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Plantwise Technical Factsheet

fasciation: leafy gall (Rhodococcus fascians)

Host plants / species affected
Alcea rosea (Hollyhock)
Anemone (windflower)
Antirrhinum majus (snapdragon)
Aruncus
Asparagus densiflorus (asparagus fern)
Baptisia
Begonia tuberhybrida
Beloperone (Shrimp bush)
Beta vulgaris (beetroot)
Brassica oleracea (cabbages, cauliflowers)
Brassica oleracea var. botrytis (cauliflower)
Brodiaea
Buddleja davidii (butterfly bush)
Capsicum annuum (bell pepper)
Casuarina equisetifolia (casuarina)
Chamaemelum nobile (common chamomile)
Chrysanthemum indicum (chrysanthemum)
Chrysanthemum maximum hybrids
Chrysanthemum vestitum
Cicer arietinum (chickpea)
Cichorium intybus (chicory)
Consolida ambigua (rocket larkspur)
Crassula (Stonecrop)
Crocus
Cucumis melo (melon)
Cucumis sativus (cucumber)
Dahlia pinnata (garden dahlia)
Datura innoxia (downy thorn apple)
Dianthus barbatus (sweet williams)
Dianthus caryophyllus (carnation)
Erysimum allionii
Erysimum cheiri (wallflower)
Euphorbia (spurges)
Euphorbia pulcherrima (poinsettia)
Forsythia suspensa
Fragaria (strawberry)
Fragaria ananassa (strawberry)
Fragaria vesca (wild strawberry)
Freesia
Fritillaria
Gladiolus hybrids (sword lily)
Gloriosa
Glycine max (soyabean)
Gypsophila paniculata (baby’s breath)
Hebe
Hebe andersonii hybrids
Helianthemum (rock-rose)
Hyacinthus (hyacinth)
Impatiens (balsam)
Impatiens walleriana (Busy-lizzy)
Kalanchoe
Kalanchoe blossfeldiana (flaming katy)
Lactuca sativa (lettuce)
Lathyrus odoratus (sweet pea)
Lilium (lily)
Lilium longiflorum (Easter lily)
Lilium regale (Regal lily)
Mesembryanthemum
Muscari botryoides (grapehyacinth)
Nicotiana alata (sweet-scented tobacco)
Nicotiana rustica (wild tobacco)
Nicotiana tabacum (tobacco)
Osteospermum ecklonis
Pelargonium (pelargoniums)
Pelargonium zonale hybrids
Petunia hybrida
Phaseolus coccineus (runner bean)
Phaseolus vulgaris (common bean)
Phlox
Physalis (Groundcherry)
Pisum sativum (pea)
Rhododendron (Azalea)
Rubus idaeus (raspberry)
Rudbeckia (coneflower)
Saponaria ocymoides (rock soapwort)
Solanum lycopersicum (tomato)
Sorbaria sorbifolia
Spinacia oleracea (spinach)
Tagetes erecta (African marigold)
Tagetes patula (French marigold)
Tanacetum coccineum (common pyrethrum)
Triteleia
Triteleia laxa (ithuriel's spear)
Tropaeolum majus (common nasturtium)
Tulipa (tulip)
Urtica dioica (stinging nettle)
Viburnum opulus (Guelder rose)
Vicia faba (faba bean)
List of symptoms/signs
Leaves  -  abnormal forms
Stems  -  fasciation
Stems  -  stunting or rosetting
Stems  -  witches broom
Symptoms
The nature of fasciation induced upon R. fascians infection is dependent on the host plant (genus, species and cultivar; Lacey, 1939), age of plant (young growing tissue is particularly sensitive but becomes less sensitive as it matures; Roussaux, 1965; Faivre-Amiot, 1967), bacterial strain (avirulent to virulent strains have been characterized; Eason et al., 1995) and on plant growth conditions and infection path (Faivre-Amiot, 1967; Vereecke et al., 2000).

Symptoms range from witches'-broom and over-fasciation to leafy gall (Faivre-Amiot, 1967). Witches'-broom is characterized by the development of bunches of fleshy, thick stems with misshapen and aborted leaves that develop at or below the soil level on the crown of the host plant. In sweet pea, the growth of the epicotyl is initially stimulated (Roussaux, 1975) but soon growth of the terminal bud is inhibited and affected plants become dwarfed and have a reduced flower production (Brown, 1927; Tilford, 1936; Lacey, 1936; Baker, 1950). Fasciations are formed when several hypertrophied shoots coalesce. They carry malformed, small leaves that show thickened petioles and veins (Roussaux, 1965). Fasciation further develops into leafy galls when the growth of the fleshy shoots is completely inhibited and their structure is disorganised. Meristematic sites on galls are either the axillary buds developing from nodes of these lateral shoots (Roussaux, 1975) or de novo formed meristems from reinitiated cell divisions in the outer cortical cell layers of the petioles or the stems. The root system is generally not affected, although severe infection can lead to partial inhibition of the radicle. The main root may then become thickened with the inhibition of secondary roots (Lacey, 1936; Tilford, 1936; Roussaux, 1965; Faivre-Amiot, 1967; Vereecke et al., 2000). R. fascians has been isolated from root galls on raspberry (Rubus idaeus) (Jones et al., 1977). On monocotyledonous plants, R. fascians provokes severe malformation of the bulbs and the formation of long side shoots giving rise to abnormal plants with diminished flower production (Miller et al., 1980; Vantomme et al., 1982; Scortichini, 1988).

Wounding of the host is not essential for infection, hence symptoms can be induced when the bacteria are present on the surface of healthy tissue (Lacey, 1939; Baker, 1950; Roussaux, 1965). Nevertheless, when wounding does occur, symptoms are more severe and develop more rapidly. The continuous presence of the bacteria is required for symptom persistence, because they provide a continuous stimulus leading to progressive growth of the leafy gall (Lacey, 1936; Crespi et al., 1992, 1994; Eason et al., 1996; Temmerman et al., 2000; Vereecke et al., 2000). The pathogen is present on the surfaces of the plants (Lacey, 1936) and within plant tissue in the intercellular spaces.
Prevention and control
R. fascians is the subject of phytosanitary measures in Japan where plant quarantine inspections are supported by detection methods of specific antisera and selective media (Takayama et al., 1985; Kobayashi, 1990). In Peru, pea seeds must be fumigated prior to shipment.

Cultural control and plant hygiene are the main control methods. Planting material has been maintained as pathogen-free by avoiding the use of infected plants for root divisions for Shasta daisy (Oduro, 1975) and by regular renewal and screening of mother plants for Pelargonium (Angiboust, 1975). Begonia planting material has been freed of the pathogen by treating it for 10 minutes at 50°C (Van Hoof et al., 1979). Systematic disinfection of glasshouses, materials and protective clothing is essential (Angiboust, 1975; Digat, 1977). For lilies, the removal of deformed bulbs (Muller, 1979) followed by treatment with hot water before planting (Muller, 1979; Kruyer and Boontjes, 1982) is considered to offer practical control.

Chemical control can be attempted using copper containing chemicals (Digat, 1977).

There are no records on biological control.

Removal in the field of suspect plants can prevent further spread to other plants. Suspect plants may have hypertrophied shoots that emerge from the crown and sometimes form a leafy gall at the base of the main stem, may have retarded growth, or may be poorly flowering plants.
Impact
Although the disease is widespread, it is sporadic in its occurrence and there is rarely a high local incidence of disease. Even under intense horticultural conditions severe outbreaks are rare, apparently occurring where good sanitation practices were not observed or there was an unusual environmental factor. The disease is most serious on bulb, floral and greenhouse crops. In the floral industry, serious commercial losses have been reported for sweet pea in Ohio (Tilford, 1936) and New Jersey, USA (Brown, 1927), for chrysanthemum in England, UK (Lacey, 1936), for lilies in the Netherlands (Miller et al., 1980) and Belgium (Vantomme et al., 1982), and for several ornamental and crop plants in former Czechoslovakia (Ulrychová and Petru, 1983).

In the UK, for Schizanthus retusus, 50% or more of nursery plants were affected each year over a considerable period of time, and in a carnation nursery 5% of the plants showed symptoms for 10-12 years (Lacey, 1939). In France, on Pelargonium up to 90% field contamination was observed (Digat, 1977) and some Dahlia plantings were completely affected (Faivre-Amiot, 1967). Also in France, a combination of R. fascians and nematode infection led to the complete loss of a strawberry crop (Faivre-Amiot, 1967). Strawberry harvest was also impaired in the Moscow region of Russia with a reduction in yield of 28-38% (Matveeva and Yakubovich, 1972).

In California, USA, there are several records of losses in floral crops. On Esther Read daisy in nurseries, R. fascians led to seriously reduced yields of cut flowers and plants available for multiplication (Baker, 1950). In some Chrysanthemum maximum crops, virtually all plants were diseased and the severity increased with the progressive harvest of the apical buds (Oduro, 1975). Stem fasciation was observed on 90% of Impatiens wallerana plants and on 20% Hebe speciosa cv. Rubraand and H. elliptica (Cooksey and Keim, 1983).
Related treatment support
 
External factsheets
University of Illinois Extension Factsheets, University of Illinois, 1991, English language
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