“Rock-Ad”, a new wild rocket (Diplotaxis tenuifolia) mutant with late flowering and delayed postharvest senescence

Wild rocket (Diplotaxis tenuifolia) is a leafy herb in salads and cooked dishes originating in the Mediterranean basin. The leaves contain many nutrients, plus beneficial phytochemicals such as flavonoids and glucosinolates. Rocket suffers from two major limitations: early bolting during growth and leaf yellowing after harvest, both of which affect both yield and market quality. We have used ethyl methanesulfonate (EMS) to induce mutation in wild rocket, and selected a mutant line (registered as cv. “Rock-Ad”), which has a two week delay in flowering time compared to current commercial cultivars. “Rock-Ad” plants began to flower when more than 50% of commercial plants had flowered. Storage properties of the mutant were also better than the commercial cultivar. In storage, after simulation of shipment by sea, there was no yellowing in young “Rock-Ad” leaves, chlorophyll levels were higher, fewer flower buds developed, and hydrophilic antioxidant levels decreased less than the commercial cultivar. Holding leaves in 5 kPa CO2 in air decreased yellowing and decay significantly in both cultivars compared to air storage, while exposure to 2.23 μmol L−1 ethylene increased yellowing and decay. When ethylene and CO2 were applied together (5 kPa and 2.23 μmol L−1, respectively), yellowing and decay decreased in both cultivars compared to air storage. 1-MCP treatment reduced yellowing and decay in leaves of the commercial variety, but had no effect on leaves of “Rock-Ad”. The respiration rate of the leaves increased after 7 days of storage in both cultivars, but was significantly higher in leaves of the commercial cultivar, and 1-MCP significantly moderated this increased respiration. Although treatment with 1-MCP led to increased ethylene levels on the first day after harvest, during storage, ethylene levels decreased in all treatments and cultivars.