Citrus Black Spot Case Study

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2.5.1 Citrus Black Spot (Phyllosticta citricarpa) - Origin and Distribution Phyllosticta citricarpa originated collectively with its host, Citrus L., from South East Asia (Smith et al., 1997). McAlpine in 1899 first described the asexual form of the fungus as Phoma citricarpa from symptomatic citrus fruit in Australia. Kiely (1948) described the sexual form as Guignardia citricarpa from citrus leaf litter in Australia. The spermatial state or synanamorph is a Leptodothiorella and the species has not currently been described (Baayen et al., 2002). Schubert et al., (2010) reported that the citrus black spot pathogen occurs in the following citrus growing countries: Indonesia, Kenya, Argentina, Australia, Brazil, Ghana, India, United States of…show more content…
This poses a phytosanitary risk. Symptoms can develop on more than 90% of a fruit produced from unsprayed orchards, ranging from one to thousand spots per fruit (Calavan, 1960). Temperature and fruit maturity influence the types of symptom that may appear. Diagnosis of black spot is very difficult unless typical hard-spot symptoms containing pycnidia of the fungus are seen on the fruit (Kotze, 1981). The symptoms that are widely recognized are hard, freckle and virulent spot as well as speckled blotch and cracked spot (Kotzé, 1963 and De Goes et al., 2000). Hard and virulent spot might contain pycnidia in the lesions, though freckle spot can turn into virulent spot and speckled blotch may also turn into hard spot as the period progresses (Kotzé, 1981). Fruit with freckle spot are more unappealing than those with hard spot only (Kiely, 1948). After period of hot weather, the growth of the fungus in the lesions can rapidly increase and lesions briskly enlarge. Individual lesions may combine to form a tearstain lesion comparable to melanose (Diaporthe citri F.A.Wolf) or develop further into virulent spot (Baayen et al., 2002). These symptoms mostly appear following colour change from green to orange (Kotzé, 1981). Symptom expression on mature fruit is facilitated by rising temperatures, high light intensity…show more content…
These proved superior as compared to copper based products (Kellerman and Kotzé, 1977) since it did not retard fruit colouration (McOnie and Smith, 1964). Strobilurins were indicated to be a good replacement for benomyl in orchards with known resistance of the CBS pathogen to benomyl (Schutte et al., 1996; Tollig et al., 1996; Schutte et al., 2003). The strobilurins protect, cure, eradicate and provide long-lasting residual disease control (Gold and Leinhos, 1995) and is commended in combination with other fungicides such as mancozeb or copper to control citrus black spot (Schutte et al., 2003and Miles et al.,
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