomi, used as reference (isolate 70473 from International Mycological Institute, U.K., and an isolate from myrtle from the Institute of Plant Pathology, University of Catania, Italy). Conversely, the electrophoretic phenotype of the P. cinnamomi isolates from avocado was clearly distinct from those of reference strains of eight other species included in Waterhouse's taxonomic group VI. Pairings with isolates of a known mating type of P. cinnamomi, P. cryptogea, and P. drechsleri revealed that all the isolates from avocado were A2 mating type. It is possible that P. cinnamomi had been introduced into the experimental field on infected symptomless nursery trees. In Italy, root rot caused by P. cinnamomi could have a significant impact on commercial avocado plantings extending over about 20 ha. Moreover, this polyphagous pathogen may be a threat to other crops as well as to forest trees. References: (1) D. W. Chen and G. A. Zentmyer. Mycologia 62:397, 1970. (2) M. D. Coffey. Plant Dis. 71:1046, 1987. (3) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN. (4) H. Masago et al. Phytopathology 67:425, 1977.