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Reaction of US GEM Temperate Accessions to Cercospera zeae-maydis

John E Ayers & Melvin W Johnson

Pennsylvania State University

Twenty-seven temperate accessions from the GEM collection were planted at two locations in Pennsylvania with a history of Gray Leaf Spot [GLS] caused by Cercospera zeae-maydis.  Three check hybrids were added so the experiment could be designed as a 5x6 rectangular lattice; three replications were planted at each location.  Lycoming Co. (LC) was planted on May 1 in a field that had been chisel plowed and disked one time prior to planting.  Franklin Co. (FC) was planted with no prior tillage on May 8 in a field that had been in continuous no-till corn for several years.  Growing conditions were very good at both locations until mid-July, when moisture and heat stress occurred.  [GLS] appeared early at FC, but the drought and heat stress kept disease severities lower than anticipated based on the amount of disease seen in late June and early July.  Entries at FC only were rated on Aug. 9 and 29 on a 0.5 to 5 scale where 0.5 equals few or no lesions and 5 equals plants prematurely dead.  Average disease ratings on Aug. 29 ranged from 0.7 to 3.3 with the later maturing entries (higher grain moisture at harvest) showing the least amount of disease (r=-0.74).  There were, however, some entries (ex, [UR10001], [UR11003], and [UR13088]) with slightly above average grain moistures and below average [GLS] ratings, suggesting there might be a potential for extracting some resistance factors without greatly increasing time to maturity.  Other agronomic characteristics were measured.

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Evaluation of Germplasm for Resistance to Gray Leaf Spot (Cercospera zeae-maydis) Under Inoculation Disease Pressure.

Charlie Martinson & Davy Simumba

Department of Plant Pathology, Iowa State University

Sixty crosses were selected for study on the basis of disease severity.  The mean Gray Leaf Spot [GLS] rating and standard deviations for the crosses are presented [see raw data] and range from 1.0 to 6.5.  Out of sixty entries, more than half of the entries in the germplasm crosses have mean [GLS] ratings below 3.5 [0 = no lesions on the plant, 1 = a few restricted lesions on lower leaves and 9 = abundant lesions on all leaves].  Germplasm crosses [BR51501:S11a], [PRICGP3:N11a], [BR51403:N16], [CUBA164:S22], [CHIS775:S19] and [SCROGP3:N20] have mean ratings below 1.5.  [CASH:N14] and [AR16035:S19] have the highest [GLS] rating of 6.5 followed by [AR01150:N04] with 6.0.

Accessions are significantly different in their response to the disease inoculation, with mean Gray Leaf Spot ratings ranging from 3.7 to 5.0.  A comparison made in this case is the variation between the accessions without necessarily looking at how each individual ear performed within the accession.  [Raw data] show the means and standard deviations for each accession.  The low [GLS] ratings for the accessions clearly indicate that there is a high level of performance in terms of resistance.

There were variations within each row and averages are estimated from whatever number of plants existed in each row.  This is expected since these entries are not pure lines.  However, some of the plants had severe damage from Helminthosporium turcicum [NCLB] which spread from the neighboring research plot, masking or hindering the spread of [GLS].  Smuts and leaf spots were also observed.

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Variability for Resistance to Aspergillus flavus and Maize Weevil Feeding.

Manjit S Kang

Department of Agronomy, Louisiana State University

Sixty-one tropical x temperate crosses were planted at Baton Rouge, LA (three replications; randomized complete-block design).  Fifteen days after midsilk, 10 ears/plot were inoculated with Aspergillus flavus [ASPER] spore suspension (20 million spores/ml) using the needle-in-silk-channel technique.  The remainder of ears (second sub-sample) were used to obtain percent ear moisture loss/day during a 30-d post-midsilk and harvest period.  Number of ears/plot and grain weight/ear for the second sub-sample were recorded at harvest.  Variability among crosses for ear moisture loss rate (mean=0.8%/day; range=1.0 to 0.6%/day) and grain weight/ear (mean=118.7g; range=148.2 to 86.5g) was significant.

Percent kernel infection by Aspergillus flavus: All inoculated ears/plot were shelled and bulked.  A sample of 156 kernels/plot is being used to obtain percent kernel infection.  The procedure involves plating the surface-sterilized kernels on Czapek solution agar, incubating for 5-6 days and recording percentage of kernels showing infection.  This work is expected to be completed by the end of February, 1996.

Resistance to Maize Weevil [WEEVIL]: An aliquot of shelled grain (100 g/plot) was taken to evaluate differences among entries for resistance to weevil feeding.  The samples are being evaluated in a free-choice environment.  After 90-100 days of infestation by the weevils, grain weight will be recorded.  This work is in progress and is expected to be completed by the end of February, 1996.

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Evaluation of Anthracnose Stalk Rot Resistance in Selected LAMP Accessions.

Margaret E Smith & Lorraine Ericson

Department of Plant Breeding, Cornell University

We evaluated the levels of resistance to Anthracnose Stalk Rot [ANTH], caused by Colletotrichum graminicola (Ces.) G.W. Wils., in 30 GEM 50% exotic crosses together with the susceptible (B73) and resistant (LB31) inbred checks and a commercial hybrid (Mycogen 725cb).  Each entry was planted in a two-replication randomized complete block design at Aurora, NY.  Ten competitive plants from each plot [a single 20-plant row] were inoculated shortly after flowering...in the first extended  node above ground level.  Stalks of 8 inoculated plants were split open and rated for the lower 8 internodes [0=no tissue discolored; 1=1-5% discoloration; 2=6-25%; 3=26-75%; 4=76-99%; 5=100% discoloration].

Stalk rot pressure was generally quite high, with even resistant inbred check LB31 showing a rating of 35%.  This rating may be partially an artifact of differences in maturity and vigor,  as checks were small and severely shaded by tall and vigorous GEM crosses.

Several entries showed promising levels of Anthracnose Stalk Rot resistance.  [AR01150:N04], [GOQUEEN:N16], and [FS8B(T):N18] all had mean severity ratings lower than that of the resistant check; [FS8B(T):N18] also had good standability and relatively little natural [ECB-] damage.  [CH04030:S09], [FS8B(T):N11a], and [UR10001:N17] showed Anthracnose severity similar to that of the resistant check; [CH04030:S09] was the best of the entries involving a Stiff-Stalk parent.  In general, the non-Stiff Stalk parents showed better levels of resistance, as might be expected.  There appears to be good selection potential for Anthracnose Stalk Rot resistance among the GEM crosses noted.

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Evaluation of US GEM Project Germplasm for Leaf Blights and Rind Puncture Resistance.

John W Dudley & Donald G White

Department of Crop Sciences, University of Illinois

In 1995, 138 temperate accession x either B14/B73 or Oh43/Mo17 crosses were evaluated for Northern Corn Leaf Spot (races 2 and 3) [NCLS], Anthracnose Leaf Blight [ANTH], Nothern Corn Leaf Blight [NCLB], Southern Corn Leaf Blight [SCLB], and Gray Leaf Spot [GLS] resistance.  In addition, flowering date, rind puncture resistance, plant height, and ear height data were obtained.  For the leaf blights, data were obtained from one replication for each leaf blight.  Rind puncture resistance readings, obtained using a rind penetrometer, on the internode below the ear-bearing node, were taken approximately three weeks following pollination on three replications of 10 plants each.  Flowering date, plant height, and ear height were collected from three replications.  Means by population cross are shown [see raw data].  On average, as expected, crosses to B14/B73 averaged lower in rind puncture resistance and had higher leaf blight ratings then crosses to Oh43/Mo17.  Plant and ear heights were greater for the crosses to B14/B73.  The crosses to B14/B73 also were slightly later than the crosses to Oh43/Mo17.

Accessions with greater rind puncture resistance tended to have lower leaf blight ratings [see raw data].  When population means averaged over testers were used, correlations of rind puncture readings with leaf blight ratings ranged from 0.08 to -0.42 [see raw data].  Correlations among leaf blight ratings were positive and ranged from 0.12 between Northern Corn Leaf Spot race 3 and Northern Corn Leaf Blight to 0.43 between Northern Corn Leaf Spot race 2 and Anthracnose Leaf Blight.  Leaf blight ratings were negatively correlated to flowering date and plant height.  Correlations among traits by individual testers [see raw data] were generally similar.  However, the correlation of rind puncture resistance and anthracnose leaf blight for the B14/B73 tester was significantly positive (0.28) and was -0.21 for the Oh43/Mo17 tester.

Although the results obtained from the two testers were similar, correlations between testers, using the 66 populations crossed to both testers, were relatively low except for flowering date [see raw data].  Of the leaf blight ratings, only the correlation for southern corn leaf blight was significant and it was low (0.30).

When ratings were taken, a high degree of segregation for disease reaction within plots was noted.  None of the population crosses evaluated appeared to have extremely high levels of resistance.  Based on rind puncture resistance and leaf blight resistance, 12 accessions were selected to be entered into a study evaluating the potential of these accessions for improving elite germplasm.  The accessions selected [and currently in use by GEM] are: [AR16026] and [AR16035].  In our proposed work for 1996, we plan to include these accessions along with the tropical accessions crossed to either B73 or Mo17 and the tropical hybrids crossed to either B73 or Mo17.  The objective is to evaluate these materials for their potential to improve an elite hybrid for grain yield, leaf blight resistance, and rind puncture resistance.

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1995 Evaluations of Maize for Resistance to Corn Rootworm Larvae.

Jon Tollefson & Xiaoling Wang

Department of Entomology, Iowa State University

All 57 original GEM accessions were evaluated for resistance to Corn Rootworm larvae [RTWORM].  The experiment was conducted at three locations that had a high probability of natural Corn Rootworm infestation.  The experimental design was a randomized complete block with three replications.  Treatments consisted of paired rows, 5 m in length [overplanted and thinned].  Vertical root-pull resistance was measured with a recording dynamometer.  Washed roots were evaluated for rootworn larval damage [1=no damage or few scars; 2=feeding scars evident, no roots eaten off to within 1 1/2 in. of plant; 3=several roots eaten to within 1 1/2 in. of plant; 4=one node of roots completely destroyed; 5=two nodes destroyed; 6=three or more nodes destroyed], degree of secondary root development [1=smallest roots, 6=largest and most vigorous secondary roots], and root size [1=smallest roots, 6=largest and most vigorous roots].

Results show significant differences among germplasms for all traits studied.  There was a significant germplasm * location interaction for both plant lodging and root-pull resistance.  Root damage was related to plant lodging.  Correlations between root size, root-pull resistance, and root damage were negative.  High, positive correlations were observed between root size and secondary root development and root-pull resistance.  Data indicate that germplasms with high root-pull resistance are most tolerant of Corn Rootworm feeding damage.

[CHIS775] and [BR51403] exhibited the least amount of root damage in the test, comparable to the resistant check (NGSDCRW1) and significantly less than the susceptible check (B73xMo17).  [CHIS775] also had the largest root size and highest root-pull strength of all entries tested.  [BR52060] and [FS8A(T)] had high levels of secondary-root development, with [FS8B(S)] the best for all entries and significantly better than NGSDCRW1.  [XL212] exhibited the least amount of lodging by a wide margin.

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Resistance to First and Second Brood European Corn Borer & Corn Rootworm

Dean Barry & Bruce Hibbard

Plant Genetics Research Unit, USDA-ARS (Columbia, Missouri)

Original GEM accessions were evaluated for resistance to European Corn Borer first generation [ECB1] and second generation [ECB2].  Two locations were utilized with three replications each.  Resistance to Corn Rootworm [RTWORM] was also noted.  [ECB1] was rated on a scale of 1 to 6 with 1 indicating more resistance and 6 indicating less resistance.  [ECB2] was rated as length of stem tunneling in inches.  [DREP150], [GUAD05], [BARBGP2], and [DK212T] appear to have fared well at all locations/reps for European Corn Borer.  [AR16035], [FS8A(T)], [CHIS740], and [DKB830] were selected to be retested for Corn Rootworm [RTWORM].  Additional data found no GEM accessions better than NGSDCRW1(C4)S2 for resistance to [RTWORM], however.

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Evaluation of GEM Accessions for Resistance to Fall Armyworm & Southwestern Corn Borer.

W Paul Williams & Frank M Davis

Corn Host Plant Resistance Research Unit, Mississippi State University

Fifty maize accessions and seven hybrids were evaluated for resistance to leaf feeding by Fall Armyworm, Spodoptera frugiperda (JE Smith) [FAWORM], and Southwestern Corn Borer, Diatraea grandiosella Dyar [SWCB], at Mississippi State, MS.  These genotypes and known resistant and susceptible checks were grown in single-row, 20-plant plots arranged in a randomized complete block design with three replications for each insect.

The experiment for evaluating Fall Armyworm resistance was planted 6 April 1995, and the experiment for evaluating Southwestern Corn Borer resistance was planted 10 April.  In both experiments, plants were infested with 30 neonates each on 19 May.  Leaf feeding damage for each insect was visually rated 14 days later using a scale of 0 (no damage) to 9 (heavy damage) (Williams, Buckley, & Davis. 1989. Crop Science 29:913-915).

Most genotypes sustained heavy damage from both insects; a few accessions appeared to exhibit low levels of resistance and did not differ significantly from MpSWCB-4, a resistant check.  Those accessions showing less damage to Fall Armyworm also exhibited lower levels of damage to Southwestern Corn Borer.  Among the accessions that may be potentially useful as sources of resistance to these insects are: [CUBA117], [DREP150], [SCROGP1], [ANTIG03], [GUAD05], and [SCROGP3].

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Maize Plant Resistance to Fall Armyworm Larvae & Corn Earworm Larvae

Billy R Wiseman

Insect Biology & Population Management Rsch Lab, Coastal Plain Expt Sta, USDA-ARS (Tifton, GA)

Fifty-four Plant Introductions from the US GEM Project plus a resistant and a susceptible check were evaluated in the field at Tifton, GA, for leaf-feeding resistance against the Fall Armyworm [FAWORM].  The experiment was arranged as a randomized complete block design with 3 replications.  At the 8-leaf stage, 2 applications of 20 Fall Armyworm larvae were introduced into the whorls of 10 plants per plot/replication.  Plots were rated for leaf feeding by the larvae at 7 and 14 days after inoculation on a 0-9 rating scale where 0=no damage and 9=severe damage to the whorl.

[CUBA117] had the lowest ratings (most resistant) of the accessions for 7 and 14-day ratings.  [PRICGP3], [UR01089], and [DREP269] were also rated well.

Fifty-three Plant Introductions from the US GEM Project plus a resistant and a susceptible check and regular bean diet and a bean diet plus celufil checks were evaluated as oven-dried silks mixed into pinto bean-diets at Tifton, GA, for resistance against larvae of the Corn Earworm [CEW].  The experiment was arranged as a randomized complete block design with 30 replications.  When silks had emerged two days, they were excised to the ear-tip, brought to the laboratory, oven dried at 41 C for 10 days, ground with a Cylotec 1093 sample mill and mixed into pinto bean diets at 50 mg/ml.  Diet mixtures were dispensed into plastic cups and 1 neonate earworm was placed onto the diet/cup.  Weight of larvae were recorded 8 days after infestation. 

[CUBA117] showed the least weight gain for all accessions.  [FS8B(S)], [UR05017], [DK212T], [UR13061] also showed low weight gains (in increasing order).

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Variation in Value-Added Properties of GEM Material

Lawrence A Johnson & Suvrat Singh

Center for Crops Utilization Research, Iowa State University

Fifty-three Latin American (LA) accessions along with two commercial dent corn hybrids and two inbreds were evaluated for their compositions, physical properties, and wet-milling characteristics, and evaluation of the functional properties of starches recovered from them was begun.

Wide variations in compositional properties were observed among the LA accessions.  Kernels of the LA accessions had a wide range in starch content (70.9 to 75.1% versus 73.3% for commercial dent hybrids).  On average, protein (9.9%) and oil (4.8%) contents were higher in the LA accessions than in commercial dent hybrids (8.4 and 4.0%, respectively).

There were wide ranges in test weights (52.4 to 68.2 lb/bu) and 1000 kernel weights (240 to 316 g) among the LA accessions, but, on average, were comparable to commercial hybrids.  Absolute densities were consistently higher for the LA accessions (1.32 versus 1.29 g/cc).  Absolute density is highly correlated with protein content and kernel hardness.  US dent corn in general is quite soft, while the LA accessions are much harder, making them less susceptible to breakage and more suitable for dry milling.

The wet-milling properties of the LA accessions were not nearly as good as for the commercial dent corn hybrids (starch yields averaged only 54.4% for the LA accessions versus 64.8% db for the commercial dent hybrids).  Gluten yields were much greater for the LA accessions than for the commercial dent hybrids, which was attributed to starch ending up in the gluten fraction (increasing starch loss and reducing the protein content of the gluten).  Occasionally, high fiber yields were also obtained for the LA accessions, indicating that the starch did not separate well from the fiber.

The evaluation of starch functional properties has not yet been completed, but preliminary evidence indicates there are considerable differences in starch properties among the LA accessions that may be worth exploiting.  On average, starches from LA accessions gelatinized at lower temperatures (70.0 versus 71.3 C) and over narrower ranges (7.9 versus 10.5 C) than did the starches from the commercial dent hybrids.  On average, heats of gelatinization (enthalpy) were similar for starches from the LA accessions and commercial dent hybrids.

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Physical and Compositional Grain Quality

Richard C Pratt

Horticulture and Crop Science Department, Ohio State University

Twenty-nine temperate accession x Corn Belt crosses plus two checks were planted near Wooster, Ohio, on 16 May 1995, in a replicated randomized complete block design according to standard agronomic practices.  Plots were harvested on 20 November 1995.  A high level of stalk lodging (72% average) occurred in the plot.  Average yield [YIELD] and harvest moisture [MOIST] values of the plot were 8.21 Mg/ha [~130.9 bu/ac] and 24.1%, respectively.  One GEM entry, [FS8A(S)], displayed noticeably superior performance.  Many other GEM entries were not statistically different than the check hybrids.

Grain samples were harvested and dried in a low-temperature, forced-air drying oven.  Ear samples were also taken from all entries planted at another location and low-temperature dried.  Ear and grain physical compositional testing has commenced and will take some time to complete.

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UW GEM Project - Silage Potential of GEM Populations

James G Coors

Department of Agronomy, University of Wisconsin

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. Samples were analyzed for stover neutral detergent fiber [NDF-ST], stover acid detergent fiber [ADF-ST], stover lignin [LIG-ST], stover protein [CP-ST], stover in vitro dry matter digestibility [IVD-ST], stover cell wall digestibility [CWD-ST], whole-plant neutral detergent fiber [NDF-WP], whole-plant acid detergent fiber [ADF-WP], whole-plant lignin [LIG-WP], whole-plant protein [CP-WP], whole-plant in vitro dry matter digestibility [IVD-WP], whole-plant cell wall digestibility [CWD-WP]. All chemical and digestibility constituents are reported as percentages on a dry matter basis. Near infra red reflectance [NIR] was used to predict all constituents. An internal calibration set was developed for NDF-ST, ADF-ST, LIG-ST, NDF-WP, ADF-WP, and LIG-WP. Other constituents were predicted using our global NIR calibration set developed over the past four years. Agronomic traits that were evaluated included days from July 1 to mid-pollen [FLOWER], stover and whole-plant % moisture [H2O-ST and H2O-WP], stover and whole-plant dry matter yield in tons/acre [YLD-ST and YLD-WP] and percent ear [%EAR].

Several of the populations were not adapted to conditions in Wisconsin. This was reflected in either the FLOWER 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 FLOWER 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 11 populations in 1996: AR16021:S9, AR16035:S19, AR17026:N10, AR17056:S12, CH05015:N15, UR10001:N17, UR13085:S19, UR13085:N2, AR01150:N4, CH04030:S9, and GOQUEEN:N16. These populations and 21 related 25% exotic populations will be reanalyzed in Wisconsin during the current season. The populations will be stagger planted according to their maturities so that all will be at a relatively similar physiological stage at harvest.

Of the 11 selected populations, one in particular, UR10001:N17, had notably higher nutritive value, particularly on a stover basis. It had low NDF, ADF, and lignin concentrations, and high protein. On a whole-plant basis, most quality components were average, 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.

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