DURABLE RESISTANCE TO COMMON RUST IN SWEET CORN, GENETICS AND BREEDING OF VEGETATIVE PHASE CHANGE AND ADULT PLANT RESISTANCE

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0205741
• Project No.: WIS01020
• Project Start Date: Oct 1, 2005
• Project End Date: Sep 30, 2008

Project Director
Tracy, W.

Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218

Performing Department
AGRONOMY

Non Technical Summary
Common rust is a major pathogen of sweet corn. Rust reduces yield and often requires the use of expensive fungicides for its control. Two types of genetic resistance exist, monogenic resistance, which can rapidly lose its effectiveness and adult plant resistance (APR), which is much more durable. However APR is more difficult for breeders to work with and new sources must be identified. The purposes of this experiment are to understand the mechanism and genetic control of APR in commercial sweet corn hybrids, to screen tropical germplasm for improved APR to common rust and to develop commercial sweet corn with good APR.

Animal Health Component

(N/A)

Research Effort Categories

Basic

35%

Applied

45%

Developmental

20%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
201	1480	1080	30%
202	1480	1080	40%
212	1480	1080	30%

Knowledge Area
202 - Plant Genetic Resources; 212 - Pathogens and Nematodes Affecting Plants; 201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
1480 - Sweetcorn;

Field Of Science
1080 - Genetics;

Keywords

zea mays

maize

corn

puccnia sorghi

development

resistance

vegetative phase change

Goals / Objectives
Objective 1: Determine if there is relationship between vegetative phase change (VPC) and adult plant resistance (APR) in commercial sweet corn hybrids. Objective 2: Map QTL affecting VPC and APR in a population of S2 sweet corn lines. Objective 3: Screen tropical germplasm for improved APR to common rust and introgress APR genes into commercially viable temperate sweet corn.

Project Methods
We will select 20 hybrids with a range of adult plant resistance (APR). We will identify eight hybrids with strong APR, eight with weak APR and four with intermediate levels. The juvenile-vegetative phase marker, epicuticular (juvenile) wax gives the leaf a dull, bluish-gray appearance, while cuticular (adult) wax has a glossy-green appearance. From the base of the culm of the plant upward, the first few leaves of maize plants are completely covered in juvenile wax. Juvenile wax becomes progressively confined to smaller regions at the tip of the leaf at later stages of shoot development until it is completely absent. Evaluation for last leaf with juvenile wax will be conducted when the last branch of the tassel is completely visible. Last leaf with juvenile wax will be evaluated for each of five plants in each plot by counting upward or downward from the eighth leaf marked as the point of reference to the last leaf with visible juvenile wax on its adaxial surface. Other vegetative phase change (VPC) and agronomic traits will be evaluated. The center two rows will be inoculated with P. sorghi into the whorl of each plant. The level of resistance will be based on a visual estimate of the percent leaf area infected on the same plants evaluated for VPC. We will also rate the ear leaf and the leaf two nodes below the ear leaf. We will also give the plot an overall rating based on the general appearance of plants in the two center rows. The data will be analyzed on a plot mean basis. QTL mapping of VPC and APR in the same populations in the same environments will provide us with additional information on the genetic relationship of these two traits. We have obtained 133 S2 families derived from a cross between a rust susceptible line and rust resistant line. Using SSR markers we genotyped these families. We will grow these families in at least two environments with a minimum of two replications per environment. Evaluation of the families rust reaction and rate of VPC will be recorded as described above. We will use QTL cartographer to map QTL affecting VPC and APR. We have collected germplasm from regions of the world with the greatest pressure and diversity of common rust and therefore diverse and high levels of APR. These materials are unadapted to temperate regions and need to be crossed with temperate sweet corn. Sweet corn sources to be crossed with the tropical materials will include high quality sugary enhancer and shrunken2 (sh2) hybrids and inbreds. These crosses will be crossed to high quality sugary enhancer hybrids. We will begin screening progeny ear-rows of these breeding populations, selecting for APR to common rust and quality factors important to sweet corn. We will continue with a pedigree breeding program in the following seasons always selecting for APR and sweet corn quality factors. After the fifth generation of selfing we test cross the lines and evaluate their performance in hybrid combination.

Progress 10/01/05 to 09/30/08

Outputs
OUTPUTS: We gathered, analyzed, and published data on the relationship between vegetative phase change and resistance to common rust (Puccinia sorghi). Data from these studies were presented at the Crop Science Society of America annual meeting in Houston and the Maize Genetics Meeting in Washington DC PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Sweet corn breeders sweet corn growers PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Vegetative phase change, or the transition from juvenile vegetative to adult vegetative tissues, is essential to the lifecycle of higher plants. In maize, juvenile and adult vegetative tissues have distinctly different traits that may confer differing amounts of resistance to disease and insect infestations. Vegetative phase change has been linked to resistance to insects and common rust (Puccinia sorghi). Seven cycles of divergent recurrent selection for early and late phase change were evaluated to determine effects of selection on phase change, insect resistance, and agronomic traits. Last leaf with juvenile wax, a trait indicative of the timing of phase change, was the selected trait. Divergent recurrent selection was effective in creating populations that underwent vegetative phase change at distinctly different developmental stages. Last leaf with juvenile wax moved from leaf 8.70 in the original population to leaf 14.48 in the late direction and 6.04 in the early direction. First leaf with adult wax moved from leaf 6.36 in the original population to leaf 8.15 in the late direction and 5.28 in the early direction. Several agronomic traits were also significantly altered by selection including plant and ear height, leaf number, kernel row count, and days to silking. C7Late plant averaged four more leaves, were taller and later flowering than C7Early plants. European corn borer feeding damage on the second leaf above the ear was significantly greater in the late phase change direction, and significantly correlated with last leaf with juvenile wax. Most ear traits and European corn borer stalk damage resistance were not altered in a consistent way by selection.

Publications

• Riedeman, ES, M.A. Chandler, and W.F. Tracy. 2008. Divergent recurrent selection for vegetative phase change and effects on agronomic traits and corn borer resistance. Crop Sci. 48: 1723-1731.
• Sassenrath, G.F., P. Heilman, E. Luschei, G.L. Bennett, G. Fitzgerald, P. Klesius, W. Tracy, J.R. Williford, and P.V. Zimba. 2008. Technology, complexity and change in agricultural production systems. Renewable Agriculture and Food Systems: 23:1-11.
• Chandler, M.A. 2008. Endogenous variation revealed by selection in sugary1 maize (Zea mays L.). Ph.D. Dissertation. Madison, WI

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: 1. Vegetative Development: Eric Riedeman is continuing our work on the genetics of vegetative development. Based on recent work from Sarah Hake's lab at Albany CA we now know that microRNAs play a significant role in regulating vegetative phase change. Eric is trying to determine whether microRNAs or the targets of microRNAs have changed as a result of the divergent recurrent selection for timing of vegetative phase change. 2. Genetics of endosperm modification: We are studying the genetics and biochemistry of the smooth versus wrinkled phenotype that segregates as a single gene in homozygous su1 background. This material was derived from a cross between a su1 inbred and a sugary enhancer hybrid. The wrinkled phenotype is significantly sweeter and may be the sugary enhancer1 locus. We have mapped this gene to the long arm of chromosome 2. We are attempting to fine map and sequence the gene. Mike Chandler is using the same endosperm microarray to study the genes involved in our selection program for endosperm appearance. We believe that two factors code for the recessive pseudostarchy appearance (figure), and one of them is on chromosome. 3. Genetics of traits for weed competitiveness: Jared Zyskowski is studying the genetics of weed competitiveness and yield loss using a seven line diallel and sorghum as a model weed. He report on his first year data at the ISCDA meeting. 4. Effects of recurrent selection for germination under cold conditions: We have done recurrent selection for cold germination on three different populations that are 50% Mexican high altitude germplasm. After 4 or 5 cycles of selection we have improved various parameters related to germination. PARTICIPANTS: W.F. Tracy P Flannery E. Reidemann (training) J. Zyskowski(training) L. Viesselmann(training) M. Chandler(training) J. Rutkoski(training) T. van Ert (training) TARGET AUDIENCES: Sweet corn growers and processors

Impacts
Examining the relationship between plant development and disease and insect resistance will increase our understanding of certain forms of quantitative or adult plant resistance and may lead to improved cultivars or management strategies. The work with new endosperm combinations may lead to improved quality sweet corn or new industrial uses of corn. The new sources of disease resistance may be useful to commercial breeders in diversifying their germplasm and increasing the stability of resistance.

Publications

• Basso, C.F., M.M. Hurkman, E.S. Riedeman, and W.F. Tracy. 2008. Divergent selection for vegetative phase change in maize and indirect effects on response to Puccinia sorghi. Accepted by Crop Science
• Riedeman, E.S., M.A. Chandler, and W.F. Tracy. 2008. Seven cycles of divergent recurrent selection for vegetative phase change and indirect effects on resistance to common rust (Puccinia sorghi) and European corn borer (Ostrinia nubilalis). Accepted by Crop Science.
• Chandler, M. A. and W. F. Tracy. 2007. Identification of Genomic Regions Affecting Vegetative Phase Change in a Sweet Corn (Zea mays L.) Population. Maydica (accepted)
• Cohen, J.I. and W.F. Tracy. 2007. The world surrounding Walton C. Galinat's research: Personalities, students, history, and disputes. A tribute. Maydica 52:3-11.
• Lee, E.A. and W.F. Tracy. 2008. Modern Maize Breeding, In The Maize Handbook Edited by Sarah Hake and Jeff Bennetzen. Springer

Progress 01/01/06 to 12/31/06

Outputs
Vegetative development in corn can be divided into juvenile and adult phases. Vegetative phase change occurs at the nodes at which juvenile traits are replaced by adult traits. The timing of phase change is highly heritable and in some populations has been associated with resistance to common rust. We have used a number of different approaches to study vegetative phase change. In 2004/5 we did a QTL study on sweet corn population consisting of 130 F3 families we found one region associated with phase change. This region was closely linked to gl15, a gene known to be involved in phase change in the epidermis. In 2005 we analyzed changes associated with 7 cycles of divergent selection for last leaf with juvenile wax (LLJW). We found that this trait is strongly affected by selection. Likewise first leaf with adult wax (FLAW) responded to selection for LLJW. Interestingly the size of the transition zone, the area between fully juvenile leaves and fully adult leaves also changed, so that cycle7 in the late directions has nearly 7 transition leaves while cycle 7 in the early direction has only one transition leaf. LLJW was correlated with leaf area below the ear damaged by rust (r = 0.81) and corn borer damage (r = -0.74).

Impacts
Examining the relationship between plant development and disease and insect resistance will increase our understanding of certain forms of quantitative or adult plant resistance and may lead to improved cultivars or management strategies and reduction of pesticide usage.

Publications

• Abedon, B.G., R.D. Hatfield, and W.F. Tracy. 2006. Cell wall composition in juvenile and adult leaves of maize (Zea mays L.) Journal of Agricultural Food Chemistry 54:3896-3900.