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Vivek B.S.,Indian International Crops Research Institute for the Semi Arid Tropics | Krishna G.K.,Indian International Crops Research Institute for the Semi Arid Tropics | Krishna G.K.,Bayer Crop Science Ltd | Vengadessan V.,Indian International Crops Research Institute for the Semi Arid Tropics | And 16 more authors.
Plant Genome | Year: 2017

More than 80% of the 19 million ha of maize (Zea mays L.) in tropical Asia is rainfed and prone to drought. The breeding methods for improving drought tolerance (DT), including genomic selection (GS), are geared to increase the frequency of favorable alleles. Two biparental populations (CIMMYTAsia Population 1 [CAP1] and CAP2) were generated by crossing elite Asian-adapted yellow inbreds (CML470 and VL1012767) with an African white drought-tolerant line, CML444. Marker effects of polymorphic single-nucleotide polymorphisms (SNPs) were determined from testcross (TC) performance of F2:3 families under drought and optimal conditions. Cycle 1 (C1) was formed by recombining the top 10% of the F2:3 families based on TC data. Subsequently, (i) C2[PerSe_PS] was derived by recombining those C1 plants that exhibited superior per se phenotypes (phenotype-only selection), and (ii) C2[TC-GS] was derived by recombining a second set of C1 plants with high genomic estimated breeding values (GEBVs) derived from TC phenotypes of F2:3 families (marker-only selection). All the generations and their top crosses to testers were evaluated under drought and optimal conditions. Per se grain yields (GYs) of C2[PerSe_PS] and that of C2[TC-GS] were 23 to 39 and 31 to 53% better, respectively, than that of the corresponding F2 population. The C2[TC-GS] populations showed superiority of 10 to 20% over C2[PerSe-PS] of respective populations. Top crosses of C2[TC-GS] showed 4 to 43% superiority of GY over that of C2[PerSe_PS] of respective populations. Thus, GEBV-enabled selection of superior phenotypes (without the target stress) resulted in rapid genetic gains for DT. © Crop Science Society of America.


Mir C.,French National Institute for Agricultural Research | Zerjal T.,French National Institute for Agricultural Research | Combes V.,French National Institute for Agricultural Research | Dumas F.,French National Institute for Agricultural Research | And 16 more authors.
Theoretical and Applied Genetics | Year: 2013

Maize was first domesticated in a restricted valley in south-central Mexico. It was diffused throughout the Americas over thousands of years, and following the discovery of the New World by Columbus, was introduced into Europe. Trade and colonization introduced it further into all parts of the world to which it could adapt. Repeated introductions, local selection and adaptation, a highly diverse gene pool and outcrossing nature, and global trade in maize led to difficulty understanding exactly where the diversity of many of the local maize landraces originated. This is particularly true in Africa and Asia, where historical accounts are scarce or contradictory. Knowledge of post-domestication movements of maize around the world would assist in germplasm conservation and plant breeding efforts. To this end, we used SSR markers to genotype multiple individuals from hundreds of representative landraces from around the world. Applying a multidisciplinary approach combining genetic, linguistic, and historical data, we reconstructed possible patterns of maize diffusion throughout the world from American "contribution" centers, which we propose reflect the origins of maize worldwide. These results shed new light on introductions of maize into Africa and Asia. By providing a first globally comprehensive genetic characterization of landraces using markers appropriate to this evolutionary time frame, we explore the post-domestication evolutionary history of maize and highlight original diversity sources that may be tapped for plant improvement in different regions of the world. © 2013 Springer-Verlag Berlin Heidelberg (outside the USA).


Jampatong C.,Kasetsart University | Jampatong S.,Kasetsart University | Jompuk C.,Kasetsart University | Sreewongchai T.,Kasetsart University | And 3 more authors.
Maydica | Year: 2013

Sorghum downy mildew (SDM) is one of the most destructive diseases of maize (Zea mays L) in South-East Asia. Understanding the genetic basis of downy mildew resistance (DMR) could increase the efficiency of breeding for disease resistant germplasm. The objectives of this study were to determine the number, genomic positions and genetic effects of quantitative trait loci (QTL) conferring resistance to SDM. The study included 251 F2:3 families derived from a cross between the two inbreds, Nei9008 (Thailand) and CML289 (CIMMYT), resistant and susceptible, respectively. Individuals in the population were genotyped for simple sequence repeat (SSR) and phenotypic resistance data were evaluated as percentage disease incidence in replicated field trials at three environments by Triple Lattice design. Heritability across environments was 94.3%. Traits were analyzed within and across environment using composite interval mapping. Nine QTLs were identified for resistance to SDM, one QTL each on chromosome 2, 3, 4, and 6, three QTLs on chromosome 5, and two QTLs on chromosome 9. Just one QTL on chromosome bin 5.07 came from the susceptible parent, all others from the resistant parent, Nei9008. The QTLs in chromosome bins 2.09 at umc1736, 5.03 at bnlg1902, and 6.01 at bnlg1867 had major effects and were consistent over all environments. A common map shows intriguing collocations of SDM QTLs with those for other disease and insect resistance QTLs from literature. As several consistent QTLs for downy mildew resistance are available now, an avenue is open for pyramiding multiple genes by marker assisted selection (MAS) that may control different mechanisms for resistance.


Xue Y.,Huazhong Agricultural University | Warburton M.L.,Mississippi State University | Sawkins M.,Generation Challenge Program | Zhang X.,Huazhong Agricultural University | And 8 more authors.
Theoretical and Applied Genetics | Year: 2013

Drought can cause severe reduction in maize production, and strongly threatens crop yields. To dissect this complex trait and identify superior alleles, 350 tropical and subtropical maize inbred lines were genotyped using a 1536-SNP array developed from drought-related genes and an array of 56,110 random SNPs. The inbred lines were crossed with a common tester, CML312, and the testcrosses were phenotyped for nine traits under well-watered and water-stressed conditions in seven environments. Using genome-wide association mapping with correction for population structure, 42 associated SNPs (P ≤ 2.25 × 10-6 0.1/N) were identified, located in 33 genes for 126 trait × environment × treatment combinations. Of these genes, three were co-localized to drought-related QTL regions. Gene GRMZM2G125777 was strongly associated with ear relative position, hundred kernel weight and timing of male and female flowering, and encodes NAC domain-containing protein 2, a transcription factor expressed in different tissues. These results provide some good information for understanding the genetic basis for drought tolerance and further studies on identified candidate genes should illuminate mechanisms of drought tolerance and provide tools for designing drought-tolerant maize cultivars tailored to different environmental scenarios. © 2013 Springer-Verlag Berlin Heidelberg.


Cairns J.E.,International Maize and Wheat Improvement Center | Crossa J.,CIMMYT | Zaidi P.H.,CIMMYT | Grudloyma P.,Nakhon Sawan Field Crops Research Center | And 9 more authors.
Crop Science | Year: 2013

Low maize (Zea mays L.) yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and southern Africa. Climate projections suggest higher temperatures within drought-prone areas. Research in model species suggests that tolerance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproductive stage drought stress, heat stress, and combined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Significant genotype × trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically distinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors tolerant to drought and combined drought and heat stress, notably La Posta Sequia C7-F64-2-6-2-2 and DTPYC9-F46-1-2-1-2, need to be incorporated into maize breeding pipelines. © Crop Science Society of America.


Windhausen V.S.,University of Hohenheim | Atlin G.N.,International Maize and Wheat Improvement Center | Hickey J.M.,International Maize and Wheat Improvement Center | Crossa J.,International Maize and Wheat Improvement Center | And 11 more authors.
G3: Genes, Genomes, Genetics | Year: 2012

Genomic prediction is expected to considerably increase genetic gains by increasing selection intensity and accelerating the breeding cycle. In this study, marker effects estimated in 255 diverse maize (Zea mays L.) hybrids were used to predict grain yield, anthesis date, and anthesis-silking interval within the diversity panel and testcross progenies of 30 F2-derived lines from each of five populations. Although up to 25% of the genetic variance could be explained by cross validation within the diversity panel, the prediction of testcross performance of F2-derived lines using marker effects estimated in the diversity panel was on average zero. Hybrids in the diversity panel could be grouped into eight breeding populations differing in mean performance. When performance was predicted separately for each breeding population on the basis of marker effects estimated in the other populations, predictive ability was low (i.e., 0.12 for grain yield). These results suggest that prediction resulted mostly from differences in mean performance of the breeding populations and less from the relationship between the training and validation sets or linkage disequilibrium with causal variants underlying the predicted traits. Potential uses for genomic prediction in maize hybrid breeding are discussed emphasizing the need of (1) a clear definition of the breeding scenario in which genomic prediction should be applied (i.e., prediction among or within populations), (2) a detailed analysis of the population structure before performing cross validation, and (3) larger training sets with strong genetic relationship to the validation set. © 2012 Windhausen et al.


Koshawatana C.,Field Crops Research Institute | Grudloyma P.,Nakhon Sawan Field Crops Research Center | Indan W.,Nakhon Sawan Field Crops Research Center
Kasetsart Journal - Natural Science | Year: 2010

In Nakhon Sawan 3 hybrid seed production, conventional planting uses a 4:1 ratio of female to male rows. After pollination has finished, the male rows are eliminated, causing an empty space in the production field. To increase the yield and utilization of the area by female plants, in 2008, an experiment was conducted to study a compact planting technique involving planting male inbreds between female rows at the Nakhon Sawan Field Crops Research Center. The experiment used a split-plot design with three replications, with the main plot consisting of two plantings of parent material: 1) planting female and male inbreds on the same day; and 2) planting female inbreds two days later. Sub-plots consisted of four male planting methods: 1) compact planting between 65 cm female rows; 2) compact planting between 75 cm female rows; 3) compact planting between 85 cm female rows; and 4) planting female to male rows in the ratio of 4:1. The results showed that all compact plantings tended to increase yield by 12-28% compared with that of a female to male row planting ratio of 4:1. Compact planting between 75 cm female rows produced the highest yield of 2,381 kg ha -1. Compact planting between female rows at 85 cm, 65 cm and planting female to male rows at a ratio of 4:1 produced a yield of 2,288, 2,081 and 1,856 kg ha -1, respectively. Increased yield was due to the number of ears harvested per hectare increasing by up to 10-25%. All compact planting options delayed the time to 50% pollen shedding from 63 d (in planting female to male rows at a ratio of 4:1) to 64, 65 and 66 d in compact planting between rows of 85 cm, 75 cm and 65 cm, respectively. There was no effect of compact planting on the number of days to 50% silking of female inbreds and on male and female height. The results showed that planting inbreds on the same day tended to increase yield by 20% compared with that of planting female two days later.


Sharman M.,Khan Research Laboratories | Lapbanjob S.,Nakhon Sawan Field Crops Research Center | Sebunruang P.,Nakhon Sawan Field Crops Research Center | Belot J.-L.,Instituto Mato Grossense do Algodao | And 3 more authors.
Australasian Plant Disease Notes | Year: 2015

Partial virus genome sequence with high nucleotide identity to Cotton leafroll dwarf virus (CLRDV) was identified from two cotton (Gossypium hirsutum) samples from Thailand displaying typical cotton leaf roll disease symptoms. We developed and validated a PCR assay for the detection of CLRDV isolates from Thailand and Brazil. © 2015, Australasian Plant Pathology Society Inc.

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