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What are gametophytic factors?
And why is there an interest in
them?
Gametophytic factors limit the
types of pollen that can effect
fertilization.
They can be used to screen out
unwanted pollen sources.
Examples include:
Eliminating pollen of yellow corn
from white corn production fields.
Preventing field corn from
pollinating popcorn.
Preventing undesirable sweet corn
combinations (su/sh2, etc.).
Preventing transgenics from
crossing with organics.
The best known and most widely
used such factor is Ga1-s.
It has been used to protect
popcorn quality and is often
referred to as “Dent Sterile”.
Ga1-s effectively blocks normal
pollen when homozygous.
NC State has released 24 Ga1-s
inbreds since 1990.
NC296 has been described as the
line with the highest yield potential
of all lines that allow “freedom to
operate”.
NC296 is Ga1-s.
NC296 x 5 Pioneer sister-line testers
(2 yr., 8 env.)
YLD H2O EP
HYBRIDS
t/ha % %
3 PHI SS x NC296 9.40 20.0 98
2 PHI NS x NC296 9.06 19.9 97
DeKalb 697
8.76 19.6 93
Pioneer 31D58
8.81 19.2 99
Pioneer 31G66
9.10 19.1 99
Pioneer 31P41
8.92 19.0 100
Pairwise .05 LSD 0.69 0.7 5
C.V.%
8
4
5
.
NC Line Source
NC296 105.5
NC296A 105.5
NC302 105.5x101
NC336 105.5
NC338 105.5x304.504
NC346 105.5
NC348 105.5x155
NC352 105.5
NC354 105.5x304.101
NC396 105.5x101
NC400 300.348
NC440 B73.296*4
NC Line Source
NC444 258.296*4
NC448 105.5x155
NC460 298.296
NC462 304.296
NC464 300.348
NC466 298.7905
NC470 B73p.296)2
NC490 258.296
NC494 258.'352'
NC514 258.296*3
NC520 258.296
NC522 258.296
.
.
To test for cross contamination of
Ga1-s hybrids, we grew enough
various homozygous Ga1-s hybrids in
an iso to produce a minimum of
220,000 kernels if pollinated well.
The male ‘parent’ was P33M54. All
Ga1-s plants were detasselled. Only
110 kernels were harvested for a
contamination rate of 0.05%.
But can Ga1-s combinations be found
that yield (and stand up)?
We had never knowingly crossed
Ga1-s lines until our organic folks
decided that gametophytic hybrids
might be an alternative to the 108 day
organic hybrids being used for
isolation from 115 to118 day
transgenics.
Data were available for the 24 NCGa1-s lines. We took that data and
tested various Ga1-s hybrids of allNC origin.
The results were not surprising.
(2yr, 10 env)
PEDIGREE
NC522 x NC338
DeKalb 697
Garst 8288
LH132 x LH51
NC320 x NC368
Pioneer 31D58
Pioneer 31G66
Pioneer 31P41
Pioneer 33M54
LSD.05 ENTRY x LOC)
C.V.% (ENTRY x LOC)
YLD %
B/A H2O
100
131
118
109
133
130
136
136
125
11
12
21.0
18.9
19.8
17.9
18.8
19.1
18.2
19.2
18.9
0.8
5
%
EP
71
81
86
81
77
86
83
86
86
8
12
What are we trying now:
Crossing our better Ga1-s lines
with other materials to lower the
average coefficient of parentage.
OTHER MATERIALS INCLUDE:
“Better” ex-PVP lines
Ga1-s synthetics from Frank Kutka
Ga1-s lines from Walter Goldstein
(2013, 5 locations)
YLD
PEDIGREE
B/A
296xG35.296 S3 x T11
153
P3737.NC354BC3S2 x P33M54 159
NC302.NC354 x BR71PM50
146
P3737.NC492*2 x NC464
130
Blue River 71PM50
119
DeKalb 697
161
DKHBA1.NC476xNC368.320
146
Pioneer 31G66
162
Pioneer 33M54
154
LSD .05 (ENTRY x LOC)
13
C. V. % (ENTRY x LOC)
7
T11 = FR1064.LH132
%
H2O
17.6
19.5
19.3
19.8
17.2
18.5
17.5
18.4
17.9
0.5
2
%
EP
95
94
99
90
98
98
96
99
100
7
6
At that point, Jesus Sanchez from the
University of Guadalajara reported a
very high rate of Ga1-M in Mexican
land races and Mexican hybrids.
Ga1-M is a ‘promiscuous’ allele. Its
carriers pollinate all and are receptive
to pollen from all other Ga1 sources.
Ga1-M in a hybrid would easily
overcome Ga1-s isolation. Our initial
estimates were that this might happen
in 20 to 40 years.
BUT we have released 10+ Ga1-M
inbreds, there is one ex-PVP inbred
with Ga1-M, and Tom Hoegemeyer
(who holds a Ga1 patent himself)
reports that there is a 114 day Pioneer
hybrid in Nebraska with Ga1-M.
NC Line
300
340
356
390
396
416
442
458
468
512
Ga1-M Source
306.5x105
306.5x105
TROPHY
TROPHY
105.5x101
'300'.262A
258.296*4
KU2301.PM703
TROPHY
QK37x105.155
358 & 394,
both from
TROPHY,
vary.
As a possible alternative to Ga1-s,
Jerry Kermicle has developed (and
patented) Tcb1, a dominant
crossing barrier from teosinte.
We are still backcrossing Tcb1 into
numerous lines, but the initial yield
trials suggest serious yield drag.
2 yr, 10 env
PEDIGREE
P4639.Tcb1*2 x
NC522.Tcb1*2 x
NC320 x NC368
Pioneer 33M54
LSD.05(ENTRY x
C.V.% (ENTRY x
P33M54
P33M54
LOC)
LOC)
YLD
B/A
116
106
157
144
10
10
%
%
MOIS EP
17.9 95
18.1 95
18.5 98
18.1 100
0.3
4
2
5
Our situation is roughly as follows:
Source
% Yield
Best Commercial Hybrids
100
Best NCSU Single Cross
95+
Best NC State Double-crosses 85+
Best NC State Ga1-s SC
75
Typical NC State Ga1-s SC
60
Best NC State Tcb1 Cross
60
Best NC State Ga1-s x +/+ SC 100
The problem is NOT yield potential of
Ga1-s materials; it is high coefficients
of parentage among our Ga1-s lines.
What have we tried (& so far basically
failed):
1. Outside materials carrying Ga1-s
2. Sources of Tcb1 (from teosinte
in a maize background)
What are we trying now:
Crossing (and backcrossing)
dominant gametophytic factors from
Mexican maize accessions.
Jesus Sanchez of the University of
Guadalajara hypothesized that
specialty corns (popcorns and
sweetcorns, for example) might have
unstudied isolating mechanisms.
Some of accessions we used were
suggested by Sanchez: Jal78,
Jal300, Jal304, Zac182.
Others have been discovered by
Matt Krakowsky as he developed
BC lines in the Allelic Diversity
Project of GEM.
We shared some of our earliestmaturing materials with Jerry
Kermicle.
His conclusions, based on crosses
with his testers, were that no new loci
were involved (other than Ga1-s and
Tcb1), but one accession, Jal78, had
both Ga1-s and Tcb1.
The material sent to Jerry included
derivatives of Jal78 and Jal304, two of
Jesus Sanchez’s suggestions.
The initial crosses with these two
accessions (plus those of Jal300)
were made possible by seed donated
by Jim Holland and winter nursery F1s
arranged by Randy Holley of Pioneer.
The accessions from Matt’s Allelic
Diversity work include:
Gto141, Gto181, Gto100, Zac40,
Bnz875, Z07011, Bnz878, and
Mich412
in order of frequency of apparent
discovery.
We are in our 2nd season with the
GEM Allelic Diversity materials (the
3rd if you include Matt’s efforts), and
the fourth with the Sanchez materials
(5th if you include Pioneer’s crosses).
There are many false negatives
(dead pollen, aged silk, heat, wet
bags, etc.). But there’s little doubt that
Dominant Gametophyte Factors exist
in populations of Maíz Dulce.
The fishing expedition we follow varies
somewhat, but here is one cast:
1. Cross Accession x PHB47
2. Use individual F1 plants as males in
backcrosses to B47
3. Pollinate those F1s with normal pollen
(all such seed are eventually junked)
4. Keep only those crosses with no seed
set on the corresponding F1s
5. Repeat process with BC1 plants
6. Try to obtain selfed seed on 2nd ear
7. Topcross and yield test 2nd ears
We are crossing and backcrossing
these to DKHBA1, NC296, NC320,
NC368, NC476, PHP38, PHN46,
and 1274-1 (an NC320 relative
with fusarium resistance) and
several other semi-random lines
(mostly ex-PVPs) which happened
to be flowering when not much
else was.
Whether dominant factors are single
genes or gene complexes (and all
essentially identical to Ga1-s and/or
Tcb1) is unknown.
Will the dominance be lost during
backcrossing?
Are any resistant to Ga1-M? Several
(1222-2 and 1228-2) seem to be. Will
know more in January.
We have released 1222-2 from Jal78
as a genetic stock. It appears to be
completely dominant, and is classified
by Jerry Kermicle as Tcb1-s.
Several attempts to cross it as female
by Ga1-M males failed.
Further tests have been made in our
winter nursery and we should have
definitive results by mid-January.
And why didn’t Ga1-M reach the US
with other Mexican corn “exports”?
Tcb1 may limit interchange between
maize and teosinte, and hence have a
limited distribution.
But Ga1-M is all over Mexico at high
frequencies. Why didn’t it get here?