Progress 06/01/06 to 05/31/08
Outputs
OUTPUTS: Most tissue culture labs use the multiple explant containing culture vessels due to cost and efficiency of transfer. Three types of containers were used here: 25 mm test tubes, 8 dram shell vials and GA-7 Magenta boxes. These containers compared individual versus multiple cassava shoot explant populations on in vitro growth and root development. Both nodal segments and terminal shoots were studied to determine the influence of the carbohydrate concentration on an actively growing shoot tip or a quiescent lateral bud. Results from this work have been presented at the International Symposium on Biotechnology of Temperate Fruite Crops and Tropical Species, Caribbean Food Crops Society meeting and the First International Meeting on Cassava Breeding, Biotechnology and Ecology. PARTICIPANTS: University of the Virgin Islands Agricultural Experiment Station Biotechnology Program conducted the research in the Biotechnology lab. TARGET AUDIENCES: The target audiences are the local crop farmers and backyard growers. These producers normally have less than two acres under production. The Virgin Islands has only three producers with total production acreage over two acres. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Sucrose has a stimulatory effect on root initiation up to a concentration of 8%. There were no difference in the growth between the shoot tip and distal nodal segments. Narrow individual vessels, test tubes and shell vials, forced the developing roots to grow horizontally and vertically. When plants are removed from the gelled medium, they are pulled out of the in vitro culture vessel and the adhering medium is rinsed from the roots. Plants grown in Magenta boxes produced roots that grew horizontally. As the roots grew horizontally in the Magenta boxes, they became greatly entwined after growing 28 days in vitro. Much damage occurred as the plants were being removed and the adhering gel removed from the roots. Survival ex vitro was 30-40% regardless of the sucrose concentration of the media. However, plants grown in test tubes and shell vials had a 60-70% survival rate. Understanding that root damage during transfer and handling ex vitro, a set of experiments were conducted using vermiculite in place of a gelling agent in the tissue culture medium. The MS medium in the vials of vermiculite contained either 0 or 2% sucrose. Explants used came from the plants developed from the previous sucrose concentration trials. Only shoot tips were used as the plants were severed from the in vitro rooted base. Shoots transferred to 0% or 2% sucrose saturated vermiculite all survived. The shoots from the 0% sucrose when transferred to 2% sucrose had active growth while the similar shoots put on 0% sucrose stagnated. After two weeks in vermiculite, roots were observed on all shoots in the 2% sucrose. However, vermiculite without sucrose only induced rooting on shoots originating from 4% to 10% sucrose. As the plants are removed from the vials with vermiculite, the vermiculite easily falls away and no washing of the roots is required. The plants are directly transplanted with their root system intact. The survival rate for the vermiculite system was 85-95%. This high survival rate is attributed to the reduced root damage during transfer to pots. Shoots taken from gelled tissue culture media from 0-2% sucrose did poorly when induced to root in potting mix. Transfer to potting mix was lethal for the 0% and 1% sucrose plants. However the shoots taken from plants grown on 4% to 10% sucrose all survived to initiate roots. The plants remained robust and continued to grow with expanded leaves when transferred to the potting mix.
Publications
- Zimmerman, T.W., Williams K., Joseph L., Wiltshire J. and Kowalski J.A. 2007. Rooting and acclimatization of cassava (Manihot escultenta) ex vitro. Acta Hort. 738:735-742.
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Progress 06/01/06 to 05/31/07
Outputs
Micropropagation of cassava is relatively straight forward and shoots from microcuttings can root without plant growth regulators in vitro. However, acclimatizing in vitro rooted shoots can result in high mortality. Cassava roots are prone to deterioration following wounding or bruising causing great losses during acclimatization. Direct rooting was conducted of cassava shoots pretreated by growing them in vitro on 0% to 10% sucrose. Shoots, 1.5 cm in length from the varying sucrose media were rooted in vitro in medium grade vermiculite or in situ in ProMix potting medium. Sucrose levels >6% caused shorter plants than the other treatments. Shoots rooted equally well with both media. A success rate of >95% was obtained following rooting in vermiculite followed by transfer and acclimatization in a ProMix potting medium. Vermiculite was easily removed from cassava roots reducing the damage normally occurring during the rinsing and removal of adhering gelled medium. In
vitro rooting of cassava in vermiculite increases survival rates during acclimatization. Direct rooting in pots was most successful from shoots grown on 4% to 8% sucrose.
Impacts
New cassava can be efficiently made available to farmers from tissue culture and used within a short amount of time. Farmers have quicker access to enhanced cassava varieties.
Publications
- Zimmerman, T.W., K. Williams, L.Joseph, J. Wiltshire and J.A. Kowalski. 2006. Rooting and Acclimatization of Cassava (Manihot esculenta) Ex Vitro. Acta Hort. (in press).
- Zimmerman, T.W. 2006. Influence of Carbohydrate Concentration on Cassava Growth In Vitro. J. Inter. Soc. Trop. Hort. 52: (in press).
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