Optimum Grading Conditions for Identifying Lesions of Citrus Canker (Xanthomonas citri subsp. citri, Xcc) on Grapefruit, Poster Board #012

While current rules allow fresh citrus to be shipped within the U.S. even if they contain minor symptoms of citrus canker (Xanthomonas citrisubsp. citri, Xcc), export markets are governed by the receiving country and many of these (i.e., members of the European Union) still do not allow fruit with canker symptoms. Experiments were conducted over three seasons to determine the best conditions for identifying and removing grapefruit with canker lesions. Washed fruit were first evaluated for the number of canker lesion and minimum and maximum lesion size, which ranged between 1 to 10 lesions per fruit, and 1 to 10 mm in size. Each fruit received a unique bar code for rapid identification during the grading process. The experiments were conducted on a recirculating grading line (1.0 m x 4.6 m) evaluating grading conditions such as lighting, speed of fruit flow, roller color, number of graders, and percentage of fruit infection. Grading personnel from commercial packinghouse were utilized for some of the experiments. As expected, slower line speeds (6.1 m/min.) allowed significantly better detection of canker lesions than faster speeds (12.2 m/min.), and each additional grader, from 1 to 3, significantly increased the removal percentage of fruit with canker symptoms. Sixty five percent of the fruit with canker were correctly identified and removed when three graders evaluated the fruit. While this may appear like a relatively low percentage at first glance, keep in mind that an average of 22 graders evaluate the fruit on each Florida packingline. In addition, while canker removal was not significantly different if the overall percentage of symptomatic fruit was 2% or 5%, significantly more fruit with canker were left undetected as the abundance of symptomatic fruit increased to 10% and 20%. Greater lighting intensities between 1,000 and 2,000 lux only occasionally improved canker detection at the highest value. However, some graders commented of excessive glare at 2,000 lux. The use of gray rollers significantly improved canker detection compared to the use of white rollers. We also found that with each additional canker lesion per fruit, graders were 2.8% more likely to identify the fruit as having canker and removing it. In the same way, increasing canker lesion size by 1 mm resulted in a 6.2% increase in the likelihood of detecting it on the grading line. The relationship between these results and commercial grading practices will be discussed.