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  • Author or Editor: Stanley Freeman x
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Colletotrichum spp. are broad-range pathogens, meaning that many species can infect a single host and a single species can infect diverse hosts. For example, Colletotrichum acutatum J.H. Simmonds affects a wide range of crops, causing disease symptoms on apple, almond, anemone, citrus, lupin, peach, pecan, strawberry, and others, whereas Colletotrichum gloeosporioides Penz. (Penz. & Sacc.) can affect many of the previous hosts as well. Anthracnose is one of the major fungal diseases of strawberry occurring worldwide. In Israel, the disease is caused primarily by the species C. acutatum. The pathogen causes irregular leaf spot, bud rot, petiole and stolon necrosis, and black spot on fruit. The pathogen is most destructive when it causes root necrosis and crown rot, which usually kill the plants in nurseries and transplants in the field. To maintain a disease-free crop, nuclear and foundation stock material, as well as field nurseries, must be routinely monitored and tested for presence of the pathogen. Strawberry cultivation using plasticulture as an overhead cover of the crop can significantly control anthracnose disease incidence by reducing inoculum spread and infection, both in nurseries and in production fields. C. acutatum from strawberry can survive on several cultivated plant species, such as pepper, eggplant, tomato, bean, and weed species, without causing disease symptoms. This indicated that they may serve as a potential inoculum reservoir for strawberry infection between seasons. Although C. acutatum survives in soil under certain conditions, no specific resting structures have been observed indicating that the pathogen does not behave as a typical soilborne fungus.

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Severe damage has been observed in Israeli date palm (Phoenix dactylifera L.) plantations of the Medjool cultivar as a result of drying and dropping of fruit bunches. Both fractures and rot occurred during peduncle (fruit stalk) development at proximal points located deep within the crown. The phenomenon has been previously described as “cross–cut” or “V-cut.” The present study aimed to characterize the phenomenon and identify the main causal factors. Annual surveys have revealed high levels of fruit bunch drop in all ‘Medjool’ cultivation areas in Israel. Arenipses sabella and other insects were only occasionally detected in the damaged fruit stalks. Similar damage levels observed in insecticide-treated and untreated plots suggested that insects were not directly responsible for this phenomenon. Tissue decay was detected in many of the freshly fallen fruit stalks. The pathogenic fungus, Fusarium proliferatum, was detected in most of the necrotic fruit stalks. Fusarium proliferatum isolates from infected fruit stalks generated necrotic lesions in fruit stalk tissue in vitro. However, fungicide treatments on trees in the orchards were ineffective in reducing bunch drop. On the other hand, restraining the growth rate of the fruit stalk, by reducing irrigation levels (to 20%) during the period of fruit stalk development and growth, significantly reduced bunch drop levels in most of the examined plots. These data suggest that bunch drop in ‘Medjool’ date palm is caused mainly by physiological disorders related to fruit stalk development and growth.

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