Wild rocket (Diplotaxis tenuifolia) from the Brassicaceae family is a Mediterranean plant with the common name – Rucola. In Italy, rucola is widely consumed where its pungent qualities are appreciated, both in a salad and as a garnish. Rucola is a fast growing, cool-season crop and flowers under long days and high temperature. This crop is well adapted to the Israeli climate which offers the possibility of growing it all year round, in the open field and with season extension techniques as it is adapted to greenhouse culture. The main obstacles to this crop appear to be early flowering during spring and autumn and limited storability. Flower stems are not desirable at harvest time, because they continue to grow during storage and reduce the adjacent leaf quality.
Since rucola is edible and genetically modified organisms (GMO) are forbidden in Europe this method could not be usable to try to modify flowering time of the plants. An alternative method, used in this study to address the problem, was by mutagenesis of the commercial cultivar, and selection of mutant lines carrying the desired traits. Here we present the analysis of a new line of rucola named Rock-Ad, created by Ethyl Methane Sulphanate (EMS) mutagenesis. This cultivar has a delay in flowering time and improved postharvest storability compared to the commercial cultivar (Kenigsbuch et al. 2009) as seen in fig.1.
Flowering time was measured either by number of rosette leaves until the first emerged bolt or by the percentage of flowering plants. After several generations and selections, the rucola cultivars were grown in a greenhouse and allowed to mature and flower. The number of leaves in the rosette was counted when the first bolt emerged. At the beginning of flowering time, the mutant cultivar Rock-Ad had a significant delay in flowering with 18-20 leaves per plant compared to 12-14 in the commercial cultivar. In addition, flowering plants were counted in each line since the first flower appeared every 3-4 days and percentages were calculated. When about 50% of commercial cultivar plants were flowering the cultivar Rock-Ad had no flowers yet. The commercial cultivar plant began to flower on the 28th day while Rock-Ad plants flowered two weeks later, on 42nd day (fig. 2).
The crop quality
The quality requirements of the market for rucola are for leaves to be dark green, rough and lobed shaped. Flawless shaped leaves are known as Rocket /Eruca. Counting lobed shape leaves at the stage of bolting of rucla, grown under greenhouse conditions, gave the average of 13.5±0.9 leaves per plant of Rock-Ad, compared to 9.2±1.3 leaves per plant of the commercial type. Similar results were obtained when the rucola was grown in the field. These experiments showed that the percentage of leaves suitable for marketing from the Rock-Ad cultivar was 75% compared to 65% in the commercial cultivar.
The requirment for sea shipment is at least 14 days in storage and shelf life. The postharvest quality of the rucola was not sufficient because of the leaf yellowing and decay. The current methods for maintaining the quality of fresh cut products are based on modified atmosphere during storage and shelf life. Martinez-Sanchez et al. (2006) showed that rucola storage under low O2 and high CO2 conditions helped preserve the sensory and microbiological quality as well as the content of health-promoting phytonutrients.
Rucola plants were grown at winter-spring seasons in the Western Negev and in the Jordan Valley in Israel. Freshly cut leaves, packed in 1 kg boxes, as in a commercial packaging, were placed in either modified atmosphere (in polyethylene bags with micro-perforation (MP)) or in ventilated atmosphere (in polyethylene bags with multi micro-perforation (MMP)), for seven days at 20oC. Yellowing was quantified on a scale of 0-100% (0 – fresh green leaves with no color change and 100- all the leaves turned yellow).
Rock-Ad showed less damage in both modified and ventilated atmospheres. In modified atmosphere (MP), the commercial cultivar showed 27.5% and Rock-Ad had only 12% of leaf yellowing (Table 1). The damage increased in ventilated atmosphere (MMP) with 32.5% in the commercial cultivar and 17.5% in Rock-Ad (Table 1, Fig. 3).
In summary, we developed a new rucola cultivar, named Rock-Ad. This cultivar has promise to be preferred by growers and customers due to late flowering, and can be harvested several times per season. It is also suitable for sea shipment and has better qualities after storage than the commercial cultivar.
This work was supported, in part, by the grant No. 430/0065 from the Herbs Growers Organization in Israel. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No.619/11
Thanks to Dr. Susan Lurie for critical review.
Martinez-Sanchez, A., Marin, A., Llorach, R., Ferreres, F. and Gil, M.I. 2006. Controlled atmosphere preserves quality and phytonutrients in wild rocket (Diplotaxis tenuifolia). Postharvest Biol. Technol. 40:26-33.
Kenigsbuch, D., Ovadia A, Ivanova, Y., Chalupowicz, D., Maurer, D., Aharon, Z., Vinokur, Y. and Aharoni, N. (2009) Wild Rocket (Diplotaxis tenuifolia) Mutant with Late Flowering and Delay in Postharvest Senescence. Acta Horticulturae. 830:91-96.
Fig. 1: Rucola in a net-house, both types sowed and planted at the same time: behind, the commercial
with the heavy yellow flowering. In front, the Rock-Ad crop with very little flowering.
Fig. 2: percent of flowering plants per days.
Fig. 3: bunches of the two types after storage: the commercial rucola (left) is much yellower than the Rock-Ad (right).
27.5 ± 6.7
12.0 ± 5.2
32.5 ± 7.1
17.5 ± 4.5
Table1. Leaf yellowing after harvest. Freshly cut wild type rucola leaves from the commercial cultivar and mutant Rock-Ad were placed in modified atmosphere or in ventilated atmosphere for seven days at 20oC.
Dalia Maurer, Daniel Chalupowicz, Alona Ovadia, Shahar-Ivanov Yelena and David Kenigsbuch*.
Dept. of postharvest science of fresh produce, ARO, The Volcani Center, Bet-Dagan, Israel.