Posts Tagged ‘crop science’

Overview and Application of QTL for Adult Plant Resistance to Leaf Rust and Powdery Mildew in Wheat

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 54 (51907-1925, 2014

Zaifeng Li;Caixia Lan; He Zhonghu; Singh, R.P.; Rosewarne, G.M.; Xinmin Chen; Xianchun Xia

Leaf rust and powdery mildew, caused by Puccinia triticina and Blumeria graminis f. sp. tritici, respectively, are widespread fungal diseases of wheat (Triticum aestivum L.). Development of cultivars with durable resistance is crucially important for global wheat production. This paper reviews the progress of genetic study and application of adult plant resistance (APR) to wheat leaf rust and powdery mildew. Eighty leaf rust and 119 powdery mildew APR quantitative trait loci (QTL) have been reported on 16 and 21 chromosomes, respectively, in over 50 publications during the last 15 yr. More important, we found 11 loci located on chromosomes 1BS, 1BL, 2AL, 2BS (2), 2DL, 4DL, 5BL, 6AL, 7BL, and 7DS showing pleiotropic effects on resistance to leaf rust, stripe rust, and powdery mildew. Among these, QTL on chromosomes 1BL, 4DL, and 7DS also correlate with leaf tip necrosis. Fine mapping and cloning of these QTL will be achieved with the advent of cheaper high-throughput genotyping technologies. Germplasm carrying these potential resistance genes will be useful for developing cultivars with durable multidisease resistance. In addition to its non-NBS–LRR (nucleotide binding site–leucine rich repeat) structure, the senescence-like processes induced by Lr34 could be the reason for durability of resistance; however, more information is needed for a full understanding of the molecular mechanism related to durability. Adult plant resistance genes have been used by CIMMYT for more than 30 yr and have also been transferred to many Chinese wheat varieties through shuttle breeding.

Physiological factors underpinning grain yield improvements of synthetic derived wheat in South Western China

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science, 2014

Yonglu TangRosewarne, G.M.Chaosu LiXiaoli WuWuyun YangChun Wu.

Synthetic hexaploid wheat (SHW) is a valuable source of genetic diversity for germplasm enrichment in wheat breeding. In China, SHW derived material has shown significant yield increases. A three year field experiment at Guanghan and Jiangyou in the Sichuan Basin of China was conducted to characterize the potential of three SHW-derived cultivars (SDCs) with five local elite non-synthetic derived cultivars as checks (NSCs). SDCs showed on average an 11.5% or 951 kg ha-1 yield increase as compared to NSCs. This yield gain was mainly attributed to increases in both grain number m-2 (5.7%) and thousand kernel weight (5.9%). A higher rate of above-ground dry matter accumulation, especially in the early growth stages, was observed in the SDCs. The SDCs also had better partitioning to the grain, as evidenced through an increased harvest index (HI). The SDCs had a relatively compact and erect plant type with medium and upper leaves having a mean EC45° increase of 8.4% over the NSCs at 20 d after flowering. Correlations between grain yield components and physiological traits were analyzed. We concluded that the use of SHW has the potential to significantly increase wheat yield grown under rain-fed environments with low photosynthetically active radiation.

Accessing Spelt Gene Pool to Develop Well-Adapted Zinc- and Iron-Rich Bread Wheat

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science, 2014

Srinivasa, J.Arun, B.Mishra, V.K.Chand, R.Sharma, D.Bhardwaj, S.C.Joshi, A.K.

Breeding for higher Zn and Fe content in the wheat grain can be justified in the context of malnutrition. This breeding study set out to gauge the potential of crosses between spelt (Triticum aestivum ssp. spelta) and bread wheat (Triticum aestivum L. em. Thell) for enhancing the Zn and Fe content of wheat cultivars adapted to the northeastern plains zone (NEPZ) of India. BC1F8 populations were developed from two spelt × bread wheat combinations: H+ 35 × HUW 468 and H+ 15 × HUW 234. Their performance was evaluated at three locations in NEPZ. Around four genes were found to control inheritance of grain Zn concentration. Grain Zn and Fe concentration varied among the lines, as did other yield-related traits. Significant positive correlations were recorded between the grain content of Zn, Fe, and protein, but also negative correlations between them and the important agronomic characteristics plant height, grain yield, and thousand grain weight (TGW). Some of the derived lines showed increased mineral concentration without any decrease in grain size. The best ten selections in each population were all significantly superior to their respective bread wheat parent with respect to grain Zn and Fe content as well as some of the agronomic traits, which included resistance to spot blotch, stem rust, and leaf rust.


Evaluation of genomic selection training population designs and genotyping strategies in plant breeding programs using simulation

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science, 2014

 Hickey, J.M.Dreisigacker, S.Crossa, J.Hearne, S.Babu, R.Prasanna, B.M.Grondona, M.Zambelli. A.Windhausen, V.S.Mathews, K.Gorjanc, G. 

Genomic selection offers great potential to increase the rate of genetic improvement in plant breeding programs. This research used simulation to evaluate the effectiveness of different strategies for genotyping and phenotyping in order to enable genomic selection in early generation individuals (e.g., F2), in breeding programs involving bi-parental or similar (e.g. back cross or top cross) populations. By using phenotypes that were previously collected in other bi-parental populations selection decisions could be made without waiting for phenotypes that pertain directly to the selection candidate to be collected, a process that would take at least three growing seasons. If these phenotypes were collected in bi-parental populations that were closely related to the selection candidates only a small number of markers (e.g. 200-500) and a small number of phenotypes (e.g. 1000) were needed to achieve effective accuracy of estimated breeding values. If these phenotypes were collected in bi-parental populations that were not closely related to the selection candidates, as many as 10000 markers and 5000 to 20000 phenotypes were needed. Increasing marker density beyond 10000 markers did not show benefit and in some scenarios reduced the accuracy of prediction. This study provides a guide, enabling resource allocation to be optimized between genotyping and phenotyping investment dependent on the population under development.

Genotype by environment interaction and stability analysis for grain yield of single cross hybrids using AMMI Biplots

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science, 2014

Ndhlela, T.Herselman, L.Magorokosho, C.Setimela, P.Mutimaamba, C.Labuschagne, M.

Maize (Zea mays) is the most important cereal crop in Zimbabwe and is grown by both large and small scale farmers who are located in different agro-ecological zones of the country. The development and dissemination of adapted and high yielding maize cultivars to these agro-ecological zones involves conducting multi environment trials (METs). This study was conducted with the objectives of i) understanding complex G x E interaction and stability of single cross hybrids generated using CIMMYT elite drought tolerant lines and Department of Research &Specialist Services (DR&SS) elite drought susceptible lines for grain yield across stress and non-stress environments and ii) to identify genotypes to recommend for further use in the breeding programme. Initially yield data of 80 maize single cross hybrids tested across seven environments during the 2009/10 and 2010/11 seasons were analyzed using the AMMI biplot method. The analysis was further done for 20 best performing genotypes to facilitate less congested graphical presentation. Combined analysis of variance showed highly significant differences for the G x E interaction indicating the possibility of selection for stable genotypes. The five AMMI IPCAs (IPCA1, IPCA2, IPCA3, IPCA4 and IPCA5) explained 82.41% of the variation and they were highly significant. The results showed three genotypes with high yield performance and broad adaptability whilst narrow adaptations were also observed. Agricultural Research Trust farm was the most powerful site in discriminating among genotypes and the most representative environment.

Combining ability of certain agronomic traits in quality protein maize under stress and non-stress environments in Eastern and Southern Africa

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 54 (3) : 1004-1014, 2014

Dagne Wegary GissaVivek, B.Labuschagne, M.T.

Growing maize (Zea mays L.) hybrids tolerant to drought and low N stress would significantly reduce yield losses occurring in Africa. This study evaluated the performance of quality protein maize (QPM) F1 hybrids, and general (GCA) and specific combining ability (SCA) of QPM inbred lines for grain yield and other agronomic traits under stress and non-stress environments. A diallel cross of 15 QPM inbred lines was evaluated under drought and low N stresses and optimal conditions in a total of 17 environments in Eastern and Southern Africa. Significant variations were observed among the hybrids for all measured traits. TZMI703 x (6207QB/6207QA), GQL5 x (6207QB/6207QA) and CML159 x (6207QB/6207QA) were identified as the best single crosses across environments. GCA and SCA mean squares were significant for all measured traits, indicating that additive and non-additive genetic effects were important in this set of genotypes under all test environments. GCA effects were more important under drought stress, and SCA effects were more important under low N and optimal conditions for grain yield. There was preponderance of GCA effects for most agronomic traits tested in all environmental conditions. Inbred lines CML159SR, GQL5, CML159 and CML312SRQ exhibited favorable GCA effects for grain yield under stress and optimal conditions, indicating that the genetic systems controlling a given trait under different conditions are at least partially similar. Cross combinations with favorable SCA effects for grain yield and other traits were also identified. Generally, this study provided evidence that good performance can be achieved under stress and non-stress conditions in QPM germplasm.

Variability of grain-filling traits in early maturing CIMMYT tropical maize inbred lines

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 54 (2) : 530-536, 2014

Gasura, E.; Setimela, P.S.;Amsal Tesfaye Tarekegne; Icishahayo, D.; Edema, R.; Gibson, P.T.; Okori, P.

Grain-filling rate (GFR), effective grain-filling duration (EGFD), and total grain-filling duration (TGFD) are important physiological traits of maize (Zea mays L.) grain yield (GY) formation. To devise effective breeding strategies, the genetic nature of these traits is a prerequisite for improvement in early maturing maize. A study was conducted at CIMMYT-Zimbabwe using an α-lattice design with two replications in two environments to investigate the genetic variability of grain-filling traits in 18 early maturing tropical maize inbred lines derived from CIMMYT germplasm. Highly significant differences were observed for GY, thousand-grain weight (TGW), GFR, EGFD, TGFD, kernels per row (KR), and rows per cob (RC). The broad-sense coefficient of genetic determination (the fixed parent equivalent of broad-sense heritability) was above 70% for all of the traits. The highest GY was obtained from the inbred line T032-30 (79.2 g plant–1) and the lowest from inbred line CML506 (37.6 g plant–1), respectively. Therefore, selecting for higher GFR and longer TGFD, especially the EGFD, can increase GY of early maize without extending days to physiological maturity (DPM).

Relationship of line per se and testcross performance for grain yield of tropical maize in drought and well-watered trials

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 53 (4) : 1228-1236, 2013

Kebede, A.Z.; Melchinger, A.E.; Cairns, J.E.; Araus, J.L.; Makumbi, D.; Atlin, G.N.

To optimize the efficiency of maize (Zea mays L.) drought breeding, the ability to predict testcross performance (TP) under drought stress using line per se performance (LP) of the parental inbreds would be useful. We evaluated LP and TP of tropical inbreds in well-watered and drought environments in Kenya and Mexico. Our main objective was to determine if LP under drought stress was predictive of TP for grain yield under drought stress and if selection for LP under drought stress would result in reduced yield potential for TP under well-watered conditions. Average yield reduction under drought stress was 77% for lines and 68% for testcrosses. Average genotypic correlations between lines and testcrosses under drought stress were positive and low (genotypic correlation = 0.48), but correlations increased with increasing levels of drought stress in both LP and TP trials. Averaged over all sets, indirect selection for LP was predicted to be only 57% as effective as direct selection for TP under drought stress but was on average substantially higher in testcross sets where yield reduction due to drought was 70% or more. Therefore, LP under drought stress could be used to develop hybrids for severely drought-prone environments. Moreover, LP under drought stress was uncorrelated with TP for grain yield under well-watered conditions, showing that selection of lines per se for drought tolerance would likely not reduce yield potential of testcrosses.

Doubled haploids versus conventional breeding in CIMMYT wheat breeding programs

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 53 (1) : 74-83, 2013

Huihui Li; Singh, R.P.;Braun, H.J.; Pfeiffer, W.H.; Jiankang Wang

Doubled haploid (DH) technology has been used in breeding programs for several decades and is currently the method of choice in a number of crop species, including barley (Hordeum vulgare L.), rapeseed (Brassica napus L.), maize (Zea mays L.), and wheat (Triticum aestivum L.). In this study we investigated via computer simulation the benefit of using DHs compared with the conventional wheat breeding strategy used at CIMMYT. Two strategies using DHs were considered: DH lines directly derived from F1 hybrids (F1–DH), and DH lines derived from F3 individuals that are retained following selection for agronomic traits in the F2 generation (F3–DH). Genetic gains per cycle, per year, and per dollar spent were consistently higher for conventional breeding than for DH breeding strategies, especially gains per dollar. Though the F1–DH strategy saved 1 yr in completing a breeding cycle, genetic gains per year for the adaptation trait from F1–DH were much lower than those from conventional breeding, where two growing seasons are used per year. Though the DH breeding strategy showed no significant advantages over the conventional wheat shuttle-breeding regime of CIMMYT, we did not exclude the possibility that the DH breeding strategy may have advantages when genetic gains per unit of time are considered, and only one generation is grown per year. The conventional shuttle regime will continue to be the major wheat breeding strategy at CIMMYT, where two cycles can be grown per year and breeders can do selection in large populations in both cycles.

Insights into genotype × tillage interaction effects on the grain yield of wheat and maize

Posted by Carelia Juarez on , in Journal Articles

Published in Crop Science 53 (5) : 1845-1859, 2013

J.M. Herrera, N. Verhulst, R.M. Trethowan, P. Stamp and B. Govaerts

No tillage or zero tillage (NT) is the extreme form of reduced tillage; NT with residue retention is a main component of conservation agriculture. Using a literature survey and meta-analysis, this study aimed to (i) summarize the results of studies comparing the grain yield of wheat [Triticum aestivum L. and Triticum turgidum L. subsp. durum (Desf.) Husn. (syn. Triticum durum Desf.)] and maize (Zea mays L.) genotypes under contrasting tillage, (ii) identify sources of variation in the grain yield response of wheat and maize genotypes to tillage practices, and (iii) identify potential traits for NT breeding programs. Grain yield was compared under NT and conventional tillage (CT) for 112 wheat genotypes (44 spring, 60 winter, and eight durum wheat genotypes) across 12 locations and 24 yr and for 93 maize hybrids across six locations and 5 yr. Most of these studies showed slightly higher grain yields under CT for maize (+5%) and winter (+5%) and spring (+2%) wheat. In the few studies where selection had been conducted under NT, the effect of tillage on the grain yield was modified significantly by genotypes. Traits associated with the emergence of vigorous seedlings and resistance to a changed spectrum of diseases increase genotype performance under NT. There is a need to evaluate genotypes developed under NT and extend the research on genotype performance under NT to locations with reduced input use and, in addition to tillage, investigate other factors that differentiate conservation agriculture from conventional practice.