Location: Crop Germplasm Research2016 Annual Report
This project aims to utilize recent advances in high-throughput genotyping, bioinformatics, and molecular biology to acquire knowledge of sorghum genes and germplasm, and utilize this information to enhance the rate of genetic gain for complex traits such as grain yield through the development of new adapted breeding material. Sorghum breeding stocks, landraces, and elite tropical sorghums will be phenotyped and genotyped with an amalgamation of approaches, and knowledge of the genetic basis for key traits that impact productivity will be acquired. New sorghum genetic stocks will be developed, characterized, and released with new genes and traits not presently available to sorghum breeders. Specifically, during the next five years the project will focus on the following objectives. Objective 1: Develop and use markers in molecular marker-assisted approaches to introgress day-neutral flowering response into elite tropical sorghums and thereby create new sources of temperate-zone adapted sorghum germplasm. Objective 2: Identify genes and alleles in sorghum breeding stocks for pollen fertility restoration, and exploit this information to accelerate development of new parental lines. Subobjective 2.A: Identify an exhaustive set of fertility restoration (Rf) and partial fertility (Pf) genes in cultivated sorghum using genetic linkage analysis, association mapping methodology, and bioinformatics. Subobjective 2.B: Elucidate the genetic and molecular basis of cytoplasmic male-sterility (CMS) in sorghum A1 cytoplasm by sequencing mitochondrial genes and transcripts in CMS- and normal cytoplasms, and examine the effect of Rf genes and unfavorable temperatures on the expression of CMS-associated genes.
The long-term goal of this project is to utilize recent advances in high-throughput genotyping, bioinformatics, and molecular biology to acquire knowledge of sorghum genes and germplasm, and utilize this information to enhance the rate of genetic gain for complex traits such as grain yield through the development of new adapted breeding material. The challenge facing scientists is how to exploit the vast amount of knowledge and tools in molecular biology, genomics, and bioinformatics to accelerate the rate of genetic gain in applied breeding programs. We have targeted several agronomically critical objectives that include introgressing day-neutral flowering response into elite tropical sorghums to create new sources of temperate-zone adapted sorghum germplasm, and identifying genes and alleles in sorghum breeding stocks for pollen fertility restoration, and exploit this information to accelerate development of new parental lines. In ongoing collaboration with scientists at Texas A&M University and private sector plant breeders at MMR Genetic LLC, a classical breeding approach augmented with robust genomic and bioinformatics tools will be used to identify elite tropical sorghums and convert these lines to temperate adaptation. The approach developed under Objective 1 will introduce new germplasm and favorable genes for complex traits, including grain yield, into sorghum breeding programs in the USA and worldwide. In ongoing collaborations with our collaborators in Queensland and Perth, we will use genetic linkage analysis, association mapping methodology, and bioinformatics under Objective 2.A to identify an exhaustive set of fertility restoration (Rf) and partial fertility (Pf) genes. Under Objective 2.B, we will sequence mitochondrial genes and transcripts in CMS- and normal cytoplasms, and examine the effect of Rf genes and unfavorable temperatures on the expression of CMS-associated genes. Through the combined approaches outlined under Objectives 2A. and 2B. we will elucidate the genetic and molecular basis of cytoplasmic male-sterility (CMS) in sorghum A1 cytoplasm. The overall approach of objective 2 will permit breeders to exploit this information to accelerate development of new parental lines for hybrid production fields. Objectives 1 and 2 are complementary, and the knowledge gained under one objective will facilitate the success in all.
Work under this project during FY 2016, in collaboration with university scientists and a retired seed company breeder, resulted in significant progress in sorghum germplasm breeding through the continued utilization of classical breeding technologies to develop improved sorghum inbred lines for effective utilization by breeders in all production areas of the world (Objective 1). The germplasm selected and advanced through self-pollination in this program will be critical for the desirability and usefulness of previously unusable photoperiod-sensitive sorghum germplasm in development of higher-producing sorghum hybrids for temperate climates. Work also continued in collaboration with scientists at the University of Queensland, University of Western Australia, and bioinformaticians at Lucigen Inc. to understand the expression of all sorghum mitochondrial genes including those mitochondrial genes controlling cytoplasmic-male sterility in sorghum; the work resulted in the identification of three candidate mitochondrial genes with one gene likely central to cytoplasmic male sterility (Subobjective 2.B). Progress was made, cooperatively with Australian collaborators, toward the identification of fertility restoration (Rf) and partial fertility restoration (Pf) genes (Subobjective 2.A). The work will provide a better understanding of cellular events controlling the restoration of pollen fertility in cytoplasmic male sterility lines, a trait that is critical to advancing commercial hybrid seed production in sorghum.
1. Tropical sorghums converted to short stature, early flowering temperate-zone adapted germplasm. Sorghum is an important grain crop in many areas of the U.S. and other temperate regions worldwide. However, much of the potentially valuable sorghum germplasm is tropical in origin and does not successfully flower and produce seed in temperate environments, making these sources of genetic variability unavailable to many of the world's sorghum producing areas. ARS researchers at College Station, Texas, working with a retired private seed company scientist, used molecular tools in conjunction with classical plant breeding techniques to convert ARS tropical sorghums to short stature, early flowering versions with the objective of making new elite inbreds available to the sorghum industry. Three hundred seventy-five plots of converted germplasm were screened visually by breeders and desirable individuals self-pollinated for the development of higher-producing sorghum inbreds for farmers in the U.S. and worldwide.
2. Genetic knowledge of cytoplasmic male-sterility/nuclear fertility restoration systems enables effective production of hybrid sorghum. In sorghum, the combination of moderately complex genetic control and environmental variation in cytoplasmic male (pollen) sterility and pollen fertility restoration makes the development of new male and female lines both laborious and costly. ARS researchers at College Station, Texas, working with bioinformaticians at Lucigen Inc., and with Texas A&M University scientists, identified novel mitochondrial genes and characterized their expression with the objective of identifying the sequences that control cytoplasmic-male sterility in sorghum. Detailed knowledge of cytoplasmic male-sterility/nuclear fertility restoration systems in sorghum provides insight into a process critical to hybrid seed production and will facilitate the development of molecular diagnostic tools to rapidly assess breeding material for use in hybrid breeding programs.
Klein, R.R., Miller, F.R., Bean, S., Klein, P.E. 2016. Registration of 40 converted germplasm sources from the reinstated sorghum conversion program. Journal of Plant Registrations. 45:57-61.