I am providing a service to the seed corn industry of developing cytoplasmic male sterility conversions of corn inbred lines used as females in seed production by using a unique efficient technique. The use of such male sterile female parents significantly reduces the costs of seed production by (1) reducing or eliminating the costs of detasseling, (2) increasing seed yields from 15 to 30% as compared to mechanically detasseled seed production, (3) reducing the risks of insufficient detasseling labor and weather influences, and (4) decreasing the exposure to safety incidents due to detasseling by hand.
- The resulting conversions from this method will have 100% of the nuclear genetic component of the converted inbred in a male sterile cytoplasm (C, S, Sd or T).
- Such male sterile females will cause no hybrid yield drag that is possible due to remnant linkages that will result from traditional backcross conversion methods, even with genetic markers yielding 95 to 99% recovery. No yield testing is needed.
- Inbreds are converted in only two breeding generations. An additional generation is used for phenotypic verification and the initial hand pollinated seed increase to produce an amount sufficient for breeder seed production.
The conversion technique used is the indeterminate gametophyte (ig) system involving paternal haploids and cytoplasmic male sterility. Significant advantages of the results of this conversion technique include:
I have recently retired with over 35 years of experience in the seed corn industry with a major seed company in the areas of corn breeding, research station and regional management, corn seed production research, male sterility conversions and parent seed management. I have been involved with the “ig” male sterility conversion system since the mid 1970’s when Dr. John Laughnan provided the initial genetic stocks to the industry corn breeders during the Illinois Corn Breeders School. There have been inbred conversions from my development programs that have been used significantly in the industry during the past 15 years.
I earned a Ph.D. in Plant Breeding and Genetics at the University of Wisconsin-Madison after earning BS and MS degrees in Ag Education and Agronomy, respectively, at Purdue University. I continue to be a student of the “ig” technique and am developing efficiency improvements to the system. I am doing this during my retirement because I enjoy the outdoor field nursery work, seeing the results of an inbred male sterile conversion going through the paternal haploid stage and adding value as a perfect genetic and phenotypic recovery.
How the “ig” Male Sterile Conversion System Works:
The system utilizes the effects of the “ig1” gene on the abnormal development of the female gametophyte in the W23 genetic background. Progeny of a cross of an inbred to be converted as a pollinator on the ig stock will include a low percentage of haploid plants, about 2/3 of which are of paternal origin genetically.
The stock used as the female in the cross includes the male sterile cytoplasm which will be inherited maternally by the paternal haploids; thus these paternal haploid plants will carry 100% of the pollen donor’s nuclear genome along with the male sterile cytoplasm. These haploid plants are then backcrossed as the female to the donor inbred and due to chance a few kernels are generally produced. Nearly all these kernels originate from a few “unreduced female gametes” that occur by chance during meiosis in the haploid plant.
Nearly all of these kernels are viable and grow as diploid plants and are identical phenotypically and genetically to the donor inbred with the desired exception of being male sterile due to the cytoplasm genetic effects if the donor inbred does not carry restoring genes. These are the plants that are increased during the 3rd generation of the process, where the phenotype and male sterility is verified. Of course the increase of the male sterile plants is done by crossing with the original inbred being used as the “maintainer”.
Service History (as of 1/29/2013) and Timelines:
I started this service with a two clients utilizing a 2011-12 off-season nursery planted in south Florida. This first “class” of projects was finished during the 2012-13 off-season. Six inbred/cytoplasmic conversions were verified as successful for phenotype and male sterility and increased.
A second “class” of 10 conversion projects was begun during the summer of 2012 with the selection and pollination of paternal haploids done in the 2012-13 off-season. A third class of 18 conversion projects was started during the 2012-13 season with crosses to the “ig” cytoplasmic stocks.
Generally, I prefer to begin projects in an off-season nursery planted approximately on the first of October in south Florida where the inbreds are crossed onto the “ig” cytoplasmic stocks and cytoplasmic male sterile testers. The testcrosses are immediately sent to Puerto Rico and evaluated in a grow-out in for the inbred’s ability to maintain male sterility with the absence of residual nuclear restorer genes. This information can be available before planting the second generation. Those projects where the inbred restores a male sterile cytoplasm are dropped. An irrigated summer nursery is used for paternal haploid selection and pollination. Kernels of male sterile cytoplasm conversions may be available in October or a larger increase with phenotype verification will be done during the next off-season nursery with seed delivery before spring planting in the corn-belt.
Based on past and recent experience, I expect to be able to convert 85-90% of the inbreds initiated that do not possess residual restorer genes for a specific cytoplasm, depending on their genetics and any restoring factors they may have. Several options are available to meet your conversion needs. Details of timelines, costs, contracts, etc. are presented below.
Options, Timelines and Fees of the “ig” CMS Conversion Service
The conversion process may be started in the off-season or summer nursery, although the off-season start is preferred and may involve lower fees. Seed of the conversion may be provided after either 2 or 3 generations, depending on whether further backcrossing to traits is being done by the client or whether sufficient seed for an increase is desired after phenotype verification.
A. Basic Individual Inbred Conversion Option begun in an off-season nursery.
First Generation: For each inbred the client will provide the following by September 15:
- Your legal agreement if necessary to meet the deadline.
- Provide general inbred description and background information to me on an “Inbred Fact Sheet” that will be provided.
- A nonrefundable initiation fee of $500 for each inbred.
- Send a minimum of 100 kernels of viable seed of the inbred, fee payment,
and the completed inbred information fact sheet by September 15 to:
Cutter CMS, LLC
Attn: Gary Cutter
4539 Locust Hill Rd.
Taylors, SC 29687-6720
- Seed will be planted in a winter nursery and crossed onto my “ig” conversion stocks of your choice of 1 or 2 male sterile cytoplasms, generally C and/or Sd.
- Testcrosses will also be made to testers of these cytoplasms and immediately grown out to assess the inbred’s capability to be sterilized, having no residual restorer genes. A grow-out will be done as soon as possible in Puerto Rico to provide results before planting the second generation.
- Any inbred/cytoplasm combination conversion may be discontinued by the client for any reason before March 15 to avoid planting the second generation and to any avoid additional fees for continuing and finishing the conversion. The inbred/cytoplasm combination conversion will also be discontinued if the grow-outs show restoration of fertility in the male sterile cytoplasm tested, unless the client prefers to continue it.
- A nonrefundable continuation fee of $1000 per inbred will be invoiced before planting in the summer nursery for each inbred/cytoplasm combination that maintains male sterility in the grow-outs. As soon as the grow-out data is available, the client will determine which inbred/cytoplasm(s) are to be continued and will be invoiced immediately before planting if possible.
- The second generation of the process will be grown during the summer under drip irrigation.
- Paternal haploid plants of the source inbred in the male sterile cytoplasm will be selected and backcrossed to the source inbred to produce some seed with unreduced female gametes that are expected to occur. Such seed generally results to be the completed conversion.
Third Generation: The client has 2 options for this generation involving seed increase and phenotype verification:
- (Option 1 which is preferred): I will verify the sterility and the plant phenotype and increase the converted inbred from seed from the paternal haploids in a winter nursery to the maximum, expecting to return from 250 up to 25,000 K depending on paternal haploid seed production. Increased seed of acceptable inbred conversions will be provided by March 15, 2013 upon receiving the final payment. Seed may be returned on the ear if desired, or a few ears may be left unshelled for the client to see the ear type.
- (Option 2): Client has the option to receive seed from the second generation to do their own phenotype verification in the third generation. This seed would be that which was produced on the paternal haploids and could range from 5 to 300 kernels. This seed would be provided to be grown ear row from each paternal haploid plant to allow for discarding any family that does not have the recurrent inbred characteristics for any unexpected reason (this has not been necessary in my past experiences). Up to 10 seeds will be retained for a 3rd generation verification and increase in my winter nursery; this increased seed will also be provided to the client. (This may be an option for any non-traited male sterile converted inbred that does not need a large increase but will be further converted to traits through backcrossing and selection from this seed from the haploids; backcrossing may be started a generation earlier). Seed of the male sterile conversions from the paternal haploids may be provided before September 30, 2012 and upon receipt of the final fee payment. This final payment would be refunded if the conversion is not correct according to both client’s and my nursery observations.
- Final fee payment for either of these options would be $3000 per inbred/cytoplasm combination prior to the return shipment of the seed.
Summary of Fees: The total charge for the first cytoplasmic conversion of an inbred would be $4500 = $500 for initiation + $1000 for the second generation planting + $3000 for return of seed increase after the third generation (Option 1) or second generation (Option 2). A second cytoplasm conversion of the same inbred would be $500 less because the initiation fee for the first generation is based on an inbred basis, not an inbred/cytoplasm basis, thus totaling $4000. Inbreds with residual restorer genes identified by a testcross grow-out, or dropped by the client before the 2nd generation is planted would cost only the initial $500 for the attempt.
B. Basic Individual Inbred Conversion Option begun in a summer nursery.
The two or three generations involved in the conversion process will be similar to option A with the following exceptions:
- For the first generation, seed and payment needs to be provided by March 15.
- Testcrosses made to the cytoplasm sources will be grown out in the off-season nursery at the same time that the paternal haploids are selected and pollinated because there is insufficient time to obtain grow-out results time prior to the second generation planting. (Planting the second generation is done in Florida approximately October 1, shortly after harvest of the first generation).
- As a result the non-refundable second generation fee will need to be paid for all inbred/cytoplasms involved whether the inbred will or will not restore male fertility. (An alternative is to wait a growing season after grow-out results are obtained in the winter)
- If the grow-out results show fertility during the second generation, the inbred/cytoplasm combination will not be grown and increased in the third generation or provided after the second generation; thus no final fee of $3000 will be applicable.
- Seed of converted inbreds that do maintain male sterility based on the grow-outs will be provided after the second generation as described above by March 15 or after the third generation of phenotype verification and increase by September 15.
- Summary of Fees: This would be the same as Option A described above, except the second fee is paid for each inbred/cytoplasm continued into the second generation whether the inbred is determined to restore fertility or not based on the grow-out being grown concurrently.
Gary L. Cutter, Ph.D.
Cell phone: 1-309-825-5149