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Plantwise Technical Factsheet

tomato leaf mould (Passalora fulva)

Host plants / species affected
Solanum lycopersicum (tomato)
List of symptoms/signs
Leaves  -  abnormal colours
Leaves  -  abnormal leaf fall
Leaves  -  fungal growth
Leaves  -  necrotic areas
Symptoms
The first symptoms are pale chlorotic spots, with an indefinite margin, on the upper surface of the leaf. Sporulation, which occurs on the lower surface of the leaf beneath the spots, is downy, light grey but becoming buff to tawny-brown or olive green. Defoliation may occur if the infection is severe enough. The optimum temperature for disease development is 22-24°C and, therefore, in temperate regions the disease is almost invariably limited to greenhouse crops. In the tropics, the disease is most severe during cooler periods when relative humidity is high. Leaf and sepal penetration is via stomata; there are no appressoria formed. The importance of high relative humidity for penetration, lesion growth and sporulation has long been recognized.
Prevention and control
Cultural Control and Sanitary Methods

It has been shown that in the glasshouse, disease incidence can be decreased (and yield increased) by limiting the periods of high relative humidity. There was less leaf mould at a constant 20°C compared with a 20°C (day) and 13°C (night) regime (Winspear et al., 1970). However, other means have been tested. Vakalounakis (1992) grew two tomato cultivars in a greenhouse covered with a long-wave infrared absorbing (IRA)-vinyl film, which absorbs infrared emission by soil and plants during the night, and in a control greenhouse covered with a common agricultural (CA)-polyethylene film. At the end of the crop seasons, total disease index for leaf mould, caused by P. fulva (amongst other fungi), on both cultivars was much less in the IRA-vinyl greenhouse than in the CA-vinyl greenhouse. Another method used soil sterilization by solar heating by polyethylene mulching, followed by covering the soil again with plastic and planting seedlings through holes made in the covers. Hasan (1989) found that this reduced the severity of tomato leaf mould (P. fulva) as well as tomato yellow leaf curl bigeminivirus and early blight (Alternaria solani).

Host-Plant Resistance

Breeding work in N. America and Europe has used oligogenic resistance in a range of Lycopersicon species (such as L. chilense, L. hirsutum, L. peruvianum and L. pimpinellifolium) to introduce resistance genes into L. esculentum: for instance, the Cf-2 gene was introduced from L. pimpinellifolium and Cf-9 from L. esculentum var. cerasiforme (Dickinson et al., 1993). The highest percentage of effective sources of resistance to P. fulva and Tobacco mosaic virus were found in Lycopersicon peruvianum, L. hirsutum and L. chilense (Vlasova, 1986). For further details about the mechanism of resistance and pathogenicity see section on Biology and Ecology: Physiological races and genetics.

Apart from generating a hypersensitive response, it appears that some tomatoes can produce a glycoalkaloid, tomatine, which is toxic to P. fulva, the degree of toxicity depending on the pH and nutrient status of the assay medium. Dow and Callow (1978) found that tomatine exerted both fungistatic and fungicidal effects.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Biological Control

A number of fungi are antagonistic to P. fulva, most notably Acremonium strictum, Dicyma pulvinata (= Hansfordia pulvinata), Trichoderma harzianum (Bedlan, 1997) and Trichothecium roseum. In greenhouse trials in Moscow, USSR, P. fulva on tomatoes was inhibited by T. roseum (84%), Trichoderma viride strain 3 (66%) and A. strictum (53%) (Kashyap, 1979).

A great deal of work has been carried out on the mycoparasite Dicyma pulvinata which is known to occur on a range of cercosporoid leaf-inhabiting fungi. The possibilities of this fungus were first suggested by Peresse and Picard (1980). Dicyma pulvinata, A. strictum and another species of Acremonium act as hyperparasites of P. fulva, with hyphal coiling and even penetration. Scanning electron microscopy shows that D. pulvinata, after a biotrophic phase, becomes necrotrophic, draining the cytoplasmic content of P. fulva (Picard et al., 1987). When used as a biocontrol agent in commercial greenhouses, Tirilly et al. (1987) found that 80% or more of blotches due to P. fulva were overgrown by D. pulvinata. The efficacy of this control method is limited by the inability of D. pulvinata to come into contact with P. fulva and by the poor natural spread of the hyperparasite. D. pulvinata produces a sesquiterpene toxin, deoxyphomenone, which is detectable in hyperparasitized lesions on tomato leaves. A study of the kinetics of synthesis of this toxin suggests that it plays a role during the first stages of hyperparasitism. Studies on the effects of deoxyphomenone on plasmalemma activities and permeability of plant cells indicates that the toxin is non-specific and acts at the plasmalemma levels, not killing the host cells, but causing their dysfunction (Tirilly et al., 1991b).

Some other fungi are also effective against P. fulva, such as the hyperparasitic Sporotrichum vile (Polyakov et al., 1976) and species of Penicillium which were capable of destruction of the pathogen in leaf mould lesions similar to that induced by fungicides when the leaves are treated with spore suspensions. Penicillium pinophilum had a limited effect against infection while P. stipitatum strongly affected sporulation in a manner similar to dichlofluanid (Okasha et al., 1989).

Kim and Cho (1995) found that Bacillus subtilis isolated from sclerotia of Rhizoctonia solani showed antifungal activity. The antifungal activity of the extracted substances, identified as iturins, was evaluated against 16 phytopathogenic fungi by measuring growth inhibition. The substances gave >80% growth inhibition of P. fulva.
Impact
In UK glasshouse tomatoes, P. fulva was found in 28% of crops but was severe in only 3% (Fletcher and Harris, 1979). However, a recent quantification of the impact of P. fulva in economic terms is not available. In developed countries the seriousness of P. fulva outbreaks has decreased as the means of control have been improved and new varieties introduced.
Related treatment support
Plantwise Factsheets for Farmers
Zhao, S.; CABI, 2012, Chinese language
 
 
External factsheets
Pestnet Factsheets, Pestnet, English language
Ontario CropIPM factsheets, Ontario Ministry of Agriculture, Food and Rural Affairs, Canada, 2015, English language
Ontario CropIPM factsheets, Ontario Ministry of Agriculture, Food and Rural Affairs, Canada, 2015, French language
Pestnet Factsheets, Pestnet, English language
Solomon Islands Ministry of Agriculture and Livestock Farmer Fact Sheets, Solomon Islands Ministry of Agriculture and Livestock, 2012, English language
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