Enzimi, acidi organici ed altri metaboliti coinvolti nella patogenesi di Penicillium spp
Creators: name: Donati, Irene <1977>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2008
Subjects: AGR/12 Patologia vegetale

description: Blue mould caused by Penicillium expansum Link is one of the most destructive
rot of pome fruit in all growing areas (Snowdon, 1990; Jones and Aldwinckle, 1991;
Tonini,1996) In the past, Penicillium rot has been controlled by fungicide postharvest
treatment mainly by thiabendazole (TBZ) and benomyl (Hardenburg and Spalding,
1972), but their intense use produced the appearance of resistant strains with a
great reduction of their activity
The aims of the present study were to characterize the isolates of Pencillium sp
causing blue mold on pear in Italy by physiological and biochemical parameters.
In particular differencing also the behavior of isolates to relationship with sensitivity
or resistance to TBZ treatments.
We have examined the early stage of infection in relation to enzyme activity, local
modulation of pH, production of organic acids, and to secondary metabolism of
pathogen.
The results described here confirm that the majority of P. expansum isolates from
pears packing houses are resistant to TBZ,
Among the TBZ-resistant isolates scored in this work, different isolates (RR) showed
higher percentage of conidial germination on TBZ-amended medium compared to non
amended medium. This may indicate a stimulatory effect of TBZ on conidial
germination. Therefore TBZ treatments are not only ineffective for controlling P.
expansum, but they may also increase the severity of blue mould on fruits.
In the absence of fungicide, isolates showed a significant difference for infection
severity, R and RR isolates are characterized by higher pathogenic fitness on fruits,
producing larger lesions than S isolates. These data are supported by the study with
laboratory-induced resistant isolates, which shows the lack of correlation between
TBZ resistance and osmotic sensitivity, and highlights the association between TBZ
resistance and infection severity (Baraldi et al 2003).
Enzymatic screening gave a positive reaction to esterase, urease, pectinase activity,
in addition, the pathogen is able to synthesize a complex enzyme act to degrade the
main components of the cell wall especially pectin and cellulose.
Isolated sensitive and resistant are characterized by a good activity of pectinase,
especially from poligactoronase, which, as already reported by several studies
(D'hallewin et al, 2004; Prusky et al, 2004), are the basis of degradative process of
cell wall. Also, although the measure was minor also highlighted some activities of
cellulase, but even note in the production of this kind of cellulase and hemicellulase
P. Expansum were not targeted, studies have found no other source of information in
this regard.
Twenty isolates of Penicillium expansum, were tested in vitro ad in vivo for acid
production ability and pH drop.
We have found that modulation of pH and the organic acids extrusion were influence
to various parameter:
 Initial pH: in general, the greatest reduction of pH was observed in isolates
grown at pH 7, except for four isolates that maintained the pH of the medium
close to 7, the others significantly decreased the pH, ranging from 5.5 to 4.1..
In extreme acid condition (pH 3,0) growth and modulation of pH is most lower
respect optimal condition (pH 5,0). Also isolates R and RR have showed a
greater adaptation to environmental condition more than isolates S.
 Time: although the acidification continues for some days, PH modulation is
strongest in early hours (48-72 hours)of inoculation process. Time also affects
the quality of organic acids, for example in vitro results showed an initial
abundant production of succinc acid, followed to important production of
galacturoinc acid.
 Substrates: there are many differences for the type of acids produced in vitro
and in vivo. Results showed in vivo an abundant production of galacturonic,
malic, and citric acids and some unknown organic acids in smaller
concentrations.
Secondary metabolite analysis revealed intra-specific differences, and patulin was
found in all isolates, but most significant reduction was observed between in vitro and
in vivo samples.
There was no correlation between the concentration of patulin, and the percentage of
infected fruits, but sample with a lower infection severity of rotten area than the
others, showed a significantly lower mycotoxin concentration than samples with a
higher lesion diameter of rotten area. Beyond of patulin was detected the presence
of another secondary metabolite, penitrem A.