2019 ASHS Annual Conference

Seed availability of in demand rootstocks remain at an all-time high due to the severe pressure for replanting and resetting HLB-affected groves in Florida. Currently, there is a major concern among citrus nursery operators and growers for availability of vigorous seeds that can produce strong rootstocks for budding. The seed vigor however depends on seed maturation and can also be influenced by the extent of cold storage. In general, the more mature a seed, the longer it can be stored. The maturation stage at which citrus seeds from the major rootstocks can germinate is unknown. Natural calamities such as Hurricane Irma on September 10^th, 2017 severely affected the ability of our industry to produce adequate seeds necessary to satisfy nurseries needs. In the hardest hit areas, there was massive fruit drop, especially from the US-802, US-812, US-897 and US-942 varieties and at a time when fruit was almost ready to be harvested and processed for supplying the seeds to the nurseries. Seed availability from the SWFREC Immokalee, USDA Fort Pierce, and Whitmore Foundation in Leesburg decreased by 66% as compared to previous season, resulting in a shortage in seed availability. For this reason, we started a research project to know in advance when the fruit contains viable seeds, with the purpose of make better decisions on harvesting. This will allow us to adjust the harvest of the fruit from each variety, facilitating to work around the peak of the hurricane season. We focused on identifying external, non-destructive markers to predict when the seeds are mature enough to germinate, and in determining seed shelf life under cold storage and the duration of seed viability depending on its maturation stage. Among markers assayed, we have been able to relate external peel coloration and responsiveness to ethylene and evolution of fruit abscission during fruit maturation with seed development in late-maturing varieties US-897 and US-942. As a result, we were able to advance fruit harvesting and seed extraction by 1.5 months, which resulted in an increase of 21% and 25% respectively in the number of viable seeds. These results will allow our industry to maximize seed production by advancing harvesting of late maturing rootstock varieties, which are among the most demanded by growers.