Comparison of Monoecious and Gynomonoecious Eastern Gamagrass Breeding Systems for Foliar Disease Susceptibility and Agronomic Traits

Abstract:

The discovery of a gynomonoecious sex form (GSF) of eastern gamagrass (Tripsacum dactyloides) has greatly increased our expectations for high seed yield from this species. Reported estimates range from 12 to 20 fold increase in seed number and 2 to 4 fold increase in seed yield (Dewald and Dayton, 1985a and 1985b; Vogel et al., 1985).

The original GSF plant is an unthrifty, highly disease susceptible plant, collected from a wild population in Ottawa County, KS. We were interested in determining whether the GSF character is associated with disease susceptibility in other genetic backgrounds, and also if there are inherent advantages or disadvantages in the GSF trait or associated characteristics which would suggest its long term value in eastern gamagrass breeding.

Kulakow, P.A., M.K. Handley, J. Henson, and C.L. Dewald (1990). Comparison of Monoecious and Gynomonoecious Eastern Gamagrass Breeding Systems for Foliar Disease Susceptibility and Agronomic Traits. Eastern Gamagrass Conference Proceedings, January 23-25, 1989, Poteau, Oklahoma, pp. 41-44. Reprinted with permission.

Originally published by the Kerr Center for Sustainable Agriculture, ©1990. To get a free copy of the entire proceedings call 918.647.9123. To view other publications and a publications order form, go to www.kerrcenter.com.

Methods and Materials

This paper describes one aspect of a joint project between The Land Institute and The Kerr Center for Sustainable Agriculture. The paper in this volume by Handley et al. describes our methods in more detail. The breeding program at the USDA-ARS Southern Plains Range Research Station in Woodward, Oklahoma, has introduced the gynomonoecious trait into a variety of genetic backgrounds. Half-sib families, representing 18 parents, were collected from the Woodward breeding plots and grown at the Land Institute in 1986 (Bohlen, 1986). Ten families were selected, based on their leaf rust severity in 1986, and 30 individuals from each family were transplanted into clonally replicated trials at Salina and Poteau, Oklahoma. These plots were not fertilized. Some irrigation was used in Poteau for initial establishment. Plots were weeded as needed. As these plants flowered in 1987, they were scored for flowering type. A subset of 100 genetic individuals was chosen to evaluate in more detail. We compared 5 MSF and 3-5 GSF individuals from each family. Seed yield, tiller number, leaf length, and leaf width were measured on the subset of 100 individuals in each replicate.

Plants were individually hand harvested three times at Salina (July 7, 16, and 28), air dried, and individually weighed. Plants were also hand harvested several times in Poteau, but seed was bulked for each plant, air dried, and weighed following the final harvest. Yields are reported as seed yields which consists of the caryopsis and the hard fruitcase. Disease severity and basal circumference were evaluated for all individuals. Analysis of variance based on family means was done with both years and locations combined for each factor.

Results and Discussion

There were consistent differences between MSF and GSF plants for severity of anthracnose in both locations for most rating periods in 1987 and 1988 (Figure 1). The analysis of variance did not indicate that these overall differences among sex forms were significant due to the presence of family by sex form interactions. There were no differences between GSF and MSF plants for leaf rust severity (Figure 2). These data indicate that the gynomonoecious trait increases susceptibility to anthracnose in several genetic backgrounds. Since anthracnose adversely affects growth and yield (see Handley, et al., this volume) it will be important to monitor disease susceptibility in eastern gamagrass breeding, especially when using the gynomonoecious character.

Table 1 compares the overall means of 4 agronomic characters between MSF and GSF individuals in the 2 locations. Total seed yield was higher for GSF plants although under the conditions of our study the difference was 17 to 18% on a per plant basis and 36 to 63% on a per culm basis. The overall seed yields were significantly different only in Salina; however, on a per culm basis, GSF seed yields were significantly higher at both locations. Individual half-sib families varied in the relative performance of the two types, but these were not consistent between locations. In Salina, the families ranged between 22% lower yield from GSF plants to 105% greater yield. In four of the ten families GSF plants yielded at least 25% greater then MSF plants, and these differences were significant. In Poteau, the range was much greater. GSF plants in family 2 yielded 65% lower than MSF plants. In family 5 the GSF yield was 144% greater than from MSF plants. Both of these differences were significant. GSF plants had significantly fewer reproductive culms in both locations, with a 9% reduction in Salina and a 25% reduction in Poteau. GSF plants were also smaller than MSF plants, with a 6-11% reduction in basal circumference which was consistent between years. Ibis difference was also significant. There was considerable variation between families for the magnitude of the difference between sex forms for all of these traits.

GSF plants tended to be earlier maturing and more synchronous than MSF plants, even though there was no difference in time of flowering (Table 2). In the earliest of three harvests, 56.7% of the seed on GSF plants was mature, while only 35.2% of the MSF seed was harvested. The percentages were nearly equal in the second harvest, but at the third harvest 25.8% of the seed from MSF plants was collected, while only 9.3% of seed remained on GSF plants. Thus at the first harvest, GSF plants outyielded MSF plants by 89.6%, but at the third harvest GSF was nearly 60% lower yielding than NSF plants. Percentage caryopsis mass was similar for both types (Table 3). Percentage seed fill was lower in GSF plants, and seed weight was much lower (Table 3).

Conclusions

The gynomonoecious trait was associated with increased susceptibility to anthracnose. Leaf rust susceptibility was not influenced by sex form. There were differences between half-sib families for the association with anthracnose susceptibility, and also differences between individuals in a family for the level of disease observed. Careful selection of breeding material will probably identify individual GSF plants which are not highly susceptible to anthracnose.

GSF plants yielded more seed than monoecious plants, but this difference was only significant in Salina. The yield increase overall was less then 20% in both Poteau and Salina. The magnitude of the seed yield increase was reduced considerably by lower numbers of reproductive culms on GSF plants. The gynomonoecious character appears to be useful for increasing seed yield, but until further selections are made the difference will not be dramatic. Alternative ways of achieving yield increases should be explored, including screening germplasm populations for yielding ability and developing new populations using interpopulation hybridization.

Since GSF plants are associated with lower growth rates and smaller seed size than normal plants, they may be more difficult to establish and less competitive in seeded stands. This will be extremely important to explore before widespread use of GSF plants of eastern gamagrass is proposed.

Literature Cited

Bohlen, P. 1986. Multiplication and evaluation of Tripsacum dactyloides accessions segregating for a recessive pistillate mutant. The Land Report Research Supplement 3: 30-34.

Dewald, C. L. and R. S. Dayton. 1985a. A prolific sex form variant of eastern gamagrass. Phytologia 57:156.

Dewald, C. L. and R. S. Dayton. 1985b. Registration of gynomonoecious germplasm (GSF-I and GSF-II) of eastern gamagrass. Crop Science 25:715.

Vogel, K. P., C. L. Dewald, H. J. Gorz, and F. A. Haskins. 1985. Improvement of switchgrass, indiangrass, and eastern gamagrass: current status and future. pp. 159-170 in Proceedings of the 38th Annual Meeting of the Soc. for Range Mgmt. Salt Lake City, UT. Feb. 1985.