BREEDING FOR DISEASE AND INSECT RESISTANCE

Authors: Panella, Leonard; Lewellen, Robert; HARVESON, ROBERT - UNIVERSITY OF NEBRASKA

Submitted to: Compendium of the Beet Diseases and Insects
Publication Type: Book / Chapter
Publication Acceptance Date: 4/1/2007
Publication Date: 5/28/2009
Citation: Panella, L.W., Lewellen, R.T., Harveson, R. 2009. Introduction - Breeding for Disease and Insect Resistance. Pages 3-5 In: Compendium of the Beet Diseases and Insects, edited by R.M. Harveson, L.E. Hanson, and G. L. Hein, ets. APS Press, St. Paul, MN, pp. 140.

Interpretive Summary: Genetic improvement in sugar beet is complicated by its breeding system. The sugar beet plant is biennial and flowering requires long-day photoperiod and vernalization. After vernalization, the rosette from the previous year produces a flower stalk . Both genetic and CMS types of male sterility occur, which makes hybrid cultivar production practical. In the wild type, two or more flowers occur as fused clusters to produce multigerm seedballs. Modern agriculture is dependent upon single seeded cultivars due to the need for precision sowing. This trait is known as monogermity, and is recessively inherited. Hybrids are composed of two or more parental components. Unlike the highly uniform, pure line cultivars of self-fertile crops such as lettuce, soybean, or wheat, considerable genetic variability may still occur within sugar beet hybrid cultivars. Because most of the known resistance to sugar beet diseases is controlled by more than one gene, much experimental effort is needed to identify differences among plants. Sugar beet breeding in the United States has primarily concentrated on developing resistance to disease and environmental stresses. Because developing disease resistance cultivars became a top priority, the USDA began making collection trips to look for sources of resistance to diseases such as cercospora leaf spot and curly top resistance in wild sea beet, as well as in the other species in the genus Beta. The development of disease and pest resistant germplasm was a collaborative effort among USDA-ARS researchers, university researchers, sugar company agriculturists, and commercial plant breeders.

Technical Abstract: Genetic improvement in sugar beet is complicated by its breeding system. The sugar beet plant is biennial and flowering requires long-day photoperiod and vernalization at 10 degrees celsius or lower for 80 to 120 d. After vernalization, the rosette from the previous year produces a flower stalk (bolt) with indeterminate inflorescences. Flowers of sugar beet are perfect but incomplete with five stamens and one ovary usually with one embryo, and are mainly wind pollinated with some insect pollination possible. Both genetic and CMS types of male sterility occur, which makes hybrid cultivar production practical. In the wild type, two or more flowers occur as fused clusters to produce multigerm seedballs. Modern agriculture is dependent upon single seeded cultivars due to the need for precision sowing. This trait is known as monogermity, and is recessively inherited. Wild type beet is also highly allogamous, enforced by a complex self-incompatibility system that allows almost any two plants to inter-pollinate, while preventing self-pollination. A dominant gene for self-fertility, Sf, can circumvent this out-crossing behavior of beet, and is widely used by breeders to manage population improvement programs based upon selfed-progeny performance and to develop inbred lines for hybrids. Hybrids are composed of two or more parental components. Unlike the highly uniform, pure line cultivars of self-fertile crops such as lettuce, soybean, or wheat, considerable genetic variability may still occur within sugar beet hybrid cultivars. Because most of the known resistance to sugar beet diseases is quantitative (polygenic, i.e., controlled by more than one gene), more experimental efforts are needed to identify differences among plants compared to those required for qualitative resistance (monogenic). Sugar beet breeding in the United States has primarily concentrated on developing resistance to biotic and abiotic stresses. Because developing disease resistance cultivars became a top priority, the USDA began making collection trips to look for sources of resistance to diseases such as cercospora leaf spot and curly top resistance in wild sea beet, as well as in the other species in the genus Beta. The development of disease and pest resistant germplasm was a collaborative effort among USDA-ARS researchers, university researchers, sugar company agriculturists, and commercial plant breeders.