When spore concentrations are high, there are more fruit abortions when spore concentration is low, there is more internal fruit rot. Infection of fresh flowers results in more fruit infection than does infection of wilted flowers. The fungus requires two days to travel from the fresh flower into the fruit. For flower infections, the fungus grows through the stigma and style into the fruit where it causes rotting and discoloration of the central tissue. Internal fruit rot is usually introduced through the flower end, but occasionally from the stem. Guttation or exudation of droplets from ends of leaf veins. Guttation is often seen in very humid greenhouses in the early morning.įigure 7. deleafing, fruit harvest) or guttation (exudation of plant sap from the ends of leaf veins and its evaporation, which can cause a localized buildup of salts) ( Figure 7). Wounding may result from damage due to crop activities (e.g. In young plant tissue, however, wounding is not necessary for infection to occur. Wounding is another factor that facilitates infection, particularly in older plant parts. Germination and spore production, development of symptoms on stems, and infection of cucumber leaves, petioles and flowers can occur over a wide range of temperatures (5☌ to 35☌), but optimum temperatures are 24☌ to 25☌. One hour of free water on leaves is sufficient for initial infection however, continuous leaf wetness is required for subsequent expansion of lesions. The most significant contributor to establishing the infection is how long plant surfaces remain wet. Gummy stem blight develops in humid conditions and in free moisture on leaf surfaces. Both types of spores are also spread on fingers, knives, wet hands and clothing. The fungus essentially produces two types of spores: conidia that may be dispersed by splashing water, and ascospores that are spread by air current. Disease Cycleĭidymella bryoniae is highly resistant to dry conditions and it can survive as dormant mycelia or hardy structures called chlamydospores in undecomposed debris for up to two years. Advanced V-shaped symptoms of gummy stem blight infection on mature leaf. Early symptoms of gummy stem blight infection on leaf beginning at leaf tip.įigure 6. Lesions may also consist of circular spots on the leaves.įigure 5. Sometimes the entire margin is affected, creating a brown edge and a downward cupping of the leaf. Leaf symptoms are usually visible at the tips ( Figure 5) as pale yellow or brown dead tissue, often with a yellow halo, extending backwards in a V-shape ( Figure 6). Advanced external symptoms of gummy stem blight. Internal discolouration and rotting of fruit due to gummy stem blight.įigure 4. Narrowing of blossom end of fruit due to gummy stem blight infection.įigure 3. Stem cracks, amber-coloured gummy droplets and tiny black spore-producing bodies at base of cucumber stem.įigure 2. Symptoms become visible mostly during storage.įigure 1. These lesions are soft, wet, sunken, and often contain spots of gummy exudate at the centre. External fruit lesions appear as irregular circular spots that are initially yellow, then grey to brown. If the disease is more severe, the blossom end tapers even more directly to a point and becomes black due to the profusion of fruiting bodies externally ( Figure 4). The brownish-black internal discoloration often extends for 1-2 cm along the length of the fruit. Internal fruit rot is not externally visible and is characterized by a tapering of the blossom end ( Figure 2) and discoloured centrally located tissues ( Figure 3). Fruitsįruits can be affected internally and externally. If seeds are contaminated with this pathogen, damping-off will occur. Such lesions often occur at the base of the main stem, and if girdling by the lesions is complete, wilting and plant death will result. They may also crack and exude a gummy amber-coloured sap ( Figure 1). These lesions become dotted and almost entirely covered with tiny black spore-producing fruiting bodies. Symptoms StemsĮarly symptoms consist of pale brown lesions at wounds created by removing leaves, fruits and lateral shoots. The fungus attacks all parts of the plant, and under favourable conditions, causes severe economic losses. This pathogen infects only members of the cucurbit family such as cucumber, squash, melon, pumpkin, vegetable marrows, bitter melon and zucchini. In Europe, this disease is also called mycosphaerella rot. It is caused by the fungus Didymella bryoniae, previously named Mycosphaerella melonis and M. Gummy stem blight is a common disease found worldwide in greenhouse cucumber.
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