Rapid Cycling Brassica

Rapid Cycling Brassica Investigations Jeffery Gray

Abstract: Rapid-cycling brassicas has been used by researchers because of traits that make it convenient to study such as: short life cycle, rapid flowering time and seed maturation, small size, and ability to grow under 24 hour fluorescent light, etc... These traits make RCBr's valuable laboratory models for students to study inheritance and selection along with evolution. Trichome/hairs on plants are extremely variable in their presence across species, location on plant organs, density, and therefore functionality The investigation conducted supports the hypothesis that trichrome number is a heritable trait that can be artificially selected for by breeding two select
populations of RCBr's with one another.

introduction Rapid-cycling populations of important species in the genus Brassica have unusual potential for resolving many problems in plant biology and for use in education.
Rapid-cycling Brassicas can produce up to ten generations of seed per year and serve as models for research in genetics, host-parasite relation, molecular biology, cell biology, plant biochemistry, population biology, and plant breeding. Brassicas are a highly diverse group of crop plants that have great economic values vegetables and as sources of condiment mustard, edible and industrial oil, animal fodder, and green manure. These plants can also be used in the classroom as convenient, rapidly responding, living plant materials for ‘hands on' learning at all levels of our educational system. Trichome/hairs on plants are extremely variable in their presence across species, location on plant organs, density, and therefore functionality. However, several basic functions or advantages of having surface hairs can be listed. It is likely that in many cases,
hairs interfere with the feeding of at least some small herbivores and, depending on stiffness and irritability to the predator, large herbivores as well. Hairs on plants growing in areas subject to frost keep the frost away from the living surface cells. In windy locations, hairs break up the flow of air across the plant surface, reducing evaporation. Dense coatings of hairs reflect solar radiation protecting the more delicate tissues underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud drip, hairs appear to enhance this process. Cross pollinating rapid cycling brassicas containing 11-15 trichomes with plants containing 16-20 and 21-25 Trichome will produce significantly more offspring with more than 15 Trichome visible on their first true leaves.

materials and methods

protocol: The first lab, session six containers of three Rapid cycling brassicas (RCBr's) each were planted, three fertilizer pellets were added to each container(14,14,14), and the containers were watered by a passive watering/ wick system.
Day 7: two or three seedlings were observed in each container approximately two and a half inches tall. All except one seedling was kept in each container and the others were cut out. Day 28: Group data was compiled by counting the numbers of Trichome on the first true leafs of each RCBr left. Day 35: Plants were pollinated with bee sticks, five 11-15 trichrome plants were cross pollinated with one 16-20 trichrome plant and with one 21-25 trichrome plant. Day 49: twenty days after the last pollination, plants were removed from the watering system and allowed to dry for five days. The seeds were then harvested by gently rolling dry seed pods between a pair of hands over a collecting pan. The seeds were transferred to new growing containers and planted according to the day one protocol. Day 70: F1 offspring were cut and the number of Trichome was observed under a dissecting microscope for counting to compile group
data.

Results and discussion:

The Rapid cycling Brassicas planted on day one had the following number of Trichome on the first true leafs: twenty-two plants with 0-5 Trichome, ten plants with 6-10 Trichome, five plants with 11-15 Trichome, and one plant with 16-20 Trichome and one plant with 21-25 Trichome. The number of Trichome on the first true leafs of the F1 generation of RCBr's, whose parent plants were crossed pollinated with bee sticks, from rapid cycling brassicas containing 11-15 trichomes with plants containing 16-20 and 21-25 Trichome, were observed under a dissecting microscope. The compilation of group provided: five plants with 0-5 Trichome on the first set of true leaves, three plants with 6-10 Trichome, five plants with 11-15 Trichome, four plants with 16-20 Trichome, two plants with 21-25 Trichome, three plants with 31-35 Trichome, and one plant with 36-40 Trichome. The data observed from the F1 generation leads to the following conclusions: The ratio of plants with 0-15 Trichome to plants with greater than 15 Trichome decreased from 18.5:1 in the parental generation to less than 1.3:1 in the F1 generation. This supports the hypothesis: Cross pollinating rapid cycling brassicas containing 11-15 trichomes with plants containing 16-20 and 21-25 Trichome will produce significantly more offspring with more than 15 Trichome visible on their first true leaves. The percentage of plants with less than 15 Trichome visible on their first true leaves was reduced from 95% in the parent generation to 56% in the F1 generation, which is a significant decrease and the percentage of plants with more than 15 Trichome increased significantly from 5% in the parent generation to 44% in the F1 generation. The result further supports the hypothesis that cross breeding two plants with larger numbers of Trichome will result in offspring with more Trichome. The results support the idea that the number of Trichome on the plant is heritable from their parents, due to the increase in the number of Trichome on the F1 generation compared to the parental generation also, artificially selecting for plants with larger number of Trichome on the leaves can be achieved by artificial selection by pollinating with bee sticks.