1a. Objectives (from AD-416)
Transfer high levels of resistance to soybean cyst nematode from Glycine tomentella to soybean.
1b. Approach (from AD-416)
Working with scientists at the University of Illinois we have developed and perfected techniques for successfully deriving fertile progeny from crosses between soybean and a distant, perennial relative, Glycine tomentella. We are the only place in the world that this research has been successfully completed. The Glycine tomentella parent that we are currently using is a tetraploid with 2n=78 chromosomes and is nearly immune to the two common soybean cyst nematode (SCN) biotypes to which it has been tested. Glycine tomentella and soybean do not share the same genome so developing genetically stable lines from such a cross requires extraordinary means. Traditional cross pollination techniques are used but to keep embryos from aborting a daily hormonal spray is applied for 30 days. Approximately a month after pollination, the embryos are excised and placed on a culture medium. With proper control of the medium the embryo can be induced to produce callus from which many plantlets can be derived. A different medium is used to stimulate root development and eventually the plant can be transplanted and grown to maturity in the greenhouse. The hybrid plant has 39 Glycine tomentella chromosomes and 20 soybean chromosomes and is sterile. Treatment with colchicine is used to double the chromosome number to produce a plant with a full complement of chromosomes from both species. This plant is then backcrossed to soybean. The first backcross progeny has all 40 soybean chromosomes and one copy of each Glycine tomentella chromosome. We will develop many different second backcross lines to increase the probability that of all Glycine tomentella chromosomes will be represented in advanced backcross populations. As we continue to backcross, the Glycine tomentella chromosomes are randomly lost but in each cycle of crossing the possibility of transferring genes from Glycine tomentella exists. There are two goals either of which can occur after 3 to 5 backcrosses. We will develop fully fertile, genetically stable soybean lines with 2n=40 chromosomes with introgressed genes from Glycine tomentella or we can identify fertile, genetically stable lines with 2n=42 that have 40 soybean chromosomes and one pair of Glycine tomentella chromosomes. To date we have produced nearly 3000 fertile, genetically stable lines and will continue to produce new lines each year. These lines will be evaluated to identify those with SCN resistance.
3. Progress Report
Seeds from the more than 3000 self-fertile single plants were planted. Genetically stable lines will be bulk harvested for future screening for SCN resistance. We have completed two rounds of testing. In our first test of 300 lines, we identified 18 lines that tentatively had useable levels of soybean cyst nematode (SCN) resistance. In order to test as many lines as possible, each line is only evaluated once in these initial tests. In the retest of these lines, we were able to confirm 1 line that was moderately resistant and 6 lines that had low levels of resistance. In this test, the resistant line had a female index of 29 which means that it had 29% of the cysts as the susceptible check. Dwight, the susceptible parent of this line, had a female index of 95. In the second test of 250 lines, we also identified 7 new lines with female indexes that ranged from 2 to 39. These lines will be retested. The line with a female index of 2 has 42 chromosomes and the others have 40 chromosomes, which is the same number of chromosomes as soybean. We are currently preparing for a third round of testing to retest those tentatively identified as resistant and test additional lines from the 2010 harvest. This summer we will cross with the line with confirmed resistance to begin the process of determining if the genes conditioning this resistance are different from the genes currently being used. Activities of this project were monitored through quarterly reports, meetings, and periodic phone calls and e-mails.