Selection For Grain Yield Research Articles

Effect of Recurrent Selection on the Genetic Structure of Two Broad‐Based Spanish Maize Populations

ABSTRACTMaize (Zea mays L.) landraces are useful materials that can introduce new diversity into breeding programs, but they will need to be selected to maximize their agronomic performance. The objective of this study was to use molecular markers to investigate the changes in the genetic diversity and structure over the cycles of a maize breeding program that combined intra‐ and interpopulation recurrent selection for grain yield in two broad‐based Spanish maize composites. Using 76 polymorphic simple sequence repeat (SSR) markers and two flowering time related indels, this study looked at 10 populations derived from a breeding program designed to exploit the heterotic pattern northern Spain × southern Spain. Agronomic evaluations demonstrated that the selection effectively increased the yield of the composites and their crosses, but, as the molecular data from this study show, the improvement was at the expense of some variability. The genetic distance between populations increased with selection, which is accordant with the increment of heterosis found in the agronomic evaluation. The changes observed were consistent with a model in which genetic drift is the main force, although selection could also play a role in the changes observed in EPS7 and EPS13. Allele frequencies changed significantly for one marker during intrapopulation selection and three markers under interpopulation selection, pointing to regions 3.04, 7.03, 9.01, and 9.03 as quantitative trait loci (QTL) related to grain yield.

Relative changes in genetic variability and correlations in an early-maturing maize population during recurrent selection

Four cycles of S(1) family recurrent selection to improve grain yield and resistance to Striga hermonthica have been completed in TZE-Y Pop STR C(0.) In order to determine whether or not to continue with the recurrent scheme, it was desirable to evaluate the amount of residual genetic variance and associated parameters in the population. The objective of this study was to characterize the relative changes in the levels of the genetic variances, heritability estimates and genetic correlation coefficients, and to predict future gains from selection for grain yield, Striga resistance and other agronomic traits. Fifty S(1) families, derived from each cycle, were evaluated under Striga-infested and Striga-free conditions at Mokwa, Ikenne and Abuja, Nigeria, in 2005 and 2007. Under Striga infestation, genetic variances for grain yield, days to anthesis, plant height and Striga damage generally increased in the advanced cycles of selection. In contrast, the genetic variances for days to silk, anthesis-silking interval, ears per plant, ear aspect and number of emerged Striga plants decreased with selection. The advanced cycles of selection significantly out-yielded the original cycle in both research environments. Heritabilities for grain yield, Striga damage and number of emerged Striga plants were significantly greater than zero. The realized gains from selection for grain yield under Striga infestation (52kgha(-1)cycle(-1)) and Striga-free conditions (130kgha(-1)cycle(-1)) were remarkably lower than the predicted gains (350 and 250kgha(-1)cycle(-1), respectively). Adequate genetic variability exists in cycle 4 of the scheme to ensure future gains from selection.

The relative merits of pedigree selection for grain yield of bread wheat under drought stress and sensitivity to environments

The relative merits of pedigree selection for grain yield of bread wheat under drought stress and sensitivity to environments

Full-sib reciprocal recurrent selection in the maize populations Cimmyt and Piranão

We estimated the genetic gains of the 12th cycle of reciprocal recurrent selection for maize traits of agronomic interest. We used 23 ISSR molecular markers in an attempt to maximize genetic variability among and within populations based on selection of S(1) progenies. To this end, 138 full-sib families were evaluated in a randomized block design in two environments (the municipalities of Campos dos Goytacazes and Itaocara, in the State of Rio de Janeiro, Brazil), with replications within sets. Direct selection for grain yield was used for the selection of the families. To assess genetic diversity among and within populations, we examined plants produced from part of the S(1s) seeds from the parents that originated the 42 full-sib families that were selected from the agronomic traits. Direct selection for grain yield provided good gains for the traits evaluated, with estimated improvement of -0.87 days for days to flowering, 0.35 plants, 1.79 ears per plot, 0.58 g per 100-grain weight, 308.21 g ear weight per plot, and 261.83 kg/ha grain yield. Application of molecular markers at the stage of superior progeny selection led to increased genetic distance among populations, which is a very important factor for utilization of heterosis and providing greater longevity to the reciprocal recurrent selection program.

Field Phenotyping Strategies and Breeding for Adaptation of Rice to Drought†

This paper is a section of the book “Drought phenotyping in crops: from theory to practice” (Monneveux Philippe and Ribaut Jean-Marcel eds, published by CGIAR Generation Challenge Programme. Texcoco, Mexico). The section describes recent experience in drought phenotyping in rice which is one of the most drought-susceptible crops. The section contains genetic and genomic resources for drought adaptation and methods for selection of drought-resistant varieties in rice. In appendix, there is experience from Thailand on integration of direct selection for grain yield and physiological traits to confer drought resistance.

Selection and Adaptation to High Plant Density in the Iowa Stiff Stalk Synthetic Maize (Zea mays L.) Population: II. Plant Morphology

ABSTRACTThe plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era while grain yield on a per plant basis has increased little. Changes in plant characteristics including flag leaf angle, anthesis‐silking interval, plant height, tassel branch number, and total number of leaves have been characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have not been studied extensively in a temperate maize recurrent selection program. The objective of this experiment was to determine if direct selection for grain yield and agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population has indirectly improved adaptation to high plant density. Material from an unselected base population, BSSS per se, was compared to four selected populations per se at four plant densities ranging from 38,300, to 95,700 plants ha−1. Treatments were replicated twice in each of two locations in 2 yr and arranged in a split plot design with plant density as whole plot and breeding population as subplot treatment. Selected populations had reduced anthesis‐silking interval and fewer tassel branches. Increasing plant density increased anthesis‐silking interval in the base population whereas increasing plant density did not increase anthesis‐silking interval in the most advanced populations. These results demonstrated that selected populations were better adapted to high plant density than the unselected base population.

Pedigree Selection for Grain Yield in Spring Wheat (Triticum aestivum L.) under Drought Stress Conditions

Pedigree Selection for Grain Yield in Spring Wheat (Triticum aestivum L.) under Drought Stress Conditions

Selection and Adaptation to High Plant Density in the Iowa Stiff Stalk Synthetic Maize (Zea mays L.) Population

The plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era, whereas grain yield on a per plant basis has increased little. Changes in grain yield, grain moisture, test weight, and stalk and root lodging have been well characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have yet to be examined in a recurrent selection program. The objective of this experiment was to determine if direct selection for grain yield and agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population has indirectly improved adaptation to high plant density. Material from an unselected base population, BSSS, was compared to the most advanced cycles of selection from three different recurrent selection programs at seven Iowa locations in 2008 and 2009. Populations were compared at densities of 38,300, 57,400, 77,500, and 95,700 plants ha−1. Treatments were replicated twice at each location and arranged in a split plot design. Selection produced notable improvement in adaptation to high plant density for grain yield and stalk lodging. Selection did not have large impacts on density response for root lodging, test weight, or grain moisture. Because of the improvement in density response for grain yield and stalk lodging without major negative changes in other traits, our data suggest that selection has improved adaptation to high plant density in these populations.

Genetic Analysis of Carbon Isotope Discrimination and its Relation to Yield in a Wheat Doubled Haploid Population

Carbon isotope discrimination (Δ(13)C) is considered a useful indicator for indirect selection of grain yield (GY) in cereals. Therefore, it is important to evaluate the genetic variation in Δ(13)C and its relationship with GY. A doubled haploid (DH) population derived from a cross of two common wheat varieties, Hanxuan 10 (H10) and Lumai 14 (L14), was phenotyped for Δ(13)C in the flag leaf, GY and yield associated traits in two trials contrasted by water availability, specifically, rain-fed and irrigated. Quantitative trait loci (QTLs) were identified by single locus and two locus QTL analyses. QTLs for Δ(13)C were located on chromosomes 1A, 2B, 3B, 5A, 7A and 7B, and QTLs for other traits on all chromosomes except 1A, 4D, 5A, 5B and 6D. The population selected for high Δ(13)C had an increased frequency of QTL for high Δ(13)C, GY and number of spikes per plant (NSP) when grown under rain-fed conditions and only for high Δ(13)C and NSP when grown under irrigated conditions, which was consistent with agronomic performance of the corresponding trait values in the high Δ(13)C progeny; that is, significantly greater than that in the low Δ(13)C. Therefore, selection for Δ(13)C was beneficial in increasing grain yield in rain-fed environments.

Indirect selection for grain yield in spring bread wheat in diverse nurseries worldwide using parameters locally determined in north-west Mexico

SUMMARYThe relationships of normalized water index three (NWI-3) and canopy temperature (CT) with grain yield in north-west Mexico were determined in a set of wheat lines planted in multi-location yield trials. Advanced wheat lines developed by The International Maize and Wheat Improvement Centre (CIMMYT) were included and tested internationally in the trials including the 24th Elite Spring Wheat Yield Trial (ESWYT), the 11th Semi-Arid Wheat Yield Trial (SAWYT) and the 11th High Temperature Wheat Yield Trial (HTWYT). In north-west Mexico, NWI-3, CT and grain yield were determined in three growing seasons (2006, 2007 and 2008) and three environments (well irrigated, water-stressed and high-temperature), while grain yield was measured at international locations in the same advanced lines of the 24th ESWYT, the 11th SAWYT and the 11th HTWYT . The CIMMYT database was used to obtain grain yield from worldwide nurseries. The mean grain yield ranged from 0·8 to 12·7 t/ha for the 24th ESWYT (59 international sites), from 0·6 to 8·2 t/ha for the 11th SAWYT (28 international sites) and from 0·4 to 7·5 t/ha for the 11th HTWYT (26 international sites). NWI-3 and CT for the advanced lines in the three yield trials measured in north-west Mexico in distinct environments showed significant associations with the grain yield from a few international locations (0·12–0·23 of sites). Locations from Central Asia and North Africa had the best associations with NWI-3 and CT. The lack of more associations may be due to either an interaction of other factors (low rainfall and limited irrigations), which affected yield performance, or few of the advanced lines were well adapted to local growing conditions at each testing site, or a combination of these factors. The present results indicate that NWI-3 and CT have limited potential to predict yield performance at international sites.

Genetic resources of lentil and its utilization in India

Lentil is recognised as the most nutritious rabi pulse and, with respect to acreage, it ranks next to chickpea. It is grown throughout northern and central India. A large percentage of Indians are vegetarian and lentil has long been part of India's indigenous diet, and is a common source of protein. Of about 60 varieties released in India to date, 13 have been developed by hybridization, mostly from parents not distantly related. The narrow genetic base of the presently cultivated varieties and losses due to biotic and abiotic stress factors remain the main cause of concern. Introgression of genes betweenmicrospermaandmacrospermagroups of lentil from closely related species likeL. culinarissubspp. Orientalisand use of biotechnological tools, wherever necessary, have been recommended by various workers to broaden the genetic base of this crop. Direct selection for grain yield through important component traits such as pods/plant, seeds/pod, number of clusters/plant, harvest index, biological yield, early maturing and breeding for better yield quality have been suggested. Realizing the significance of plant germplasm, special efforts have been made by the national bureau to collect the genetic resources of lentil from different states of India. A large number of accessions were characterised and evaluated for various agro-morphological traits, using the lentil minimal descriptor. The core collection comprising 287 promising accessions recorded variation for seed yield and its important component traits; variation was also observed for important morphological traits, using mutation breeding approaches. These genetic resources of lentil have also been screened for tolerance to several biotic stresses and a few lines showed immunity against rust, blight and fusarium wilt and these have been utilized as donors in cross-breeding programmes. On the other hand, wildLensspecies revealed substantial genetic diversity for phenological and agro-morphological characters, including some important diseases of lentil. From these genetic resources, potential donors of desirable traits have been selected after evaluation and characterization and have been utilized in the genetic improvement of cultivars.

The relationships of some traits in Turkish winter bread wheat landraces

In this study, 42 bread wheat pure lines obtained from 340 landraces, collected from 35 provinces of 7 regions in Turkey, and 7 modern bread wheat cultivars were evaluated under rainfed conditions in Konya, in 2005-2006 and 2006-2007 growing seasons. Experiments were conducted in a 7 × 7 lattice design in 3 replicates. Both genotype-traits (GT) biplot analysis and path analysis were used to investigate the relationships between grain yield and 12 traits. Applying both types of analyses to the multiple traits data revealed that GT biplot graphically displayed the interrelationships among traits (breeding objectives), identified traits that are positively or negatively associated, and facilitated visual comparison trait profiles (strength and weakness) of genotypes, which is important for parent as well as variety selection. Vast variations existed in traits (number of grains m^{-2}, harvest index, number of spikes m^{-2}, number of grains spike^{-1}, and weight of grains spike^{-1} and biological yield) and grain yield. It was found that either pure lines or cultivars with the highest grain yield had the highest biological yield, number of grain m^{-2}, and harvest index. The results showed that pure lines combined with favorable traits G43 (Kars-TR15796-7), G33 (Kars-TR15796-4), G20 (Kütahya-TR55167-3), and G11 (Kütahya-TR55212-4) can be evaluated in multi-environment trials for a candidate winter bread wheat registration trial. Some pure lines that had high quality traits G26 (Samsun-TR37926-3), G45 (Erzurum-TR32881-6) and G49 (Erzurum-TR32668-1) might be good parents for enhancing quality in bread wheat. In conclusion, for the short-term improvement of Turkish bread wheat landraces may be possible through an indirect selection of the number of grain m^{-2} and biological yield, or direct selection for grain yield per se. In the long-run, crossing programs between indigenous and introduced exotic germplasm may be necessary for high industrial quality characters of bread wheat.

Estimation of genetic progress after eight cycles of recurrent selection for common bean grain yield

The objective of this study was to estimate the genetic progress of eight cycles of recurrent selection for common bean lines with high yield. The base population was obtained from 10 parents differing in several characters. To date, eight selection cycles have been performed. In each cycle the selection process continues after recombination, until lines are established, which are then evaluated more extensively in the experiment of evaluation of elite lines together with lines of other programs. The genetic progress was estimated based on the data of evaluations of these lines in each cycle over the years. The estimated genetic progress of 3.3 % per cycle allows the conclusion that recurrent selection for grain yield is efficient.

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

Realized gains from selection for spring wheat grain yield are different in conventional and organically managed systems

Breeding spring wheat (Triticum aestivum L.) specifically for organic production has been suggested by producers and researchers alike. To investigate the effects of management systems on selected spring wheat breeding line performance in multi-location tests in the northern Great Plains, we used a randomly derived population of 79 F6-derived recombinant inbred lines (RILs) from a cross between the Canadian hard red spring wheat cultivar AC Barrie and the CIMMYT derived cultivar Attila. The population, including the parents, was grown on conventionally and organically managed land in 12 environments over 3 years. Direct selection in each management system (10% selection intensity based on grain yield) resulted in three lines being retained in each management system, over the multi-location testing. Gains from 10% selection for grain yield in a ‘selection’ year were 3.4 times greater in conventional multi-site yield trials than in organically managed trials. Two lines (BA 05 and BA 36) ranked in the top 10% of both the conventional and organic selection trial of 2005, remained ranked 2nd and 1st, respectively, under conventional management in multi-site yield trials. However, these lines ranked 53rd and 21st, respectively, for grain yield in the multi-site organic yield trials. Selected lines were each yield stable within the management system in which they were selected. Following replicated multi-location yield trials, three lines from the population (BA 02, 29 and 58) ranked within the highest 10% yielding lines in both conventional and organic systems. The results of this study suggest that selection differences occur across multi-location tests, and that selection for grain yield in organic systems should be conducted within organic systems. It is evident, however, that data obtained from conventional yield trials also has some relevance towards breeding for organic environments.

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

ABSTRACTStriga hermonthica (Del.) Benth threatens maize (Zea mays L.) production in sub‐Saharan Africa. In an extra‐early population, S1 families derived from four cycles of recurrent selection for grain yield and Striga resistance were evaluated with and without Striga infestation at three locations in Nigeria for 2 yr to determine relative changes in genetic variances, heritabilities, and genetic correlations for yield and other traits. Under infestation, yield was not correlated with other traits at C0 but was significantly correlated with ears per plant (EPP), Striga damage, and emerged Striga plants in advanced cycles. Genetic correlations between yield and most traits were significant in C0 when Striga‐free but was reduced in advanced cycles. Genetic variances and heritabilities for yield and ear aspect increased in advanced cycles. Genetic variances decreased with selection for emerged Striga counts and EPP under infestation. A response to selection for improved yield, Striga emergence and EPP is expected in subsequent cycles. Low genetic variances and heritabilities for Striga damage and low predicted gain cycle−1 for all traits except numbers of emerged Striga plants suggest a need to introgress novel resistance genes into the population for faster progress from selection for increased yield.

PHENOTYPIC AND GENOTYPIC ANALYSIS OF SOME RICE VARIETIES FOR GROWTH AND YIELD TRAITS UNDER STRESS CONDITION

Field experiments including 100 rice genotypes from different sources (selected from local and exotic materials) were carried out as a preliminary screening nursery (PSN) at two locations in Sakha Agriculture Research Station (drought conditions) and at New Valley Agriculture Research Station under heat conditions during 2007 rice growing season. Each genotype was planted in four rows, five meter long and 20 cm a part with three replications, where two the outer rows were used as borders and the two inner rows were used to record the data. The best selected genotypes, under both drought and heat conditions, according to their desirable traits, were evaluated under the same conditions during 2008 and 2009 rice growing seasons. These experiments included 18 and 20 out of 100 rice genotypes under drought and heat conditions, respectively. The results indicated that, the vegetative characters comprising of days to heading, plant height, tillers number/plant and leaf area. Also, root characters, comprising root length, root volume, root to shoot ratio and roots number/plant, could be considered as parameters related to tolerance. These traits could be used as selection criteria since they helped the plant to maintain a favorable water balance and, hence, controlled, early stomata closure. Analysis of variance showed significant variations among the vegetative and root characters under drought conditions. Heritability estimates were higher for grain yield (0.92), plant height (0.88), leaf area (0.82), number of grains per panicle, root/shoot ratio (0.81) and days to heading (0.88). Consequently, selection for grain yield and its components could be more effective in the selected genotypes under drought and heat conditions.

Implications of genotype × input interactions in breeding superior genotypes for favorable and unfavorable rainfed upland environments

Resource-poor farmers in India cultivate upland rice as a subsistence crop in poor soil with minimum inputs, often applying little or no fertilizer and controlling weeds by hand. Consequently, upland rice yields are very low. In our study, the response to management intensification of fertilizer application at rates of 40 N ha −1, 13 P ha −1, and 16.7 K ha −1 and two weed control treatments as compared with no fertilizer, and one hand weeding practice commonly followed by farmers in rainfed upland areas was examined with a large set of advanced breeding lines and adapted upland varieties tested over 3 years in multi-location trials. Highly significant genotype × environment interaction was observed in combined analyses across environments, leading to sub-grouping of sites into the high-yielding or favorable and low-yielding or unfavorable upland environment groups. A significant effect of management regime was observed. Averaged over 15 environments, the moderate-input treatment out-yielded the low-input treatment by nearly 65% or 0.8 t ha −1 under favorable environments and by nearly 48% (0.3 t ha −1) in unfavorable environments. A significant genotype effect and genotype × input management interaction for yield at favorable sites was observed. However, the same was not significant at unfavorable sites. Varietal differences were relatively small at unfavorable sites across input levels. The heritability estimates for grain yield were moderately high in both moderate- and low-input conditions in favorable environments. The genetic correlation between yields in moderate- and low-input conditions was high in both favorable and unfavorable environments. The study indicated that improved varieties performed well relative to landraces under low-input management. Improved varieties along with modestly intensified management offer an attractive option to increase the productivity of rainfed upland environments. For both favorable and unfavorable environments, indirect selection under moderate-input conditions was less efficient than direct selection for grain yield in low-input conditions, indicating upland breeding programs to adopt selection for grain yield under both moderate- and low-input conditions.

Breeding resilient and productive genotypes adapted to drought-prone rainfed ecosystem of India

Drought is the predominant cause of yield reduction in rainfed rice production systems, but until recently, little systematic effort has been made to breed drought-tolerant cultivars. The complex nature of drought tolerance, genotype × environment interaction, and the difficulty of effective drought tolerance screening complicate the development of drought tolerant varieties. This study reports on progress made by a collaborative network of Indian rice breeding programs, in partnership with International Rice Research Institute (IRRI), to develop lines combining high yield potential with drought tolerance by employing direct selection for grain yield under drought stress, and testing their performance in rainy season managed-drought screenings (RSMDS) of different stress severity levels at several locations during the main season in rainfed rice production areas in India. Advanced-generation breeding lines of less than 100 days, 100–120 days, and greater than 120 days duration generated at eight national institutes and IRRI using diverse drought tolerant donors were evaluated in 2005–2007 under RSMDS. Stress was imposed at the reproductive stage, either by draining paddies shortly after transplanting for lowland trials, or by stopping irrigation before flowering for upland trials. Yield reduction of 34–53% under moderate stress and 65–88% under severe stress was achieved in comparison to irrigated controls. Several varieties that have been widely grown in rainfed environments in India for many years, including IR 36, IR 64, Mahamaya, Sambha Mahsuri, and Swarna, were shown to be highly susceptible. Breeding lines were identified that perform consistently better than these and other widely grown rainfed varieties under both moderate and severe drought stress without any yield penalty under fully irrigated conditions. In the combined analysis over locations and years, these promising breeding lines outyielded the widely grown controls by about 0.5 t ha −1 under moderate stress and 0.7–1.0 t ha −1 under severe stress. IRRI breeding lines contributed to the network were developed using a selection protocol involving replicated dry season managed-drought screening (DSMDS) in dry season at Los Banos, Philippines. For a subset of lines extensively tested both at IRRI and in India, correlations between yield under DSMDS in the Philippine and yield in RSMDS in India were moderately high, indicating the efficacy of dry-season MS screening at IRRI in identifying tolerant lines for India. Drought tolerant lines developed by the network members have been released in several Indian states and in the Philippines. Overall, these results indicate that managed stress screening for drought tolerance, with a focus on selection for yield under stress, is effective in generating drought-tolerant cultivars.

S1 selection of local maize landraces for low soil nitrogen tolerance in Zambia.

Low soil nitrogen (N) limits maize production in Zambia. S1 selection was used to select for tolerance to low N among ninety-six maize landraces during 2004 - 2007 in Zambia. The landraces were evaluated under low N, drought and optimal conditions; and selfed in a nursery, under optimal conditions. Data on grain yield (GY), number of ears per plant, leaf senescence and anthesis-silking interval were used to calculate selection indices. Fourteen S1 lines, from each of the best four landraces under each environment and across all environments were evaluated under the three environments, and at the same time crossed to a tester. Twenty-two best S1 lines under each environment and across were identified and also their testcrosses were evaluation under the three environments. Significant GCA effects for GY under low soil N were found, suggesting that population improvement under soil N stress was effective. Heritability for GY under low soil N conditions was low (0.38) implying that selection based on GY was ineffective. TherG for GY under low soil N and optimal environments was moderate (0.458), suggesting that selection for GY in one environment was not as effective as in the other. Low soil N tolerant landraces were identified and should be used to breed for the low soil N conditions. Key words: Maize, landrace, heritability, correlation, nitrogen, tolerance, stress.