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Corn Breeding and Genetics, Dep. of Plant Sciences, North Dakota State Univ., Fargo, ND 58105-5051. The development of early maturing yellow-dent lines is supported by North Dakota State Board of Agricultural Research and Education (SBARE), the North Dakota Corn Growers Association, and North the Dakota Corn Council Utilization
* Corresponding author (marcelo.carena{at}ndsu.edu).
ABSTRACT
ND2005 (Reg. No. PL-354, PI 650885) and ND2006 (Reg. No. PL-355, PI 650886) are two new maize (Zea mays L.) inbred lines developed for use as parents for 70-80 relative maturity (RM) hybrids by the North Dakota State University maize breeding program and released by the North Dakota Agricultural Experiment Station in February 2007. ND2005 originated from the improved breeding population NDSM(M)C5 through a modification of pedigree selection including six years of early and late generation testing across 64 environments. ND2006 derived from the improved breeding population NDSBF(LM)C7(HGR)C4 through pedigree selection including five years of early and late generation testing across 31 environments. On the basis of their grain moisture at harvest, ND2005 and ND2006 were released as parents for development of very early maturing hybrids (<80RM). In addition to early maturity, ND2005 produced hybrids with above-average test weight and lodging resistance. ND2006 produced hybrids with above-average grain protein content. ND2005 and ND2006 combined best with Iodent and LH82 derived testers. ND2005 also combined well with early B14 types across eastern and western North Dakota.
Abbreviations: NDSU, North Dakota State University • RM, relative maturity
Maize (Zea mays L.) production in cooler climates, especially North Dakota, has significantly increased its economic importance. However, maize breeding for cooler climates continues to have a stronger importance in the public sector, with much more cooperation with the private sector. In 2007, North Dakota farmers planted more than 1 million ha of corn, placing it in the number-one crop position (with wheat) based on total crop state production. This is a 460% increase when compared to the same maize acreage 10 years ago. Breeding for early maturity and dry down, drought tolerance, and grain quality are some of the reasons corn is becoming adapted to these once considered marginal areas. The North Dakota State University (NDSU) corn breeding program has been in existence for 77 years, and it is the most northern public breeding program in North America. Ethanol plants have been established in areas (e.g., western North Dakota) where only NDSU research locations for drought tolerance are present. Corn germplasm has become adapted to North Dakota based on a long-term program that was initiated to increase the genetic diversity of hybrids in the U.S. north-central region.
ND2005 (Reg. No. PL-354, PI 650885) and ND2006 (Reg. No. PL-355, PI 650886) are two new maize inbred lines that were developed for use as parents for 70 to 80 relative maturity (RM) hybrids (Tables 1 and 2 ). They were developed by the NDSU maize breeding program and released by the North Dakota Agricultural Experiment Station on 5 Feb. 2007. During development and testing, the lines were coded as ND99-8 and ND00-24, respectively.
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Methods
The process of developing a diverse and elite maize inbred line is quite different from a self-pollinating crop and requires germplasm adaptation, long-term genetic improvement before inbreeding, early and late generation hybrid testing, and inbred line per se testing. For the general breeding methodology utilized by the NDSU maize breeding program on germplasm improvement and pedigree selection, see the NDSU maize breeding Web page (NDSU, 2007).
Germplasm Improvement, Inbreeding, and Evaluation
ND2005 and ND2006 were developed through an integration of recurrent selection and pedigree breeding methods (Fig. 1
). Maize populations adapted through many cycles of recurrent selection for production in North Dakota growing environments provided the germplasm base from which ND2005 and ND2006 were developed through modified pedigree selection. The procedure is similar to the one used to develop B73 and broadens the genetic base of maize.
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ND2005 [NDSM(M)C5-3-3-1-1-1] was derived by pedigree selection from NDSM(M)C5 (Cross and Wanner, 1991; Carena and Cross, 2003; Hyrkas and Carena, 2005). It was identified after five generations of stratified mass selection (Gardner, 1961) on NDSM (Reg. no. GP-229, PI542101), five generations of pedigree selection on NDSM(M)C5, and 6 yr of early and late generation testing on ND99-8. NDSM originated by intercrossing 13 yellow-dent inbred lines of approximately AES100 to AES300 maturity that were chosen for good general combining ability, resistance to stalk breakage, and high grain yield. NDSM(M)C5 was developed from NDSM by stratified mass selection to improve grain yield and resistance to stalk lodging (Carena and Cross, 2003; Hyrkas and Carena, 2005). The proportion of individuals selected in each cycle of stratified mass selection was 1% on a sample size of 3000 individuals, and selection was performed for grain yield, lodging resistance, and reduced tillers at a plant density of 20,000 plants ha–1 (Cross and Wanner, 1991). ND99-8 was selected from NDSM(M)C5 as an S0:1 in the 2000 Fargo, ND, breeding, disease, and testcross nurseries. Therefore, based on a sample size of 3000 individuals, the top 30 selections of NDSM(M)C5 were included. Starting in 2000–2001 testcross and single-cross nurseries were planted in the winter (Kauai, HI; Puerto Rico; and Santiago, Chile) to have yield trials across North Dakota environments every year. S1 and S2 generations were evaluated per se across locations for early vigor and emergence percentage before flowering to reduce the number of lines for testcrossing and pollination. In the S3 generation, three ears were harvested per row until uniformity was evident and no off-types were observed. Testcross hybrids of ND2005 were evaluated for genetically complex traits in 64 environments from 2001 to 2006 with commercial check hybrids included in each trial.
ND2006 [NDSBF(LM)C7(HGR)C4-1-1-2-1-2] was identified by pedigree selection from NDSBF(LM)C7(HGR)C4 after seven cycles of selection for low ear moisture (LM) at physiological maturity on NDSBF (Cross et al., 1987), four selection cycles for high growth rate (HGR) based on average leaf expansion rate on NDSBF(LM)C7 (Cross, 1990), five generations of pedigree selection on [NDSBF(LM)C7(HGR)C4], and 5 yr of early and late generation testing on ND00-24. NDSBF (Reg. No. GP-151, PI 550572) is a yellow-dent early maturing population released in 1986 and developed by one cycle of full-sib recurrent selection among 78 full-sib families between NDSB(FS)C1 and NDSF(FS)C1 of AES100 maturity (Cross, 1987). The top 20 families were identified using a rank-summation index including grain yield, grain moisture at harvest, root lodging, and stalk lodging after their evaluation in three North Dakota environments. Two cycles of recombination were produced among selected families for producing NDSBF. Divergent mass selection for ear moisture (HM = high moisture, LM = low moisture) was performed on NDSBF for seven cycles. Approximately 300 plants were grown to maturity for each selection cycle. Pair crosses without reciprocals were made, and ears were harvested at 45 d after pollinations. Ears were weighed, placed in a forced-air dryer at 40°C for 7 d and reweighed to calculate moisture content. Seed quantities were taken from each selected ear (the proportion of individuals selected was 10%) and bulked in balance to form the next cycle for selection. NDSBF(LM)C7 was further improved for high growth rate with the goal of increasing leaf area without delaying maturity. Selection for high growth rate was on an individual plant basis using the formula for average leaf expansion rate (Cross, 1990). Population sample sizes and selection intensities were similar to the ones for low moisture selection. ND2006 was visually selected from the 2000 maize breeding nursery from a sample size of over 5000 S0 plants and was assigned experimental number ND00-24. The early generation line was included as an S0:1 progeny and evaluated in the 2001 breeding, disease, and testcross nurseries. Testing of ND2006 in hybrid combinations was performed for genetically complex traits across several experiments and 31 environments from 2002 to 2006.
Inbred lines were grown in the Fargo breeding nursery in sets of three rows 7 m long. Three ears were harvested from the most uniform row. Once rows were uniform, lines were maintained as one progeny row per line. At harvest, the best ear from the best plant of that row was kept for nursery planting and the remaining ears bulked for distribution. ND2005 and ND2006 plants were grown in nursery plots at NDSU and rated for uniform type across years. Plants in these nursery rows appeared uniform and were self-pollinated. Bulked seed from a 2004 source was planted in nursery rows and in replicated inbred yield tests of NDSU and commercial inbreds per se based on a randomized complete block design (RCBD). Observations taken at several times during the growing season indicated plants in these rows were uniform and true to type.
Experimental Designs and Statistical Analyses
Both hybrid and inbred line trials were performed. Hybrid trials were evaluated in experiments with two replications arranged in partially balanced lattices. Simple lattice designs were used across years and testers, in most cases ranging from 8 by 8 to 12 by 12 partially balanced lattice designs. Occasionally, RCBD with two replications (e.g., a low number of entries in uniform land) or augmented designs (e.g., nonreplicated trials with a high number of entries, especially in early generation trials) were utilized. Experimental units were one and three-row plots (5 to 15 m2). Plots were planted and harvested by machines adapted for small experimental plots. Data collected at most locations included stand, grain yield (adjusted on a 15.5% grain moisture basis), grain moisture at harvest, root and stalk lodging, dropped ears, and grain quality (test weight, grain starch, protein, and oil). Weights, grain moisture at harvest, and test weight were measured at the time of combining. All data were summarized in Microsoft (Redmond, WA) Excel files and then imported to SAS (SAS Institute, 1990) for analyses. Analyses of variance were performed for all traits at each location, as well as across locations using the SAS Lattice procedure and the SAS GLM and ANOVA procedures (SAS Institute, 1990). For the combined ANOVAs, adjusted means by incomplete blocks were utilized when the relative efficiency of lattices was higher than 105% compared with an RCBD (Cochran and Cox, 1992). Expected mean squares were calculated following the rules of Schultz (1955) and were based on a mixed linear model that considered environments (and replications when RCBD was used) as random effects and entries as fixed effects. Mean comparisons were assessed by Fisher's protected least significant difference (LSD) since it has been shown to be an adequate test for detection of differences (Carmer and Swanson, 1971). In addition, we screened for emergence percentage and seedling vigor through a rank-summation index. Pedigree selections were, in most cases, obtained through heritability and rank-summation indices including several traits. A 1 (susceptible) to 9 (resistant) rating scale was used to generate disease resistance data. The first stage of selection was also based on maturity, stalk and root lodging, ear quality, drought tolerance, and seed set.
Inbred trials including 35 inbred lines were used to compare NDSU experimental lines with five commercial testers (currently used in northern U.S. hybrid production; some were coded) in replicated plots across three North Dakota locations (Table 1). Data were collected on 50 traits across 24 observations per line. Traits were measured on four randomly selected plants per plot (except silking and pollen shed data that were measured per plot). After determining that the error mean squares were homogeneous, combined ANOVAs were computed assuming that samples, replicates, and locations were random variables in the linear model. As with hybrid trials, comparisons among lines were made using the LSD. Inbred per se data as well as in hybrid combination through testcross, and single-cross data were extensively gathered across environments.
Characteristics
ND2005 is a yellow-dent line that has shown no susceptibility reactions to natural infection by eyespot (caused by Kabatiella zeae Narita and Hiratsuka) and common smut, caused by Ustilago maydis (D.C.) Corda [syn. U. zeae (Beckm.) Unger] (Table 1). However, it has shown a level of susceptibility to natural infection by common rust (caused by Puccinia sorgui Scwein.).
ND2005 has a dark green plant color with leaves that are usually long and wide. Its plant height is similar to ND2000 (Reg. No. PL-306, PI 631394) (Carena and Wanner, 2003), but its ear height is higher than ND2000. Pollen shed is good with the longest tassel among 35 inbred lines. ND2005 silks before TR1017Bt and flowers at least 5 d earlier than LH176 and TR3621Bt under North Dakota conditions. It has intermediate to high husk tightness and tends to produce more than one ear per plant of average length but with 12-kernel rows and white narrow cobs. Kernels are deep and heavy compared with ND2006. ND2005 has shown very high seed yield (5.6 Mg ha–1) per se compared with 35 elite North Dakota and commercial inbred lines (trial average of 3.3 Mg ha–1), while ND291 showed the highest mean of 6.5 Mg ha–1 (Reg. No. PL-305, PI 631393). Therefore, both ND2005 and ND291 should be seriously considered for cost-effective hybrid seed production. Inbred trials have also shown that ND2005 had excellent lodging resistance when compared to commercial checks.
ND2006 is a yellow-dent line that has shown no symptoms under natural infection of eyespot and common smut. However, susceptibility to common rust was observed (Table 1). ND2006 has a dark green plant color with a large number of leaves per plant. However, the leaves are usually short and narrow compared with most lines. ND2006 is a relatively short line that silks at least 3 d earlier than LH176 and TR3621Bt under North Dakota conditions. Even though days to pollen shed and silk may not make this inbred very early maturing, it dries very quickly, making this inbred very early based on grain moisture at harvest. It has intermediate husk tightness and tends to produce only one ear per plant that is often longer than average and with a low number of kernel rows. ND2006 has shown good seed yield (4.0 Mg ha–1), statistically similar grain moisture at harvest comparable to ND2005, and excellent test weight compared with other lines in the test.
Since the purpose of both early and late generation trials in maize breeding is to discard thousands of genotypes utilizing different experiments and testers, it would be inappropriate to present data combined over years. Data across the entire set of experiments showed that ND2006 had an average performance of 13.24% for grain protein content, test weight of 71.1 kg hL–1, and 17.4% grain moisture at harvest compared with average commercial check values of 11.6% for grain protein content, 70.5 kg hL–1 test weight, and 18.3% grain moisture at harvest. ND2005 had an average test weight of 71.5 kg hL–1 and 17.7% grain moisture at harvest.
Table 2 shows subsets of grain yield and grain moisture at harvest specific combining ability data for early maturity trials in 2004, 2005, and 2006. Even though grain yield of ND2005 hybrid combinations was the only one statistically superior to checks in only one of the years, this line transferred good alleles for test weight, stalk lodging resistance, and grain moisture at harvest. Hybrids including ND2005 showed superior performance for these traits statistically. In addition to test weight and grain moisture at harvest, hybrids including ND2006 showed statistically better performance in grain protein concentration. These data and the extensive testing involved in these lines per se and in hybrid combinations, especially for the most important North Dakota traits, largely justified the release of ND2005 and ND2006 as parental sources of very early maturing germplasm bred for early maturity and dry down, drought tolerance, and grain quality. We encourage the development of early-maturing industry testers since very few options are available.
Availability
Seed for ND2005 and ND2006 was produced in the Fargo breeding nursery, and progeny rows indicated excellent uniformity. North Dakota State University has transferred ownership of these materials to the NDSU Research Foundation (NDRF). Requests should be made directly to Dale Zetocha (dale.zetocha{at}ndsu.edu). Material transfer, inbred research, and/or commercialization agreements will need to be signed before the breeder is authorized to send seed lots. Breeder seed will be maintained by the NDSU maize breeding program and will be distributed (50 kernels per request) from the corresponding author on approval by the NDRF. After 20 yr from the date of publication, seed may be obtained from the National Plant Germplasm System.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication January 26, 2008.
References
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