STUDIES IN MYCOLOGY 55: 65–74. 2006.
Characterisation of Phomopsis spp. associated with die-back of
rooibos (Aspalathus linearis) in South Africa
Johan C. Janse van Rensburg1, Sandra C. Lamprecht1*, Johannes Z. Groenewald2, Lisa A. Castlebury3 and Pedro
W. Crous2
1ARC
Plant Protection Research Institute, P. Bag X5017, Stellenbosch, 7599; 2Centraalbureau voor Schimmelcultures, Fungal Biodiversity
Centre, P.O. Box 85167, NL 3508 AD, Utrecht, The Netherlands; 3USDA-ARS, Systematic Botany & Mycology Laboratory, Rm 304, Bldg 011A,
Beltsville, MD 20705, U.S.A.
*Correspondence: Sandra Lamprecht, lamprechts@arc.agric.za
Abstract: Die-back of rooibos (Aspalathus linearis) causes substantial losses in commercial Aspalathus plantations in South Africa. In the past,
the disease has been attributed to Phomopsis phaseoli (teleomorph: Diaporthe phaseolorum). Isolates obtained from diseased plants, however,
were highly variable with regard to morphology and pathogenicity. The aim of the present study was thus to identify the Phomopsis species
associated with die-back of rooibos. Isolates were subjected to DNA sequence comparisons of the internal transcribed spacer region (ITS1,
5.8S, ITS2) and partial sequences of the translation elongation factor-1 alpha gene. Furthermore, isolates were also compared in glasshouse
inoculation trials on 8-mo-old potted plants to evaluate their pathogenicity. Five species were identified, of which D. aspalathi (formerly identified
as D. phaseolorum or D. phaseolorum var. meridionalis) proved to be the most virulent, followed by D. ambigua, Phomopsis theicola, one
species of Libertella and Phomopsis, respectively, and a newly described species, P. cuppatea. A description is also provided for D. ambigua
based on a newly designated epitype specimen.
Taxonomic novelties: Diaporthe aspalathi Janse van Rensburg, Castlebury & Crous stat. et nom. nov., Phomopsis cuppatea Janse van
Rensburg, Lamprecht & Crous sp. nov.
Key words: Elongation factor 1-alpha gene, Diaporthe, endophytes, ITS, pathogenicity, Phomopsis die-back, systematics.
INTRODUCTION
Rooibos (Aspalathus linearis) is a leguminous shrub
that is indigenous to the Western Cape Province of
South Africa, and used for the production of rooibos tea.
A serious die-back disease of plants in the Clanwilliam
area was first observed in 1977 and officially reported in
the scientific literature by Smit & Knox-Davies (1989a,
b), who identified the causal organism as Phomopsis
phaseoli (Desm.) Sacc. [teleomorph: Diaporthe
phaseolorum (Cooke & Ellis) Sacc.]. Since die-back
of rooibos was originally reported, it has developed
into a disease of considerable economic importance,
affecting up to 89 % of plants in 3-yr-old plantations
(Lamprecht et al., unpubl. data).
The genus Phomopsis (Sacc.) Bubák contains a
large number of cosmopolitan plant pathogens, many
of which incite blights, cankers, die-backs, rots, spots,
and wilts in a wide assortment of plants of economic
importance (Kulik 1984, Uecker 1988). Phomopsis
diseases usually manifest themselves in the production
of characteristic symptoms, some of which can
culminate in the death of the host plant (Kulik 1984).
In rooibos, symptoms manifest themselves as a dieback of harvested branches, with pycnidia forming on
dead tissue, and a characteristic internal discoloration
of infected branches. Eventually this leads to death of
the host plant, after which perithecia form just below
the soil surface (Fig. 1).
Contrary to earlier reports (Smit & Knox-Davies
1989a, b), preliminary surveys and pathogenicity studies
revealed the Phomopsis isolates associated with the
disease to be highly variable with regards to morphology
and virulence, indicating the possible existence of more
than one species. To develop a sustainable die-back
management programme for the rooibos industry, it was
necessary to determine which species were involved in
this disease complex and which of these were the most
important pathogens. The aim of the present study
was to characterise the Phomopsis/Diaporthe spp.
associated with die-back symptoms of rooibos bushes.
This was done by generating DNA sequence data of
the ITS region and partial translation elongation factor1 alpha (TEF1 or EF1-α) gene and analysing these
data with morphological and cultural observations. A
further aim was to conduct pathogenicity studies with
the various species identified and to determine which
of these were the most virulent pathogens involved with
the die-back disease of Aspalathus.
MATERIALS AND METHODS
Isolates
Symptomatic plants were collected throughout the
rooibos-producing area ranging from Citrusdal in the
south to Nieuwoudtville in the north. Isolations were
made from surface-disinfected host tissue onto Petri
dishes containing 2 % potato-dextrose agar (PDA;
Difco, Becton Dickinson, Sparks, MD, U.S.A.). A total
of 28 Phomopsis isolates representing the different
morphological groups recognised on PDA were selected
for further molecular characterisation. The origin of
isolates, as well as plant parts from which they were
isolated, are listed in Table 1. Reference strains were
deposited in the Centraalbureau voor Schimmelcultures
in Utrecht, the Netherlands (CBS).
65
JANSE VAN RENSBURG ET AL.
Fig. 1. Aspalathus linearis plants with Phomopsis die-back. A. Healthy plants under cultivation. B. Plants after harvest. C. Aspalathus bush
with die-back symptoms. D–E. Stem cankers. F. Pycnidial formation on dead stem tissue. G. Formation of perithecia on stems just below the
soil surface.
Table 1. Phomopsis and Diaporthe isolates from South Africa used in this study.
Species
Strain no.1
Farm, area
Rainfall2
Plant
part
Lesion
length
Collector
(cm)3
D. ambigua
D. aspalathi
66
GenBank
numbers
(EF, ITS)4
CBS 117167; CPC 5414; R86AM
Taaibosdam,
Gifberg
High
Crown
3.44d–g
J.C. Janse van
Rensburg
DQ286237,
DQ286263
CBS 117170; R59O
Vaalkrans,
Nardouwsberg
Low
Branch
5.63b
J.C. Janse van
Rensburg
DQ286238,
DQ286264
CBS 117371; CPC 5421; R350U
Uitsig, AgterPakhuis
Low
Branch
4.83b–d
J.C. Janse van
Rensburg
DQ286239,
DQ286265
CBS 117372; CPC 5411; 10040K
Clanwilliam
High
Root
2.17g–k
S.C. Lamprecht
DQ286240,
DQ286266
CBS 117373; CPC 5427; R408AP
Langebergpunt,
Clanwilliam
High
Root
0.69j–l
J.C. Janse van
Rensburg
DQ286241,
DQ286267
CBS 117374; CPC 5418; R165AI
Karnemelksvlei,
Citrusdal
High
Crown
5.36b–c
J.C. Janse van
Rensburg
DQ286242,
DQ286268
CPC 5409; 9963K
Clanwilliam
High
Crown
4.00b–e
S.C. Lamprecht
DQ286243,
DQ286269
CPC 5412; R66I
Taaiboskraal,
Agter-Pakhuis
Low
Root
0.61j–l
J.C. Janse van
Rensburg
DQ286244,
DQ286270
CPC 5413; R78U
Nardouw,
Nardouwsberg
Low
Crown
0.94i–l
J.C. Janse van
Rensburg
DQ286245,
DQ286271
CPC 5419; R337AR
Vaalkrans,
Nardouwsberg
Low
Branch
3.06d–h
J.C. Janse van
Rensburg
DQ286246,
DQ286272
CPC 5423; R366A
Taaibosdam,
Gifberg
High
Branch
2.25e–j
J.C. Janse van
Rensburg
DQ286247,
DQ286273
CPC 5425; R379S
Vondeling,
Nardouwsberg
Low
Branch
2.25e–j
J.C. Janse van
Rensburg
DQ286248,
DQ286274
CBS 117168; CPC 5420; R338E
Vaalkrans,
Nardouwsberg
Low
Crown
10.00a
J.C. Janse van
Rensburg
AY339353,
AY339321
CBS 117169; CPC 5428; R412AY
Langebergpunt,
Clanwilliam
High
Branch
10.00a
J.C. Janse van
Rensburg
DQ286249,
DQ286275
CBS 117500; CPC 5408; 9940AF
Clanwilliam
High
Crown
9.67a
S.C. Lamprecht
DQ286250,
DQ286276
CPC 5410; 9996D
Clanwilliam
High
Crown
10.00a
S.C. Lamprecht
DQ286251,
DQ286277
PHOMOPSIS ON ASPALATHUS
Table 1. (Continued).
Species
Strain no.1
Farm, area
Rainfall2
Plant
part
Lesion
length
Collector
(cm)3
GenBank
numbers
(EF, ITS)4
CPC 5430; R425B
Koelfontein,
Clanwilliam
High
Branch
10.00a
J.C. Janse van
Rensburg
DQ286252,
DQ286278
CBS 117163; CPC 5426; R380Z
Vondeling,
Nardouwsberg
Low
Branch
1.81g–k
J.C. Janse van
Rensburg
DQ286253,
DQ286279
CBS 117164; CPC 5429; R424T
Koelfontein,
Clanwilliam
High
Crown
2.64e–i
J.C. Janse van
Rensburg
DQ286254,
DQ286280
R686I
Snorkfontein,
Gifberg
High
Root
0.72j–l
J.C. Janse van
Rensburg
DQ286255,
DQ286281
R699H
Pendoringkraal,
VanRhynsdorp
Low
Root
0.78j–l
J.C. Janse van
Rensburg
DQ286256,
DQ286282
CBS 117499; CPC 5431; R433R
Kossak se werf,
Clanwilliam
High
Branch
1.19i–l
J.C. Janse van
Rensburg
AY339354,
AY339322
CPC 5416; R162AO
Berg-en-dal,
Citrusdal
High
Crown
3.94b–f
J.C. Janse van
Rensburg
DQ286257,
DQ286283
R164AN
Karnemelksvlei,
Citrusdal
High
Branch
1.61h–l
J.C. Janse van
Rensburg
DQ286258,
DQ286284
Phomopsis
sp. 9
CBS 117165; CPC 5417; R162L
Berg-en-dal,
Citrusdal
High
Crown
0.42k–l
J.C. Janse van
Rensburg
DQ286259,
DQ286285
P. theicola
CBS 117166; CPC 5415; R120AB
Boskloof,
Niewoudtville
High
Branch
4.75b–d
J.C. Janse van
Rensburg
DQ286260,
DQ286286
CBS 117501; CPC 5422; R353AH
Uitsig, AgterPakhuis
Low
Branch
5.39b–c
J.C. Janse van
Rensburg
DQ286261,
DQ286287
CPC 5424; R374AP
Snorkfontein,
Gifberg
High
Branch
3.72c–f
J.C. Janse van
Rensburg
DQ286262,
DQ286288
Libertella sp.
P. cuppatea
Control
1CBS:
2Low
Centraalbureau voor Schimmelcultures, Utrecht, The Netherlands; CPC & R: Culture collection of Pedro Crous, housed at CBS.
= 180–200 mm/yr; High = 250–400 mm/yr.
3Values
4EF:
0.00l
in a column followed by the same letter do not differ significantly (P = 0.05).
partial elongation factor 1-alpha gene; ITS: internal transcribed spacer region.
Sequence Analysis
Mycelium was grown on PDA plates and isolated using
the protocol of Lee & Taylor (1990). PCR amplification
and sequencing of the ITS rDNA, as well as partial
EF1-α gene introns and exons, were performed as
described by Van Niekerk et al. (2004). Newly generated
sequences have been deposited in GenBank (Table 1)
and the alignment in TreeBASE (S1506, M2708).
Sequences were manually aligned using Sequence
Alignment Editor v. 2.0a11 (Rambaut 2002). Additional
sequences were obtained from GenBank and added to
the alignment. In the phylogenetic trees, downloaded
sequences are labelled with GenBank accession
numbers; newly generated sequences are indicated
with strain numbers. Two datasets were created and
analysed using PAUP v. 4.0b10 (Swofford 2002) as
described by Van Niekerk et al. (2004).
Taxonomy
Strains were grown under continuous near-ultraviolet
light (400–315 nm) (Sylvania Blacklight-Blue, Osram
Nederland B.V., Alphen aan den Rijn, The Netherlands)
at 25 °C. Media used were PDA, and 2 % water agar
containing pieces of autoclaved Aspalathus twigs
using 9 cm diam Petri dishes. Growth rates and colony
diameters of cultures incubated in darkness were
measured on PDA. Structures were mounted in lactic
acid, and 30 measurements at × 1000 magnification
were made of each structure. The 95 % confidence
levels were determined, and the extremes of spore
measurements given in parentheses. Images were
taken from slides mounted in lactic acid. Macroscopic
characters of colonies were described after 14 d using
the colour charts of Rayner (1970).
Pathogenicity
The 28 isolates used in the molecular studies were
also used to conduct the pathogenicity trials. Rooibos
plants were cultivated for 8 mo in 18 cm diam pots in a
pasteurised sand : soil : perlite medium (1 : 1 : 1) (3 plants
per pot). Plants were maintained in a glasshouse at
25 ºC (night) and 30 ºC (day) temperature, and watered
three times a week. Nitrosol (Fleuron) (Universal
selected services, Braamfontein, S.A.) fertiliser was
applied every second week at 200 mL/pot. Colonised
PDA agar plugs (5 mm diam) of the respective isolates
were used to inoculate plants (three pots per isolate,
with three plants per pot). Plant stems were trimmed to
a uniform length of 20 cm. A cut was made 10 cm from
the top of the main stem of a rooibos seedling, and an
67
JANSE VAN RENSBURG ET AL.
10 changes
Cylindrocladiella peruviana AY793459
Phomopsis sp. 8 AY485743
Phomopsis sp. 7 AY485742
87
CBS 117166
100 CBS 187.27
AF230762
AF230759
Phomopsis theicola
58
AY485724
63
52 CPC 5424
CBS 117501
Phomopsis sp. 4 AY485726
Phomopsis quercina AJ293877
87 Phomopsis magnoliae AY622995
56
AY485732
100
98 AY485734 Phomopsis sp. 6
AF317563 Phomopsis vaccinii
72
AF317557
Phomopsis sp. 5 AY485727
100
98 AF102997
AF230755 Phomopsis amygdali
100
AF230760
51
AF230765 Diaporthe perjuncta
AF000567
Diaporthe caulivola
93 AF000563
Diaporthe phaseolus var. caulivora AJ312360
AF001016
CBS 117500
CBS 117169
98 CPC 5430
CPC 5410
Diaporthe aspalathi
CBS 117168
85
AF001015
95 AF000564
AF000566
100 AY485765
AF230751
62 AY485775
Phomopsis viticola
60 AY485757
59
AF230763
100 R164AN
Phomopsis cuppatea
CPC 5416
66
CBS 117499
98
CBS 117165
Phomopsis sp. 9
88 AJ312366
AJ312348
Diaporthe phaseolorum U11323 & U11373
100 AF000207
Phomopsis longicolla
U97658
AF000211
Phomopsis sp. 3 AY485725
CBS 117167
CPC 5419
CPC 5409
CBS 117170
CBS 117374
CPC 5425
66
100 CBS 117373
Diaporthe ambigua
CPC 5412
CPC 5413
CBS 117371
CPC 5423
CBS 117372
AJ458389
71
64 AF230768
AF230767
AJ312363
100
AJ312364
AJ312358
Diaporthe helianthi
AY705842
72
AJ312354
100
Phomopsis columnaris AF439625
Phomopsis sclerotioides AF439626
100 CBS 117164
R686I
100
64 CBS 117163 Libertella sp.
R699H
96
Eutypella vitis AJ302466
Eutypella leprosa AJ302463
Fig. 2. One of 176 equally parsimonious trees obtained from a heuristic search with 10 random addition replicates of the ITS sequence alignment.
The scale bar shows ten changes and bootstrap support values from 1000 replicates are shown at the nodes. Thickened lines indicate branches
present in the strict consensus tree and isolates obtained from Aspalathus linearis are shown in bold print. The tree was rooted to Cylindrocladiella
peruviana.
68
PHOMOPSIS ON ASPALATHUS
RESULTS
agar plug inserted into the cut, and sealed with Parafilm.
Three months after inoculation, plants were evaluated
for disease symptoms, and lesion length measured.
Survival of plants was also recorded. Re-isolations
were made from plant material with disease symptoms
onto PDA amended with 0.02 % novostreptomycin. A
standard one-way analysis of variance was performed
on these data using SAS statistical software v. 6.08
(SAS Institute, Cary, NC). The Shapiro-Wilk test was
performed to test for normality (Shapiro & Wilk 1965).
There was no evidence against normality and the
original data were analysed. Student’s t-least significant
differences were calculated at the 5 % level to compare
ranked means.
Sequence Analysis
Approximately 510 and 340 bases were sequenced
for ITS and EF1-α, respectively. As EF1-α sequences
were not available for the taxa for which ITS sequences
could be downloaded from GenBank, a tree was
generated for all of them using only ITS sequences
(Fig. 2). A partition homogeneity test did not indicate
significant incongruence between the two genes (P =
0.7630) and the two genes were combined into a single
alignment for isolates with both gene sequences (Fig.
3). Using different outgroups did not change the clades
presented in Figs 2–3; nor did analyses using 1000
Cylindrocladiella peruviana
100
CBS 117166
CBS 187.27
Phomopsis theicola
CPC 5424
51
CBS 117501
Diaporthe phaseolorum FAU458
65
69
Phomopsis sp. 9 CBS 117165
100
R164AN
100
CPC 5416
Phomopsis cuppatea
CBS 117499
CBS 117167
98
CBS 117170
CBS 117373
CPC 5413
CBS 117372
100
CPC 5409
100
CBS 117374
Diaporthe ambigua
CBS 117371
CPC 5419
79
CPC 5425
CPC 5412
CPC 5423
CBS 117169
10 changes
100
CBS 117168
CBS 117500
62
Diaporthe aspalathi
CPC 5430
CPC 5410
CBS 117164
100
62
R686I
CBS 117163
Libertella sp.
R699H
Fig. 3. One of eight most parsimonious trees obtained from a heuristic search with 10 random addition replicates of the combined ITS and EF1-α
alignment. The scale bar shows ten changes; bootstrap support values from 1000 replicates are shown at the nodes. Thickened lines indicate
the strict consensus branches and type strains are shown in bold print. The tree was rooted to Cylindrocladiella peruviana (ITS: AY793459; EF:
AY725736).
69
JANSE VAN RENSBURG ET AL.
random taxon additions change the number of trees
found or the scores calculated (data not shown).
The ITS data matrix contains 78 taxa (including the
outgroup) and 353 positions including alignment gaps
(the sequence of the 5.8S rDNA gene of Diaporthe
phaseolorum strain FAU458 was not available on
GenBank and this region was therefore excluded from
the analysis). Only the sequences of the Eutypella and
Libertella species were variable in this excluded region.
Of these characters, 191 are parsimony-informative, 49
are variable and parsimony-uninformative, and 113 are
constant. Neighbour-joining analysis using substitution
models representative of three different assumptions
(uncorrected “p”, Kimura-2-parameter and HKY85) on
the sequence data yielded trees with similar topology and
bootstrap values. Parsimony analysis of the alignment
yielded 176 equally parsimonious trees (Fig. 2; TL =
698 steps; CI = 0.626; RI = 0.896; RC = 0.561), most of
which differed only in the order of taxa within terminal
clades. The same terminal clades were found in both
the parsimony and neighbour-joining trees, although the
order of branching was not always congruent (data not
shown). Isolates from Aspalathus linearis are present
in six clades (Fig. 2). The first clade (100 % bootstrap
support) is identified as P. theicola Curzi, containing
sequences from the ex-type strain CBS 187.27. The
second clade (98 % bootstrap support) is identified
as D. aspalathi sp. nov. and contains isolates from A.
linearis, as well as isolates from Glycine max. The third
and fourth clade containing Aspalathus linearis isolates
are described as P. cuppatea sp. nov., and Phomopsis
sp. 9, with bootstrap support values of 100 % and 88 %,
respectively. Two sequences obtained from GenBank
from Helianthus annuus isolates group together with
the A. linearis isolate in the Phomopsis sp. 9 clade.
Aspalathus linearis isolates in the final two clades belong
to Diaporthe ambigua (containing GenBank sequence
AF230767 of the ex-epitype; 100 % bootstrap support)
and a Libertella sp. (100 % bootstrap support). The
Libertella Desm. species groups with 100 % bootstrap
support with sequences of Eutypella (Nitschke) Sacc.
species obtained from GenBank.
The combined data matrix contains 31 taxa
(including the outgroup) with 755 positions including
alignment gaps. Of these characters, 438 are
parsimony-informative, 142 are variable and parsimonyuninformative, and 175 are constant. Parsimony analysis
of the alignment yielded eight most parsimonious trees
(TL = 1196 steps; CI = 0.823; RI = 0.931; RC = 0.766),
one of which is shown in Fig. 3. The same six species
that were identified in the ITS tree (Fig. 2) were found in
the analysis of the combined dataset. In all cases where
multiple isolates are available, the bootstrap support for
the species is 100 %. Neighbour-joining analysis using
three substitution models (uncorrected “p”, Kimura 2parameter and HKY85) on the sequence data yielded
trees with similar topology and bootstrap values, except
for the position of the Libertella Desm. sp. clade which
was placed as a sister clade to D. aspalathi sp. nov.
in the Kimura 2-parameter (57 % bootstrap support)
and HKY85 (59 % bootstrap support) analyses (data
not shown). The trees obtained using neighbour-joining
70
differed from those obtained using parsimony only with
respect to the branching of the deeper nodes, which are
not supported by bootstrap analysis (data not shown).
Taxonomy
Diaporthe
ambigua
Nitschke,
in
Nitschke,
Pyrenomycetum Germanicum: 311. 1867. Fig. 4.
Anamorph: Phomopsis ambigua (Sacc.) Traverso,
Fl. Ital. Cryptog., Pars 1: Fungi. Pyrenomycetae.
Xylariaceae, Valsaceae, Ceratostomataceae 2(1): 266.
1906.
≡ Phoma ambigua Sacc. Grevillea 2: 91. 1880.
Perithecia globose, solitary to aggregated, up to
500 µm diam. Perithecial neck dark brown to black,
subcylindrical, smooth, tapering towards the apex,
up to 1000 µm long, 250 µm wide at the base, 70 µm
wide at the apex; ostiole red-brown, obtusely rounded.
Asci unitunicate, cylindrical–clavate with a refractive
apical ring, 8-spored, biseriate, 50–60(–65) × 7–8(–9)
µm. Paraphyses constricted at the septa, unbranched,
tapering towards the apex with a rounded tip, extending
above the asci, up to 150 µm long, and up to 7 µm wide
at the base, and 3–4 µm wide at the apex. Ascospores
hyaline, smooth, fusoid–ellipsoidal, widest just above
the septum, tapering towards both ends, medianly
septate, constricted at the septum at maturity, with 1–2
guttules per cell, (12–)13–15 × (3–)3.5–4 µm. Pycnidia
formed on PDA and on Aspalathus twigs. Conidiophores
subcylindrical, branched below or unbranched, 0–1septate, 15–45 × 2–3 µm. Alpha-conidia ellipsoidal,
biguttulate, with an obtuse apex, tapering to an obtuse
or bluntly rounded base with a visible scar, 6–7(–8) ×
2(–3) µm, corresponding to the dimensions reported
for the anamorph (Uecker 1988). Beta-conidia not
seen. Description based on CBS 114015 = CPC 2657;
cultures homothallic.
Cultural characteristics: Colonies on OA olivaceousblack, spreading with patches of white, with sparse
aerial mycelium and cream conidial masses; colonies
on PDA flat, spreading, with sparse, white, dense aerial
mycelium; surface with solid patches of olivaceousblack in the central part; outer region dirty-white to
cream; aerial mycelium sparse, consisting of a dense
layer of dirty white to cream mycelium; reverse with
solid, iron-grey patches in the central part, also with
isolated patches in the outer region, surrounded by
cream areas.
Specimens examined: Germany, Nordrhein-Westfalen, Landkreis
Unna, on Pyrus communis, Th. Nitschke, Aug. 1866, holotype in B.
South Africa, on Pyrus communis, S. Denman, CBS H-19685, epitype designated here, culture ex-epitype CBS 114015 (= AF230767).
Notes: As shown in the present study, the host range
of D. ambigua is wider than originally suspected by
Nitschke (1867), but not as extreme as stated by
Wehmeyer (1933). The type specimen is depauperate,
containing perithecia of a Pleospora sp. and Togninia
minima, and some remnants of Diaporthe ambigua.
A few ascospores were observed, 12–15 × 3.5–4
µm, that were constricted at the median septum, and
guttulate. Diaporthe ambigua was originally described
PHOMOPSIS ON ASPALATHUS
Fig. 4. Diaporthe ambigua (epitype). A. Pycnidia forming on Aspalathus stems in culture. B–C. Conidiophores. D. Alpha-conidia. E. Perithecia.
F–G. Asci with ascospores. Scale bars: A, E = 70 µm, B = 4 µm, C–D, F–G = 2 µm.
from cankers on pear in Germany (Nitschke 1867),
and the name was subsequently used for the organism
causing cankers on apples, pears and plums in South
Africa (Smit et al. 1996).
(6–)7–8(–9) × (2–)2.5(–3) µm. Beta- and gammaconidia absent. Description based on CBS 117169;
cultures homothallic.
≡ Diaporthe phaseolorum var. meridionalis F.A. Fernández,
Mycologia 88: 438. 1996. [non D. meridionalis Sacc., Syll. Fung.
I: 638. 1878].
Cultural characteristics: On OA flat, spreading with
sparse to no aerial mycelium; surface with irregular
patches of pale white to cream and olivaceous-grey,
with sparse strands of pale white aerial mycelium; on
PDA flat, spreading, with sparse to no aerial mycelium;
surface smoke-grey; reverse smoke-grey to olivaceousgrey.
Etymology: Named after Aspalathus, on which it causes
a prominent die-back disease.
Specimen examined: South Africa, Western Cape Province,
Clanwilliam, Langebergpunt, on Aspalathus linearus, J. Janse Van
Rensburg, CBS H-19686, culture CBS 117169.
Perithecia globose, solitary, scattered to aggregated,
up to 500 µm wide. Perithecial neck black, cylindrical,
mostly smooth, but tapering near the apex, up to
800–1000(–2000) µm long, 150 µm wide at the
base, 90 µm wide at the apex; ostiole widening once
spores discharge, 90–130 µm wide. Asci unitunicate,
cylindrical with a refractive apical ring, 8-spored,
biseriate, 52–55(–60) × 7–8(–10) µm. Paraphyses
septate, unbranched, tapering towards the apex with
a rounded tip, extending above the asci, up to 110 µm
long, and up to 8 µm wide. Ascospores hyaline, smooth,
fusoid, widest at the septum, tapering towards both
ends, medianly septate, not constricted at the septum,
with 1–2 guttules per cell, (12–)13–15(–16) × 3(–3.5)
µm. Pycnidia formed on PDA and on Aspalathus twigs.
Alpha-conidia biguttulate, fusoid with obtuse ends,
Notes: Isolates (see Table 1) readily produce
perithecia on PDA and on Aspalathus twigs. Diaporthe
phaseolorum var. meridionalis, which was described
as causing soybean stem canker in the South-eastern
U.S.A. (Fernández & Hanlin 1996), is not closely
related to D. phaseolorum as earlier expected. Although
morphologically similar, this species clusters apart from
the reference strain of D. phaseolorum (Figs 2–3).
Diaporthe phaseolorum var. meridionalis is also the
main causal organism of canker and die-back of rooibos,
and not D. phaseolorum as reported earlier (Smit &
Knox-Davies 1989a, b). The name D. meridionalis
Sacc. (1878) is preoccupied, and represents a species
similar to D. eres Nitschke (Wehmeyer 1933), and
hence a new name, D. aspalathi is proposed here for
the species pathogenic to Aspalathus and soybean.
Diaporthe aspalathi Janse van Rensburg, Castlebury
& Crous, nom. et. stat. nov. MycoBank MB500803.
Fig. 5.
71
JANSE VAN RENSBURG ET AL.
Fig. 5. Diaporthe aspalathi (CBS 117169). A–B. Perithecia. C–F. Asci and ascospores. G. Conidia. Scale bars: A = 150 µm, B = 70 µm, C = 3
µm.
Phomopsis cuppatea Janse van Rensburg, Lamprecht
& Crous, sp. nov. MycoBank MB500804. Fig. 6.
aerial mycelium; surface smoke-grey to pale olivaceousgrey; reverse smoke-grey.
Etymology: Named after the primary use of the host
substrate, which is to make “rooibos” tea.
Specimen examined: South Africa, Western Cape Province,
Clanwilliam, Kossakse werf, on Aspalathus linearis, J. Janse van
Rensburg, CBS H-19687, culture CBS 117499.
Conidiophora cylindrica, 1–3-septata, 30–80 × 3–5 µm. Cellulae
conidiogenae rectae vel curvatae, in collare modice distensum ad 3
μm longum exeuntes, exigue periclinaliter inspissatae, 10–35 x 1.5–
2 μm. Alpha-conidia fusoidea–ellipsoidea, sursum hebeter rotundata,
ad basim obtusa vel subtruncata, bi- vel multiguttulata, (10–)12–13(–
14) × (3–)4(–5) µm.
Phomopsis sp. 9
Cultural characteristics: Colonies on OA flat, spreading
with sparse dirty-white aerial mycelium; surface and
reverse with diffuse patches of fuscous-black and dirtywhite; colonies on PDA flat, spreading, with sparse,
dirty-white aerial mycelium at the edge of the dish;
surface and reverse having a translucent to ochreous
central part; outer region umber. Description based on
CBS 117165.
Pycnidia eustromatic, black, scattered or aggregated,
globose to conical, convulated to unilocular, singly
ostiolate, up to 400 µm wide; pycnidial wall consisting
of brown, thick-walled cells of textura angularis; conidial
mass globose, pale-luteous to cream. Conidiophores
cylindrical, noticeably flexuous and tall, well-developed,
branched above or below, 1–3-septate, 30–80 × 3–5
µm. Conidiogenous cells straight to curved, tapering
slightly towards the apex, collarettes slightly flaring, up
to 3 µm long, with minute periclinal thickening, 10–35
× 1.5–2 µm. Alpha-conidia fusoid–ellipsoidal, apex
bluntly rounded, base obtuse to subtruncate, bi- to
multiguttulate, (10–)12–13(–14) × (3–)4(–5) µm; betaand gamma-conidia not observed. Description based
on CBS 117499.
Notes: When CPC 5417 was deposited in the CBS
collection as 117165, it was sterile, and thus could
not be named in the present study. Connecting to the
numbering system used by Van Niekerk et al. (2005),
it is thus referred to as Phomopsis sp. 9. Two ITS
sequences obtained from GenBank represent strains
isolated from Helianthus annuus, and grouped together
with this isolate, proving that this species may have a
wider host range than just Aspalathus.
Cultural characteristics: Colonies on OA flat, spreading,
with sparse, dirty white aerial mycelium; surface
with irregular patches of olivaceous-black and pale
olivaceous-grey; on PDA flat, spreading, with sparse
Pathogenicity
In inoculation experiments, the longest lesions were
observed for isolates of D. aspalathi, which proved
to be the most virulent species. Significantly shorter
72
PHOMOPSIS ON ASPALATHUS
Fig. 6. Phomopsis cuppatea (holotype). A–B. Conidiophores. C–D. Conidia. Scale bar = 4 µm.
lesions were observed for isolates of the other taxa
tested (P = 0.05) (Table 1).
Three months after inoculation, 95.56 % of plants
inoculated with isolates belonging to D. aspalathi
were dead, followed by 25.71 % of plants inoculated
with P. theicola, and 16.67 % of plants inoculated with
the Libertella sp. Only 14.14 % of plants inoculated
with isolates of D. ambigua died. The new species, P.
cuppatea and Phomopsis sp. 9, proved to be the least
virulent, and in both cases only 8.33 % of the inoculated
plants died. All inoculated taxa could be successfully
re-isolated from inoculated plants, which in many cases
ended up with dead tissue being covered in pycnidia
and perithecia. None of the controls died, or showed
any disease symptoms.
DISCUSSION
Contrary to earlier reports which were based on
morphological observations alone (Smit & Knox-Davies
1989a, b), the current study has revealed that up to five
Phomopsis spp. are involved with die-back of rooibos
bushes, while a sixth Phomopsis-like taxon proved to
be better accommodated in Libertella, which clustered
among Eutypella teleomorphs.
Mostert et al. (2001) isolated a species of Phomopsis
from grapevines, which also proved to be present
on Protea and Pyrus in countries such as Australia,
Portugal and South Africa. As no name could be
attributed to this species it was eventually referred to
as Taxon 3. The same species was again encountered
in the Phomopsis study on grapevines by Van Niekerk
et al. (2005), where 15 species were distinguished,
and taxon 3 was referred to as Phomopsis sp. 1. In
the current study we finally managed to identify this
species, as its ITS DNA sequence is identical to that
of the ex-type strain of P. theicola Curzi (CBS 187.27),
which was originally described from Camellia sinensis
in Italy (Uecker 1988). This species obviously has a
wide host range and distribution, which once again
underlines the difficulties mycologists encounter when
trying to identify species of Phomopsis.
Several isolates which also formed a Diaporthe state
in culture, proved to be identical to D. phaseolorum var.
meridionalis based on morphology and sequence data.
Although this pathogen was originally identified as D.
phaseolorum by Smit & Knox-Davies (1989a, b), the
reference strain available to us of D. phaseolorum (Figs
3–4) (treated as authentic by F.A. Uecker and preserved
at BPI), clustered apart from the Aspalathus pathogen.
Furthermore, as D. phaseolorum var. meridionalis is
clearly not a variety of D. phaseolorum, and as the
name D. meridionalis is already preoccupied, a new
name is proposed for this pathogen as D. aspalathi.
Another species which proved to be very common on
Aspalathus matched GenBank sequences for Diaporthe
ambigua. Diaporthe ambigua was originally described
from branches of Pyrus communis from Germany, and
was later associated with a Diaporthe canker of apple,
pear and plum rootstocks in South Africa (Smit et al.
1996). To reduce any further confusion surrounding this
name, we have thus chosen to designate an epitype
specimen and ex-epitype culture in the present study,
from which DNA sequence data are derived.
Two new Phomopsis spp. were also encountered
during the current study, namely P. cuppatea, and
Phomopsis sp. 9. As the culture of the latter proved
to be sterile, further collections are required before its
taxonomy can be resolved.
Several isolates of a Libertella sp. were also isolated
from Aspalathus during the present study. Although
Libertella is an anamorph of Eutypella and Eutypa Tul.
& C. Tul. and this taxon grouped with Eutypella spp.
known from GenBank sequence data, no teleomorph
was ever observed on host material or induced in
culture.
Lesions and pycnidia formed faster downwards
than upwards on stems of inoculated plants. Previous
reports stated that after infection of blueberry twigs,
hyphae of Phomopsis spp. move to the stem cortex
(Daykin & Milholland 1990). Movement through the
stem cortex takes place through the intercellular spaces,
and intracellularly through the parenchyma of the outer
cortex. Only after the cortex has been completely
colonised, does the fungus invade the vascular tissue
and pith (Daykin & Milholland, 1990). Phomopsis
infection of sunflower follows the same pattern where,
after penetration in the host, infection hyphae invade the
intercellular spaces in the cortex (Muntañola-Cvetković
73
JANSE VAN RENSBURG ET AL.
et al. 1981). Xylem elements are invaded, but affected
less than the phloem and parenchyma tissues which
disintegrate completely (Muntañola-Cvetković et al.
1981). Daykin & Milholland (1990) suggested that the
formation of vast numbers of tyloses inside the xylem in
advance of infection together with phloem plugging due
to gums and hyphae, causes the lesions associated
with die-back. From these masses of hyphae pycnidia
are initiated (Muntañola-Cvetković et al. 1981).
Tyloses form in xylem vessels of most plants under
various conditions of stress and during invasion by a
pathogen (Agrios 2004). Formation of these structures
is an attempt by the plant to close off invaded cells
to limit fungal movement in the plant (Sinclair et al.
1987). This shutting down of infected vascular tissues
reduces the flow of water from the roots upward. At
this point, reduced water flow and toxins often result
in external symptoms (Sinclair et al. 1987). In rooibos
these external symptoms are twig die-back, reduction
in biomass and eventually plant death.
Although the pathogenicity data obtained in the
present study are still preliminary, and need to be
confirmed in the field, they clearly show that D.
aspalathi was the most virulent taxon, producing the
longest stem lesions and also causing the most plant
death. In contrast, the Libertella sp. hardly caused any
tissue discoloration. The latter could be due to the fact
that symptoms were rated after 3 mo, and that species
from the Eutypa/Eutypella complex, as observed in
grapevines, generally take much longer for symptom
expression. Further studies will be necessary, however,
to fully resolve the phylogenetic status of the various
other Phomopsis spp. associated with die-back of
Aspalathus, which in this study appeared to be of less
importance than D. aspalathi.
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