Journal of Plant Pathology (2010), 92 (4, Supplement ... - Sipav.org

Journal of Plant Pathology (2010), 92 (4, Supplement), S4.71-S4.105 S4.91
Powdery mildew, caused mostly by Podosphaera xanthii, is an
important disease of cucurbits in the Mediterranean basin. The
fungicides known as QoI are largely used to control the disease,
but resistance has been observed in many phytopathogenic fungi,
including P. xanthii. Here we present the results of a monitoring
of resistance to trifloxystrobin in P. xanthii populations in Apulia.
Sixty-four isolates of P. xanthii were sampled from 32 cucurbit
fields in 2002-2007, and assayed at seven trifloxystrobin (Flint®)
concentrations. Alternative respiration was inhibited by adding 1
mg ml -1 of salicylhydroxamic acid to fungicide suspensions. Portions
of zucchini cotyledons (cv. Diamant 1) were dipped for 1
min in the fungicide suspension, placed on Blaich medium in
Petri dishes, inoculated at a single point with about 20 conidia,
and maintained at 25°C under a 12 h photoperiod. After 10 days,
the percentage of infected surface was estimated using an empirical
scale based on six infection classes, and EC 50 and MIC were
assessed. Results pointed out a high variability in the response to
trifloxystrobin, with EC 50 ranging from 375 µg ml -1 , and
MIC from 10 to >375 µg ml -1 . About half of isolates had EC 50
>375 µg ml -1 trifloxystrobin, a concentration three times greater
than the normal field rate (125 µg ml -1 ), with no differences attributable
to the host plants or the geographical origin. In conclusion,
resistance to QoIs is very common in Apulia, and this
should induce growers to implement more stringent anti-resistance
strategies.
FIRST REPORT OF LEAF SPOT CAUSED BY STEMPHYLI-
UM HERBARUM ON BORAGO OFFICINALIS. L.C. Moretti,
M. Quaglia, M. Orfei, C. Cappelli. Dipartimento di Scienze Agrarie
e Ambientali, Università degli Studi, Borgo XX Giugno 74, 06121
Perugia, Italy. E-mail: chiaraluce.moretti@unipg.it
Borage (Borago officinalis L.) is an ornamental plant, widely
present in nature in different areas of Italy. During spring 2009,
in private gardens and on the border of Trasimeno lake (Central
Italy), leaf spots on cultivated and wild borage plants were observed.
Initial symptoms were recorded on basal leaves as small
brown circular spots (2 mm diameter), greyish-white in the middle
and surrounded by a reddish halo. The symptoms developed
on the upper leaves and later severe yellowing and necrosis of the
leaf tissue were observed. Due to unfavourable climate conditions
(hot temperature and low humidity), new foliages did not
show symptoms and the disease disappeared but the plants, especially
those present in the gardens, seemed less vigorous. A fungus,
morphologically identified as Stemphylium herbarum Simmonds
[anamorph of Pleospora herbarum (Fr.) Rabenh.], was
consistently isolated. To assess its pathogenicity to borage plants,
two fungal isolates were used. Plants were sprayed with conidial
suspensions (5x10 5 conidia ml -1 ) from 10-day-old agar cultures.
After 7-8 days, the plants inoculated with both fungal isolates
showed small spots, identical to those observed under natural
conditions, whereas no symptoms were observed on control
plants sprayed with water. S. herbarum was consistently reisolated
from inoculated borage leaves. The fungus is known to cause leaf
spots on several herbaceous hosts, including lettuce and onion.
However, to our knowledge, this is the first report of a leaf spot
disease of borage caused by S. herbarum.
MULTIPLE BOTRYOSPHAERIACEAE INFECTION IN
FOREST TREES: SYNERGISTIC OR ANTAGONISTIC IN-
TERACTION? S. Moricca 1 , A. Uccello 1 , E. Turco 2 , B. Ginetti 1 ,
A. Ragazzi 1 . 1 Dipartimento di Biotecnologie Agrarie, Sezione di
Protezione delle Piante, Piazzale delle Cascine 28, 50144 Firenze,
Italy. 2 Istituto per la Protezione delle Piante del CNR, Via Madonna
del Piano, 50019 Sesto Fiorentino (FI), Italy. E-mail: andrea.uccello@unifi.it
Botryosphaeriaceae an Ascomycetes family well known as endophytes
of woody hosts under temperate and subtropical climates.
It includes several species that may turn to a pathogenic
habitus when hosts undergo physiological stress. Previous pathogenicity
studies have focused their attention on the interactions
between a single fungal species and their hosts. However, the
type of interaction established when two or more botryosphaeriaceous
fungi colonize the same host tissues is till unknown. Isolates
of Botryosphaeria dothidea, Diplodia seriata and Neofusicoccum
parvum were tested on two-year-old seedlings of Acer
campestre, Carpinus betulus, Fraxinus excelsa and Quercus cerris
to verify disease severity and to evaluate the effect of single and
combined infections. N. parvum proved the most virulent of the
three species, causing lesions significantly larger than those
caused by the other species. Seedlings inoculated with the mixture
of isolates showed smaller lesions than those caused by N.
parvum alone. These preliminary results allow us to hypothesize
that a sort of antagonistic interaction may occur between
Botryosphaeriaceae in host tissues.
STUDIES ON THE AETIOLOGY OF THE DISEASE
KNOWN AS OCHRACEOUS LEAF SPOTS OF APPLE IN
FRIULI VENEZIA GIULIA. S. Moruzzi, M. Martini, R.
Musetti, P. Ermacora, S. Borselli and R. Osler. Dipartimento di
Biologia e Protezione delle Piante, Università degli Studi, Via delle
Scienze 208, 33100 Udine, Italy. E-mail: serena.moruzzi@uniud.it
An apple disease known as ochraceous leaf spots is known
since 1950, but its aetiology is still unclear. The disease is common,
especially in orchards where apples are grown under organic
regime. In Friuli Venezia Giulia, this disease is present in different
areas, in orchards of commercial and autochthonous apple
varieties. Symptomatic leaves were sampled in three farms to
study disease aetiology. In total 825 fungal colonies were obtained,
grouped according to morphological features, and characterized
by molecular tools, by analysis of rDNA ITS region. Isolations
yielded fungi belonging to Phoma spp. (about 37% subdivided
in: P. macrostoma, 16.9%; P. glomerata, 4%; P. epicoccina,
15%; P. exigua, 2.5%), Alternaria spp. (about 35%), and other
minor genera. In pathogenicity tests, leaves inoculated with all
four Phoma species developed classical necrotic lesions, while Alternaria
spp. developed some atypical necrosis, suggesting Phoma
spp. as the most probable causal agent of leaf spots. Portions of
symptomless leaves were also investigated: Phoma spp. accounted
for 23% of the obtained colonies and Alternaria spp. for 58%,
indicating that the latter fungal genus might behave mainly as a
plant endophyte. In plants with leaf symptoms, part of the xylem
appeared to be damaged under the electron microscope. Therefore,
further investigations were conducted using different techniques,
showing that P. macrostoma colonized also young branches.
P. macrostoma isolates from leaves and young branches were
characterized molecularly based on the ITS and ″-tubulin gene
sequences. No molecular differences were found in these genomic
regions among fungal isolates.
FUNGAL ENDOPHYTES IN NEEDLES AND BRANCHES
OF PICEA ABIES FROM THE PANEVEGGIO FOREST. R.
Musetti 1 , R. Polizzotto 1 , F. De Luca 2 , S. Grisan 1 , R. Osler 1 . 1 Dipartimento
di Biologia e Protezione delle Piante, Università degli