Sunday, January 11, 2015

Native Trait Recovery

 

 
 

Native Trait Recovery
 
 

The Development of EaSYTM and CT StartTM  Traits
 
 
NT RECOVERYTM is a  technology for recovering genes of agronomic importance from ancestral strains of maize (corn).  To date, the focus of our research program has been the recovery of native traits such as drought resistance and cold tolerance.  In the future, the scope of our program will cover traits that improve high-end yield potential as well as the ability to tolerate adverse environments.  The purpose of this blog post is to introduce NT RECOVERYTM technology to parties that are not currently collaborating with Native Traits Corporation.  Two native traits, EaSYTM and CT StartTM, are used to illustrate the successful application of NT RECOVERYTM technology.
 
CT StartTM confers tolerance to the cold temperatures that occur throughout the Midwest during early spring.  It also provides resistance to drought and the high temperatures that may occur later in the growing season.  However, the first application of NT RECOVERYTM technology was for the development of EaSYTM and that initial success was to set the stage for the development of CT StartTM.
 
 
Development of B73EaSYTM

 
 
Originally known as ESY (Enhanced Seed Yield), EaSYTM was at the onset simply an effort to improve the per se performance of B73.  First popular as the female parent of the hybrid B73 x MO17 (see Figure 1), it has been estimated that at least twenty percent of the corn hybrids currently planted in the United States utilize an improved version of B73.  The development of a trait that would reduce seed (not grain) production expense was the goal - little thought was given to the possibility of increasing hybrid yield – the objective was to improve inbred yield. 
 
  
 
 
 

Figure 1.  B73 (left), MO17 (right), and B73 x MO17 (center).

 
 
At the very beginning, it was recognized that a new and more cost-effective breeding technique would be required in order to improve the yield of B73 as an inbred.  NT RECOVERYTM is essentially mass selection with some elements of Gardner’s grid design.   However, two significant modifications were made and as it turned out, these modifications were successful beyond all expectations.  Not only was seed yield enhanced, but hybrid yield was improved as well.  The following is a brief non-confidential summary of these modifications:

 
 
First, a novel approach to reducing soil variability was developed along with a proprietary algorithm to adjust for any remaining variability in the field.  It has long been generally assumed that variability in the soil makes it impossible to measure the true performance of individual plants within a research plot.  Without a fundamental improvement in plot design and yield measurement, it would have been impossible to implement the other key feature of NT RECOVERYTM technology, namely, single ear descent.
 
Briefly, it was decided to create “mini-isolation” plots where the progeny of a single ear could be evaluated with the best single plant providing seed for the next generation.  The advantage of single ear descent is that consanguinity  increases with each generation.  Residual heterozygosity, although initially a concern, did not appear to affect the outcome of the selection program.  The adoption of single ear descent as a breeding design is probably responsible for the improvement in hybrid yield.
The starting material for the B73EaSYTM program was derived from a synthetic population that was 75% B73 and 25% exotic germplasm from Latin America.  Three generations of selection were practiced using grid selection/single ear descent.  The resulting material was then backcrossed twice using a similar grid selection protocol except individual ear-rows were de-tasseled and pollinated by alternating rows of B73.  In this manner, eight backcross (BC3) lines were developed.  These lines were evaluated under drought conditions in a paired-comparison with B73 in 2010 (Table 1).
 
 
Table 1.  Per Se Performance of B73EaSY-BC3 lines Compared to B73 Grown under Drought Stress* near Kalamazoo, Michigan in 2010.

 

                                       Seed Yield (Bu/Acre)**

Pair/BC3

B73EaSY

B73

% Advantage

1

    52

33

158

2

    55

40

138

3

    57

36

158

4

    61

41

149

5

    72

48

150

6

    76

52

146

7

    64

50

128

8

    64

46

139

Average

    63

43

146

*Total rainfall in the seven weeks prior to anthesis was 0.41 inches.

**Each plot was a single 30-foot row.
 
 

Based on these encouraging results, an additional generation of selection and backcrossing was practiced.  A total of 10 BC4 lines were recovered.  These lines were bulked and selected again for two generations using the NT RECOVERYTM method.  The vigor of the recombined BC4 material was extraordinary (Figure 2).

 
 
 
 
Figure 2.  B73EaSYTM-BC4 Nursery
 
 
 

The hybrid performance of the recycled BC4 generation was evaluated using a narrowed-based synthetic (B98rly) as a tester.  LH132 was used as a check.  In this way, the effect of EaSYTM was determined at 4 locations in 2013 and 17 locations in 2014.  Hybrid performance is shown in Table 2 below.

 

 

 
Table 2.  The Effect of EaSYTM on Hybrid Grain Yield (Bushels/Acre)
 
Female Parent*
2013
2014
Average
B73EaSYTM
223
179
201
LH132
214
171
193
EaSY TM Benefit
+9
+8
+8
*B98rly was the male parent.  B98rly is a narrow-based synthetic derived from B98, B97, LH82, and LH123.

 
B73EaSYTM, averaged over two years, exhibited an eight bushel per acre advantage compared to LH132, a line that is was introduced as a replacement for B73.  In other words, not only did EaSYTM bring the hybrid performance of B73 up to that of LH132 – it actually surpassed LH132 by eight bushels per acre.  NT RECOVERYTM had proven to be more than a program to enhance yield per se, in fact, it was eventually shown to be useful for the development of another trait, CT StartTM.

 
Development of CT StartTM

 
Following the initial success with EaSYTM, a project to improve cold tolerance was initiated.  A cold tolerant (CT) source population was crossed to LH132 to create a population that was theoretically 50% LH132, 37.5% B73, and 12.5% open-pollinated germplasm.  Three cycles of selection were performed using the NT RECOVERYTM method.  In 2012, an initial version of CT StartTM (LH132CT) was compared to B73EaSYTM at 12 locations under conditions of severe heat and drought.  The results of this study are shown in Table 3.
 
 
Table 3.  Performance of LH132CT and B73EaSY Hybrids Averaged over 12 Stress Environments* in 2012.
 
Female
  Parent**
Grain Yield
Bu/A
Grain Moist.
%
Stalk Lodging
%
Root Lodging
%
LH132CT
131
23.5
2
1
B73EaSYTM
122
23.7
6
1
*Data are the average of locations in Iowa (3), Illinois (6), and Indiana (3).
**The male parent was a narrow-based synthetic derived from B98, B97, LH82, and LH123.
 
 
 
Clearly, under conditions of extreme heat and drought, LH132CT was superior to B73EaSYTM.  The experiment was repeated in 2014 with LH119 and LH132 included as additional checks.  Remarkably, LH132CT yielded 10 bushels per acre more than the check, LH132 (Table 4).

 

 

Table 4.  Performance of LH132CT Compared to Check Hybrids (B73EaSYTM, LH119 and LH132) Averaged over Four Locations in Illinois and Indiana in 2013.

 
Female
Parent
Grain Yield
Bu/Acre
Grain Moist.
%
Stalk Lodging
%
Root Lodging
%
LH132CT 
224
21.7
1
0
B73EaSYTM
223
22.5
1
1
LH132
214
21.3
3
0
LH119
201
22.1
2
0
*B98rly was the male parent.  B98rly is a narrow-based synthetic derived from B98, B97, LH82, and LH123.

 
In 2014, an expanded test with 10 CT StartTM recoveries was conducted using LH132 and B73EaSYTM as checks.  Based on 12 locations of data, CT Start-6 out-performed LH132 by 11 bushels per acre (Table 5).    

 

 

Table 5.  Performance of CT Start-6 Compared to Check Hybrids (B73EaSY and LH132) Averaged over Twelve Locations in 2014.

 
Female
Parent
Grain Yield
Bu/Acre
Grain Moist.
%
Lodging
%
Test Weight
Lbs
CT Start-6 
189
23.6
5
55.6
B73EaSY
185
23.2
7
56.5
LH132
178
23.1
5
57.1

*B98rly was the male parent.  B98rly is a narrow-based synthetic derived from B98, B97, LH82, and LH123.

 
Interestingly, the best CT StartTM recoveries (CT Start-5, CT Start-6) were superior to LH132 only if planted early (Table 6).  In fact, of the four best lines, only one, CT Start-7, exhibited any significant yield advantage when planted later.  All of this is as expected - without cold stress there is no need to have cold tolerance.  Additional research will be needed to determine if CT Start-7 is a true exception. 
Yield drag was a confounding effect.  The average yield of all CT StartTMrecoveries was less than that of LH132 (see bottom of Table 6).  CT StartTMwas introgressed into a genetic background that was only one-half LH132.  The remaining half (37.5% B73, 12.5% open-pollinated germplasm) no doubt resulted in considerable yield drag. Introgressing the trait into a more elite background is a vital next step.
 
 
Table 6. Hybrid Performance of CT StartTM Entries Compared to B73EaSY and LH132 in 2014.
(Highlighted Numbers Are Equal to or Greater than LH132)
 
 
Grain Yield (Bu/A)
 
Female Parent
 Early Planting*
   Late Planting**
Mean of 17 Locations
CT Start-6
             189
              148
                  177
CT Start-5
             184
              153
                  174
CT Start-7
             176
              162
                  172
CT Start-8
             177
              155
                  171
B73EaSY
             185
              165
                  179
LH132
             178
              154
                  171
Mean of all CT Start Entries (10)
             171
              150
                  165
 *Twelve locations planted mostly in April.    **Five locations planted in May.



 
Summary

 
NT RECOVERYTM technology is an effective means of improving cold tolerance, drought resistance and high-end yield potential.  Although other traits are under development, the immediate objective is to combine EaSYTM with CT StartTM and to transfer the combined EaSY StartTM trait to elite commercial lines.  Native Traits Corporation is actively seeking research partners for an allele harvesting program.  For more information, please contact Dr. James W. Friedrich

 

 

 

 

 
 
 

 
 




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