Role of citrus volatiles in host recognition, germination and growth of Penicillium digitatum and Penicillium italicum

Postharvest Biology and Technology (Impact Factor: 2.22). 09/2008; 49(3). DOI: 10.1016/j.postharvbio.2008.01.016
Source: OAI


Volatiles emitted from wounded peel tissue of various citrus cultivars had a pronounced stimulatory effect on germination and germ tube elongation of both Penicillium digitatum and P. italicum; however, P. digitatum appeared to be more sensitive to the stimulatory action of citrus peel volatiles. When exposed to volatiles from grapefruit peel discs, the percentage of germinated spores of P. digitatum and P. italicum was 75.1% and 37.5%, respectively, whereas germination of controls was 6.8% and 14.7%, respectively. In contrast, Botrytis cinerea and P. expansum were either not affected or inhibited by the peel volatiles. GS-MS analysis of volatiles present in the peel of various citrus fruit cultivars revealed that limonene is the major fruit peel volatile. Its percentage ranged from 89% to 95% at the early stages of fruit development throughout the harvest season. Myrcene and α-pinene made up the second and third greatest amounts among the volatiles found in these oils, ranging from 2.12% to 2.33% and from 0.71% to 1.25%, respectively. All four monoterpenes, limonene, α-pinene, β-pinene and myrcene were stimulatory to P. digitatum and P. italicum but inhibitory to or had no effect on P. expansum and B. cinerea. Germ tube elongation in P. digitatum responded most strongly to limonene and less strongly to α-pinene and β-pinene while myrcene had little effect. In contrast in P. italicum, myrcene stimulated germ tube elongation the most followed by limonene, with α-pinene, and β-pinene being about equal. Germination of P. italicum conidia was highest in response to myrecene with the effect of the other compounds being about equal at concentrations of 5μL or more per plate.

Download full-text


Available from: Samir Droby
  • Source
    • "The effect of 1,8-cineole on V. longisporum germination was investigated according to Droby et al. (2008). Ten-microliter droplets of V. longisporum spore suspension (4 9 10 5 spores ml "
    [Show abstract] [Hide abstract]
    ABSTRACT: The fungus Verticillium longisporum is a soil-borne plant pathogen of increasing economic importance, and information on plant responses is limited. To identify genes and components involved in the early stages of infection, transcripts in roots of V. longisporum-challenged Arabidopsis Col-0 and the susceptible NON-RACE SPECIFIC DISEASE RESISTANCE 1 (ndr1-1) mutant were compared using ATH1 gene chips. The analysis revealed altered transcript levels of several terpene biosynthesis genes, including the monoterpene synthase TPS23/27. When transgenic 35S:TPS23/27 and TPS23/27-amiRNA plants were monitored the over-expresser line showed enhanced fungal colonization whereas the silenced genotype was indistinguishable from Col-0. Transcript analysis of terpene biosynthesis genes suggested that only the TPS23/27 pathway is affected in the two transgenic genotypes. To confirm changes in monoterpene production, emitted volatiles were determined using solid-phase microextraction (SPME) and GC-MS. Levels of all identified TP23/27 monoterpene products were significantly altered in the transgenic plants. A stimulatory effect on conidial germination and hyphal growth of V. longisporum was also seen in co-cultivation with 35S:TPS23/27 plants and upon exposure to 1,8-cineole, the main product of TPS23/27. Methyl jasmonate (MeJA) treatments of myc2-1 and myc2-2 mutants and analysis of TPS23/27:uidA in the myc2-2 background suggested a dependency on jasmonic acid, mediated by the transcription factor MYC2. Taken together, our results show that TPS23/27-produced monoterpenes stimulate germination and subsequent invasion of V. longisporum in Arabidopsis roots.This article is protected by copyright. All rights reserved.
    Full-text · Article · Dec 2014 · The Plant Journal
  • Source
    • "During harvest, injuries are more than likely to be inflicted and these increase the risk for infection (Rose et al., 1951). When a wound is inflicted on the rind of a citrus fruit, volatile compounds are released and if conidia from P. digitatum are present in the wound it will be stimulated to germinate by these volatiles (Eckert and Ratnayake, 1994; Droby et al., 2008). The exudations from the injured peel and pectin will in turn stimulate infection and growth of the fungus (Kavanagh and Wood, 1971; Stange et al., 2002). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Green mould (Penicillium digitatum) is a major cause of postharvest losses in citrus. Wounds and infection can be inflicted during the harvest process and should be controlled during postharvest stages to prevent decay. Imazalil (IMZ) in the sulphate formulation is currently applied by the majority of South African packhouses through an aqueous dip treatment. In this study the effects of incubation time (infection age), exposure time, solution pH, wounds size and fruit brushing after dip treatments on residue loading and curative green mould control were investigated. Exposure time did not have a significant effect on residue loading on fruit dipped in pH 3 solutions of IMZ (<2.00 μg g−1). Increasing the pH to 6 resulted in significantly increased residue loading, which increased with longer exposure time, but mostly to levels below the maximum residue level of 5 μg g−1 after 180 s. Post-dip treatment brushing reduced residue levels obtained in IMZ pH 3 solutions by up to 90% to levels <0.5 μg g−1; however, curative control of the IMZ sensitive (S) isolate was mostly unaffected, but with poor sporulation inhibition. At pH 6, post-dip brushing reduced residues to ≈60%; again curative control of the sensitive isolate was unaffected, but with better sporulation inhibition than the pH 3 treatments. Wounded rind sections loaded higher residue levels compared with intact rind sections, and large wounds loaded higher levels than small wounds (≈10.19, ≈9.06 and ≈7.91 μg g−1 for large, small and no wound, respectively). Curative control of infections originating from large wounds was significantly better than those from small wounds. The ability of IMZ to control sensitive green mould infections declined from 6 and 12 h after inoculation on Clementine mandarin fruit of infections inflicted by small and large wounds, respectively; on navel orange fruit, curative control declined 18 and 36 h after inoculation for the respective wound size treatments. This work shows the importance of timely fungicide treatment after harvest especially on more susceptible citrus types. Results also indicate that excess residues can be stripped from the fruit, retaining residues necessary for curative control in the wound sites. However, reduced residue loading compromised the sporulation inhibition activity of IMZ.
    Full-text · Article · Nov 2014 · Postharvest Biology and Technology
  • Source
    • "In addition, the lemon odour of C. citratus is more compatible with citrus fruits than those of many of the other essential oils are expected to be. P. digitatum, P. italicum and G. citri-aurantii are all opportunistic wound pathogens (Droby et al., 2008) that erode the profit margins of citrus producers. The development of an EO or EOcombination crop product that can simultaneously protect against these pathogens would provide industry with a competitive advantage , particularly in the organic sector. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Fifty-nine commercially available essential oils and some of their major components were screened todetermine their effects on the mycelial growth of G. citri-aurantii using toxic medium assays. Nine of theseessential oils totally inhibited the mycelial growth of the pathogen at 1000 �l/l. Gas chromatographicanalysis revealed the compositions of the most effective oils. Exposure to the vapours of selected essentialoils (Thymus vulgaris, Citrus aurantium var. amara, Cymbopogon citratus, Cymbopogon martinii, Origanumvulgare, Geranium graveolens roseum Bourbon) proved fungistatic, rather than fungicidal, towards thepathogen. ‘Valencia’ oranges, inoculated with G. citri-aurantii, were treated with the most promisingbotanicals. Essential oils (1000 �l/l) of C. citratus, C. martinii, O. vulgare and G. graveolens roseum Bourbon,incorporated into coating or applied as a curative dip, resulted in a drastic reduction in decay when com-pared to the negative control. No physiological breakdown of the fruit was evident at this concentration. C.citratus (lemongrass) was selected as the most cost-effective option for control of G. citri-aurantii. Previouscommercial trials indicated the protective properties of Mentha spicata essential oil against Penicilliumdigitatum. To develop an effective multi-target protection product against G. citri-aurantii, P. digitatumand Penicillium italicum, essential oil of C. citratus was combined with that of M. spicata. A toxic medium,containing both essential oils, each at 750 �l/l, totally controlled all three pathogens. Although individualessential oil-amended coatings have previously been applied for postharvest control, this study proposesa mixture of these essential oils for control of two serious citrus pathogens (G. citri-aurantii, P. digitatum),in addition to P. italicum.
    Full-text · Article · Nov 2014 · Industrial Crops and Products
Show more