Showing papers by "International Maize and Wheat Improvement Center published in 1998"
TL;DR: The efficient and effective application of marker-assisted selection for polygenic trait improvement certainly needs new technology but, more importantly, it requires the development of innovative strategies that bypass the conceptual bottlenecks imposed by current approaches.
475 citations
TL;DR: Lower rates of nitrogen fertilizer, applied later in the crop cycle, reduced the loss of nitrogen without affecting yield and grain quality, saving farmers money and reducing environmental costs.
Abstract: Nitrogen fertilization is a substantial source of nitrogen-containing trace gases that have both regional and global consequences. In the intensive wheat systems of Mexico, typical fertilization practices lead to extremely high fluxes of nitrous oxide (N2O) and nitric oxide (NO). In experiments, lower rates of nitrogen fertilizer, applied later in the crop cycle, reduced the loss of nitrogen without affecting yield and grain quality. Economic analyses projected this alternative practice to save 12 to 17 percent of after-tax profits. A knowledge-intensive approach to fertilizer management can substitute for higher levels of inputs, saving farmers money and reducing environmental costs.
471 citations
TL;DR: The establishment of an international network to coordinate data collection and link sites would facilitate more precise prediction of agroecosystem sustainability and future global change.
Abstract: Long-term agroecosystem experiments can be defined as large-scale field experiments more than 20 years old that study crop production, nutrient cycling, and environmental impacts of agriculture. They provide a resource for evaluating biological, biogeochemical, and environmental dimensions of agricultural sustainability; for predicting future global changes; and for validating model competence and performance. A systematic assessment is needed to determine the merits of all known experiments and to identify any that may exist in tropical and subtropical environments. The establishment of an international network to coordinate data collection and link sites would facilitate more precise prediction of agroecosystem sustainability and future global change.
374 citations
TL;DR: Two F6 RILs were identified from the above population that lacked Lr34 and Lr46 but carried the leaf rust resistance gene in 7BL, hereby designated Lr68, and γ-irradiation-induced deletion stocks that lackedLr68 but possessed Lr14b showed that Lr 68 and L r14b are different loci.
Abstract: The common wheat cultivar Parula possesses a high level of slow rusting, adult plant resistance (APR) to all three rust diseases of wheat. Previous mapping studies using an Avocet-YrA/Parula recombinant inbred line (RIL) population showed that APR to leaf rust (Puccinia triticina) in Parula is governed by at least three independent slow rusting resistance genes: Lr34 on 7DS, Lr46 on 1BL, and a previously unknown gene on 7BL. The use of field rust reaction and flanking markers identified two F6 RILs, Arula1 and Arula2, from the above population that lacked Lr34 and Lr46 but carried the leaf rust resistance gene in 7BL, hereby designated Lr68. Arula1 and Arula2 were crossed with Apav, a highly susceptible line from the cross Avocet-YrA/Pavon 76, and 396 F4-derived F5 RILs were developed for mapping Lr68. The RILs were phenotyped for leaf rust resistance for over 2 years in Ciudad Obregon, Mexico, with a mixture of P. triticina races MBJ/SP and MCJ/SP. Close genetic linkages with several DNA markers on 7BL were established using 367 RILs; Psy1-1 and gwm146 flanked Lr68 and were estimated at 0.5 and 0.6 cM, respectively. The relationship between Lr68 and the race-specific seedling resistance gene Lr14b, located in the same region and present in Parula, Arula1 and Arula2, was investigated by evaluating the RILs with Lr14b-avirulent P. triticina race TCT/QB in the greenhouse. Although Lr14b and Lr68 homozygous recombinants in repulsion were not identified in RILs, γ-irradiation-induced deletion stocks that lacked Lr68 but possessed Lr14b showed that Lr68 and Lr14b are different loci. Flanking DNA markers that are tightly linked to Lr68 in a wide array of genotypes can be utilized for selection of APR to leaf rust.
369 citations
TL;DR: In this article, the effects of agronomic practices on soil resources were evaluated using on-farm participatory research, and three components of organic matter technology were evaluated: (1) residue quality; (2) the role of deep rooting systems; and (3) tradeoffs between legumes grown for grain versus soil regeneration.
239 citations
TL;DR: This research synthesizes the two approaches in order to examine farmer selection of local wheat landraces in relation to that of modern varieties in three provinces in western Turkey.
Abstract: This paper focuses on the value of landraces (traditional and local crop varieties) to farmers in centers of agricultural diversity. Additional information on the factors contributing to the private value which farmers assign to landraces may help to identify a strategy for ensuring the conservation of the crop genetic resources (CGRs) which are embodied in landraces while at the same time minimizing the costs. Economic and ethnobotanical approaches for examining the value of landraces complement one another. A formal economic approach establishes a framework for quantitative analysis while ethnobotanical methods provide qualitative data for assessing the likelihood that particular farmers or farm sectors will maintain landraces. Our research synthesizes the two approaches in order to examine farmer selection of local wheat landraces in relation to that of modern varieties in three provinces in western Turkey. Multiple farmer concerns (e.g. yield, risk, quality), environmental heterogeneity, and missing markets contribute to the persistence of landraces. Household characteristics informing variety choice will also affect the household's perceptions of the importance and value of landraces.
183 citations
TL;DR: A breeding system is described that integrates single-copy and multiplex markers with confirmation of the target phenotype in doubled-haploid lines phenotyped in field tests and may be useful for simultaneously producing agronomically useful germplasm and contributing to an understanding of quantitatively inherited traits.
Abstract: Genome-analysis tools are useful for dissecting complex phenotypes and manipulating determinants of these phenotypes in breeding programs. Quantitative trait locus (QTL)-analysis tools were used to map QTLs conferring adult plant resistance to stripe rust (caused by Puccinia striiformis f.sp. hordei) in barley. The resistance QTLs were introgressed into a genetic background unrelated to the mapping population with one cycle of marker-assisted backcrossing. Doubled-haploid lines were derived from selected backcross lines, phenotyped for stripe-rust resistance, and genotyped with an array of molecular markers. The resistance QTLs that were introgressed were significant determinants of resistance in the new genetic background. Additional resistance QTLs were also detected. The susceptible parent contributed resistance alleles at two of these new QTLs. We hypothesize that favorable alleles were fixed at these new QTLs in the original mapping population. Genetic background may, therefore, have an important role in QTL-transfer experiments. A breeding system is described that integrates single-copy and multiplex markers with confirmation of the target phenotype in doubled-haploid lines phenotyped in field tests. This approach may be useful for simultaneously producing agronomically useful germplasm and contributing to an understanding of quantitatively inherited traits.
167 citations
TL;DR: The T1BL.1RS wheat (Triticum aestivum L.) - rye (Secale cereale L.) translocations) translocations have been of particular interest and are widely used in bread wheat breeding programs, especially for reduced irrigation or rainfed environments.
Abstract: The T1BL.1RS wheat (Triticum aestivum L.) - rye (Secale cereale L.) translocations have been of particular interest and are widely used in bread wheat breeding programs. The objective of this study was to determine the effect of the T1BL.1RS chromosome on grain yield and its components using 20 near-isolines of spring bread wheat cultivar ‘Seri M82’ (10 homozygous for chromosome 1B substitution and 10 homozygous for T1BL.1RS). The test lines have been produced by substituting the 1B chromosome in Seri M82 (T1BL.1RS, T1BL.1RS) through backrossing. Two field experiments were evaluated under optimum (five irrigations) and reduced (one irrigation) moisture conditions for two consecutive production cycles at the Mexican National Agricultural Research Institute, Ciudad Obregon, Sonora, Mexico. The presence of T1BL.1RS had a significant effect on grain yield, harvest index, grains/m2, grains/spike, 1000-grain weight, test weight, flowering date and physiological maturity in both moisture conditions. The agronomic advantage of the 1B substitution lines on above-ground biomass yield at maturity, spikes/m2and grain-filling duration was expressed only under the optimum moisture condition. The presence of T1BL.1RS increased grain yield 1.6% and 11.3% for optimum and reduced moisture conditions, respectively. These results encourage further use of T1BL.1RS wheats in improving agronomic traits, especially for reduced irrigation or rainfed environments.
164 citations
TL;DR: Replicated trials using near-isogenic lines of spring wheat 'Seri 82' were conducted for 2 yr under non-moisture stress and simulated moisture stress conditions to determine the effects of the 7DL.7Ag and 1BL.1RS translocations on grain yield and related traits.
Abstract: In hexaploid wheat (Triticum aestivum L.) disease resistance genes transferred from alien sources are often associated with undesirable traits. Replicated trials using near-isogenic lines of spring wheat 'Seri 82' were conducted for 2 yr under non-moisture stress and simulated moisture stress conditions to determine the effects of the 7DL.7Ag and 1BL.1RS translocations [from Agropyron elongatum (Host) Beauv. and Secale cereale L., respectively] on grain yield and related traits. Mean grain yield of the 1B lines was significantly higher (3.2%) than that of the 1BL.1RS translocation lines in non-moisture stress trials, but not significantly higher in the moisture stress trials. The mean grain yields of the five highest yielding reconstituted Seri 82 genotypes (1BL.1RS) were significantly lower than that of the genotypes without the 1BL.1RS translocation in non-moisture stress (3.2%) and moisture stress (5.2%) conditions. Incorporation of the 7DL.7Ag translocation caused a significant increase (9%) in biomass at harvest in non-moisture stress trials. The mean grain yields of the five highest yielding 7DL.7Ag lines were significantly higher (8.2%) than the reconstituted Seri 82 genotypes in non-moisture stress conditions and more than 16% lower under moisture stress. Lower grain yields of the 7DL.7Ag lines under moisture stress could be due to their excessive pre-heading biomass production. Several yield-related traits of the near-isogenic genotypes varied significantly. Presence of each translocation caused lateness and, when present together, the 1BL.1RS and 7DL.7Ag translocations delayed heading and maturity by 7 and 5 d, respectively. The genetic background of the recipient wheat can affect the utility of a translocation.
139 citations
TL;DR: The main objectives of this study were to develop the Modified Location model (MLM) that allows empty cells in some subpopulations under the assumption that the means and the variance-covariance matrices depend on a given subpopulation instead of on a specific cell.
Abstract: Hierarchical and nonhierarchical clustering methods are used for classifying genetic resources. In hierarchical clustering methods, all variables (categorical and continuous) can be used to form the subpopulations (groups or clusters), but in standard nonhierarchical methods only the continuous variables are incorporated in the analysis. The Location model (LM) allows classifying individuals into homogeneous subpopulations by continuous and categorical variables. In practice, the multinomial variable of the LM that arises from the combination of all the categorical variables usually shows empty cells in some subpopulations with the consequence of not allowing estimation of cell means and within-cell variances and covariances. The main objectives of this study were (i) to develop the Modified Location model (MLM) that allows empty cells in some subpopulations under the assumption that the means and the variance-covariance matrices depend on a given subpopulation instead of on a specific cell, (ii) to show how to use the MLM in the context of two-stage clustering in which the Ward method is used to form the initial groups and the MLM is applied to those groups (Ward-MLM), and (iii) to show how to apply the Ward-MLM to three different data sets to study some of its features and to compare results with other methods. The two-stage clustering strategy of finding initial groups by the Ward method and then improving the composition of the groups by the MLM produces compact and well-separated groups with respect to all the variables (categorical and continuous) compared with classifications obtained with only categorical variables, with only continuous variables, and with the standard Location model.
126 citations
TL;DR: The analysis revealed the tetrasomic nature of the inheritance of the chromosomal segment controlling apomixis, which contradicts the usually accepted hypothesis of an allopolyploid origin of apomictic species.
Abstract: Polyploids in Tripsacum, a wild relative of maize, reproduce through the diplosporous type of apomixis, an asexual mode of reproduction through seeds. Diplosporous apomixis involves both the failure of meiosis and the parthenogenetic development of the unreduced gametes, resulting in progenies that are exact genetic copies of the mother plant. Apomixis is believed to be controlled by one single dominant allele, responsible for the whole developmental process. Construction of a linkage map for the chromosome controlling diplosporous apomixis in Tripsacum was carried out in both tetraploid-apomictic and diploid-sexual Tripsacum species using maize restriction fragment length polymorphism (RFLP) probes. A high level of collinearity was observed between the Tripsacum chromosome carrying the control of apomixis and a duplicated segment in the maize genome. In the apomictic tetraploid, there was a strong restriction to recombination, as compared to the corresponding genomic segment in sexual plants and maize. This suggests that apomixis, although inherited as a single Mendelian allele, might really be controlled by a cluster of linked loci. The analysis also revealed the tetrasomic nature of the inheritance of the chromosomal segment controlling apomixis, which contradicts the usually accepted hypothesis of an allopolyploid origin of apomictic species. The implications of these data for the transfer of apomixis into cultivated crops are discussed, and a new approach to studying the genetics of apomixis, based on comparative mapping, is proposed.
TL;DR: Although GDE PED was not well suited for identifying degree of relatedness among individuals, it may be adequate for assessing overall patterns of genetic variation among regionally adapted germplasm, and AFLP may have more utility for identifying parental combinations with maximum allelic variation.
Abstract: Comparing results of different genetic diversity estimation methods may be indicative of their utility as parental selection tools for plant breeders. Forty-three spring and winter wheat lines (Triticum aestivum L.) from the Pacific Northwest (PNW) were used to compare pedigree and amplified fragment length polymorphism (AFLP)-based genetic diversity estimates (GDE PED and GDE respectively). The mean of the 903 GDE PED pairwise comparisons was 0.96, and 89% of the values were >0.90. In contrast, GDE AFLP values were normally distributed (mean = 0.54), suggesting that this diversity measure was better able to identify pairs of genotypes representing the entire range of possible GDEs. Thus, GDE AFLP may have more utility than GDE PED for identifying parental combinations with maximum allelic variation. Despite the substantially different means and distributions of the two diversity measures, a moderate rank correlation (r s = 0.42, P < 0.001) was detected between the two GDE matrices. AFLP fragments from hypomethylated portions of the genome (generated with Pst I:Mse I) were more highly associated with GDE PED than were fragments generated with the methylation insensitive combination Eco RI:Mse I (r s = 0.44 and 0.28, respectively). Pedigree and AFLP-based GDEs detected a similar hierarchical pattern of genetic diversity among the 43 cultivars evaluated. Although GDE PED was not well suited for identifying degree of relatedness among individuals, it may be adequate for assessing overall patterns of genetic variation among regionally adapted germplasm. It remains to be determined which method, if either, provides predictive estimates of heterosis or genetic variance among progeny from specific parental combinations.
TL;DR: Results indicated that relative performance of cultivars is influenced by differential sensitivity to minimum temperatures during the spike growth period, and the PLS method was effective in detecting environmental and cultivar explanatory variables associated with factors that explained large portions of GEI.
Abstract: The partial least squares (PLS) regression method relates genotype × environment interaction effects (GEI) as dependent variables (Y) to external environmental (or cultivar) variables as the explanatory variables (X) in one single estimation procedure. We applied PLS regression to two wheat data sets with the objective of determining the most relevant cultivar and environmental variables that explained grain yield GEI. One data set had two field experiments, one including seven durum wheat (Triticum turgidum L. var. durum ) cultivars and the other, seven bread wheat (Triticum aestivum L.) cultivars, both tested for 6 yr. In durum wheat cultivars, sun hours per day in December, February, and March as well as maximum temperature in March were related to the factor that explained more than 39% of GEI, while in bread wheat cultivars, minimum temperature in December and January as well as sun hours per day in January and February were the environmental variables related to the factor that explained the largest portion (>41%) of GEI. The second data set had eight bread wheat cultivars evaluated in 21 low relative humidity (RH) environments and 12 high RH environments. For both low and high RH environments, results indicated that relative performance of cultivars is influenced by differential sensitivity to minimum temperatures during the spike growth period. The PLS method was effective in detecting environmental and cultivar explanatory variables associated with factors that explained large portions of GEI.
TL;DR: It is concluded that while the grain yield potential of CIMMYT-derived cultivars has increased significantly over the years, progress in protecting this yield potential through the incorporation of genes that confer slow rusting resistance has been more dramatic.
Abstract: Leaf rust, caused by Puccinia recondita Roberge ex Desmaz., is an important disease of wheat (Triticum aestivum L.) worldwide. To estimate the genetic progress in reducing grain yield losses through breeding for resistance to leaf rust, replicated trials including 15 popular CIMMYT germplasm-derived wheat cultivars released between 1966 and 1988 in northwestern Mexico were sown in that same area; normal and late planting dates were used for four and two seasons, respectively. Leaf rust epidemics were established by inoculating spreader rows planted adjacent to plots of the cultivars which were not protected by fungicide. Average losses in grain yields of the cultivars due to leaf rust ranged between 6.6 and 62.7% and were highly correlated with final disease severity (r = 0.898, P < 0.01) and relative area under the disease progress curve (r = 0.917, P < 0.01). The losses in grain yield were mostly due to reductions in kernel weight, kernels per square meter, and grain fill rate. Grain yield losses (7.7-10.4%) in slow rusting cultivars Cocoraque 75, Nacozari 76, Opata 85, and Bacanora 88 were similar to those observed in the immune 'Oasis 86' (6.6%) or resistant 'Ciano 79' (10.2%). The average annual progress in grain yield potential achieved through breeding averaged over the six trials was estimated to be 0.48% (r 2 = 0.38, P < 0.01) for fungicide protected and 2.21% (r 2 = 0.47, P< 0.01) when not protected by fungicide. We conclude that while the grain yield potential of CIMMYT-derived cultivars has increased significantly over the years, progress in protecting this yield potential through the incorporation of genes that confer slow rusting resistance has been more dramatic.
TL;DR: These results, along with those from other mapping studies at CIMMYT, are allowing us to formulate marker-assisted selection schemes to complement the breeding efforts for such complex traits as borer resistance.
Abstract: Development of multiple insect resistance in tropical maize represents a major effort of the maize breeding programme at CIMMYT Resistance to the southwestern corn borer (SWCB) is polygenically controlled with primarily additive gene action Our main objective was to identify quantitative trait loci (QTL) involved in resistance to SWCB Other objectives were to detect QTL in the same population for plant height, female flowering, and the anthesis-silking interval (ASI) A population of 472 F2 individuals derived from a cross between the susceptible line Ki3 and the resistant inbred CML139, was restriction fragment length polymorphism (RFLP) genotyped using 110 maize probes F3 families were rated for leaf-feeding damage after artificial infestation at one location in three consecutive years Height and flowering were measured in protected trials in two locations QTL analyses were conducted using joint composite interval mapping Seven QTL on chromosomes 3, 5, 6, 8, and 9 explained 30% of the phenotypic variance (σ2p) for SWCB damage Most QTL alleles conferring resistance were contributed from CML139 QTL showed dominance, partial dominance and additive gene action Eleven QTL dispersed across the genome were determined to affect plant height and explained 43% of σ2p Four of these were in close proximity to loci with qualitative effects on plant height Thirteen QTL (50% of sigma;2p) were identified for days to female flowering and nine (30% of σ2p) for ASI Our results, along with those from other mapping studies at CIMMYT, are allowing us to formulate marker-assisted selection schemes to complement the breeding efforts for such complex traits as borer resistance
TL;DR: In this article, the authors used a BK Precision 810 capacitance meter to estimate root fresh mass in maize (Zea mays L.) using a technique that allows a rapid and noninvasive capacitance reading.
Abstract: Time and expense are major constraints limiting the detection of genotypic differences in the length, structure, and growth rate of root systems in the soil. Recent development of a hand-held capacitance meter could enable the routine quantification of root mass. The objective of this study was to determine the accuracy with which a BK Precision 810A capacitance meter can estimate root fresh mass in maize (Zea mays L.) using a technique that allows a rapid and noninvasive capacitance reading. The capacitance meter measured root capacitance of maize grown under greenhouse (8 genotypes) and field (6 genotypes) conditions. After the capacitance readings, 14 plants per genotype were uprooted, roots were washed thoroughly, and root fresh mass was obtained. The statistical relationship between capacitance and root fresh mass in greenhouse experiments was significant early in the growth seasqn for all genotypes (r 2 = 0.73, P < 0.001), and significant only late in the growth season for inbreds (r 2 = 0.56, P < 0.001). Field studies showed that capacitance and root fresh mass were statistically correlated for all genotypes at flowering (r 2 = 0.69, P < 0.001). In conclusion, capacitance meters equipped with a clamp for rapid attachment to the plant may facilitate the nondestructive identification of genotypes with root characteristics that confer adaptation to various environments. Conditions for accurate capacitance measurements included a moist medium around the plant's root system and a consistent placement of the electrode at 6 cm above the crown.
TL;DR: Chances of successful application of marker-based selection (MBS) for corn borer resistance are reduced when QTL are not identified in the germplasm in which the final selection will be carried out.
Abstract: The southwestern corn borer (SWCB, Diatraea grandiosella Dyar) and sugarcane borer (SCB, Diatraea saccharalis Fabricius) are two related insect species that cause serious damage in maize production in subtropical and tropical regions of Central and Latin America. We analyzed quantitative trait loci (QTL) involved in resistance to the first generation of both borer species in two recombinant inbred line (RIL) populations from crosses CML131 (susceptible) × CML67 (resistant) and Ki3 (susceptible) × CML139 (resistant). Resistance was evaluated as leaf feeding damage (LFD) in replicated field trials across several environments under artificial infestation. Leaf protein concentration and leaf toughness were evaluated in one environment as putative components of resistance. The method of composite interval mapping was employed for QTL detection with RFLP linkage maps derived for each population of RIL. Estimates of the genotypic and genotype × environment interaction variances for SWCB LFD and SCB LFD were highly significant in both populations. Heritabilities ranged from 0.50 to 0.75. In Population CML131 × CML67, nine and eight mostly identical QTL were found for SWCB LFD and SCB LFD, respectively, explaining about 52% of the phenotypic variance () for each trait. In Population Ki3 × CML139, five QTL for SWCB LFD were detected, explaining 35.5% of . Several of these QTL were found in regions containing QTL for leaf protein concentration or leaf toughness. A low number of QTL in common between the two RIL populations and between RIL and corresponding populations of F2:3 indicated that the detection of QTL depended highly on the germplasm and population type. Consequently, chances of successful application of marker-based selection (MBS) for corn borer resistance are reduced when QTL are not identified in the germplasm in which the final selection will be carried out.
TL;DR: The greater resistance of CML202 may be due to allelic differences at the msv1 locus or due to the minor QTL on C 2, 3, and 4 which were not detected in Tzi4, an inbred line from IITA.
Abstract: Resistance to maize streak virus (MSV) is an essential trait of improved maize varieties in sub-Saharan Africa. We mapped quantitative trait loci (QTL) for resistance to MSV in a population of 196 F2:3 lines derived from a cross between the maize inbred lines CML202 (resistant) from CIMMYT-Zimbabwe and Lo951 (susceptible) from Italy. Field tests were planted at two locations in Zimbabwe, inoculated with viruliferous leaf hoppers (Cicadulina mbila), and scored twice (21 and 83 days after infesting, DAI) on a 1–5 scale. The mean final streak intensity (score 2) of the parent lines was 2.2 (CML202) and 4.8 (Lo951). Genotype × location interaction was large for score 1 but negligible for score 2. Consequently, the heritability was higher for score 2 (0.93) than for score 1 (0.62). By composite interval mapping across locations, using a linkage map with 110 RFLP loci, four significant (LOD ≥3.0) QTL were identified for score 1 on chromosomes (C) 1, 2, 3, and 4, respectively. All four were contributed by CML202. For score 2, only the QTL on C 1 was significant (LOD =37), explaining 59% of the phenotypic and 64% of the genotypic variance. The QTL's partially dominant gene action was consistent with the nearly intermediate resistance of the F1 generation (relative heterosis for resistance 12%). The presence of one major QTL is consistent with the bimodal frequency distribution of the mapping population showing a clear 3:1 segregation. This gene seems to be allelic or identical to Msv1, a major resistance gene which was previously identified in the same genomic region in Tzi4, an inbred line from IITA. Inbred CML202 had lower final disease ratings than Tzi4. The greater resistance of CML202 may be due to allelic differences at the msv1 locus or due to the minor QTL on C 2, 3, and 4 which were not detected in Tzi4.
TL;DR: In this article, a pilot study among indigenous farmers in the Sierra de Santa Marta, Mexico, raises questions about the benefits of participatory crop improvement strategies, given the high rates of seed replacement for the same varieties.
TL;DR: Molecular markers linked with diplospory were used to analyse various generations of maize–Tripsacum hybrids and backcross derivatives and to derive a model for the inheritance of diplosporous reproduction, suggesting that the gene or genes controlling apomixis in TripsACum are linked with a segregation distorter-type system promoting the elimination of the apomIXis alleles when transmitted through haploid gametes.
Abstract: Apomixis is a mode of asexual reproduction through seeds. The apomictic process bypasses both meiosis and egg cell fertilization, producing offspring that are exact genetic replicas of the mother plant. In the Tripsacum agamic complex, all polyploids reproduce through the diplosporous type of apomixis, and diploids are sexual. In this paper, molecular markers linked with diplospory were used to analyse various generations of maize–Tripsacum hybrids and backcross derivatives and to derive a model for the inheritance of diplosporous reproduction. The results suggest that the gene or genes controlling apomixis in Tripsacum are linked with a segregation distorter-type system promoting the elimination of the apomixis alleles when transmitted through haploid gametes. Hence, this model offers an explanation of the relationship between apomixis and polyploidy. The evolutionary importance of this mechanism, which protects the diploid level from being invaded by apomixis, is discussed.
TL;DR: In this paper, the responses of two rice cultivars to three N regimes and two soil moisture regimes were evaluated on a Haplaquept noncalcareous brown floodplain soil at the Wheat Research Center, Nashipur, Bangladesh.
Abstract: Rice (Oryza sativa L.) followed by wheat (Triticum aestivum L.) is a dominant cropping sequence under a range of management regimes in South Asia, with variable productivity. Simulation models can be used to extrapolate experimental results to other sites of interest in variable environments. Experiments were conducted to quantify the responses of two rice cultivars to three N regimes and two soil moisture regimes, followed by the responses of the succeeding two wheat cultivars to three N regimes, two soil moisture regimes, and two dates of planting, on a Haplaquept noncalcareous brown floodplain soil at the Wheat Research Center, Nashipur, Bangladesh. CERES-Rice and CERES-Wheat models were validated using the experimental data set, and then were used to estimate the grain yields at two other sites in Bangladesh. In rainfed plots, grain yields of 'BR14' rice were reduced by 48.8, 43.4, and 39.3% relative to irrigated plots, and those of 'BR11' were reduced by 49.1, 43.8, and 42.2% (P < 0.05), for 0, 90, and 135 kg N ha -1 , respectively. The optimum N rate was between 90 and 135 kg ha -1 . In the succeeding wheat crop, at 0 N, there were no significant differences between the two moisture regimes but, at high N (180 kg ha -1 ), irrigation promoted greater yield. Relative to the high-N treatment, grain yields of irrigated 'Kanchan' wheat at 0 N were reduced by 73.0 and 71.6%, and of 'Sowgat' by 75.2 and 73.5%, for early and late plantings, respectively. Simulation investigated year-to-year variation in grain yields of both crops under their several N regimes. Rice yields tended to increase over years, but wheat yields had no definite trend. The simulation results indicated that, without N fertilizer application, N will be limiting across sites and long-term weather conditions for both rainfed and irrigated crops. Field experimentation quantified actual crop responses to a range of management practices and allowed validating the models for the rice-wheat sequence. The models were then used to extrapolate and generalize the results for two other sites in Bangladesh.
TL;DR: Development inbred lines from a cross between a resistant synthetic wheat of resistant cultivars is the preferred control measure and regions on chromo- cally show higher levels of field resistance to KB than some arms 3BS and 5AL carrying marker alleles from the Altar durum.
Abstract: Chemical control of the disease with fungicides ap- plied near flowering stage is only partially effective ow- Karnal bunt (Tilletia indica Mitra) infestation of wheat (Triticum ing to the varied modes of spore transmission. It is aestivum L.) kernels reduces grain quality. Deployment of genetic resistance would be preferable to chemical applications for control commercially impractical (Fuentes-Davila and Ra- of the disease. Inoculation studies were carried out in a wheat mapping jaram, 1994) because of the zero tolerance level for KB population with the aim of locating genes for resistance. Recombinant spores imposed by importing countries. Development inbred (RI) lines from a cross between a resistant synthetic wheat of resistant cultivars is the preferred control measure. (Triticum turgidum 'Altar 84' 3 T. tauschii ) and the susceptible The main sources of resistance in CIMMYT's breeding common wheat cultivar 'Opata 85' were inoculated with Karnal bunt program have been Chinese, Indian, and Brazilian sporidial suspension and evaluated for symptom development in the wheats (Fuentes-Davila and Rajaram, 1994). field for three seasons and in the greenhouse. Based on restriction Durum wheat (Triticum durum Desf.) cultivars typi- fragment length polymorphism (RFLP) analyses, regions on chromo- cally show higher levels of field resistance to KB than some arms 3BS and 5AL carrying marker alleles from the Altar durum
TL;DR: RFLP loci on three chromosomal regions previously known to possess genes for resistance to either southern rust or common rust were used to localize genes affecting resistance to southern rust in selected genotypes of both populations, and to estimate their genetic effects.
Abstract: The inheritance of resistance to southern rust (caused by Puccinia polysora Underw.) was investigated in two F2:3 populations derived from crossing two temperate-adapted, 100% tropical maize (Zea mays L.) inbred lines (1416-1 and 1497-2) to a susceptible Corn Belt Dent hybrid, B73Ht×Mo17Ht. The inbred lines possess high levels of resistance to southern rust and may be unique sources of resistance genes. Heritability for resistance was estimated as 30% and 50% in the two populations from regression of F2:3 family mean scores on F2 parent scores, and as 65% and 75% from variances among F2:3 families on a single-plot basis. RFLP loci on three chromosomal regions previously known to possess genes for resistance to either southern rust or common rust (P. sorghi Schw.) were used to localize genes affecting resistance to southern rust in selected genotypes of both populations, and to estimate their genetic effects. A single locus on 10S, bnl3.04, was associated with 82–83% of the variation among field resistance scores of selected F2:3 families in the two populations. Loci on chromosomes 3 (umc26) and 4 (umc31) were significantly associated with resistance in the 1497-2 population, each accounting for 13–15% of the phenotypic variation for F2:3 field scores. Multiple-marker locus models, including loci from chromosomes 3, 4, and 10 and their epistatic interactions, accounted for 96–99% of the variation in F2:3 field scores. Similar results were obtained for resistance measured by counting pustules on juvenile plants in the greenhouse. An attempt was made to determine if the major gene for resistance from 1416-1 was allelic to Rpp9, which is also located on 10S. Testcross families from the cross (1416-1×B37Rpp9)×B14AHt were evaluated for resistance to southern rust in Mexico. Neither source of resistance was completely effective in this environment, preventing determination of allelism of the two genes; however, both sources of resistance had better partial resistance to southern rust than did B14AHt.
TL;DR: The benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico.
Abstract: Smale, M., Singh, R. P., Sayre, K., Pinga li, P., Rajaram, S., and Dubin, H. J. 1998. Estimating the economic impact of breeding nonspecific resistance to leaf rust in modern bread wheats. Plant Dis. 82:1055-1061. Breeding for resistance to rust diseases in wheat is an example of productivity maintenance research. Productivity maintenance research is n ecessary to avoid contractions in the wheat supply curve that result from changes in the biological or physical environment. In this study, the benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico. In the most pessimistic scenario, the gross benefits generated in the Yaqui Valley from 1970 to 1990 were 17 million U.S. dollars (in 1994 real terms). Even when costs were overstated and benefits were understated, the internal rate of return on capital invested was 13%, well within the range recommended for use in project evaluations by the World Bank. Substantial economic benefits likely are associated with deployment of nonspecific resistance in many wheat-producing areas of developing countries where farmers change cultivars slowly because of delays in cultivar release, incomplete seed markets, and ec onomic factors related to adoption or where disease pressure is heavy and the costs of treating disease outbreaks is high.
TL;DR: Electrophoretic, protein content and SDS sedimentation analyses were carried out on a large collection of accessions of durum wheat from Turkey, and compared with Italian cultivars, finding that breeding for quality should consider selection for LMW-GS and against α-type and γ-type glutenin subunits.
Abstract: Durum wheat quality is controlled by endosperm protein content and composition. Electrophoretic, protein content and SDS sedimentation analyses were carried out on a large collection of accessions of durum wheat from Turkey, and compared with Italian cultivars. A number of patterns were detected, resulting from the combination of different alleles at genomes A and B, and new allelic variants were identified. Genotypes with the same allele at Gli-B1 showed inconsistencies in the comparison of low molecular weight glutenin subunits (LMW-GS), suggesting caution in considering γ-gliadins as genetic markers for pasta quality. Variation in protein content and SDS sedimentation values was wider in the Turkish material than in the Italian cultivars, the values of which were in line with cultivars from Australia, Canada, France, and the USA. A substantial amount of the variation in gluten properties was explained in terms of protein composition, with LMW-GS making the largest contribution. Reversed phase high performance liquid chromatography (RP-HPLC) analyses were carried out on two biotypes of the Italian cultivar Lira that differ at the Gli-B1/Glu-B3 loci (Lira 42 has γ-42, LMW-1, and poor quality; whereas Lira 45 has γ-45, LMW-2, and good quality). The results indicated that differences in quality may be due to: 1) the absolute amount of LMW glutenins which was greater in LMW-2; 2) the relative predominance of LMW-s type and LMW-m type subunits in Lira 45 glutenins which act as polymer chain extenders; and 3) the higher proportion of the α-type and γ-type glutenin subunits, in Lira 42 glutenins, which have an additional (nine) cysteine residue in the N-terminal region and act as glutenin chain terminators. The conclusion reached was that breeding for quality should consider selection for LMW-GS and against α-type and γ-type glutenin subunits.
TL;DR: In this article, the authors argue that profit-oriented firms are unlikely to assume functions that cannot easily be exploited for commercial gain, so government agencies will continue to play an important role in supporting basic research, conducting applied research targeted at marginal environments, collecting and disseminating market information, and establishing industry standards.
TL;DR: Field evaluations were conducted to develop a core subset of Caribbean maize (Zea mays L.) accessions from the CIMMYT maize germplasm bank, which represents the phenotypic diversity of the clusters and have superior selection indexes.
Abstract: Core subsets of germplasm collections facilitate their evaluation and use. Field evaluations were conducted to develop a core subset of Caribbean maize (Zea mays L.) accessions from the CIMMYT maize germplasm bank. Most accessions were from the West Indies and others were from Central and South America. The accessions were divided into two trials of 249 accessions and seven common checks that were evaluated in a 16 by 16 α-lattice design with two replications. The trials were planted in two seasons at two sites in Mexico during 1992 through 1994. Data were taken on agronomic and morphological traits and the combined analysis was performed by a mixed linear model. The adjusted means of plant height, ear height, senescence, ear diameter, ear length, days to silk, days to anthesis, moisture (%), rating on ease of shelling, and number of kernel rows were used to cluster accessions into homogeneous groups. Twelve non-overlapping clusters were formed and patterns of phenotypic diversity among and within clusters were determined using canonical discriminant analysis. A selection index based on yield (Mg ha -1 ), ear rot (%), erect plants (%), and moisture (%) was calculated for each accession. The upper 20% of the accessions (100 in total) which represent the phenotypic diversity of the clusters and have superior selection indexes were used to form a core subset of the Caribbean maize collection.
TL;DR: In this paper, the kernel number per unit area (KNO) of spring wheat was investigated in three phases, with the intermediate phase II ranging approximately from early booting (DC40) to final anthesis (DC70).
TL;DR: The tolerant line from population SA5 was prone to severe root lodging, suggesting a very poor root system, and apparently, the tolerance to soil acidity in this line is not associated with a large root system.
Abstract: Acid soils severely reduce maize (Zea mays L.) yield in the tropics. Breeding for tolerance to soil acidity provides a permanent, environmentally friendly, and inexpensive solution to the problem. This study was carried out to determine the relative importance of additive, dominant, and epistatic effects on maize grain-yields in different tropical genotypes. Divergent selection in three populations (SA4, SA5, and SA7) provided inbred lines tolerant or sensitive to acid soils. The tolerant and sensitive lines from each population were used to obtain the F1, F2, F3, back-crosses, second back-crosses, and selfed back-cross generations. In addition, the tolerant lines from SA4 and SA5 were crossed with a sensitive line from the Tuxpeno Sequia population, from which the same generations were also derived. All generations from each of the five sets of crosses were evaluated in three acid-soil environments and one non-acid-soil environment. A generation-mean analysis was performed on each set for yield. The sequential sum of squares associated with additive, dominance, and digenic epistatic effects were used to estimate the relative importance of each genetic effect. Epistasis was not important in any set in the non-acid-soil environment, with dominance accounting for 80.76% of the total variation among generation means across sets. In acid-soil environments, epistasis was more important. The relative importance of digenic epistasis was greater in those evaluations with large experimental errors. The tolerant line from population SA5 was prone to severe root lodging, suggesting a very poor root system. Apparently, the tolerance to soil acidity in this line is not associated with a large root system.
TL;DR: Aegilops sources of resistance could be exploited for transferring Hessian fly resistance to wheat by expressing antibiosis as the mechanism of resistance against first instar HessianFly larvae.
Abstract: Hessian fly, Mayetiola destructor (Say), is the major insect pest of wheat in Morocco. Host plant resistance has been the most effective and practical method of controlling this pest. When 347 accessions of Aegilops species were screened in the greenhouse for resistance to Hessian fly, several accessions of Ae. geniculata Roth, Ae. triuncialis L., Ae. neglecta Req.ex Bertol., Ae. ventricosa Tausch, Ae. cylindrica Host and Ae. markgrafii (Greuter) Hammer showed resistance reaction. All expressed antibiosis as the mechanism of resistance against first instar Hessian fly larvae. These Aegilops sources of resistance could be exploited for transferring Hessian fly resistance to wheat.