Grafting Capsicum Annuum Onto C. Chinense (Habaneros) and C

Grafting Capsicum annuum onto C. chinense (Habaneros) and C. baccatum (Aji)

Andrey A. Vega

INTRODUCTION Grafting fruiting vegetables is practiced widely in several regions and countries of the world (Lee et al 2010) mostly to prevent soil borne diseases. Moreover, the use of grafting in fruit vegetables has been expanded in recent years as a tool to enhance yields and induce plant tolerance against abiotic stress (Louws et al 2010). In the production of grafted plants healing and acclimatization is a critical period for them to survive and grow as healthy plants. Successful grafted pepper plants have been usually healed and acclimatized by setting specific environmental conditions. High relative humidity (RH > 85 %) and low intensity of light to stimulate a healing environment (Mun et al 2011). A healing chamber could create this healing conducive environment. Sweet peppers show low survival rates when grafted compared to other vegetables like tomato or eggplant (Johkan et al 2009). Light intensity, RH, and temperature are three of the most important environmental factors that influence the healing and acclimatization of grafted transplants (Jang et al 2013). Another critical point is the grafting method. Usually grafting methods greatly vary and depend mostly on the experience of the worker, the number of transplants to graft, or the purpose of grafting (Lee et al 2010)

MATHERIALS AND METHODS I. Producing the pepper seedlings: I recommend you use the 72-cell trays, most of them come in units of 6 cells. 1. Fill up the tray with the commercial substrate (Pro-Mix), 2. Once in the tray,water the substrate enough to make it easier to plant 3. Make a little hole with your fingers and place one or two seeds in every cell, then cover the top of seeds with more substrate and water again 4. Label every tray of the cultivar you are planting with plastic stakes. We need to know that we are using distinct species namely: Capsicum annuum (Sweet pepper), Capsicum chinense (Habanero) and Capsicum baccatum (Ajís), all of them with different growing rates, so we need to plant first the rootstocks and one week after we plant the scion (Calif. Wonder, Nathalie and Dulcitico) so that we have equal diameter at the time of grafting. (See Program Below). Once planted the seeds in the trays they must be watered at least once every other day when just planted. Use the fertilizer once or twice a week after emergence. Rootstocks must be grown for 38 days and scions for 30 days. (from the day you planted the scions you wait 30 days, and they will be ready to graft). Once the seed emerges, thin to one plant per cell. This is very important to reach the right diameter in the stem of rootstocks and scions (around 2mm).

II. Building the healing chamber Healing chambers can be built like the ones shown in Figure 1, with materials available at home. 1. First we need to build the water reservoir at the bottom of the chamber. The reservoir can be built using pieces of wood, and a plastic film, forming water reservoir with the pieces of wood and/or bamboo and then laying the plastic film to contain the water at the bottom of the chamber. If the chamber is big and you cannot keep the water level uniform in the bottom of the chamber. I recommend splitting the reservoir into two by just adding a piece of bamboo underneath the plastic film forming 2 reservoirs (See Figure 1-D). Alternatively, you can use a flat tray that contains water and place them at the bottom of the chamber This reservoir will increase humidity and create a healing conducive environment. 2. The upper structure can be built with bamboo and then covered with a muslin fabric. Once it is covered tight with the muslin fabric (cheese cloth), we cover it again with a plastic film. 3.A piece of bamboo can be tied at the end of the muslin fabric in order to hook it and keep it tight, the plastic film lays on top of the muslin fabric (Figure 1-A,B).

Figure 1. A- Healing chamber covered with plastic film and a muslin fabric underneath it. B- Healing chamber covered with muslin fabric. C- inside of the healing chamber, with a temperature and relative humidity logger hanging from the bamboo structure. D- Water reservoir needed to keep the relative humidity high.

The fabric muslin provides shade that slows down photosynthesis in the healing plant. The balance of light temperature and relative humidity is critical to create a healing conducive environment. Usually the grafting chamber temperature is about 28 °C in average during the day and 24 °C during the night, the Relative Humidity is close to 99% during the night and 95% during the day.

III. Grafting technique: the grafting technique we are going to use is called, cleft grafting. It is very simple yet needs dedication and patience. Below there is a 1-minute video on how to graft the pepper seedlings (Make sure you have internet connection to watch the video). In the video, it is shown how to do the grafting, in this video I graft above the cotyledons, we can graft below or above the

cotyledons it is up to you, but every plant must be grafted the same way. You should choose if you want to graft above or below the cotyledons. I encourage you to practice several times and find the best way of grafting for you. Figure 3 shows the result of grafting above and below the cotyledon. If you can’t play the video below copy and paste this link in your browser https://youtu.be/PZq28C2IGSw

IV. Grafting process: 1. Select carefully the rootstock and the scion to be grafted, they should be similar in diameter. 2. Remove larger leaves and keep only the meristematic leaves, this is done to reduce the risk of dehydration, and cut the end of the stem in the form of a wedge, so that it fits the rootstock. 3. Decapitate the rootstock below or above the cotyledons (as you decided before) and make a cut with the razor blade straight into the center of the previously cut rootstock about 0.7 cm to1.0 cm deep. Keep the razor inside the cut and try to connect the wedged scion stem with the cut in the rootstock you just made. It is important to know that if you cut above the cotyledons in the rootstock’s stem, you must cut the scion’s stem above the cotyledons. Same thing if you cut below the cotyledons in the rootstock’s stem, you must cut below cotyledons in the scion’s stem. This is because there is less compatibility between upper-lower tissue than there is in upper-upper or lower-lower tissue. Once the plant is grafted put it inside the healing chamber. Prevent the substrate to touch the water in the lower pit of the chamber.

V. Grafting considerations: Wash your hands with hand soap and use gloves when grafting, you can graft bare hand if you prefer. Also wash the razor blades with a little soap to remove the grease that comes with it. Table 1. Proposed chronogram of activities.

Month April May June

Activity/Week I II III IV I II III IV I II III IV

Build chamber Plant Rootstock seed

Plant scion seed

Water seedings Fertilize Seedlings

Grafting week (35 days after planting scion seed) Keep grafted plants in Chamber

Take grafted plants out of Chamber, keep inside greenhouse

Take grafted plants outside greenhouse to expose to sunlight but cover with a shade with a shade

Figure 2. Timeline to prepare the grafted plants. Plant Rootstock’s seed on day 0, one week after, plant Scion’s seed and then let the scion grow for four more weeks. Once the four weeks passed, scions and rootstocks should be ready to graft (scions will be 4 weeks old and rootstock 5 weeks old) adapted from Rivard and Louws 2006 without permission.

Figure 3. A, B. Pepper plants grafted adobe cotyledons, after a few days after grafting, pepper plants produce an undesirable bud that must be carefully removed. C, D. Pepper plants grafted below cotyledons, no buds grow when this kind of graft is performed, that is one of the reasons for what it is preferred.

REFERENCES Lee, JM; Kubota, C; Tsao, SJ; Bie, Z; Hoyos-Echeverría, P; Morra, L; Oda, M. 2010. Current status of vegetable grafting: Diffusion, grafting techniques, automation. Scientia Horticulturae 127:93-105. Louws, FJ; Rivard CL; Kubota, C. 2010. Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds. Scientia Horticulturae 127:127-146. Mun, B.H., Y.A. Jang, E. Goto, Y. Ishigami, and C.H. Chun. (2011). Measurement System of whole-canopy dioxide exchange rates in grafted cucumber transplants in which scions were exposed to different water regimes using a semi-open multichamber. Sci. Hort. 130:607-614. Johkan, M., Mitukuri, K., Yamasaki, S., Mori, G., & Oda, M. (2009). Causes of defoliation and low survival rate of grafted sweet pepper plants. Scientia Horticulturae, 119(2), 103-107. Jang, Y., Mun, B., Seo, T., Lee, J., Oh, S., & Chun, C. (2013). Effects of light quality and intensity on the carbon dioxide exchange rate, growth, and morphogenesis of grafted pepper transplants during healing and acclimatization. Korean Journal of Horticultural Science and Technology, 31(1), 14-23.