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Andrew K. Miles, Malcolm W. Smith, Nga T. Tran, Timothy A. Shuey, Megan M. Dewdney and André Drenth

Citrus black spot (CBS), incited by the fungus Phyllosticta citricarpa ( Kiely, 1948 ; McAlpine, 1899 ), is an important disease of citrus in most humid tropical and subtropical growing areas worldwide, including parts of continental Australia

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Jiaqi Yan, Megan M. Dewdney, Pamela D. Roberts and Mark A. Ritenour

Citrus black spot is a fungal disease caused by G . citricarpa Kiely [anamorph Phyllosticta citricarpa (McAlpine) van der Aa]. This disease was first described in Australia in the 1890s and has since been found in the humid subtropical regions

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Alireza Pourreza, Won Suk Lee, Mark A. Ritenour and Pamela Roberts

Citrus black spot (CBS) is a fungal disease caused by Phyllosticta citricarpa (synonym Guignardia citricarpa). CBS causes fruit lesions and significant yield loss in all citrus (Citrus) species. The most distinguishing CBS symptom is called hard spot, which is a circular lesion with gray tissue at the center surrounded by a black margin. The spectral characteristic of CBS lesions was investigated and compared with the spectral signature of healthy fruit tissue to determine the best distinguishing wave band. Healthy and CBS-affected samples presented similar reflectance below 500 nm and above 900 nm. However, healthy samples reflected more light between 500 and 900 nm, especially within the visible band. Also, spectral reflectance of the same symptomatic lesion was acquired six times over a 2-month period to determine the variation of symptom’s spectral signatures over time after being harvested. A two-sample t test was employed to compare each pair of consecutive repetitions. The results showed that the spectral signature of the CBS lesion did not change significantly over 2 months. The wavelengths between 587 and 589 nm were identified as the distinguishing band to develop a monochrome vision–based sensor for CBS diagnosis. A support vector machine (SVM) classifier was trained using the spectral reflectance data at the selected bands to identify CBS-affected samples in each repetition. The overall CBS detection accuracies varied between 93.3% and 94.6%.