By Megan Dewdney, Mark A. Ritenour and Liliana M. Cano
In the last few years, 89% of Florida grapefruit growers have struggled with a disorder that they refer to as greasy-green, leading to losses between $20,000 to $1.7 million per year. The disorder causes the fruit to have large, diffuse green patches on the rind after degreening, making it no longer suitable for the fresh market. The disorder visually resembles rind blotch, caused by the fungus Zasmidium citri-griseum (formerly known as Mycosphaerella citri), but when the trees are observed, there are few symptoms on the leaves.
The cause of greasy-green remains unclear, but University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers started a project in spring 2022 to determine if the Z. citri-griseum sporulation cycle was responding to changes in the host caused by huanglongbing (HLB), a warmer environment or cultural practices. UF/IFAS will also be investigating possible physiological changes or burns of the fruit in response to newer pesticide and nutritional programs that are commonly used to combat the effects HLB.
Last season, flush and fruit growth stages were monitored. Fruit and leaf samples were taken at each observation date to observe whether spores were present and germinating or if there was significant fungal growth and will be matched with the flush data. No disease was observed on the leaves, but there was disease on the fruit.
Post-harvest degreening trials were conducted. It was found that degreening, with or without cold treatments (24 hours at 38 degrees), improves fruit color but not enough to remove green color from the rind. Further experiments on the length of degreening time are being analyzed.
Funding for this project is provided by theCitrus Research and Development Foundation.
Megan Dewdney is an associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred. Mark A. Ritenour is a professor, and Liliana M. Cano is an assistant professor, both at the UF/IFAS Indian River Research and Education Center in Fort Pierce.
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