In vitro effects of water activity, temperature and solutes on the growth rate of P. italicum Wehmer and P. digitatum Sacc.

Abstract

In vitro effects of water activity, temperature and solutes on the growth rate of P. italicum Wehmer and P. digitatum Sacc. IntroductionCitrus fruits are generally stored in temperatures ranging from 0 to 7°C and relative humidities from 85% to 90%. During their storage, fruits are affected by several decays (Brown and Miller 1999). Penicillium digitatum Wehmer and P. italicum Sacc. are the main postharvest pathogens of citrus fruits, responsible, respectively, for green and blue decay. In turn massive spore production by these two pathogens ensures their presence wherever fruit is produced, handled and stored. Contamination takes place only through wounds where nutriments are available to AbstractAims: To evaluate the effect of water activity (a w 0AE98-0AE89, adjusted with glycerol, sorbitol, glucose, or NaCl) and temperature (5-25°C) on the lag phase and radial growth rate (mm day )1 ) of the important citrus spoilage fungi, such as Penicillium italicum and Penicillium digitatum grown in potato dextrose agar (PDA) medium. To select, among models based on the use of different solutes, a model fitting accurately the growth of these species in relation to a w and temperature. Methods and Results: Extensive data analyses showed for both Penicillium species a highly significant effect of a w , temperature, solutes and their interactions on radial growth rate (P < 0AE0001). Radial growth rate was inhibited and the lag phase (i.e. the time required for growth) lengthened as the a w of the medium decreased. NaCl appeared to causes the greatest stress on growth when compared with other nonionic solutes. Penicillium italicum stopped growing at 0AE96 a w and P. digitatum at 0AE93 a w . Under the dry conditions where growth was observed, P. italicum grew faster than P. digitatum at low temperature and P. digitatum remained more active at ambient temperature. Multiple regression analysis applied to the square roots of the growth rates observed in the presence of each solute showed that both the 'glycerol model' and the 'sorbitol model' yielded a good prediction of P. italicum growth and the 'sorbitol model' gave an accurate fit for P. digitatum growth, offering high-quality prediction within the experimental limits described. Conclusions: Mathematical models describing and predicting, as a function of a w and temperature, the square root of the radial growth rate of the agents responsible for blue and green decays are important tools for understanding the behaviour of these fungi under natural conditions and for predicting citrus fruit spoilage. Significance and Impact of the Study: Implementation of these results should contribute towards a more rational control strategy against citrus spoilage fungi. spore germination. Fruit decay thus begins at the site of injury. Blue decay develops less rapidly than green decay under ambient conditions. Green decay is often observed in mixed infections. Blue decay is more common in fruit held in cold storage during the summer; it can spread through packed cartons more easily than ...

Effects of Temperature and Relative Humidity on the in Vitro and in Vivo Radial Growth of Penicillium Italicum and on the Biocontrol Activity of Pichia Guilliermondii, Strain Z1

“…1a). This result was in agreement with that reported by Lahlali et al (2006) and Plaza et al (2003) who found that the optimum growth of P. italicum was at 25°C. Growth was greatest at temperature ranging from 20 to 25°C on Valencia late oranges (Fig.…”

“…Generally, whatever the studied conditions, growth rates increased with an increase in temperature and the optimum temperature for growth was observed at 25°C, as previously reported by Lahlali et al (2006), Plaza et al (2003) and Lacey (1989). The effect of temperature on the in vitro and in vivo radial growth rates of P. italicum can be fitted by the following quadratic equations respectively: -0.014 T 2 + 0.56 T-1.36 and -0.017 T 2 + 0.637 T-0.33).…”

“…Lahlali et al (2006) modeled the in vitro effect of temperature and a w on radial growth of this pathogen and found that a w has a more pronounced effect than temperature. Figure 2b shows that antagonistic yeast strain Z1 of P. guilliermondii significantly suppressed lesion formation of P. italicum under most temperature and relative humidity combinations.…”

“…Environmental factors such as, water activity, relative humidity and temperature are the most important factors influencing spore germination and growth of propagules on the fruit surface (Magan and Lacey, 1988;Plaza et al, 234 2003). Recently, Lahlali et al (2006) have developed four models predicting the in vitro radial growth rate of this pathogenic fungus related to water activity of the medium and incubation temperature. Optimal growth was observed at a w ranging from 0.96 to 0.98 and at a temperature of 25°C.…”

Enzyme-linked immunosorbent assay for simultaneous detection of two fungicides kresoxim-methyl and trifloxystrobin in oranges

“…Fungal spore germination is highly vulnerable to strobilurin fungicides, kresoxim-methyl, and trifloxystrobin, which are typically broadly active against almost all fungi, particularly when they are applied early as a preventative measure. Additionally, these two fungicides are considered to be lower-risk fungicides than conventional fungicides due to their low mammalian toxicity and benign profile toward avian species, though they negatively affect aquatic species (Plaza et al 2002;Lahlali et al 2006).…”