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Plantwise Technical Factsheet

damping-off (Pythium aphanidermatum)

Host plants / species affected
Abelmoschus esculentus (okra)
Acacia nilotica (gum arabic tree)
Agrostis stolonifera var. palustris (bent grass)
Amaranthus (amaranth)
Amaranthus cruentus (redshank)
Arachis hypogaea (groundnut)
Beta vulgaris (beetroot)
Beta vulgaris var. saccharifera (sugarbeet)
Brassica juncea var. juncea (Indian mustard)
Brassica oleracea var. botrytis (cauliflower)
Brassica oleracea var. capitata (cabbage)
Brassica rapa subsp. pekinensis
Cannabis sativa (hemp)
Capsicum (peppers)
Capsicum annuum (bell pepper)
Carica papaya (pawpaw)
Carthamus tinctorius (safflower)
Catharanthus roseus (Madagascar periwinkle)
Citrullus lanatus (watermelon)
Crotalaria juncea (sunn hemp)
Cucumis sativus (cucumber)
Curcuma longa (turmeric)
Cymbopogon winterianus (java citronellagrass)
Cynara cardunculus var. scolymus (globe artichoke)
Daucus carota (carrot)
Dianthus caryophyllus (carnation)
Elettaria cardamomum (cardamom)
Euphorbia pulcherrima (poinsettia)
Ficus benjamina (weeping fig)
Fragaria ananassa (strawberry)
Geranium (cranesbill)
Glycine max (soyabean)
Gossypium (cotton)
Gypsophila paniculata (baby’s breath)
Hordeum vulgare (barley)
Lactuca sativa (lettuce)
Lampranthus spectabilis
Lens culinaris subsp. culinaris (lentil)
Linum usitatissimum (flax)
Luffa aegyptiaca (loofah)
Mentha piperita (Peppermint)
Mesembryanthemum crystallinum (crystalline iceplant)
Nicotiana tabacum (tobacco)
Nopalea cochenillifera (cochineal cactus)
Opuntia ficus-indica (prickly pear)
Parthenium argentatum (Guayule)
Phaseolus (beans)
Phaseolus vulgaris (common bean)
Pinus (pines)
Pisum sativum (pea)
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum tuberosum (potato)
Spinacia oleracea (spinach)
Triticum aestivum (wheat)
Vigna unguiculata (cowpea)
Zea mays (maize)
Zingiber officinale (ginger)
Ziziphus mauritiana (jujube)
List of symptoms/signs
Roots  -  necrotic streaks or lesions
Roots  -  reduced root system
Roots  -  soft rot of cortex
Roots  -  stubby roots
Vegetative organs  -  internal rotting or discoloration
Vegetative organs  -  soft rot
Vegetative organs  -  surface lesions or discoloration
Whole plant  -  damping off
Whole plant  -  dwarfing
Whole plant  -  plant dead; dieback
Pre-emergence damping-off: Failure of seedling to emerge after planting. Recovered seed has a watery rot, if the shoot or root emerges it has a dark necrosis. A number of other pathogens can cause similar symptoms, so pathogen isolation and identification is needed to confirm diagnosis.

Post-emergence damping-off: The seedling emerges from the soil but dies soon afterwards. The roots, hypocotyl and perhaps the crown of the plant will be necrotic and have a water-soaked appearance.

For some hosts, once the plant has reached a certain stage after emergence, infections by the pathogen are no longer lethal, but they can still have a significant impact on plant growth and yield. Apart from stunting of plant growth there may not be any overt symptoms of infection other than necrotic roots. In cases where root infection is heavy, wilting of plants may be observed in warm or windy weather. Foliar symptoms of nutrient deficiency also may be observed due to extensive root rotting preventing the uptake of nutrients.

Post harvest: Water-soaked lesions or a watery rot of the tissue. Under conditions of higher humidity a cottony white mycelium may be observed on the tissue.
Prevention and control

As free water is important for zoospore distribution and the development of disease, efforts to reduce soil moisture will contribute to a reduction in disease severity. These include planting on raised beds to reduce moisture content in the root zone and providing the appropriate drainage in the field to prevent waterlogged conditions. Scheduling planting times to avoid temperature and moisture conditions that are conducive to the pathogen also will reduce disease severity. When planting in containerized production systems it is important to ensure that the potting material is free of the pathogen.

Control in Hydroponic Systems

It is particularly important to control infestations by P. aphanidermatum in hydroponic production systems. Water filtration to physically remove zoospore inoculum has been found to reduce disease incidence (Goldberg et al., 1992), as has UV irradiation of the recirculating nutrient solution (Stanghellini et al., 1984). The addition of nonionic surfactants also controls the disease by disrupting the zoospore membrane and lysing the zoospores (Stanghellini and Tomlinson, 1987; Stanghellini et al., 1996; Stanghellini and Miller, 1997). Stanghellini and Miller (1997) isolated specific bacteria, which produce rhamnolipids when growing in the recirculating nutrient solution, that have a similar effect on lysing zoospores and controlling disease. Soluble silicon and chitosan also are believed to enhance crop yields in hydroponic systems by management of diseases caused by P. aphanidermatum by stimulation of host defence responses (Cherif et al., 1994a, b; El Ghaouth, 1994). Cooling the hydroponic solution to 24°C or lower also reduced disease incidence (Carrai, 1993).

Crop Rotation

In view of its broad host range, crop rotation will not completely control the pathogen, but there are some rotation practices that can reduce the pathogen's inoculum. Population densities of P. aphanidermatum in soil after vegetable cultivation were suppressed by 2- or 3-year rotation in sod compared with a fallow treatment (Johnson et al., 1997). Yields of snap bean, pepper and okra did not differ between fallow and 1 year of sod rotation, but they did following 3 years in sod compared to fallow. Planting cucumber after turnip reduced root disease severity and post emergence damping-off caused by P. aphanidermatum compared to following a groundnut rotation, but did not significantly increase yield (Sumner et al., 1983). Production practices associated with the traditional chinampa agroecosystem in Mexico also were found to be detrimental to the pathogen and disease development (Lumsden et al., 1987, 1990).

Soil Amendment

Soil amendment with specific mineral fertilizers has been found to influence disease severity of some crops. Muthusamy et al. (1973) observed that phosphorous and potassium fertilizers reduced the incidence of tomato damping-off, caused by P. aphanidermatum, in pot trials using sterilized soil while nitrogen fertilizer had no effect. Potassium and silicon fertilizers have also been found to reduced disease severity in maize (Sun et al., 1994) and gypsum and dolomite amendments affects the severity of disease of a variety of vegetable and ornamental crops (Gill, 1972). Calcium oxide or calcium hydroxide amendments not only controlled damping-off of pea, caused by Pythium spp. in the field, but also reduced P. aphanidermatum propagule densities in the soil in the absence of the host (Lewis and Lumsden, 1984). This was attributed to the alteration of the soil pH following soil amendment and the generation of ammonia in the soil atmosphere, which is toxic to the pathogen.

Several different mixtures or organic and inorganic compounds have been reported to reduce disease incidence. Lin and Lo (1988) observed that a mixture of bagasse, rice husks, oyster shell powder, mineral ash, urea and several other mineral fertilizers (termed S-H mixture) controlled P. aphanidermatum on cucumber when soil was amended at a rate of 0.5-2%; a number of other pathogens were also controlled by this amendment (Huang, 1991). This suppressiveness lasted for approximately 25 days after amendment of conducive soil and when the different components of the mixture were tested individually, urea was found to be the most active in inhibiting the pathogen (Lin and Lo, 1988). There was a good correlation between ammonia production for 15 days after soil amendment and pathogen inhibition (Lo and Lin, 1992). Another soil amendment, termed SF-21, consisting of milled pine bark and several mineral fertilizers, was reported to control P. aphanidermatum in slash pine seedling production (Huang and Kuhlman, 1991a). The mechanism of suppression was determined to be both a direct effect of the mineral fertilizers on the pathogen and an indirect effect of the mixture reducing the soil pH and stimulating soil microbial activity (Huang and Kuhlman, 1991b).

When a potting mix was amended with composted spruce or pine bark, a reduction in cucumber damping-off attributed to systemic acquired resistance was observed (Zhang et al., 1996). Composted manure + grape marc (Mandelbaum et al., 1988), manure (Mandelbaum and Hadar, 1990), composted liquorice (Glycyrrhiza glabra) roots (Hadar and Mandelbaum, 1986) or mixtures of composted sugarcane bagasse + filter mud (Theodore and Toribio, 1995) were also found to be suppressive to P. aphanidermatum. In these cases the mechanism of suppression was determined to be biological in nature. Raviv et al. (1998) observed that the addition of the coarse fraction of cattle manure that had been composted to the standard peat and vermiculite growth medium for organic vegetable transplants improved seedling growth in the nursery and reduced susceptibility to P. aphanidermatum in the field. Interestingly, Ben Yephet and Nelson (1999) observed a differential response by different types of compost on suppression of cucumber infection by P. aphanidermatum. Soil amended with leaf compost was suppressive at 20 and 24°C, while amendments with municipal compost were suppressive at 28 and 32°C. Surprisingly, the level of suppressiveness obtained with the leaf compost differed depending on the pathogen isolate examined.

Soil amendment with noncomposted residues of a variety of plant species have been reported to reduce P. aphanidermatum disease incidence in bean (Salazar-Huerta et al., 1991) and ginger (Thakore et al., 1987). Likewise, Rajan and Singh (1974) reported that disease incidence of ginger was reduced by soil amendment with sawdust + urea or several different types of oil cakes.


Solarization also has been found to provide some level of control of P. aphanidermatum on tomato (Hasan, 1989), cucumber (Hickman and Michailides, 1998), periwinkle (Kulkarni et al., 1992), watermelon (Mansoori and Jaliani, 1996) and tobacco seedlings in seedling beds (Wajid et al., 1995).

Genetic Resistance

Pythium species are generally considered to be broad-spectrum pathogens for which host resistance can be difficult to obtain, but there are examples of genetic tolerance to P. aphanidermatum in ginger (Balagopel at al., 1974; Ali et al., 1995), Poa pratensis (Brede and Willard, 1993), maize (Diwakar and Payak, 1975; Tu et al., 1986; Wang et al., 1993), Cucumis spp. (McCreight, 1983), Phaseolus vulgaris (Mohan et al., 1997), Phaseolus (Kim and Kantzes, 1972), periwinkle (Kulkarni et al., 1992) and cowpea (Koleosho et al., 1987). In the case of cowpea, the authors suggested that the level of oxalic acid and polygalacturonase produced in the tissue was positively related to a greater expression of disease symptoms (Koleosho et al., 1987). In periwinkle (Catharanthus roseus), induced autotetraploid lines were more resistant than diploid lines (Kulkarni et al., 1992). Resistance of potato tubers to leak disease also has been reported (Priou et al., 1997). Rahimian and Banihashemi (1979) observed that most melon and cucumber cultivars evaluated were susceptible to P. aphanidermatum, while watermelon was moderately resistant and squash was highly resistant. Hybrids between different species of Carica exhibited resistance to P. aphanidermatum (Mekako and Nakasone, 1975). There is evidence that, in addition to having a direct effect on host tolerance, genetic differences in the host also can contribute to differing levels of efficacy of particular strains of biocontrol organisms (Smith et al., 1997).

Biological Approaches for Disease Control

A number of organisms have been evaluated for their ability to control seed infection and root diseases caused by P. aphanidermatum, with perhaps most work done with bacteria. Moulin et al. (1996) identified several fluorescent pseudomonads that reduced cucumber losses attributed to infection by P. aphanidermatum by reducing root colonization by the pathogen. Strains of this genus were also found to reduce disease incidence in hydroponic cucumber production (Ongena et al., 1999). The mechanism of control was uncertain, but as one strain and its siderophore-negative mutant provided similar levels of control, it did not appear to be due to siderophore production. Paulitz et al. (1992) screened a number of rhizosphere bacteria from cucumber and identified several that not only stimulated shoot and root growth of the crop in a rockwool hydroponic production system, but also controlled root infection by P. aphanidermatum. Further testing of two of these species, Pseudomonas corrugata and P. fluorescens, revealed two strains (one of each species) that were effective in controlling root disease and enhancing yield compared to untreated controls (Rankin and Paulitz, 1994). On further testing, these strains were found to alter root exudates in a manner that reduced zoospore attraction to the roots and the frequency of encystment and germination on the root surface (Zhou and Paulitz, 1993). An additional mechanism of control is thought to be systemic-induced resistance (Zhou and Paulitz, 1994; Chen et al., 1998). Additional strains of Pseudomonas spp. have been found that enhanced cucumber yield in P. aphanidermatum-contaminated rockwool production systems (McCullagh et al., 1996). A strain of Bacillus cereus has been reported to reduce cucumber fruit rot caused by P. aphanidermatum (Smith et al., 1993).

Fungal biocontrol agents also have been described. Sawant and Mukhopadhyay (1991) observed that soil amendment with a wheat bran:sawdust formulation of Trichoderma harzianum enhanced control of sugarbeet damping-off of metalaxyl-treated seeds compared to planting in nonamended soil. Wu and Wu (1998) also reported that T. harzianum and T. koningii reduced damping-off of several container-grown vegetable and ornamental crops when the potting medium was amended prior to planting. Similar results were reported by Bolton (1980b) for poinsettia root rot with amendments of Trichoderma viride and a Streptomyces sp. In greenhouse trials root colonization by the vesicular-arbuscular mycorrhiza G. aggregatum reduced lethal yellowing of Java citronella (Cymbopogon winterianus) caused by P. aphanidermatum (Ratti et al., 1998). Sneh and Ichielevich (1998) reported that several isolates of nonpathogenic Rhizoctonia spp. appeared to induce resistance to P. aphanidermatum in cucumber.

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:

The economic impact of P. aphanidermatum is difficult to determine. Yield reductions due to damping-off caused by this pathogen alone, independent of other Pythium spp. or general root rotting fungal pathogens, are not widely reported. In addition to plant death, crop losses also can be caused by sublethal infections of the root system, which reduce the growth and vigour of the host with a concomitant effect on crop yield. The extent of this yield reduction would not be known unless adjacent plots lacking the pathogen were monitored. However, given its broad host range and wide geographic distribution it is anticipated that losses attributed to P. aphanidermatum could be significant, especially in the warmer regions of the world.
Related treatment support
Plantwise Factsheets for Farmers
Benh Vien Cay An Qua Dong Bang Song Cuu Long; Thuoc Vien Nghien Cuu Cay An Qua Mien Nam; CABI, Vietnamese language
Ding ShouFu; CABI, 2016, Chinese language
Islam, M. S.; Uddin, K.; CABI, 2012, English language
Islam, M. S.; Uddin, K.; CABI, 2012, Bengali language
Omid, S. A.; CABI, 2012, Dari language
Pest Management Decision Guides
Moses, E.; Akrofi, S.; Beseh, P.; CABI, 2016, English language
Cambodia, General Directorate of Agriculture; CABI, 2015, English language
Castillo, P.; Arguello, H.; Salazar, W.; Rostran, J. L.; CABI, 2012, Spanish language
Castillo, P.; Arguello, H.; Salazar, W.; Rostrán, J. L.; CABI, 2012, Spanish language
Priyantha, L.; Wickramaarachchi, W. A. R. T.; Abeykoon, A. N.; Banu, S.; CABI, 2015, English language
External factsheets
University of California IPM Pest Management Guidelines, University of California, 2012, English language
AVRDC International Cooperators' Fact Sheets, Asian Vegetable Research and Development Center (AVRDC), 2004, English language
Biovision Factsheets, Biovision Foundation, 2011, 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
Video factsheets
Agropedia ICRISAT PPT-Videos, IIT, Kanpur, 2014, English language
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