Performing Department
Agronomy
Non Technical Summary
Sweet corn plays an important role in Wisconsin's agricultural economy and rural life. It is the most important of the processing crops and contributes increased crop and economic diversity for Wisconsin farms. Processing sweet corn also provides numerous professional and unskilled jobs, and high tech engineering and other supporting industries in rural areas. Vegetable processing is an important industry in Wisconsin, which is third, following California and Minnesota, in the value of vegetables processed $43 million. Value added by processing increases the value of sweet corn to Wisconsin's economy to approximately $350 million. Both fresh and processed sweet corn are among the leading vegetables in the American diet. Sweet corn is one of the more popular vegetables among children and can add significant amounts of antioxidants and minerals to children's diets. Common rust (Puccinia sorghi) is the most serious disease of sweet corn in the Midwestern processing region. Damaging epidemics of common rust occur in most years causing both yield and quality losses in susceptible hybrids. Fungicides are available, but expense, problems with application, evolution of resistance by the pathogen, and public concern about food safety make the preferred strategy genetic resistance. Two types of genetic resistance exist, monogenic and adult plant resistance (APR). Monogenic confers resistance to specific races of the pathogen at all developmental stages and is characterized by a hypersensitive response to infection. Adult plant resistance is partial resistance that develops as the plant matures with the adult, upper leaves having increased resistance compared to juvenile, basal leaves. High levels of APR can reduce or eliminate the need for fungicides. It is generally assumed that APR is more durable than monogenic resistance. The Wisconsin sweet corn breeding program has developed and released inbreds and hybrids with both types of resistance. While vegetative phase change (VPC) plays a role in a number of economically important plant characteristics including rust resistance, the genetic control of VPC is not well understood. Objectives of this proposal include 1) identify quantitative trait loci that affect VPC in mutant and wild type maize providing breeders and developmental biologists with information on the genetics underlying this trait; 2) screen the maize germplasm core collection for VPC and APR and to introgress novel VPC phenotypes and more effective APR into adapted temperate sweet corn germplasm. Likely results and dissemination of information: New inbreds, hybrids, and genetic stocks resistant to rust and requiring less pesticide will be developed and offered to seed companies and ultimately farmers and consumers. Some new inbreds will be of commercial quality and could be used directly in commercial hybrids; others will be sources of APR or VPC to be used in other public and private breeding programs and geneticists. This program should also result in the publication of scholarly papers addressing methods and germplasm used in the identification and introgression of APR and VPC.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Cooperate and participate as a key element in the NPGS, a coordinated national acquisition and management program of plant germplasm valued for agricultural, horticultural, environmental, medicinal and industrial uses in the NCR and throughout the U.S.
Conserve seed and/or vegetative stock of more than 51,500 accessions of more than 1660 plant species.
Within the NCR, throughout the U.S., and internationally, encourage the use of a broad diversity of germplasm to reduce crop genetic vulnerability. Provide viable plant genetic resources, information and expertise that foster the development of new crops and new uses for existing crops, and cultivar improvement of established crops, thus contributing to a sustainable, biobased economy.
Contribute to understanding of plant-environment interactions, including risk assessment and communication of characteristics that differentiate a species' ability to adapt and whether it can serve as an economically viable crop or potentially become invasive in specific environments.
Educate students, scientists and the general public regarding plant germplasm issues.
Conduct research, and develop an institutional infrastructure needed to attain the preceding objectives efficiently and effectively, including advancements in software applications development to improve functionality and efficiency.
Project Methods
Germplasm: We will begin a systematic review of the maize collection focusing on ecogeographic regions where common rust is endemic and then expanding into unusual or relatively divergent races of maize. We will evaluate1000 accessions per year for vegetative phase change (VPC) and adult plant resistance (APR) to common rust (Puccinia sorghi). If we identify unusual VPC phenotypes, we will backcross these phenotypes into a few common inbreds in preparation for genetic and functional analysis. When we identify accessions with high levels of APR, we will begin to introgress that resistance into commercial quality temperate sweet corn germplasm. Evaluation of rust resistance: One row plots will be inoculated with P. sorghi by injecting 5 ml of a 106 uredospore ml-1 suspension (0.05 g of uredospores in 4 L of deionized H2O with five drops of Tween 20 added to prevent clumping) into the whorl of each plant. To avoid rapid evaporation of the inoculum suspension and to aid in uredospore germination, inoculations will be made at dusk. The level of resistance will be based on a visual estimate of the percent leaf area infected on five plants. The data will be analyzed on a plot mean basis. We will evaluate resistance at anthesis and the sweet corn harvest stage (approximately 20 days after pollination). Introgression: APR sources will be crossed to high quality sh2 inbreds and hybrids. These crosses will be crossed to high quality sugary enhancer hybrids. Thus the breeding populations will be 75% high quality and 25% tropical. We will begin screening progeny ear-rows of these breeding populations, selecting for APR to common rust and quality factors important to sweet corn. Each year, we will start selecting in 15-25 new breeding populations, sampling 50 progeny ear-rows. We will continue with a pedigree breeding program in the following seasons always selecting for APR and sweet corn quality factors. On average, the selection intensity is approximately 50% per generation. After the fifth generation of selfing, we test cross the lines and evaluate their performance in hybrid combination. Mo17Cg1 and B73Cg1 have been crossed to 206 IBM lines. The Cg1 crosses will be grown and phenotyped for their overall degree of Cg1 expression, APR, and other related traits over at least two summers. Phenotypic data on VPC and APR will be collected at developmental stage R2 on an individual plant basis from 12 plants in each row. A whole plant rating will be assigned to each plant, where a score of one is a completely normal phenotype while a score of five is a completely Cg1 phenotype. A tassel rating will be given to each plant where a score of one is a completely normal tassel and a score of three is a completely Cg1 tassel. The presence of ears, number of tillers, maximum width of the ear leaf, and plant height at the highest node will be recorded. The number of leaves from the last leaf with juvenile wax to the top of the plant will be counted, and the presence or absence of wax strips on the leaves will be determined. QTL analysis will be conducted with QTL Cartographer.