Seed Sampling Techniques and Population Size. V.L. Bradley and R.C. Johnson Western Regional Plant Introduction Station. Bulk sampling was used in grass regeneration nurseries until 2002. Central Ferry, Washington Grass Nursery, 1997. Bulk Sampling All seeds from each plant are combined.
V.L. Bradley and R.C. Johnson
Western Regional Plant Introduction Station
Central Ferry, Washington
Grass Nursery, 1997
All seeds from each plant are combined
Same number of seeds from each plant
This work indicated that generally, the combination of bulk sampling and increased regeneration cycles led to more frequent changes in allele frequency from those in the original populations.
Morphological data gathered on each plant:
--Heading date and anthesis date for each plant
--Length, width and area of the penultimate leaf from the spike measured for length
--Leaf was dried and specific leaf area was calculated
--Above ground biomass was rated from 1 (least) to 9 (most) In one block at each location actual biomass was measured so a linear equation between the ratings and actual biomass could be established and used to calculate dry weight values per plant.
Mean differences between the original seed population (R0) and samples that were balanced and bulked for three regeneration cycles in three Lolium multiflorum accessions.
*, †, Means are different from the original population at P=0.05 and P=0.10, respectively.
Three sampling methods were used on three accessions of three species of cross-pollinated grasses grown at two locations.
Counting the number of inflorescences on each plant.
Cut harvest method- each plant cut at maturity and placed in a bag.
Rub harvest method- each plant visited numerous times until it was judged that all seeds had been harvest.
Cut and rub seeds were weighed to obtain yield per plant.
Inflorescence sampling- two heads judged to be physiologically mature were taken from each plant. Each were bagged separately in order to estimate variation in seeds per head. In addition to the 3 species in the experiment, four accession of six other species were surveyed using only this method.
Relationship between the ratio of effective to census population size and increasing inflorescences sampled per plant averaged for four accessions each of six cross-pollinated grass species.
Contact Richard Johnson if you are interested in developing an inflorescence sampling curve for your crop.
Johnson, R.C. 1998. Genetic structure of regeneration populations of annual ryegrass. Crop Sci. 38:851-857.
(For abstract: http://crop.scijournals.org/cgi/content/abstract/38/3/851)
Johnson, R.C., V.L. Bradley and M. A. Evans. 2004. Inflorescence sampling improves effective population size of grasses. Crop Sci. 44:1450-1455. (For PDF file: http://crop.scijournals.org/cgi/reprint/44/4/1450)
Johnson, R.C., V.L. Bradley and M. A. Evans. Effect of seed sampling method during regeneration on genetic population structure and growth of model ryegrass populations. Plant Genetic Resources Newsletter, in press. (March, 2006)
We’re still refining our techniques.
We record the harvest method used and how many heads we cut, on the harvest label. This data is collected each year along with seed weight and volume so we can assess how well our choice of harvest method worked. This is helping us form guidelines for species we grow routinely.
Did we get enough seed from the number of heads we cut? Could we harvest fewer heads for this species?
Increasing effective population size
Faster harvesting than we thought
Seed cleaner can work through harvested materials faster
because not cleaning an overabundance of seed
Lots of seed left in field- volunteers
The Ugly (challenges)
Time consuming- lots of planning needed,
walking field during spring busy season
Keeping abreast of shattering is always a challenge, but
not much flexibility with I-sampling
Record keeping can be a nightmare
WHAT DO WE DO ABOUT ACCESSIONS WITH LOW PLANT NUMBERS?
How do you deal with:
Accessions for which there are only a few seeds
Accessions that have “zero” (or very low) germination but there are thousands of seeds
What is the minimum population you put in your nurseries?
How do you decide what is worth the extra time/money (resources)?
What do you do when you have one plant of a cross-pollinated species?