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1

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Analysing yield stability of maize genotypes using a spatial model (1988)

Crossa, J. ; Westcott, B. ; Gonzalez, C.

Springer

Theoretical and applied genetics 75 (1988), S. 863-868

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ISSN: 1432-2242

Keywords: Spatial model ; Stability ; Maize

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The yield stability of some CIMMYT tropical maize (Zea mays L.) populations of early and intermediate maturity, measured by the performance of varieties derived from them, was determined. Results of the stability analyses, conducted over international environments from 1980 to 1983, indicated that selections from Mezcla Amarilla exhibited good stability in high yielding sites. Varieties derived from Antigua-Republica Dominicana tended to be more stable in unfavourable environments, whereas selections from Blanco Cristalino-1 and Blanco Dentado-2 were stable in both low and high production sites. The combination of enviromental factors in the specific test locations, namely Poza Rica (Mexico), Tocumen (Panama), Islamabad (Pakistan), and Ferkessedougou (Ivory Coast), allowed selection of varieties that are very stable in other regions of the world. The varieties formed on the basis of multilocational data do not seem to be any more stable than those formed using data from a single location.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00258046

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2

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Predicted and realized grain yield responses to full-sib family selection in CIMMYT maize (Zea mays L.) populations (1989)

Crossa, J. ; Gardner, C. O.

Springer

Theoretical and applied genetics 77 (1989), S. 33-38

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ISSN: 1432-2242

Keywords: Multilocational progeny trials ; Full-sib selection ; Variance components ; Selection response

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The maize (Zea mays L.) improvement program of the International Maize and Wheat Improvement Center (CIMMYT) develops broad-based maize populations and, until recently, improved all of them through full-sib family selection with international testing. The purpose of this study was to estimate the genetic and genetic × environment variance components for ten of those populations and to measure expected yield improvement from full-sib selection. Mean yield ranged from 3.35–6.81 t ha−1. For five populations the average yield in the last cycle was higher than in the initial cycles. Several populations showed no improvement or yielded less in the final cycle of selection, either because selection intensity was low or because strong selection pressure was applied simultaneously for several traits. Variation resulting from differences among family means within cycles and from interaction between families and locations within cycles were significant in all populations and cycles. Results indicate that variability among full-sib families was maintained throughout the cycles for all populations. The large σ ge 2 /σ g 2 ratio shown by most populations suggests that yield response per cycle could be maximized if the environments in which progenies are tested were subdivided and classified into similar subsets. The proportion of the predicted response realized in improved yield varied for each population.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00292312

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3

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Methodologies for estimating the sample size required for genetic conservation of outbreeding crops (1989)

Crossa, J.

Springer

Theoretical and applied genetics 77 (1989), S. 153-161

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ISSN: 1432-2242

Keywords: Seed regeneration ; Sample size ; Random genetic drift ; Effective population size ; Allele frequency

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The main purpose of germplasm banks is to preserve the genetic variability existing in crop species. The effectiveness of the regeneration of collections stored in gene banks is affected by factors such as sample size, random genetic drift, and seed viability. The objective of this paper is to review probability models and population genetics theory to determine the choice of sample size used for seed regeneration. A number of conclusions can be drawn from the results. First, the size of the sample depends largely on the frequency of the least common allele or genotype. Genotypes or alleles occurring at frequencies of more than 10% can be preserved with a sample size of 40 individuals. A sample size of 100 individuals will preserve genotypes (alleles) that occur at frequencies of 5%. If the frequency of rare genotypes (alleles) drops below 5%, larger sample sizes are required. A second conclusion is that for two, three, and four alleles per locus the sample size required to include a copy of each allele depends more on the frequency of the rare allele or alleles than on the number. Samples of 300 to 400 are required to preserve alleles that are present at a frequency of 1%. Third, if seed is bulked, the expected number of parents involved in any sample drawn from the bulk will be less than the number of parents included in the bulk. Fourth, to maintain a rate of breeding (F) of 1 %, the effective population size (N e) should be at least 150 for three alleles, and 300 for four alleles. Fifth, equalizing the reproductive output of each family to two progeny doubles the effective size of the population. Based on the results presented here, a practical option is considered for regenerating maize seed in a program constrained by limited funds.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00266180

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4

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The yield stability of CIMMYT'S maize germplasm (1989)

Crossa, J. ; Westcott, B. ; Gonzalez, C.

Springer

Euphytica 40 (1989), S. 245-251

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ISSN: 1573-5060

Keywords: Zea mays ; maize ; multilocation trials ; yield stability ; principal coordinates analysis

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary Principal coordinates analysis was used to determine the yield stability of some CIMMYT maize populations (Zea mays L.) measured by the performance of the varieties selected from them. The varieties included in this study were derived from subtropical of early and intermediate maturity maize populations. The analyses included grain yield data from international trials conducted from 1979 to 1983. Results show that varieties selected from the population Blanco Subtropical were stable in low yielding sites. Of the populations considered in this study, Amarillo Bajio and ETO-Illinois produced a greater number of varieties that give stable yields under both favourable and unfavourable environmental conditions. Some selections based on multilocational data showed good stability across years in both low and high yielding sites; however, across location varieties were not always more stable than specific site selections. Varieties formed in Tlaltizapan (Mexico), and Chuquisaca (Bolivia) were very stable in other regions.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00024519

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5

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Heterosis among populations of maize (Zea mays L.) with different levels of exotic germplasm (1987)

Crossa, J. ; Gardner, C. O. ; Mumm, R. F.

Springer

Theoretical and applied genetics 73 (1987), S. 445-450

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ISSN: 1432-2242

Keywords: Unadapted germplasm ; Adapted germplasm ; Heterotic patterns ; Gardner-Eberhart model ; Composites

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Thirteen maize (Zea mays L.) populations including five adapted, five adapted x exotic, two composites of adapted and exotic, and one exotic selected for adaptability were crossed in a diallel mating system. The parents and 78 crosses and nine check hybrids were evaluated for grain yield and plant height in five environments. The Gardner-Eberhart model Analysis II indicated that additive and nonadditive gene effects accounted for 60 and 40% of the total variation among populations, respectively, for grain yield and 86% and 14% of the total variation, respectively, for plant height. Components of heterosis were significant in the combined analysis for both traits. Adapted Corn Belt populations tended to have higher performance in crosses and greater values of variety heterosis than 50% adapted populations. ‘Nebraska Elite Composite’, ‘Corn Belt’ x ‘Mexican’, and ‘Corn Belt’ x ‘Brazilian’ showed high mean yields in crosses, however, they were not among those with high estimates of variety heterosis. One exotic population (‘Tuxpeno’ x ‘Antigua Grupo 2’) and three adapted populations [‘307 Composite’, ‘NB(S1)C-3’, and ‘NK(S1)C-3’] might be combined together to form a high-yielding population. It may be possible to synthesize two useful populations for reciprocal recurrent selection by grouping ‘Tuxpeno’ x ‘Antiqua Grupo 2’, ‘NB(S1)C-3’, and ‘NS(FS)LFW-8’ into one population and ‘NK(S1)C-3’, ‘Krug’x‘Tabloncillo’, and ‘307 Composite’ in the other one.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00262514

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6

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A comparison of results obtained with two methods for assessing yield stability (1988)

Crossa, J.

Springer

Theoretical and applied genetics 75 (1988), S. 460-467

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ISSN: 1432-2242

Keywords: Zea mays L. ; Selection ; Regression analysis ; Principal coordinates analysis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary A major objective of the CIMMYT Maize Program is to develop open-pollinated varieties of maize (Zea mays L.) that are well adapted to a wide range of environments. To achieve this breeding goal, it is essential that the program use a stability technique that will identify high-yielding, stable genotypes accurately in international trials conducted under different environmental conditions. The objective of this study was to compare a spatial method with a modified conventional regression analysis method to determine the yield stability of 27 CIMMYT maize varieties evaluated at 37 locations. The methods also were compared on the basis of their consistency in assessing the stability of varieties when certain locations were omitted, and when subsets of varieties were analyzed. The varieties found to be stable by the spatial method with all sites included in the analysis were also stable (1) when the lowest and highest yielding sites were excluded from the analyses, and (2) when the varieties were considered, along with others, as a subset of the original group of materials. Stability parameters determined by regression analysis, however, varied for some varieties when (1) extreme sites were excluded, and (2) a subset of entries was considered in isolation. Because the spatial method was more consistent in identifying high-yielding stable varieties, it was considered the more useful of the two methods.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00276750

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