NOMENCLATURE SYSTEM FOR RICE GENE POOLS, POPULATIONS AND RECURRENT SELECTION BREEDING

Transcription

1 NOMENCLATURE SYSTEM FOR RICE GENE POOLS, POPULATIONS AND RECURRENT SELECTION BREEDING GENERAL USE AND CATALOGUE REGISTRATION M. ChâteI CIRAD-CA E P. Guimarâes CIAT

2 1. Introduction In 1984, a collaborative research project between CIRAD-CA (formerly IRAT) and EMBRAPA/CNPAF, Brazil, saw the beginning of a rice recurrent selection program. A few years later, CIAT and IRRI developed rice gene pools for population improvement. IARCs and NARDs have used this new germplasm in their breeding programs directly or as male sterile background to introduce new locally adapted germplasm. Several gene pools and populations are presently used but there is no clear, standardized nomenclature system. So tracking their backgrounds and selection traits, and comparing the results of breeding work and strategies, becomes increasingly difficult. A standardized nomenclature system is needed as the recurrent selection method becomes more integrated into traditional breeding programs, and as institutions increase germplasm exchange. We propose the adoption of a standard nomenclature system and that all information about gene pools and populations is registered in a catalogue. Each entry is to be fully described with special emphasis on development, genetic constitution, status of the germplasm, targeted objective(s) and ecosystems, and main agronomic characteristics. One of the institutions would be responsible for the catalogue s coordination and upkeep. 2. Existing Nomenclatures We first need to define gene pool and population. This proposal considers gene pool to be the specific and unique genetic background resulting from combinations of a group of genotypes. These may be pooled together in similar or different proportions through crossing, with or without a gene for male sterility. Population is the result of applying any breeding procedure to these backgrounds. It refers mainly to the enhancement of trait(s) and the genetic modifications (introducing up to 50% new variability) of the gene pools. EMBRAPA/CNPAF, CIRAD-CA, IRRI and CIAT have each created and named gene pools as follows: CNA-IRAT - the gene pools jointly developed in Brazil by EMBRAPA/CNPAF and CIRAD-CA (formerly IRAT); CP - the gene pools prepared at IRRI and currently used by CIRAD-CA in Mali (Africa); GC - the gene pool created by CIAT. Each gene pool received a code number for identification, (CP 122, GC 91, CNA-IRAT 4/0/0). The breeders who developed the gene pools relate these code

3 numbers to their breeding activities. In CNA-IRAT s case, after the standard institutional code (e.g. CNA-IRAT 4 gene pool) two additional numbers are used, separated by slashes. The first is the number of selection cycles made in the pool (CNA-IRAT 4/0). The second is the intermating number applied to the gene pool (CNA-IRAT 4/0/3). So the meaning of CNA-IRAT 4/0/3 is: gene pool CNA-IRAT 4, where there was no selection, but there were 3 cycles of recombination. A few populations were developed from this gene pool following the same name pattern. One example is the CNA-IRAT 4/1/3 CIAT received in The population came from the CNA-IRAT 4 gene pool after one selection cycle made in the third intermating cycle. The CNA-IRAT gene pools were formed using the male sterile gene from IR36, so some pools have the last number followed by F (CNA-IRAT 4/0/iF). In this case, the gene pool went through one cycle of intermating and the seed increase originated from heterozygote fertile plants. The same sequence of code numbers applies for the CP gene pools in Mali. An example is the population CP 1 26/1/1 F: gene pool CP 1 26 goes through one selection cycle and one intermating with seed increase made from heterozygote fertile plants. At CIAT, the letters are the initials of the scientists involved in the gene pool development and the numbers refer to the year when they obtained S0, seeds. So in 1991, Drs. Guimarâes and Correa-Victoria synthesized GC-91. Two name variations occur when gene pools or populations are used as male sterile background to introduce new variability (additional lines are crossed to male sterile plants of the gene pool or population, their genetic contribution representing at least half of the new pool): -- The germplasm name is maintained; a specific identification is added, e.g. CNA-IRAT 1 MOl is the first population developed for high altitude areas in Madagascar (MD). It was derived by introducing 13 locally adapted lines to the CNA- IRAT 1 gene pool. -- The name of the original gene pool or population is not present. The new derived population receives a new name. CNA 1 for example, comes from introducing three lines into the CNA-IRAT 4/0/SF gene pool by crossing the male sterile plants. The nomenclature used to identify the CNA-IRAT gene pools and populations only gives the number of selection and recombination cycles employed to improve them. Further information may be needed to characterize them better.

4 3. Standard Nomenclature Proposal Existing gene pools and populations and new ones need separate consideration. 3.a. Existing gene pools and populations Since rice breeders already use the germplasm, changing existing names and codes is not realistic. We propose keeping these names and codifications registered in the central catalogue. International Rice Research Notes or Crop Science could publish the registered population (See Appendix 1). 3.b.New gene pools and populations The new germplasm may be a truly new gene pool created by an institution. Or it may be an introduction of improved lines in an existing gene pool or population. There are several ways this can be done: - Combining a group of genotypes through hand crossing, or by using the male sterile genes available in their original genetic background. - Introducing more than 50% of new germplasm, crossing and backcrossing rice lines with male sterile plants of an already developed gene pool or population. -Crossing two or more gene pools or populations. -Combinations of the previous points or other alternatives. Germplasm, enhanced for specific trait(s) by using recurrent selection breeding in existing or new gene pools or populations, is a special case of new populations. In every instance, the institution that creates, modifies or selects gene pools or populations will name them using its own criteria. It will register them in the catalogue with detailed information about the genetic constitution and methodology used. For exchange and publication purposes, the catalogue nomenclature is the one officially recognized and used by the breeders. 3.c.System proposed for catalogue nomenclature of gene pools and populations Prefix - For all gene pools and population, we propose to use the prefixes GP and P (capital letters), for gene pool and population. The next letters are those of the institutions, to name their crosses (CT for CIAT, IR for IRRI, ONA for EMBRAPA/CNPAF, WAB for WARDA etc.). There is no space between any ofthe letters.

5 Numbering - The prefix is immediately followed by a dash and a number with no spaces. This numbering system is consecutive according to the registration catalogue. If the CIAT gene pool GC-91 is the first registered in the catalogue, followed by gene pools or populations from EMBRAPA/CNPAF and WARDA, its official name will be GPCT-1. The CNA 1 gene pool will be registered as GPCNA-2, the population proposed by WARDA will appear as PWAB-3. A further, later CIAT gene pool might be GPCT-4, and so on. 4. Proposal for the identification of the status of gene pool and populations Population enhancement is a continuous process of evaluation, selection and recombination. It is important to know the present status of the populations. Each institution is free to use its own criteria to name the germplasm. But we suggest the following identification of the working material as a method for breeders to handle the populations or gene pools during the enhancement process. This is useful when communicating and exchanging information before registering the germplasm as a new population. A full identification gives the number of recombination cycles of the gene pool or population both before and after selection. It gives the number of selection cycles with the traits for selection and also names the selection. Numbers and codes can represent the traits. The official registered name is used. The number of selection cycles follows, then the trait enhanced by the selection (use IRRI Standard Evaluation System for Rice acronyms). They are separated by a back slash, not the slash that is normally used for the identification of crosses. The GC-91 gene pool, catalogue name GPCT-1, has been selected once for leaf blast. CIAT would handle the populations as GPCT-1\BI. Numbers in the sequence identify how many recombination cycles were used after selection, and in which recombination cycle the selection was applied in the population. Continuing the previous example, during this planting semester, CIAT s GPCT-1\BI population would be named GPCT-1\BI\1\1, because the gene pool GPCT-1 was selected for leaf blast in the first cycle of recombination, then recombined once. In a hypothetical example, GPCT-4\0\0\0 means the gene pool produced by CIAT, fourth registered in the catalogue, with no cycle of recombination or selection. After being worked, it becomes GPCT-4\NBI\0\4, which means that a selection for neck blast, with no recombination cycle, was made in the fourth cycle of recombination of the GPCT-4 gene pool. GPCT-4\NBI\3\4 means three cycles of recombination after a selection for neck blast made in the fourth cycle of recombination of the original gene pool.

6 In most cases, selection is made for more than a single character. In such situations, the germplasm identification must give the acronyms of the traits. For example, if a population is enhanced for leaf blast and brown spot at the same time, the identification would be GPCT-4\BI,BS\2\4. Identification of a population enhanced for a certain trait in one season, and for another in the next, would be GPCT-4\BI\3\4,BS\0 - the separated trait acronyms indicating enhancement in different seasons. In the case of several selections for the same trait, we recommend identification as in the following example. Consider a CNA gene pool with four recombinations GPCNA- 4\0\0\4 submitted once to selection for neck blast and recombined twice GPCNA- 4\NBI\2\4. It is selected for the same trait the next season, then recombined five times. The identification would be GPCNA-4\NBI\2\4,NBI\5. When the germplasm has been sufficiently enhanced for the trait(s) under selection, the breeder can register it, following the same rules for including a new population in the catalogue. For example, GPCT-4\NB1\3\4 becomes PCT-10, the simpler catalogue nomenclature, the number referring to the registration. Once accustomed to the system, we can retrace all information on the enhancement of the germplasm. 5. Selection of Elite Lines Two cases of extraction of elite lines are considered; extraction using gene pools or enhanced populations, and extraction obtained from different cycles of selection/recombination during the improvement process of the germplasm. The nomenclature is based on that proposed by WARDA for traditional line development and accepted by participants of the First International Upland Breeders Workshop held at CIRAD-CA, Montpellier-France, September 6-10, a. Gene pool or enhanced populations Nomenclature of elite lines selected from gene pools or populations should indicate the germplasm used to develop the line and the institution(s) involved in the process. We propose using a symbol to separate the name of gene pool population from the assigned pedigree. Here are three examples: GPWAB-3> This is an elite line extracted by WARDA within a gene pool they have registered. PCT-5 >WAB This is an elite line extracted by WARDA within a population developed by CIAT.

7 PIR-7>23-1-WAB-3-4-CNA-4-B The population PIR-7 is produced by IRRI, within which IRRI made selection of elite line during two generations. WARDA received the line PIR-7>23-1 and selected during two more generations. Finally the line PIR.-7>23-1-WAB-3-4 was sent to EMBRAPA/CNPAF and selected for one more generation. Then the seeds were harvested in bulk. 5.b. Different cycles of Selection/Recombination (working material) PWAB-7\GQ\2\3> A WARDA population is under selection to enhance grain quality. The institution extracts elite lines from the third cycle of recombination of the population PWAB-7, selects once for grain quality and then recombines twice. 6. Further Considerations 6.a. Seed exchange and conservation Each institution will have seeds of its registered gene pools or populations (breeders seed) for exchange. When answering a seed request, the catalogue information should also be included. A minimum of 2000 seeds should be sent to the institution responsible for the catalogue, with the request for registration. Each institution will be in charge of keeping its gene pools and populations under medium-term conservation. A sample should be sent to IRRI for long-term conservation. Each institution would have to inform potential users in advance of its intention to discard a population no longer in use, and send the remaining seed to IRRI for long term conservation. 6.b. Recurrent selection - activities reports Each institution dealing with recurrent selection breeding method should report annual activities to the central coordinator, responsible for preparing a global report on the use of the rice gene pools and populations. The information will be sent to all participants whose names are in the coordinator s file.

8 References CIRAD-CA, Recommendations. International Upland Rice Breeders Workshop, September 6-10, Montpellier, France. International Rice Research Institute (IRRI), Standard Evaluation System for Rice. 3rd Edition, Los Baños, Philippines. 54p. Taillebois, J. and E. P. Guimaraes, CNA-IRAT 5 upland rice population. IRRN 14:3. West Africa Rice Development Association (WARDA). WARDA s Varietal Nomenclature System (monograph) 4p.