Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2003
Publication Date: 11/1/2003
Citation: Martinez-Reyna, J.M., Vogel, K.P. 2003. Incompatibility systems in switchgrass. Crop Science. 42:1800-1805. Interpretive Summary: Incompatibility in plants can be defined as the inability of two functional male and female gametes to produce normal seed following mating. Basic genetic research was conducted to identify and characterize the incompatibility systems present in switchgrass (Panicum virgatum L.) which is a species that is being developed as a potential biomass fuel crop. Three incompatibility systems were identified. One is pre-fertilization system that is similar to systems that exist in many other grasses which ensures cross-pollination. Two post-fertilization systems were identified that affect normal seed development and can result in shrunken seed. One system occurs between plants with the same numbers of chromosomes or ploidy level. The mechanism for this system is unknown. The other system occurs when plants with different numbers of chromosomes or ploidy levels are mated and inhibits the production of viable seed. This system is responsible for preventing inter-mating between plants with different ploidy levels in native prairies. It may be feasible to use the pre-fertilization incompatibility system to produce hybrid cultivars for use in biomass production for energy.
Technical Abstract: Incompatibility in plants can be defined as the inability of two functional male and female gametes to produce normal seed following mating. Incompatibility can occur pre-fertilization or post-fertilization. This study was conducted to determine features of the incompatibility systems present in switchgrass (Panicum virgatum L.) by studying their effect in the seed set of reciprocal matings of tetraploid, octaploid, and tetraploi x octaploid matings. Both bagged mutual pollination and manual emasculation and pollination methods were used to produce hybrids. The percentages of self-compatibility in the tetraploid and octaploid parent plants were 0.35% and 1.39%, respectively. Pre-fertilization incompatibility in switchgrass is apparently under gametophytic control since compatible and incompatible pollen were found in all matings. Differences in incompatibility indexes found between reciprocal and direct crosses indicated the involvement of more than one locus in determining incompatibility. Results indicate that the pre-fertilization incompatibility system in switchgrass is similar to the S-Z incompatibility system found in other members of the Poaceae. A post-fertilization incompatibility system also exists that inhibits intermatings among octaploid and tetraploid plants. In these interploidy crosses two very distinctive types of abnormal seed were found. When the female parent was tetraploid plant, the resulting seed was small and shriveled while when the female parent was octaploid, small seed with floury endosperm was obtained. These results are similar to those obtained for endosperm incompatibility due to the endosperm balance number system found in other species. It may be feasible to use the self-incompatibility system in switchgrass to produce hybrid cultivars.