Procedures to improve Stock 6
- Chang, MT; Coe, E
Stock 6 was named by Coe in his genetic collection. Ed recognized
its high haploid induction rate in 1952. He then converted
Stock 6 in 1960 to carry homozygous A B Pl C R-nj anthocyanin
genes, expressing purple plant color, purple plumule and purple
seed crown for easy identification of haploid seeds. The induction
rate of Stock 6 is about 2% to 3% with poor agronomic traits such
as poor stalk, poor roots, easy to lodge and ear rot. These poor
traits were improved by Chang with advice from Coe according
to the following procedures, and the rate of haploid induction was
increased by selection.
A green plant, yellow seed unfixed material (AA cc rr bb plpl)
that had shown it was producing haploids in the field was used as
female and crossed by purple plant, purple seed crown and purple
plumule Stock 6 (AA CC R-njR-nj BB PlPl) pollen.
20 F1 seeds (A/a C/c R-nj/r B/b Pl/pl) were planted and selfed
for F2 seeds.
The F2 seeds segregated nine colored crown and plumule
seeds vs. seven colorless seeds. Selected and planted 200 F2 seeds
of the most dark-colored crown and plumule to enhance the probability
of homozygous AA CC R-njR-nj plants.
Selfed F2 plants with dark purple leaves. Ears should either
segregate purple crown and colorless seeds or all homozygous colored
seeds. Selected the homozygous ears that showed seed color
fixation (AA CC R-njR-nj).
Planted 50 F3 seeds from each ear with seed color fixed. Identified
the most dark purple leaf, sheath, and tassel plants and selfed.
These plants were supposed to be homozygous for AA BB PlPl genes.
Planted 20 ear-to-row F4 seeds from each selfed F3 ear. Selected
the rows showing all purple plants to confirm plant color
fixation, and selfed all ears.
The genetic make-up of F5 seeds was fixed for AA CC R-njRnj
BB PlPl. The phenotypic expression was all purple plants and
purple crown and plumule. Planted 200 F5 seeds and also 500
hybrid seeds as tester.
Selfed each F5 plant and carried pollen to cross onto two hybrid
ears. Harvested all selfed F5 ears with ear number -1, -2, -3
and so forth. Also harvested all crossed ears with pollen source X-1,
X-2, X-3 and so forth.
Screened all crossed ears for haploid seeds production. For
example, there should be two ears crossed by -1 F5 plants or X-1.
If one ear showed 6% haploids and the other ear showed 4% haploids,
then the -1 F5 plant had a 5% induction rate. If one ear
showed 9% and the other ear 4%, the induction rate was too far
apart, so the lower 4% was assigned to define the F5 plant induction
rate. Screened all the ears and sorted induction rate from low
to high. A range of induction rate from almost 0% to 8% was
Selected the highest rate F5 ears and planted 20 F6 seeds earto-
row from 10 ears to form a 200-seed population. Also planted
500 hybrid seeds as tester, using the above procedures again to
determine induction rate of each plant. The induction rate was
increased in the range of 1% to 9% in response to selection.
Selected the highest induction rate F6 ears and planted 20 F7
seeds ear-to-row from 10 ears to form a 200-seed population. Also
planted 500 hybrid seeds as tester. Repeated the above procedures.
Also planted 200 F7 seeds with highest induction rate, selfed the
haploid plants to form a new pure Stock 6 line with higher induction
rate and better phenotypic traits.
Repeated the above procedures for a couple of more generations.
The F10 seeds from higher induction F9 ears were sibbed to
retain plant vigor and progeny were sibbed again and again. From
the progenies, several high induction lines were produced to form
new Stock 6 lines. The average haploid induction rate is 6% to 8%.
Seeds of this improved Stock 6 are being sent to the Maize
Genetics Cooperation Stock Center.