Germplasm Enhancement of Maize

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Javier Betrán
L.L. Darrah
John Dudley
Jim Hawk
Bruce Hibbard
R. Lambert
Gary Munkvold
Richard Pratt
Paul Scott
Jerry Sell
Margaret Smith
N. Widstrom
Dennis West

GEM - 1998 Public Cooperator's Report


Evaluation of GEM Exotic Breeding Crosses in Texas

Javier Betrán, Frank Fojt III, Dennis Pietsch, Leon Synatschk, Wenwei Xu, Tom Archer

Corn breeding program, Texas A&M University

The Texas corn breeding program became a cooperator of the U.S. Germplasm Enhancement of Maize (GEM) project. During the 1998 season we have evaluated GEM exotic breeding crosses provided by Dr. Linda Pollak (USDA-ISU). Several trials were conducted across different locations in Texas (from South to North: Weslaco, Corpus Christi, College Station, Lubbock and Springlake). Different traits (yield, maturity, moisture, test weight, lodging, ear and plant height, cob and grain color, texture, etc.) were recorded according with the location. Two local checks were included in these evaluations. The season was difficult because the hot and dry weather during the summer. Those conditions affected our trial evaluations. Irrigated trials at Weslaco and Springlake were fairly good. Corpus Christi (dryland conditions) was affected by drought stress, charcoal rot and aflatoxin. This trial was not harvested and yield was subjectively estimated (1-9 scale). College Station had a high incidence of charcoal rot and stalk lodging. At Lubbock-New Deal we had evaluations in collaboration with Dr. Wenwei Xu and Dr. Tom Archer (Texas A&M Agricultural Research and Extension Center) under several water regimes (full irrigated, pre-tassel stress and post-tassel stress) controlled by using drip irrigation. Due to a late harvest the data for this location is not available yet. Average yield across locations was 110.2 bu/a with89.1 bu/a at College Station, 108.9 bu/a at Weslaco and 132.6 bu/a at Springlake. The local check A633 x Tx714 was the best hybrid. CHIS775:S19, CUBA164:S20, and AR01150:S01 performance suggest that they could be potential new sources of exotic germplasm for Texas.

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Topcrossing of 120 S1 Lines of UR13085:S1912

L. L. Darrah

ARS-USDA at the University of Missouri

Reduced germplasm diversity will eventually decrease rates of yield increase through breeding. Development of improved germplasm with non-Corn Belt components will allow enhancement of the commercial germplasm base through specific value-added traits. Results from evaluating 10 random S1 progeny from 13 GEM populations showed that UR13085 had the best combination of good rind penetrometer resistance and vertical root pulling resistance.UR13085 is of the Cateto Sulino race, characterized very broadly as "tropical flint" or "Caribbean flint" and having orange, hard, flinty kernels. We topcrossed 120 S1 progenies to two testers:Mo17 Synthetic(H14)C4 and CarPop(E5)C5.The former is a yellow synthetic made up from various commercial versions of Mo17, and the latter is a population originating with Everett Gerrish, formerly of Cargill Hybrid Seeds, which has a large component of tropical dent Tuxpeno. Results from evaluating 10 random S1 progeny from 13 GEM populations showed that UR13085 had the best combination of good rind penetrometer resistance andvertical root pulling resistance. One-hundred-twenty S1 progenies have been topcrossed to two testers for evaluation in 1999.Predicted impact would be to expand the usable germplasm base with materials having enhanced root and stalk strength.Next year we expect to evaluate the topcrosses of UR13085:S1912S1 progenies to Mo17 Synthetic(H14)C4 and CarPop(E5)C5 in three-replication yield test plots at three locations in Missouri, and advance 1997 selected lines from ARO1150:N04 from S2 to S3 prior to topcrossing to testers.

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Evaluation of tropical accessions as sources of genes to improve a corn belt hybrid.


University of Illinois

To continue to increase yields at a rate that will allow feeding the world in the next 25 years requires the identification of sources of germplasm which have alleles not present in the breeding pools currently being used. Exotic populations, particularly those of tropical origin, may be a source of such alleles. Use of exotic germplasm for improvement of current elite hybrids requires, in many cases, crossing the exotic source to an adapted line before the germplasm will have sufficient adaptation to be grown and evaluated in the corn belt. Because there are hundreds of exotic populations, some method of screening these populations for their potential to increase yield, disease resistance, and other agronomic traits is needed. Work in our laboratory over several years has demonstrated the effectiveness of a procedure for identifying favorable dominant alleles not present in an elite hybrid. The purpose of this research was to apply this method to exotic populations. In particular, we were interested in the effect of different elite inbreds, in population x inbred crosses, on the ability to rank populations for the presence of favorable alleles. Thus we crossed 41 populations obtained from the GEM project with maize inbreds LH185 and FR1064 and applied our method of identifying favorable alleles to this material. Included in the exotic populations were 7 populations which had been crossed to both B73 and Mo17.This allowed a direct comparison of the effect of inbreds on the method of identifying favorable alleles. Results were obtained for grain yield, grain moisture, lodging, penetrometer reading (a measure of stalk strength), and resistance to 5 leaf diseases (Southern corn leaf blight, Northern corn leaf blight, Northern corn leaf spot, Gray leaf spot, and common rust).

As the huge populations in emerging countries raise their standard of living and change their diets to include more eggs and meat products and as the world population continues to increase, the world demand for corn and other feed grains will escalate at an increasing rate. Estimates indicate that the rate of increase in corn yields which has been maintained over the last 20 years will need tobe increased by 50% to meet this demand. Thus it is critical to develop methods of identifying and utilizing germplasm which has alleles with the potential of increasing the rate of corn yield increase.

The most significant accomplishment this past year was the identification of a number of populations which should serve as sources of genes for resistance of all five of the leaf diseases. The past year represented the second year of testing of the materials included in this project. Major results including the following:

a. None of the populations included in the tests demonstrate significant numbers of dominant favorable alleles for improving yield of the hybrid LH185 x FR1064.This was true even when the populations had been crossed to B73 or Mo17 and thus were half adapted germplasm. Likewise, none of the populations had significant numbers of favorable alleles for penetrometer resistance.

b. In contrast to the yield and penetrometer data, many of the populations had significant numbers of favorable alleles for disease resistance. When estimates of favorable alleles for a particular disease were stratified and the top group of populations identified using a range test, 7 of the populations had favorable alleles in the top group for all five diseases and 17 populations were in the top group for at least 3 diseases. Correlations between estimates of favorable alleles for different diseases were generally highly significant (except for rust and Northern corn leaf spot). Thus some of these populations may be sources of tolerance to several diseases.

c. All the populations studied had favorable dominant alleles for gray leaf spot resistance and for rust resistance. All the populations crossed to B73 or Mo17 had favorable alleles for Northern corn leaf blight not present in LH185 x FR1064.

d. The effect of B73 and Mo17 on performance of the populations to which they were crossed was apparent for Northern corn leaf blight, Southern corn leaf blight, and Northern corn leaf spot. For all three diseases, the same populations crossed to Mo17 had lower disease ratings than when crossed to B73. In addition, the crosses to LH185 had lower ratings than crosses to FR1064.This is in agreement with expectation based on known reactions of the inbreds. This suggests that comparisons of tropical populations crossed to different adapted inbreds will be confounded and may be measuring the effect of the adapted inbred more than the effect of the tropical population.

e. In general, the temperate populations studied had lower numbers of favorable alleles than the tropical populations crossed to B73 or Mo17.The one exception was a high value of Northern corn leaf spot resistance for ARZM16053.The 3 populations showing the most promise for each disease were:

Gray leaf spot: Brazil 051501xMo17, B830xMo17, and B830xB73.

Northern corn leaf blight: DK88xB73, B830xMo17, and Cuba 110xMo17.

Southern corn leaf blight: Puerto Rico GP3xMo17, Dom. Rep. 150xMo17, and Cuba 110xMo17.

Northern corn leaf spot: ARZM 16053, Cuba 164xB73, Cuba 110xMo17.

Rust: DK888xMo17, B830xMo17, B844xB73.

The field work for this project is finished. During the next year, we will finish summarizing the data and write it up for publication. The utilization of any of these populations as sources of disease resistance genes will be done by commercial corn breeders. The information is being made available to those breeders through publications and presentations at scientific meetings. The constraints of using the material identified as having genes for disease resistance may be the lack of favorable alleles for yield and stalk quality in these populations.


Kraja, A. and J.W. Dudley. 1998. Corn elite germplasm enhancement results: Use of tropical corn resources. Agron. Abstracts. P. 80. 

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Evaluation of GEM Breeding Crosses for Yield and Agronomic Performance under Delaware Irrigated and Dryland Conditions

James A. Hawk and T. Weldekidan

Department of Plant and Soil Sciences, University of Delaware

We evaluated 191 S2 lines from the DKXL212:N11a population testcrossed to LH198 at two locations (two reps/location) in Delaware, one dryland and one irrigated. The dryland location at Smyrna, DE experienced severe drought during the grain-filling period resulting in average yield of 100 bu/A. Yields ranged from 61 to 128 bu/A and a yield C.V. of 12.8. There were several hybrids with grain yields and maturities comparable to the drought tolerant hybrid Pioneer brand 3525.The irrigated location had severe stalk lodging due to European corn borer resulting in an average of 126 bu/A and a range of 71 to 189 bu/A with a yield C.V. of 20.We did not observe any hybrids with adequate resistance to European corn borer. However, several hybrids out-yielded the best commercial checks. These conclusions are preliminary and based on two locations and one year only. These testcrosses of the DKXL212:N11a S2 lines were also evaluated at additional locations in the Corn Belt with other GEM cooperators. The combined analysis should provide additional information on which lines should be advanced. The S2 lines were also evaluated per se and advanced to S3. 

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Evaluation of selected GEM accessions and crosses for European corn borer and western corn rootworm resistance

Bruce Hibbard

USDA-ARS at University of Missouri

The occurrence of pesticides in ground and surface water has become an increasing problem and more acres of crop land are treated with insecticide for control of corn rootworms than for any other insect pest in the United States. No practical alternatives to insecticide for corn rootworm control in continuous corn currently exist. A major long-term goal of our project is to develop a stable alternative method of control (host-plant resistance) for one of the pests most targeted by insecticides (corn rootworms) and make resistant germplasm available for incorporation into elite corn lines. Exotic germplasm sources such as GEM materials are the primary source of resistant materials since no resistance to corn rootworm has been found in U.S. germplasm.

Corn rootworms are among the most serious insect pests in the United States. A 1986 estimate of the cost of corn rootworms on the U.S. economy was $1 billion annually in terms of crop losses and insecticide costs and new developments have made corn rootworms an even bigger problem. Despite their major pest status, no practical alternatives to insecticides currently exist for corn rootworm control in continuous corn and new developments have eliminated even crop rotation as a viable alternative to insecticides in many parts of Illinois, Indiana, and Ohio. Development of native and/or transgenic resistance to corn rootworms may help reduce dependence on insecticides and provide alternatives to carbamates and organophosphates, which may be lost as an alternative in the future. GEM materials represent a valuable source of diverse, exotic germplasm.

We are looking to provide cost-effective strategies to reduce water contamination from agricultural lands grown to corn. Since more acres are treated with insecticide for corn rootworms than for any other insect pest, development of alternates to insecticide for this important pest complex would help reduce contamination of ground and surface water from this major source. Our research is directed at providing an alternative (host-plant resistance) to these insecticides. Success in our project would help protect corn plants from attach of corn rootworm larvae.

All GEM materials remaining in our program were evaluated very closely to firmly document resistance to corn rootworm and/or European corn borer larvae. Materials with some resistance exist, but most materials were abandoned after this season’s results. Adaptation may play a role. Those materials from 50% and 25% exotic crosses had the best levels of resistance. I suggest that all exotic crosses be screened, since many of the original materials were not adapted.

All original GEM accessions have been evaluated for resistance to western corn rootworm and European corn borer. Selected accessions were reevaluated and entered into our breeding program for resistance to these important pests. In addition, available exotic crosses with 25% and/or 50% GEM were also evaluated if they were related to the original selected accessions. Some resistance to European corn borer and some tolerance to western corn rootworm larval feeding has been identified.

We previously have evaluated the original GEM accessions for resistance to corn rootworm and European corn borer, but many of these lines were not adapted to our environment. Since evaluation of germplasm in unadapted environments may mask useful traits, we propose to evaluate all available 50% exotic GEM breeding crosses for western corn rootworm and European corn borer resistance. All 117 lines will be evaluated with three replications for western corn rootworm resistance and with 1 replication each for 1st and 2nd generation European corn borer resistance.

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Development of corn lines from Gem germplasm with improved multiple disease resistance, starch content, and grain yield

Robert Lambert

University of Illinois

The loss from major corn diseases by U.S. corn crop is significant each year. Few corn breeders are selecting for genetic resistance to multiple leaf and stalk rot diseases simultaneously. The use of genetic resistance to major corn diseases is the economical and environmental friendly way of controlling these pests. Present day corn hybrids are usually susceptible to “newer” diseases such as anthracnose leaf and stalk rot plus gray leaf spot, along with other “older” diseases present in the environment. The increased use of reduced tillage has lead to increase in certain leaf and stalk rot diseases of corn. In addition, increasing disease resistance in some corn genotypes has resulted in a yield reduction and later maturity.

To resolve this problem we are evaluating two GEM populations and selecting for improved multiple leaf and stalk rot(s) resistance plus high starch levels in the grain. Plants are inoculated with spores of the major leaf and stalk rot diseases found on corn and evaluated for resistance.

The major problem the limits corn production in the U.S. is the incidence of plant pests. In any given year some corn producers have production problems with stalk lodging or leaf diseases or kernel rots that can reduce yields. The use of genetic resistance to control corn diseases has been very effective for certain leaf blights and stalk rots.

There has been no major effort by U.S. corn breeders to simultaneously incorporate multiple disease resistance into corn hybrids and also improve yields. This has been done as a “stepwise” procedure. With increased use of reduced tillage, seedling blight, leaf blights and stalk rots will be major problems in corn production because of the plant residue on the soil surface. To be prepared for the problem multiple genetic disease resistance is needed in future corn hybrids plus increased grain yields. The development of multiple disease resistance high yielding corn hybrids will allow corn breeders to continue the yield enhancement of corn hybrids which has been about 1.4% per year for past 60 years.

We have isolated S3 genotypes from GEM population BR5101:N11A12-15 with multiple leaf diseases ratings of only 5 to 20% of the total leaf area infected (mid-September) and only one internode partially infected with stalk rot (less than 15%).Also 23 families had starch values above 70% (range 70-72.8%) with normal corn usually in the range of 66 to 68% starch. In addition, 1500 S0 plants in GEM population DREP150: N2012 were evaluated for multiple disease resistance. Ears from 127 plants with above average disease resistance were selected and assayed for starch content. The mean starch level was 68.1% with 35 (27%) ears having values above 69% (range 69 to 73.4%).

Over the past two years S3 families in the GEM population BR5101: N11A12-15 have been isolated with above average multiple disease resistance and starch values. These families have been crossed to an inbred tester to evaluate performance in 1999.Inbred lines should be produced from these material with excellent multiple disease resistance, high grain yields at high plant densities and above average starch levels in the grain. Hybrids using these lines should produce a desirable product for the wet milling industry. The same procedures, started in 1998, will be used to develop inbreds from the GEM population DREP150: N2012.

During the next year the following accomplishments are expected:

1.Grow 100 testcrosses of BR5101: N11A12-15 to an inbred tester at 4 locations and high plant densities (32,000 ppa). In addition the S3 lines will be grown in the disease nursery with additional selection for multiple disease resistance and higher starch levels. Materials developed from this could be released to corn breeders for additional testing on hybrids.

2.S1 families (about 125 families and 3,000 plants) of the GEM population DREP150: N2012 will be grown in the disease nursery selected for multiple disease resistance and selected plants crossed to an inbred tester.

3.Also S2 seed will be evaluated for starch levels and the better testcross grown in 2000.

The improved inbreds from BR5101: N11A12-15 for multiple diseases and increased starch levels could be available to the seed industry by 2001 and lines from DREP150: N2012 available by 2003.The only constraints would be weather conditions (drought) which would reduce disease infestations and also grain yields.

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Fusarium ear rot resistance screening of GEM germplasm

Gary Munkvold

Dept. of Plant Pathology, Iowa State University

Seventy-nine entries from the GEM collection were screened for resistance to ear rot diseases caused by Fusarium moniliforme [FUS] and Fusarium graminearum [GIB]. Nine entries were temperate accessions, three were semi-tropical accessions, nine were temperate crosses (50%) with public lines (B73 or Mo17), 19 were temperate crosses (50% or 25%) with proprietary lines, nine were semi-tropical crosses (50% or 25%) with proprietary lines and 16 were tropical crosses (50% or 25%) with proprietary lines. Another 15 entries were S2 lines derived from a temperate: proprietary cross. Of these, 32 entries (accessions and temperate crosses) were also inoculated with Fusarium subglutinans [SUB]. Susceptible and resistant commercial hybrid or public inbred checks were included. The pathogens were inoculated in separate plots; F. graminearum [GIB] inoculations were performed by the silk-channel method, while F. moniliforme [FUS] and F. subglutinans [SUB] inoculations were performed with a pin-bar inoculator; husks were partially removed prior to [FUS] and [SUB] inoculation. Ten plants/row in 17-ft rows were inoculated. On days without precipitation for six weeks after inoculation, approximately 5 mm of overhead irrigation was applied to the plots to maintain humidity. Field conditions were poor and many ears did not develop. Tropical crosses did not pollinate well. As a result, most of the entries had less than 10 ears to rate. Disease was rated according to a 1-7 scale, in which 1= no symptoms and 7= >75% of the ear showing symptoms. [GIB] ratings ranged from 1.5 to 6.6. Temperate accessions [UR05017], [UR01089], [UR13085] and [CH04030] are the most consistent accessions showing partial resistance to [GIB], but their level of resistance does not appear to be exceptionally high. These accessions do not always pollinate well in our studies. In 1998, accessions [UR10001], [UR13061], [UR01089], [UR05017], [CH04030], and [UR13085] had mean ratings<= 3.0. Crosses with scores <3.0 were primarily tropical crosses, but their low scores may have been related to poor pollination. Generally, the S2 lines had poorer than average resistance. Overall, there was a poor correlation among results from 1996-98. [FUS] ratings ranged from 1.8 to 6.2. Accessions [CH04030] and [AR16021] had mean ratings of <3.0. Some entries that performed well in 1997 did not produce ears to rate in 1998. Scores for [SUB] were not significantly correlated to those for [FUS]. Fumonisin B1 concentrations for 1997 were significantly correlated with [FUS] scores in 1997 (R = 0.58, P<0.0001). 

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Introgression of Grain Quality Traits from GEM Germplasm into Corn Belt Maize

Richard C. Pratt

The Ohio State University

A total of 900 S1s from the population CHIS775:S1911b, and 441 S1s from the population FS8(A):S09, were entered in the nursery and 2 controlled self-pollinations were made in all progenies. Drought was experienced during July and August and post-flowering epiphytotics of gray leaf spot and rust foliar diseases were experienced. The CHIS775 progenies were late maturing and displayed susceptibility to the foliar pathogens and many progenies also displayed aphids in the tassels during flowering. The FS8(A) progenies displayed earlier maturity and better resistance to pests and pathogens. Stalk and root lodging were minimal in both populations. Selection across progenies was practiced in both populations during late October for resistance to foliar diseases and agronomic traits (standability, plant and ear height, ear size and low grain moisture). A total of 103 S1 progenies from FS8(A), and 90 from CHIS775, were selected based on the above criteria.

Post-harvest selection was practiced for ear fill, kernel characteristics, and absence of ear rot across and within progenies. One ear was selected to represent each of 100 progenies and the seed were packeted and shipped to Ames for inclusion in the winter topcross isolation nursery. Grain compositional analysis will be performed during the upcoming winter season. Samples of FS8(A) progenies selected in Iowa will also be tested in the OSU grain quality laboratory, and the OSU selections will also be tested in Ames.

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Evaluation of the zein content of GEM germplasm

Paul Scott

USDA-ARS at Iowa State University

Corn is a common ingredient in animal feed, but it is limited by the content and composition of protein in the seed. Most of the protein in the seed is in the form of zein, a family of many related proteins. Some members of this family are better suited to animal feed than others. The effects of these nutritionally good zeins can be masked by an abundance of nutritionally poor zeins. We have developed methods to determine the zein content of a seed. This method can be used as a breeding tool to develop varieties of corn with altered zein compositions which give improved protein content and composition to the seed.

80% of the corn produced in the US, about $16 billion worth, is used to make animal feed. The poor quality of corn protein requires livestock and poultry producers to add expensive supplements to feed. Corn with improved protein quality would require less supplementation, making animal feed cheaper to produce. The poor quality of corn protein also contributes to

the high levels of animal waste produced by animal feeding facilities. This waste is a major environmental problem in some areas. Feed based on corn with an improved protein composition would reduce this waste.

We have adapted a method based on HPLC that allows us to measure the levels of each member of the zein family. We have applied this method to determine the zein composition of standard inbred lines and in lines derived from a GEM cross that is known to have unusual variation in protein content. A wide variety of zein composition and content was observed.

In the course of this project we have developed two assays to measure the zein composition of corn. The first assay was developed last year and is based on ELISA technology that allows a high-throughput, low-resolution screening of large numbers of samples. We have used this method to identify varieties with unusual zein compositions. The second method, developed this

year, is a low-throughput, high-resolution HPLC method for determining the exact zein composition of a sample. Taken together, these methods provide a tool that will enable breeders to genetically manipulate zein compositions and to develop varieties with improved feed quality.

We will continue to gather data with the high-resolution zein assay correlate the results with those of the low-resolution assay. We will also attempt to characterize individual zeins by mass spectrometry in order to identify zeins containing nutritional differences.

The results of our zein analyses of GEM material are available on request to GEM cooperators.

Iowa State University Plant Breeding Seminar: Protein and Starch quality in Maize, November 20, 1997.

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Evaluation of two varieties of experimental corns as feed ingredients for broiler chickens

Jerry Sell

Iowa State University

Corn is the USA’s major crop. The USA is also the world leader in corn production, producing over 41% of the world’s production in 1989/90.Corn is extremely important to the U.S. economy due to the amount produced, its value to industry, and its export value. Through feeding livestock that is processed into meat and dairy products, corn affects everyone in American society. It has been estimated that 90% of domestic corn grain is used as food through the feeding of livestock.

Our long-term goal is to develop corn hybrids with improved feed value that will enhance both the genetic base and competitive value of U.S. corn products, and that will lead to increasing the competitive advantage of small livestock producers and the competitive value of U.S. livestock products. Another goal is to demonstrate the value of maize genetic resources for commercial breeding, thereby increasing interest in and work with genetic resources.

Traditionally corn has been treated as a commodity. In recent years, corn grain users and processors have become more interested in the quality characteristics of the grain and how this affects their business. Because much of exotic germplasm has undergone selection for many indigenous uses (feed, foods, beverages, etc.) by various cultures, it seems likely that new grain quality characteristics will be found in exotic rather than the narrow-based germplasm now used.

Very little data that would impact grain or feed quality has been collected on maize accessions, but that which has been collected suggests that significant variability for these traits is present in maize genetic resources. On the other hand, limited variability for feed quality is found in present-day hybrids and thus in elite breeding materials. 

This project will develop diverse genetic materials that can be used by the corn industry to develop hybrids suited to the feed industry.

Four corn genotypes of varying protein levels have been increased in preparation for feeding trials. The genotypes include a Corn Belt hybrid check, an Argentine by Corn Belt experimental line, a Caribbean by Corn Belt experimental line, and the hybrid between the two experimental lines. The nutritional value for broiler chickens of four corn genotypes of varying protein content will be determined. This research will be done in two experiments. In experiment 1, the metabolizable energy (ME) value of each of the four corn genotypes will be determined by using broiler chicks from 1 to 14 days of age. The information on ME value of the corns, together with information on the protein and amino acid concentrations of the corns, will be used to formulate nutritionally balanced diets containing each corn genotype. These diets will be fed to broiler chickens from 8 to 21 days of age. Criteria to measure nutritional value of each corn will include rate of gain in body weight, feed consumption, and efficiency of feed utilization.

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Anthracnose Stalk Rot Resistance from Exotic Maize Germplasm

Margaret Smith

Department of Plant Breeding, Cornell University

General Objective:

To develop temperate-adapted maize inbreds with both anthracnose stalk rot resistance and good yield potential from GEM accessions.

Specific Objectives:

1) To continue selfing and selection for anthracnose stalk rot resistance in progenies from the 75% temperate : 25% exotic populations that have adequate testcross yield potential.

2) To evaluate testcross yield potential of the early generation inbred families and select those that are most promising for continued stalk rot selection.

Materials and Methods:

The work described herein represents one year of a multi-year inbred development effort. Results of 1995 per se evaluations were used to select five 75% temperate : 25% exotic populations with potential for anthracnose stalk rot resistance. Results of 1996 testcross yield evaluations of these populations were used to select the four with the best yield potential. For each of these four populations, 50 S1 ears were grown out ear-to-row in summer 1997.Eight plants per family were self-pollinated, injected with approximately 500,000 conidia/plant of Colletotrichum graminicola, and selected for anthracnose stalk rot resistance at harvest. In 1998, selected S2 ears were grown out ear-to-row for another cycle of inbreeding and selection for resistance, as well as for testcrossing.


Populations selected based on per se anthracnose stalk rot resistance (evaluated in 1995) and testcross yield potential (evaluated in 1996) were FS8B(T):N1802, CH04030:S0906, AR01150:N0406, and GOQUEEN:N1603.Selfing, inoculation, rating, and selection practiced on the 50 S1 families per population gave the results shown in Table 1.It should be noted that ears were saved from only the more resistant families and plants in each population. The following data represent ratings on only the saved fraction of the ears (approximately 100 ears per population).

Table 1.Means for anthracnose stalk rot rating (mean percent rotted tissue for the lower eight stalk internodes) and days to flower from plants selected in the field as the more resistant fraction 

  Stalk Rot Rating (% diseased tissue) Days to Flowering
Population Mean(± s.d.) Min. Max. Mean (± s.d.) Min. Max.
FS8B(T):N1802 11.9 (±7.2) 1.5 36.6 77 (±3) 70 83
CH04030:S0906 11.5 (±9.7) 0.8 44.1 75 (±3) 68 83
AR01150:N0406 8.0 (±5.6) 0.4 31.1 77 (±3) 73 83
GOQUEEN:N1603 8.4 (±5.2) 0.4 27.4 76 (±3) 69 83
Resis. check (15/31-4*) 13.8 (±5.2) --- --- --- --- ---
Susc. check (B37) 61.6 (±20.8) --- --- 79 --- ---
* This is our most resistant inbred, currently in the final stages of testing prior to official release.

From these sets of S2 ears, 20 per population were selected for continued inbreeding, inoculation, and selection and for testcrossing in summer 1998 based on stalk rot resistance rating and earlier flowering. The means for stalk rot ratings and days to flower for the selected fraction of each population are shown in Table 2.

Table 2.Parent plant means for anthracnose stalk rot rating (mean percent rotted tissue for the lower eight stalk internodes) and days to flower for the 20 S2 ears per population selected for continued inbreeding 

  Stalk Rot Rating (% diseased tissue) Days to Flowering
Population Mean(± s.d.) Min. Max. Mean (± s.d.) Min. Max.
FS8B(T):N1802 4.9 (±2.6) 1.5 9.0 76 (±2) 71 81
CH04030:S0906 2.4 (±0.8) 0.8 4.3 74 (±2) 68 77
AR01150:N0406 2.4 (±1.9) 0.4 6.6 76 (±2) 73 81
GOQUEEN:N1603 3.4 (±1.7) 1.1 6.6 75 (±1) 73 77

Data from the summer 1998 inoculations and ratings have been collected, but remain to be converted, analyzed and summarized. Observations from the field suggest that levels of resistance have been maintained and/or improved, while days to flowering continue to be reduced gradually.

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Evaluation of GEM Crosses for Yield and other Agronomic Traits

N. W. Widstrom

USDA-ARS-IBPMRL – P.O. Box 748, Tifton, GA 317-0748

Sixteen non-replicated yield trials with numbers of entries varying from 49-100 were grown at Tifton, Georgia in 1998. The total number of entries plus checks was 1048. The 1998 planting was delayed until April 22 because wet field conditions prevented field preparation. Rainfall during March exceeded eight inches, but averaged less than 0.4 inches per week during the eleven weeks following planting. Average daily temperatures exceeded the normal by three degrees Fahrenheit during the same period. Five irrigations of approximately 2 inches per application were not fully effective in preventing drought stress during the growing season. The resulting data, therefore, should represent yield performance of the test crosses under considerable environmental stress.

Eleven of the experiments had two or more entries with yields that exceeded all commercial checks in their respective experiments. Overall yields varied from 0 to 159 bushels/acre indicating responses to environmental stresses and soil variability for water retention. The tests were machine harvested by Pioneer Hi-Bred International. Moisture percentage of grain at harvested approximately 20% and stands averaged approximately 50 plants in 2-row plots 20 ft. in length. Disease and insects were of minimal consequence for the 1998 season at Tifton. Data were also recorded for lodging, ear height, plant and maturity.

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Cereal Breeding

Dennis West

University of Tennessee, Knoxville

Genetic diversity of maize (Zea mays L) is being enhanced by incorporating genes from Latin American races of maize into the U.S. germplasm base. Genetic vulnerability results from continued utilization of a narrow germplasm base, as has occurred in U.S. maize during the past 70 years. This genetic vulnerability makes the U.S. maize crop susceptible to wide devastation by a single castrophic biotic or abiotic event. This program allows for the introduction of new genes into the U.S. maize germplasm which may allow buffering against extremes of environmental stress.

500 new corn lines were evaluated for grain yield potential, in crosses with standard U.S. lines. Latin American maize germplasm has been crossed with elite Tennessee germplasm. Inbreeding and selection for the development of new parent lines of corn has been initiated. Next year we hope to accomplish evaluation of testcrosses, further selection and inbreeding to evaluate and select lines. New lines may become available to the U.S. seed industry within 5 years.


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