Project Proposal: Effect of foliar application of chitosan on stomatal conductance, evapotranspiration and survival of grafted transplants.
Chitosan is a natural biodegradable polymer obtained by deacetylation of chitin from crustaceans (K. Ohta 1999; Marco Bittelli 2001). Foliar applications of chitosan have been shown to elicit plant defense mechanisms resulting in stomatal closure and reduction in evapotranspiration ((Marco Bittelli 2001; Marcello Iriti 2009). Grafting vegetables is extensively used in Asia, Europe, Canada, and increasingly the United States for increased plant vigor and resistance to soil-borne pathogens. During the grafting process, xylem is severed and the scion is under extreme water stress until the xylem of the scion and rootstock heal together. In order to minimize water stress, efforts are made to reduce transpiration and water stress for a period of time immediately following grafting. Grafted vegetables are placed in healing chambers with optimal temperatures (20°C) and high relative humidity (95-100%) where light is excluded for five days ((Hassell 2008). After 5 days, light is incrementally increased while humidity and temperature is slowly decreased. As chitosan reduces evapotranspiration, foliar applications of chitosan to newly grafted plants could reduce water stress to scion and subsequently increase graft success. Chitosan therefore could provide a low-cost alternative to climate-controlled healing chambers for both conventional and organic growers with limited space and resources.
METHODS
I am currently unsure what type of plant and number of plant I will use (tomato, eggplant, or mung bean), as it depends on growth stage when I have the materials for the chitosan solution. There will be a total of 80-140 grafted transplants. There will be two treatments and a control: grafted plant without chitosan foliar application, grafted plant with no treatment, non-grafted plant. 1 g/L chitosan (75-85% deacetylated) will be dissolved in a 0.1% (w/w) D/L lactic acid solution and applied to Treatment Group 1. The chitosan solution will be applied to the adaxial and abaxial sides of the leaf (a constant number of spray shots with approximately 20 mL per plant). Plants will be placed in a growth chamber at 20°C and 85% relative humidity. The abaxial stomatal conductance will be measured with a steady state leaf porometer (Decagon SC-1) every hour for a 24 hour period. Transpiration rate (E) will be calculated from stomatal vapor conductance (Gv,s) for the 24 hour period. Grafts will be held in the healing chamber for 4 days. On Day 5, they will be reintroduced to the greenhouse environment by slowly increasing light and decreasing temperature and humidity. On Day 10, total number of successful grafts for each treatment group will be counted.
REFERENCES
Hassell, R. L., Frederic Memmot, Dean G. Liere. (2008). "Grafting Methods for Watermelon Production." HortScience 43(6).
K. Ohta, A. T., N. Konishi, and T. Hosoki (1999). "Chitosan Treatment Affects Plant Growth and Flower Quality in Eustoma grandiflorum." HortScience 34(2): 233-234.
Marcello Iriti, V. P., Mara Rossoni, Stefana Gomarasca, Nicola Ludwig, Marco Gargano, and Franco Faoro (2009). "Chitosan antitranspirant activity is due to abscisic acid-dependent stomatal closure." Environmental and Experimental Botany 66: 493-500.
Marco Bittelli, M. F., Gaylon S. Campbell, Everett J. Nichols (2001). "Reduction of transpiration through foliar application of chitosan." Agricultural and Forest Meteorology 107: 167-175.
