Plant diseases canker

Shoots blacken, wilt, and die back. Cause Canker. Also known as dieback, this disease is caused by 2 fungal organisms and most often occurs during rainy weather. Prune and destroy infected shoots thin plantings to improve air circulation. Remove and destroy severely infected plants. If canker has been a problem, use preventive sprays of bordeaux mix. 

Diseases of plants may arise from attack by fungi, bacteria, viruses, insects or parasitic plants. Insects may also act as the vectors of plant diseases and provide routes for pathogens to enter plants. The disease may be manifest by decayed or swollen roots, shrivelled or lost fruit, chlorotic or wilting leaves, necrotic lesions on the stems, leaves or fruit, excessive gum formation or the formation of cankers. In this chapter we are eoncerned with the chemistry of the fungal attack on plants that lead to these symptoms. 

Signs Plants infected with citrus canker have characteristic lesions on leaves, stems, and fruit with raised, brown water-soaked margins usually with a yellow hallow effect around the lesion. Incubation is typically 14-60 days. Older lesions may fall out, creating a shot-hole effect. Fruit production declines and then stops. The disease ultimately kills the tree. 

AAL-Toxin. Stem canker of tomato is caused by the fungal pathogen Alternaria alternata f. sp. Ivcooersici (21). Concentrations of less that 10 ng/ml of AAL-toxin [14], a host-specific toxin, can produce disease symptoms. Two phytotoxic fractions have been isolated from fungal culture filtrates that reproduce disease symptoms in susceptible plants. These fractions are termed T ... 

Cane dieback. Causes Blueberry cane canker Fusiccsccum canker. Blueberry cane canker, most pre alent in the South, shows up as reddish, conical stem swellings. The next year these swellings become blisterlike, light gray, and then black and fissured. If this disease is a problem in your area, plant rabbiteye blueberries, which are not susceptible to cane canker. Or plant highbush cultivars resistant to cane canker, including Atlantic and Jersey . 

Yellow spots that turn brown are caused by anthracnose. Infected leaves eventually die. This disease causes fruit with circular black cankers. Prevent problems by planting anthracnose-resistant muskmelon cultivars, such as Passport , and resistant watermelon cultivars, such as All Sweet , Crimson Sweet , Dixie Lee , and Sweet Favorite . 

Valsa canker is a fungal disease that enters through injured bark. To prevent bark damage, make sure trees harden off in the fall by avoiding late-season fertilization or pruning. Also plant in well-drained soil and paint trunks with white latex paint diluted with an equal amount of water to reduce bark-damaging... 

Leaves with brown edges. Cause Bacterial canker. Lower leaves wilt and curl up stems develop light-colored streaks and are brown and mealy inside. See page 229 for an illustration of this disease. Destroy infected plants. To prevent problems, presoak seed in 10 percent bleach solution, and avoid wounding plants. Don t touch plants when they are wet to avoid spreading the disease. 

Other fungal diseases cause swellings on plant parts, such as black knot of plum and cherry, or sunken areas in stems, as with Cytospora canker. On fruit, fungi can cause hard, black patches (scab), soft spots (rot), or fuzzy gray mold (Botrytis rot). 

One distinctive symptom of sonre bacterial diseases is the sticky, gummy material secreted by active bacterial cells. If the leaves on your cucumber plant arc wilting and you suspect bacterial wilt disease, cut the stem or leaf stalk with a sharp knife. If you see threads of slime when you pull the stem or stalk apart, this confirms bacterial wilt disease. Active fire blight cankers are covered with a similar bacterial slime. In many cases the bacterial slime has an unpleasant odor. 

Trees and shrubs that are fertilized too late in summer, or overfertilized with nitrogen at any time, do not harden off with the approach of cold weather in autumn. Pruning or ovcrwatcring too late in the summer can also cause a late flush of succulent growth. In the winter, insufficiently hardened plants may experience cold damage and subsequent disease problems, such as Cytospora canker, also known as Valsa canker, of peach trees. 

The pathotype responsible for tomato stem canker produces 3 related toxins (Fig. 3). Aspartate and certain products of aspartate metabolism (e.g. orotic acid) protect tomato plants against the toxins, and it is thought that toxicity may be due to inhibition of aspartate transcarbamylase. Susceptibility to the disease is controlled by a single genetic locus with 2 alleles. 

The genus Alternaria is widely distributed in nature, and a number of Alternaria spp are pathogenic to plants (66). A. alternata f sp. lycopersici was isolated from susceptible asc/asc) tomatoes with stem canker disease (33,40, 48). The active phytotoxin responsible... 

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