Germplasm Enhancement of Maize
- 1997 Public Cooperator's Report
Performance of Second Generation of Tropical x Temperate Corn Testcrosses in 1997
Department of Agronomy, Louisiana Agricultural Experiment Station
Forty two entries provided by GEM [19 exotic (tropical or temperate) accessions of corn that were top crossed to a non-Stiff Stalk tester (N=FR992 x FR1064) and a Stiff Stalk tester (S=FR615 x FR697)] and four checks (Pioneer hybrid 3165, DeKalb hybrid 689, LH132 x LH51, and S x N) were grown in 1996 at Baton Rouge, LA. At harvest in 1996, open-pollinated seed of each entry was saved.
In 1997, the second generation seed saved from each entry tested in 1996 and four tropical hybrids (XL510, XL370, XL660, and XL678C) (total entries=46) were planted in a randomized complete block design (three replications, 2-row plots of 2 x 20 ft length) on May 15, 1997. The test was harvested on September 18, 1997. Grain yield [YIELD] and harvest grain moisture [MOIST] data were recorded. The CV for YIELD was 19.6%. Significant differences among entries were found for both the traits. The test mean YIELD was 61.2 bushels/acre and the test mean MOIST was 14.9%.Five entries including the check [DK689], [DKXL380 x N], [DK888 x S], [DKXL370A x N], and [DK212T x S] ranked among the top 10 highest yielding entries in both years. The entries that ranked among the bottom 10 in both years were [CHIS775 x S], [DKB844 x S], and the check, Pioneer hybrid 3165. The rank correlation for YIELD in both years was 0.29 (p=0.06). Three of the tropical hybrids (F1) (XL510 yield=107 bushels/acre, XL678C yield=83.5 bushels/acre, and XL660 yield=81 bushels/acre) yielded higher than other entries. The LSD (p=0.05) was 19.4 bushels/acre.
Southern Yield Tests
University of Tennessee
Yield trials of experimental hybrids developed from GEM germplasm were grown at 3 locationsin TN. A total of 828 hybrids from 16 different GEM populations were evaluated, and datasummaries are currently being prepared. These hybrids were obtained from the Southern USGEM Coordinator at Raleigh NC. Inbreeding and selection in was initiated to develop new linesfrom7 GEM populations that were have been crossed to elite Tennessee germplasm. Preliminaryexperimental hybrids with these new lines will be made in 1998.
1997 Evaluations of Selected GEM Accessions and GEM Derived Lines for Western Corn Rootworm Damage
Bruce E. Hibbard, B. Dean Barry, and Larry L. Darrah
USDA-ARS, Plant Genetics Research Unit, Columbia, MO
In 1997,resistance to western corn rootworm larvae [RTWORM] was evaluated for four of the original GEM accessions (selected from 1995 and 1996 trials), available crosses of the four GEM accessions with elite, proprietary germplasm, selected S2 lines that we created from GEM materials, and crosses we created of these four accessions with Mo-45, Mo-46, and Mo-47 (European corn borer resistant inbred lines). Germplasm lines were in a randomized complete block design with 3 replicates with the first three experiments in one location and the crosses with Mo-45, Mo-46, and Mo-47 at a second location. Each plot was mechanically infested with 1,000 western corn rootworm eggs per 30.5 cm. At the time of maximum damage, four roots were selected from each of the three replicates were washed of all soil and evaluated for corn rootworm feeding damage using a 1-6 scale [1=no damage, 2=feeding scars evident, 3=one or more roots eaten to within 1.5 inches of the stalk, 4=one node of roots completely destroyed, 5=2 nodes of roots completely destroyed, 6=3 nodes of roots completely destroyed]. In our evaluation of the original GEM accessions, selected S2 lines, and GEM × elite crosses, only PI 576258 was significantly less damaged than the susceptible control, B37 × H84.All of the GEM × elite crosses were nominally less damaged than B37 × H84, but none of the S2 lines were less damaged than the susceptible control. In our evaluation of crosses of selected GEM accessions with Mo-45, Mo-46, and Mo-47, PI 516027 × Mo-47 and PI 493039 × Mo-45 were significantly less damaged than our susceptible control B37 × H84 and nominally less damaged than our resistant controls. Eight of nine of these crosses were nominally less damaged than the susceptible control.
GEM Materials That Were Rated for European Corn Borer During 1997
USDA-ARS, Columbia, MO
Three groups of GEM selections were evaluated during 1997.The first group was selections from 1995 and 1996.There were 58 selections evaluated in these trials with four checks. From these, ten selections were made for further evaluations. These selections are in our Puerto Rico winter nursery for inbreeding and seed increase. The second group consisted of 39 entries from which 17 selections were made for further evaluation. These entries were Fl's from GEM materials crossed to Mo45, Mo46, and Mo47.These selections are in our Puerto Rico winter nursery. The third group consisted on 58 selections from which 27 selections were made in 1997.The 58 selections were Fl's of material crossed to Mo45, Mo46, or Mo47.The GEM materials used in these crosses have previously been evaluated for western corn rootworm resistance and were rated favorably. The 27 selected materials had been sibbed in 1997 and are in the Puerto Rico winter nursery.
Evaluation of tropical accessions as sources of genes to improve a Corn Belt Hybrid
University of Illinois
This is the report of the second year's work on a three year project. The general objective is to identify tropical accessions with the most promise for improving corn belt hybrids for grain yield and disease resistance. As part of this objective, a specific objective is to determine the effectiveness of Dudley's method of identifying parents for discriminating among populations when the populations have been crossed to a common parent. Work in 1997 consisted of evaluating crosses to LH185 and FR1064 of 14 tropical x B73, 18 tropical x Mo17 and 11 temperate populations and the hybrid LH185 x FR1064. The inbreds LH185 and FR1064 were grown in separate but adjacent replicated trials. Data were obtained for grain yield, rind penetrometer resistance and reaction to the causal organisms of gray leaf spot, Northern corn leaf blight, Southern corn leaf blight, and Northern corn leaf spot. Because we have populations crossed to both B73 and Mo17, the ability of Dudley's method to identify sources of favorable alleles when only half the genome consists of the population beingevaluated can be determined. In addition, any differences between B73 and Mo17 in reducing discrimination between populations can be evaluated. Preliminary analysis of the data from disease evaluations suggest the tester has a major effect on disease evaluations. For all disease, crosses to FR1064 showed more disease development than crosses to LH185. In addition, the populations which were evaluated as crosses to B73nearly always had more disease development than populations which were evaluated as crosses to Mo17.Thus, to evaluate the potential of a population to contribute disease resistance to new hybrids, it appears essential to know the background and disease reaction of lines to which the population has been crossed. These results are preliminary and may change with a second year's evaluation. Penetrometer and grain yield data have not been analyzed.
Development of GEM corn lines with multiple disease resistance, increased starch content and grain yield
University of Illinois
Research in 1997 included evaluating two Gem populations DREP150:N20 and BR510:N11A12 S1 lines for multiple disease resistance and starch concentration. The disease nursery consisted of about 2200 plants of DRE150:N20.These plants were inoculated three times prior to anthesis with a spore suspension containing Northern and Southern corn leaf blight, anthracnose leaf blight, gray leaf spot, northern corn leaf spot and eyespot. Frequent "mist" irrigations allowed for good disease development. Just prior to anthesis high winds caused excessive root lodging. The lodged plants left a small population estimated at 150 plants (no root lodging). Sixty plants with good multiple leaf disease resistance were selfed. The DREP150:N20 population was too late for using under central corn belt conditions and will be crossed to an early flowering inbred in 1998.
There were 210 S1 families of BR510:N11A12 planted in the disease nursery and inoculated with multiple leaf blights as stated above (estimated 3,000 plants). At anthesis selection was between rows and within rows, selecting plants with the lowest percentage of leaf area infected. About 15 days after anthesis all selfed plants were inoculated with a spore suspension containing diploidia, anthracnose, gibberella and fusarium stalk rots. All selfed plants were rated in late August for leaf area infected and plants with greater than 50% leaf area infected discarded. At harvest the "kick and bend" test for stalk quality was used on the remaining selfed plants. About 50% of the 210 S1 families (110 families) were saved with a total of 194 ears or about 1.9 ears per family.
The oil, starch and protein concentration of seed from these 194 ears was determined using near-infra-red-transmittance. The mean starch concentration for the 194 ears was 66.0%, oil 3.8% and protein 12.7%.The range in starch values was from 59.5% to 71.8% with 138 ears in the 66 to 71% starch range. About 71% of the families were in the 66 to 71% range and 21% in the 60 to 65% range. The 138 S2 families will be grown in 1998 for further multiple disease resistance selection and also to make testcrosses using an inbred tester.
Anthracnose Stalk Rot Resistance from Exotic Maize Germplasm
Margaret E. Smith and Laraine Ericson
Cornell University, Ithaca, N.Y.
From 30 populations (50% exotic:50% temperate) screened for anthracnose stalk rot resistance in 1995, the five populations showing the most resistance according to mean resistance ratings were FS8B(T)/nSS, CH04030/SS, AR01150/nSS, CASH/nSS, and GOQUEEN/nSS. For each population, a set of 25% exotic:75% temperate testcrosses derived from that population were evaluated in 1996 yield trials including standard commercial checks, with three replications per location grown at three long-season New York locations. Additionally, inbreeding was initiated in one of the 25% exotic:75% temperate derivatives of each of the five populations in 1996.Trial results showed yield, yield/moisture ratio, and stalk lodging means (and ranges, in parentheses) as follows for the testcross sets:
Due to relatively lower yield potential and yield-moisture ratio, the CASH-derived population was dropped at the end of the 1996 season. For each of the four remaining population derivatives [FS8B(T):N1802, CH04030:S0906, AR01150:N0406, and GOQUEEN:N1603], the best 50 S1 ears were selected based on standability and ear quality at harvest and planted ear-to-row in 1997.From zero to eight S1 families per population were discarded prior to flowering due to obvious genetic defects. In most S1 families, self pollinations were made on 5-6 plants with acceptable flowering date, good nick, and good agronomic quality. All pollinated plants were inoculated with the causal organism of anthracnose stalk rot. At harvest, stalks were split and the most resistant plants were rated and their S2 ears saved for further inbreeding. Stalk rot ratings for the selected fraction of each population are not yet summarized, but will be reported for addition to the GEM database as soon as possible.
Fusarium ear rot resistance screening of GEM germplasm
Dept. of Plant Pathology, Iowa State University
Seventy entries from the GEM collection were screened for resistance to ear rot diseases caused by Fusarium moniliforme [FUS] and Fusarium graminearum [GIB]. Fourteen entries were temperate accessions, nine were semi-tropical accessions, eleven were temperate crosses (50%) with public lines (B73 or Mo17), 26 were temperate crosses (50% or 25%) with proprietary lines, and ten were semi-tropical or tropical crosses (50% or 25%) with proprietary lines. Susceptible and resistant commercial hybrid or public inbred checks were included. The two pathogens were inoculated in separate plots; F. graminearum [GIB] inoculations were performed by the silk-channel method, while F. moniliforme [FUS] inoculations were performed with a pin-bar inoculator; husks were partially removed prior to [FUS] 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. 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 1.9 to 6.3. Of four temperate accessions that performed well in 1996, only [UR05017] performed well in both years, with mean scores of 2.2 and 2.1 in 1996 and 1997. However, this accession does not pollinate well in our studies. In 1997, accessions [UR05017], [FS8A(T)], [CH04030] and [UR13085] and their crosses had mean ratings3.0. Overall, there was a poor correlation between 1996 and 1997 results; Spearman rank correlation was 0.10.[FUS] ratings ranged from 1.7 to 3.9. Accessions [AR03056], [UR13085], [AR16026], and [UR05017] and their crosses had mean ratings of2.6, whereas accession [UR1001] performed very well (1.8) but when crossed, its performance was poorer (3.4). Fumonisin B1 concentrations will be measured for [FUS] inoculations, but this has not been completed. Based on 2 years of data on [GIB], we can focus on a only few accessions or crosses for possible development of resistance. Segregation and escapes due to very late silking are causing inconsistency in our data. We need additional data to determine whether apparent partial resistance to [FUS] will be consistent.
Variation in Value-added properties of GEM Material
L.A. JOHNSON and S.K. SINGH
Center for Crops Utilization Research, Iowa State University
Forty-nine GEM accessions selected from corn of Latin American origin, two commercial hybrids, and two inbreds were evaluated for their compositional, physical, and wet-milling properties. The recovered starch was characterized to identify any unusual thermal, pasting, gelling, or retrogradation properties. Heterosis of these traits was examined in 10 selected GEM accessions crossed with each of MO17 and B73 inbreds.
The GEM accessions contained 3-6% less starch, 4-6% more protein, and up to 2-4% more fat than the commercial hybrids. Higher protein and fat contents make GEM lines energy dense and good for animal feed. On average, absolute densities were greater and 1000 kernel weights were less for GEM than for the commercial hybrids; test weights were similar.
The wet-milling characteristics of the GEM accessions were not nearly as good as for the commercial hybrids. Starch yields averaged only 54.3% for the GEM accessions versus 64.8% for the commercial hybrids. Proteins content of starches recovered from GEM were much greater than for commercial hybrids. Gluten yields were much greater while gluten protein contents were much lower for the GEM accessions than for the commercial hybrids due to difficulty in separating starch from gluten.
Thermal properties of starches recovered from GEM accessions had much wider variation than from normal dent corn. These differences were statistically significant but not of practical significance to the starch industry. These differences may be useful to corn breeders to expand genetic differences in starch. Starches isolated from GEM accessions had on average higher gelatinization temperatures, lower heats of gelatinization (enthalpy), and similar percentages of retrogradation. GEM accessions had on average greater temperatures at peak viscosity, greater peak viscosities, and greater viscosity break downs. The gel strengths were typically greater for the GEM starches than for starches from commercial hybrids.
Ten accessions were selected from the 49 original GEM lines and crossed with two dent corn inbreds (B73 and MO17). When crossing with B73, protein contents and absolute densities were greater for the cross than either parent; all other compositional, physical, and wet-milling properties were similar to the mean of the parents. When crossed with MO17, starch contents, absolute densities, starch yields, and starch recoveries were greater, and gluten yields were lower than either parent; all other compositional, physical, and wet-milling properties were similar to the mean of the parents.
Similar heterotic patterns of starch properties were observed using both inbreds. Gelatinization peak temperature of starches from the crosses were similar to those of starch from the GEM accessions. Enthalpies, peak height indices, peak viscosities, viscosity break downs, and percentages of retrogradation were greater for the crosses than for either parent. Gel strengths were similar to the mean of both parents.
PEER-REVIEWED SCIENTIFIC JOURNAL PUBLICATIONS:
1.Singh, S., L.A. Johnson, L.M. Pollak, S.R. Fox, and T.B. Bailey. 1997. Comparison of Laboratory and Pilot-Plant Corn Wet-Milling Procedures. Cereal. Chem. 74(1):40-48.
1.Singh, S.K., L.A. Johnson, and S.R. Fox. 1996. Development of a Pilot-Plant Scale Wet-Milling Procedure and Comparison with Laboratory-Scale Wet-Milling Procedures. Proceedings of the Corn Utilization Conference V. National Corn Growers' Association. St. Louis, MO.
2.Singh, S.K., L.A. Johnson, C.R. Hurburgh, P.J. White, and L.M. Pollak. 1996. Characterization of Value-Added Traits in Latin American Corn Accessions. Proceedings of the Corn Utilization Conference V. National Corn Growers' Association. St. Louis, MO.
1.Johnson, L.A. 1997. Corn: The Major Cereal of the Americas. In Handbook of Cereal Science and Technology (second edition), edited by K. Kulp and J.G. Ponte, Jr. Marcel Dekker. New York, NY. (Submitted).
1.Singh, S.K., L.A. Johnson, and S.R. Fox. 1996. Development of a Pilot-Plant- Scale Wet-Milling Procedure and Comparison with Laboratory-Scale Wet-Milling Procedures. Corn Utilization Conference VI, National Corn Growers' Association, St. Louis, MO.June 4-6.
2.Singh, S.K., L.A. Johnson, C.R. Hurburgh, P.J. White, and L.M. Pollak. 1996. Characterization of Value-Added Traits in Latin American Corn Accessions. Corn Utilization Conference VI, National Corn Growers' Association, St. Louis, MO. June 4-6.
3.Singh, S.K., L.A. Johnson, C.R Hurburgh, and L.M. Pollak. 1996. Variation in Value-Added Properties of GEM Material. 81st Annual Meeting of American Association of Cereal Chemists, Baltimore, MD. Sept. 15-19. Cereal Foods World 41(7):552, Abstract 35.
4.Singh, S.K., L.A. Johnson, and S.R. Fox. 1996. Comparison of Laboratory and Pilot-Plant Corn Wet-Milling Procedures. 81st Annual Meeting of American Association of Cereal Chemists, Baltimore, MD. Sept. 15-19.Cereal Foods World 41(7):597, Abstract 266.
5.Singh, S.K., L.A. Johnson, L.M. Pollak, P.J. White, and C.R. Hurburgh. 1997. Value-Added Traits in Latin American Corn Accessions. Annual Meeting of the Iowa Seed Association, Ames, IA. Oct. 10-12.
CHARACTERIZATION OF PHYSICAL AND COMPOSITIONAL Grain Quality Characteristics of temperate accession x Corn Belt line breeding crosses
The Ohio State University Ohio Agricultural Research and Development Center
Department of Horticulture and Crop Science
Lodging in the plots was not as severe as in 1995 so 1996 yield data are considered more reliable. GEM materials again demonstrated high levels of useful variation for both agronomic and value-added traits. Average yield and harvest moisture values of the GEM testcrosses were 7.43 Mg/ha and 30.1%, respectively. One GEM entry (UR13010:No613), displayed yield (11.42 Mg/ha) superior to that of the mean of two checks (10.42 Mg/ha).The highest yielding GEM entry in 1995 tests, FS8A(S):S09 finished second in 1996 at 10.28 Mg/ha. Mean harvest moisture of the testcrosses was 30.1 g kg-1, slightly higher than that of the check mean, 28.8 g kg-1, indicating that the many of the populations can be utilized for breeding at the latitude of northern Ohio. High levels of lodging (mean 36%) occurred the testcrosses, compared with a check mean of 5.4%.Grain samples of GEM testcrosses were obtained from one hand-harvested and one mechanically harvested plots. Kernel samples contained mean protein and oil concentrations of 8.7% and 3.6% (15% mois. basis), respectively. Check mean values for protein and oil were 7.5 and 3.3%, respectively. High protein and oil values were displayed by GEM testcrosses AR17056:S12 at 9.4%, and FS8A(T):N18 at 4.1%, respectively. Mean kernel starch content of the testcrosses was 60.2% compared to the check mean concentration of 60.7%.A high starch content of 61.4% was exhibited by GEM entry CH04030:S0906.Most GEM testcrosses displayed hard endosperm characteristic (mean density of 1.279 g/cm3 ).Mean starch concentration of the checks was 1.230g/cm3.GEM testcross AR16021:S08b06 displayed the highest kernel density, 1.314 g/cm3. These data demonstrate that 50% temperate Latin American X Corn Belt populations will provide useful genetic variability for selection of end value characteristics, and that a few demonstrate competitive agronomic characteristics in the Eastern Corn Belt.
The objectives of this test were to determine the yield and agronomic performance, and grain physical and compositional characteristics of 113 testcrosses in standard 2-row plots typically used in performance evaluations. Hand harvested ear samples were also taken from 4-row plots to examine the possible influence of pollen contamination in 2-row plots and to provide whole ear samples for passport data on ear, kernel, and cob characteristics. These tests will assist the selection of the most promising populations for the improvement of value-added compositional and physical traits among those accessions with the best agronomic potential.
One hundred and thirteen temperate accession X Corn Belt crosses plus two checks were planted near Wooster, Ohio during May 1996 in a replicated random complete block design with 4 replications according to standard agronomic practices. Eighteen tropical GEM testcrosses were planted near South Charleston, Ohio. Plots were machine harvested in November 1996 and grain samples were dried in a low temperature, forced air drying oven. Ear samples were also harvested from the inner 2 rows or all entries planted in 4-row plots at a nearby location. Ears were low temperature dried and ear samples were individually hand-shelled. Compositional traits were measured using a Tecator 1225 Whole-Grain Analyzer with the ISU/MBS System One calibration. Protein and oil values are presented on a 15% moisture basis. Data were analyzed using SAS PROC GLM procedures.
Average yield and harvest moisture values of the plot were 8.18 MG/ha and 24.2%, respectively. The average yield value was below that of the checks; however, one GEM entry, (UR13010:No613), displayed noticeably superior yield (11. 42 MG/ha) above that of the checks (10.42 Mg/ha). Several other GEM entries were not statistically different for yield in comparison with the check hybrids. A high level of stalk lodging (mean 36%) occurred in the plots. The average harvest moisture value was 1.3points above that of the checks. The maturity of many of these materials is suitable for cultivation at the latitude of northern Ohio. The average protein concentration of the testcrosses was 1.2% points above that of the check average. Several GEM testcrosses displayed total protein concentrations fully 2 points or more above that of the checks. The highest protein concentration was 9.4% of ARZM 17056S12.Mean oil concentration of the GEM testcrosses was three-tenths point higher than that of the checks. Testcross (FS8(A):T19 displayed the highest oil content, 4.1%.Average density of the testcrosses was slightly below that of the checks was higher than mean density of the checks 1.35).The testcross ARZM 16021 9 SS had a density value of 1.314, characteristic of South American flint corn.
Protein composition values were higher overall in the hand-harvested plot. Relative content of protein of tropical genotypes were similar across tests.
Most of the 18tropical GEM testcrosses were poorly adapted to the Ohio environment. Only the GEM testcross Antig03:N1216yielded as much (5.8 Mg/ha) as the poorest yielding check, B73 x Mo17.Grain compositional traits of tropical testcrosses were like those of the temperate testcrosses.
Arpat, H.-Murat.1996.Identification of major quantitative trait loci for grain quality traits in tropical maize recombinant inbred lines. M.S. Thesis, The Ohio State University. pp. 77.
Non-DIMBOA European Corn Borer Resistant Lines
Craig Abel and Richard Wilson
USDA-ARS, North Central Regional Plant Introduction Station, Ames, IA
An 8 location yield trial was conducted this past summer. Breeding populations were advanced to the BC3:F1. Some breeding lines are highly resistant to second generation European corn borer. sixteen BC2:F1 populations that showed superior European corn borer resistance were selected for a multiple maize pest resistance study. Four of the sixteen populations were resistant to three or more pests. Studies were also conducted to determine the mechanism of resistance displayed by the original Peruvian maize landraces. The mechanisms are antixenotic (larval feeding deterrent) and antibiotic with a lengthening of larval development time and mortality.
Evaluation of the zein content of GEM germplasm
USDA-ARS Ames, IA
The largest use of corn in the U.S. is animal feed. Corn is not ideally suited to this use and must be supplemented to produce nutritionally optimized feed. Protein quality is a major limitation of corn used for feed. Protein quality is determined largely by the most abundant proteins in the seed, including the zein family of storage proteins. Thus by comparing the levels of the major seed proteins in kernels, an assessment of protein quality can be made. We are developing high throughput assays for the most abundant seed proteins in order to evaluate the variation in protein quality of maize germplasm, and to provide a selection tool to breeding programs. These assays are based on the ELISA method, an antibody based method that is widely used in the health and pharmaceutical industries. We have developed assays for the two most abundant proteins of the seed, the alpha and gamma zeins. The alpha zeins are considered to be a poor nutrition source because of their lack of lysine. The gamma zeins are slightly better nutritionally and may have a role in determining kernel hardness. We have completed a preliminary analysis of gamma zein content of 50 GEM S1 lines derived from two breeding crosses. The mean gamma zein content (in mg gamma zein/g seed) was 20.3, with lines ranging from 10 to 33.A mixture of commercial commodity corn had a value of 11, and commercial high protein varieties had contents ranging from 23 to 33. These data suggest that a high degree of variation for seed protein content exists in GEM germplasm, making it a valuable resource to programs interested in developing varieties with altered seed protein composition. With assays such as the one described here, it should be possible with recurrent selection to produce corn with a defined seed protein composition. The added value of nutritionally optimized corn will benefit producers and consumers of corn-fed livestock and poultry.
Evaluation of GEM Breeding Crosses and S1 Families for Disease Resistance and Agronomic Performance
James A. Hawk and T. Weldekidan
Department of Plant and Soil Sciences, University of Delaware
In 1997, we self-pollinated 464 S1 families of DKXL212:N11a and evaluated each family for leaf blight resistance (Stewarts' wilt, Southern corn leaf blight), resistance to stalk breakage caused by European corn borer, and ear traits including grain texture, ear size, and dry down. The S1 families were well-adapted to Delaware and flowered comparable to inbred checks included in the nursery. A total of 193 S2 ears were kept from 159 selected S1 families. The selected S1 families exhibited high levels of resistance to both Stewarts' wilt and Southern corn leaf blight. Although there was a high level of natural infestation by European corn borer, we observed little stalk breakage in the selected families. Ear development was excellent, but many ears were slow drying due to extensive husk coverage. This breeding population has good potential for inbred development and the 193 S2 ears will be testcrossed for yield trial evaluations in 1998.
Evaluation for Aflatoxin Resistance
W.P. Williams and G. L. Windham
USDA-ARS Corn Host Plant Resistance Research Unit, Mississippi State, MS
Aflatoxin is a highly potent toxin that is produced by the fungus, Aspergillus flavus, which is commonly isolated from corn kernels. Aflatoxin contamination is a sporadic problem for growers in the Corn Belt and is a chronic problem for growers in the South. Drought stress, high temperatures, and insect damage have all been associated with outbreaks of aflatoxin contamination in corn. An extremely potent carcinogen, aflatoxin causes disease in livestock and humans. Therefore, contamination of corn grain with the toxin limits its marketability. In the United States, grain with levels of aflatoxin exceeding 20 parts per billion (ppb) is banned from interstate commerce. When levels exceed 300 ppb, contaminated grain cannot be used for livestock feed. Exported grain may fall under more stringent standards than those used in the United States.
A potentially effective and highly desirable method of reducing aflatoxin contamination in grain is the use of resistant hybrids. Before such hybrids can be made available to farmers, however, germplasm with resistance to aflatoxin accumulation must be identified. Corn genotypes from many different sources have been screened for aflatoxin resistance. However, very few resistant genotypes have been identified. Exotic germplasm crosses were obtained from the GEM Project with the goal of identifying resistant genotypes.
Fifty germplasm crosses (50% exotic), known resistant and susceptible hybrids and two commercial hybrids were evaluated for aflatoxin contamination at the Plant Science Farm, Mississippi State, MS. Seeds were planted on 17 April 1997 in single-row, 5.1 m plots, and seedlings were later thinned to 20 per plot. Ears were inoculated with spores of A. flavus 7 days after midsilk (50% of the plants in the row had silk emerged) using the side needle technique (Zummo and Scott, Plant Dis. 73:313-316).Ears were harvested 63 days after midsilk, dried at 38 C for 7 days, and machine shelled. Grain samples from each row were poured into a sample splitter twice to mix grain. Grain samples were ground using a Romer mill (Union, Mo). Aflatoxin contamination in 50 g subsamples from each plot was determined using the Vicam Aflatest (Watertown, MA).
Ultimately, resistant genotypes should have aflatoxin levels below 20 ppb. However, in these types of evaluations where artificial inoculations are used, aflatoxin levels are markedly higher than when plants are naturally infected with the fungus. Therefore, germplasm classified as resistant in this study had aflatoxin levels similar to the resistant hybrid controls that were included. Most of the germplasm crosses had high levels of aflatoxin contamination. Crosses BR52051:S17 and BR52060:SO2, which were some of the more resistant genotypes in 1996, had relatively low levels of aflatoxin in 1997.Two crosses (CUBA117:Sl5 and CUBA173:SO4) had aflatoxin levels comparable to the resistant checks included in the evaluation. These crosses are potential sources of resistance to aflatoxin contamination due to A. flavus and will be included in our breeding programs to develop aflatoxin resistant germplasm. When this germplasm is released to the public, hybrids can then be developed for growers to use to eliminate aflatoxin from corn.
Silage Potential of GEM Breeding Populations-Overview
Department of Agronomy, Univ. of Wisconsin
The UW corn breeding program has been an active cooperator with the GEM project since 1995, and our objective was to determine if any of the GEM germplasms would contribute to the development of high-yielding and high-nutritive value silage hybrids. We started with the evaluation of a number of temperate breeding populations, and we determined that a smaller, selected subset should be looked at in more detail. As a result of the second round of screening, we decided to develop S1 families from several advanced breeding populations for evaluation as inbreds. These activities are described in more detail below:
1995 Activities. In 1995, the UW GEM project analyzed 29 breeding populations (50% exotics) for silage nutritive value. These populations were evaluated at two locations, Madison and Arlington, WI using two-row plots with three replications/location. Ears were removed from one row, which was then harvested as stover alone. The other row was harvested as whole-plant silage. Fresh weights were recorded and 1,000 g samples collected for dry matter determination and laboratory analyses. Stover and whole-plant samples were analyzed for neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, crude protein (CP), in vitro dry matter digestibility (IVD), and cell wall digestibility (CWD). All chemical and digestibility constituents are reported as percentages on a dry matter basis in Table 1. Near infra red reflectance spectroscopy (NIRS) was used to predict all constituents. An internal calibration set was developed for NDF, ADF, and lignin. Other constituents were predicted using our global NIRS calibration set developed over the 1992 and 1993 growing seasons. Agronomic traits that were evaluated included days from July 1 to mid-pollen date (MP), stover and whole-plant % moisture (H20), stover and whole-plant dry matter yield in tons/acre and percent ear (%EAR).
Several of the populations were not adapted to conditions in Wisconsin. This was reflected in either the MP or %EAR values. We established a cutoff for future work by deciding to drop all populations with %EAR less than 40%.Because of the large range in MP or %EAR values across populations, we were also concerned that maturities and ear percentages were confounded with our laboratory assessments of nutritive value. We therefore decided to resample the following II populations in 1996: ARI6021:S9, AR16035:Sl9, AR17026:N10, AR17056:S12, CH05015:NI5, UR10001:N17, UR13085:S19, UR13085:N2, AR01150:N4, CH04030:S9, and GOQUEEN:NI6.These populations and 21 related 25% exotic populations were chosen to for continued analysis in Wisconsin during 1996.
The most desirable genotype is one with low NDF, ADF, and lignin, and high IVD, CWD, and CP. Of the 11 selected populations, one in particular, URI 000 1:N 1 7, had notably higher nutritive value, particularly on a stover basis. Population UR10001: N17 had low stover NDF, ADF, and lignin concentrations, and high protein. On a whole-plant basis, most quality components wereaverage, however protein was again relatively high. The protein concentration in adapted U.S. hybrids averages approximately 7% for stover and 8% for whole plants. Among the more adapted selected populations, UR10001:N17 had markedly higher protein concentrations on both a stover and whole-plant basis. Its low NDF, ADF, and lignin concentrations also indicate that it may have high intake potential.
1996 Activities. In 1996, the UW GEM project analyzed 32 breeding populations for silage nutritive value. These breeding populations included 11 populations (50% exotics) that were selected for further analysis based on our 1995 results and 21 advanced populations (25% exotic) that were developed from them. These populations were evaluated at two locations, Madison and Arlington, WI using one-row plots with three replications/location. The populations were stagger planted over three planting dates according to their maturities, so that they would be at a common physiological stage at harvest. At approximately 65% whole-plant moisture, ears were removed from each row, and each row was then harvested as stover alone. Fresh weights were recorded, and 1,000 g samples were collected for dry matter determination and laboratory analyses as in 1995.Near infrared reflectance was used to predict all constituents using an internal calibration set developed from samples in the 1996 study. In addition, all advanced populations were placed in the UW inbreeding nursery for selfing and selection to develop SI families for further testing if needed.
Of the eight check entries, QUALCOMP SYN I (which has been under selection for nutritive value) represents the optimum overall stover composition and commercial hybrid J4120 the worst. Of the 21 advanced breeding populations, two (AR I 7026:N I 0 1 9 and UR 1 3 08 5:NO204) had high overall nutritive value equivalent to QUALCOMP SYNI. In 1995, UR10001:N17, had markedly higher protein concentrations on both a stover and whole-plant basis, as well as low NDF, ADF, and lignin concentrations. However, in 1996, even though protein concentrations remained relatively high for UR10001:N17 and one of its related advanced populations (UR10001:N1702), several other advanced populations had better overall composition. The 1995 trial was not stagger planted to overcome confounding by maturity, and the 1996 results likely provide a more reliable measure of composition.
Based on these results, 217 S1 families from AR17026:N1019 (49 S1 families), AR17026:N013 (86 S1 families), UR13085:N0204 (46 S1 families), and UR13085:N0207 (36 S1 families) were selected for inbred per se stover evaluations in 1997.Populations AR 1 7026:NO 1 3 and URI 3 08 5:NO207 were included because of their close relation to the other two and because all populations tracing to URI 3085:N2 had excellent cell wall digestibility.
1997 Activities. In 1997, the 217 S1 families from the selected breeding populations were evaluated at Madison, WI using one-row plots and three replications. These plots were harvested at the mid-silk stage rather than at 65% whole-plant moisture, the stage at which we normally harvest hybrids and populations. We harvested inbred material at the mid-silk stage rather than later in the fall in order to avoid confounding of stover composition with ear-fill effects, which can be quite pronounced in inbred germplasm. (See Coors et al., 1997.) Samples will be analyzed for composition during the upcoming winter and spring.
Future Work. We have now pared the GEM temperate germplasms down to those with the most promise. Furthermore, the 1997 S1 results will indicate whether high-quality inbreds can be extracted from the advanced breeding populations with the highest nutritive-value. These S1 data are critical for determining the future prospects for utilizing GEM materials for silage. If the frequency of high quality S1s is higher than what we have observed in other breeding sources, then we will embark on an inbred development program to ensure that such germplasm is made available in the most useable form to private industry.
Reaction of U.S. GEM 25% Tropical Breeding Crosses to Cercospora zeae-maydis.
John E. Ayers and Melvin W. Johnson
Penn State University, University Park, PA.
Final Report. One hundred and one entries (25% tropical breeding crosses) were planted at a location near Oley, Pennsylvania (Berks County) with a history of gray leaf spot (GLS) caused by Cercospora zeae-maydis. Nine additional hybrids were added to complete a 10 ´ 11 lattice design. There were two replications. Due to wet soil conditions, planting was delayed until May 23.The experiment was planted with no prior tillage in a field that had been in continuous no-till corn production for several years. The growing season was characterized by above normal rainfall and below normal temperatures. The onset of GLS was delayed beyond the normal date expected for this region but because the crop was planted late, initial lesions appeared at about the normal stage of crop development; i.e., just past anthesis. Disease ratings were made on Sept. 23 on a 0.5 to 5.0 scale where 0.5 equals few or no lesions and 5.0 equals plants prematurely dead. The trial was harvested on Nov. 6.Data, averaged across replications, are shown in the attached table. SAS was used to analyze the data. LSD values are shown.
Analysis for Corn Rootworm Resistance
Department of Entomology, Iowa State University
The susceptibility of 57 maize germplasms to larval corn rootworm injury was evaluated at three locations during each of two years, 1995 and 1996.During the second year additional experiments were conducted at two locations to test the susceptibility of lines that had been crossed with elite Corn Belt lines to better adapt them to temperate growing conditions. Also during 1996, the ten lines that had demonstrated resistance during the first season were planted in paired rows at two locations with one row receiving an insecticide treatment. The insecticide treatments provided a comparison of root-growth characteristics with and without larval feeding. Rootworm resistance, as expressed and measured in the field, appears to be mainly due to tolerance. The germplasms that were least susceptible to corn rootworm larval injury were: Guatemala209 (PI 498583), PE11 (PI 583912), CHIS775 (PI 576258), CHIS740 (PI 583890), BRA051403 (PI 583911), BRA052051 (PI 583917), BRA052060 (PI 583918), FS8A(S) (PI 536619), FS8B(S) (PI 536621), RS8A(T) (PI 536620), FS8B(T) (PI 536622), and DK212T.The root characteristics measured appear to be relatively stable over environments and would be suitable for developing tolerant germplasms.
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