Reciprocal recurrent selection applied to Coffea canephora Pierre

Summary Genetic parameters were estimated in trials planted in connection with a reciprocal recurrent selection programme applied to Coffea canephora in Côte d'Ivoire. Narrow sense heritability values, estimated from a breakdown of the analysis of variance, were high for architectural characters (0.22 to 0.78) and medium for tree vigour (0.13 to 0.40) and for bean weight (0.15 to 0.28). Calculated heritability values for the first two harvests were high (h²>0.7), but much lower for the following harvests (less than 0.2). Heritability estimates by parent-offspring regressions gave variable results, though they were often similar to those obtained by variance analysis, especially for bean weight. Phenotypic and genetic correlations between tree vigour traits and productivity were high. Bean weight was not correlated with vigour or production. Canopy diameter of 4 year-old trees was closely correlated with cumulated productivity from 2 to 5 years in the absence of development competition between trees, but the correlation was low if trees were in competition with each other. The consequences of the results for the choice of characters to be selected among intergroup hybrids or the parents of both populations are discussed.     

Reciprocal recurrent selection applied to Coffea canephora Pierre. I. Characterization and evaluation of breeding populations and value of intergroup hybrids

Summary Two breeding populations have been identified with Coffea canephora, based on geographical and genetic differences: the Guinean group from West Africa and the Congolese group from central Africa. A reciprocal recurrent selection programme based on these groups was initiated in Côte d'Ivoire in 1984. Genotypes of both groups available in field collections are either of cultivated or wild origin.Genotypic and phenotypic variability was evaluated within and between the groups for the following characteristics: isozyme patterns, architecture, drought tolerance and vigour, technological and organoleptic traits, pest and disease resistance. Variation between and within groups was found to be large. Based on isozyme analysis and phenotypic observations, two subgroups were identified within the Congolese group. Phenotypic values of parents and testers used in the first cycle of reciprocal recurrent selection are presented.Results of two intergroup hybrid trials indicate high yield and vigour for these hybrids compared to intragroup hybrids, justifying the reciprocal selection approach. Furthermore, the variation observed indicates that recurrent selection would allow progress for selection traits for both populations and intergroup hybrids.     

Genetic gains for yield after two back-crosses of the interspecific hybrid Libusta (Coffea canephora P. × C. liberica Bull. Ex Hiern) to C. canephora P.

The Libusta (Coffea canephora P. × C. liberica B.) programme initiated in the seventies in Côte d'Ivoire aims at improving the quality of coffee grown in low altitudes, with a yield comparable to current commercial C. canephora clones. The second generation of back‐crosses to the C. canephora (CAN) parent, BC2, are now likely to be commercially exploited as far as yield is concerned. The best BC2 progeny yielded 1386 kg of green coffee/ha/y, averaged over five harvest years. On average, the genetic gain for yield from BC1 to BC2 reached 22%. In a factorial mating design, no interaction was observed between BC1 and CAN parents, while both main effects were highly significant. This explained that observed genetic gains and further genetic gains may be achieved with appropriate strategies.     

Genetic study of Coffea canephora coffee tree resistance to Meloidogyne incognita nematodes in Guatemala and Meloidogyne sp. nematodes in El Salvador for selection of rootstock varieties in Central America

Root-knot nematodes, Meloidogyne incognita in Guatemala and Meloidogyne sp. in El Salvador frequently cause very serious damage to Coffea arabica. Hypocotyledon grafting on C. canephoravar. Robusta is practiced on a very wide scale to control these pests. However, rootstock seeds come from non selected trees which provide 30–40%resistance. In this article, we examine the possibility of improving resistance to M. incognita and Meloidogyne sp. Hybrids were created using two North Carolina II factorial mating designs and tested under controlled conditions for resistance to isolates of the two nematodes. In the trial with Meloidogyne sp. the number of nematodes per plant was counted, and in the trial withM. incognita a root damage index was established. Vegetative measurements (height, weight of aerial parts and roots) were taken in both trials. The parents were classed according to their cross value and genetic variance was estimated. In the factorial trial conducted with the Meloidogynesp. isolate from El Salvador, parents T3561 and T3751transmitted high resistance levels of 56 and 54%,respectively, to their progenies, as opposed to 9% for the other parents. The cross between those two parents achieved 78% resistant plants. In the trial with the M. incognita isolate from Guatemala, similar results were found. The same two parents transmitted resistance to 64% of their progenies, as opposed to 36% for the other parents. Classification of the parents did not differ from one trial to the other. The existence of a complex nematode resistance locus in the C. canephora species seems highly likely. The results show that it is possible to select rootstock varieties that are more resistant to the main Meloidogyne nematodes in Guatemala and El Salvador. Given the average heritability values (0.28–0.30) and the possibility of applying strong selection intensity, the genetic progress expected in the next selection cycle should be substantial. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterozygous genotypes are efficient testers for assessing between-population combining ability in the reciprocal recurrent selection of Coffea canephora

Coffea canephora Pierre breeding in Côte d’Ivoire is based on indirect reciprocal recurrent selection (RRSi) using the Congolese and Guinean populations. In practice, the genotypes of each population (78 Congolese genotypes and 100 Guinean genotypes) are tested with several testers from the reciprocal population: two Guinean and three Congolese testers. These testers are heterozygous as C. canephora is a strictly outcrossing species. After a first cycle of RRSi, we judged the efficiency of these testers for yield, susceptibility to coffee leaf rust (SCLR) and hundred bean weight (HBW). All the testers discriminated the tested genotypes highly significantly (P < 0.01), even though differences were found in the degrees of discrimination. For yield and SCLR, no interaction between tested genotypes and testers was observed and correlations between test values obtained from different testers were significant or highly significant. Furthermore, test values of tested genotypes could be used to predict the yield and SCLR of between-population (BP) hybrids. Prediction was always more accurate with the best tester than with the mean of several testers. As opposed to yield and SCLR, HBW showed significant interactions between tested genotypes and testers and HBW of hybrids could not be predicted from the test value of the genotypes. We conclude that only one reciprocal tester can be used in the next cycles of RRSi applied to C. canephora. This will allow either a reduced cost of selection or increased selection intensity.     

Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. Ex Fr. II. Meiosis in F1 hybrids and back crosses to C. Arabica

Summary Melosis was studied in Coffea arabica, in induced tetraploid C. canephora, in their F₁ hybrid (arabusta hybrid) and in backcross generations of the hybrid with C. arabica as recurrent parent. Irregularities were observed, consisting of univalents (especially in the arabusta hybrid), multivalents (especially in tetraploid C. canephora) and uneven distribution of chromosomes at first anaphase. Chromosome distribution was improved by backcrossing. Meiotic irregularities wer negatively correlated with pollen fertility.     

Prediction of genetic value for coffee production in Coffea arabica from a half-diallel with lines and hybrids

Genetic analysis of yield and morphological traits has been carried out in Coffea arabica from a half-diallel including the parental lines. The trial was established in west Cameroon with completely randomized single-tree plots. Observations included yield (four years), stem diameter, height and number of primaries. General combining abilities (GCA) and specific combining abilities (SCA) as heritabilities and genetic correlations were estimated. A significant SCA variance was observed for all the traits. Morphological traits, stem diameter, plant height and number of primaries, were genetically correlated to the yield. The hybrids were, on average, better performing than lines. There was no clear relationship between performance of lines and their general combining ability. Contribution of the seven lines to the SCA sum of squares was shown to be unequal for all the studied traits, one parent (Java) being far the most interactive. This variation of interactivity seemed to be related to different levels of residual heterozygosity among parental lines. Indirect prediction of yield using morphological traits gave the same value for expected genetic gain as the prediction based on cumulated yield over four years. The multitrait indirect selection for yield operated in a different way as far as GCA and SCA are concerned. The application of these results to coffee breeding strategies involving hybrid selection is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic response to index selection for grain yield, kernel weight and per cent protein in four wheat crosses

Quantitative genetic theory was used to investigate selection differentials, expected and observed direct and correlated responses to simultaneous improvement of grain yield, kernel weight, and grain protein content in F₃ and F₄ populations of four spring wheat (Triticum aestivum L.) crosses. Selection in the F₃ generation based on the Smith-Hazel index (SH) and yield was found to be superior to the other methods studied in identifying high-yielding lines, but resulted in substantial decrease in grain protein level. Consequently, a 1.0% increase in protein from selection for protein depressed grain yield as much as 536 kg/ha below the population mean, reducing the expected yield gains per generation selection cycle by 250%. The weight-free indices (EW), particularly the index involving only yield and kernel weight (EW3) and its linear approximation (EW4), and the desired gains indices were effective in improving protein content but were less efficient in selecting top-yielding lines. Selection in the opposite direction using truncation of the lowest 10% of the population based on weight-free-index involving yield, kernel weight and protein (EW2) reduced all traits significantly compared with the mean of the unselected population indicating the effectiveness of the unweighted selection index. The observed genetic gains (Ra) from selection based on yield, the SH, EW3 and EW4 indices were slightly lower than the expected advances per cycle (R) in populations from crosses ‘Sinton’בGlenlea’ (C1), ‘Glenlea’בNB505’ (C2), and ‘A2P5’בNB320’ (C6) (Ra/R = 70 to 85%) but were higher in cross ‘NB505’בA2P5’ (C5) (Ra/R = 126 to 143%). It was concluded that weight-free and the desired gains indices can be used to improve wheat grain yield and grain protein simultaneously in F₃ generation selection, as revealed by response to selection measured in the F₄ generation.     

Application of the concepts of test value and varietal value to the study of genetic advance in recurrent selection: A synthesis

Summary The concepts of varietal ability and value in test of a genotype or group of genotypes are specified according to the type of variety (clones, hybrids, lines, synthetics) and the testing system (phenotype, S₁, General combining ability (GCA), line value, General synthesizing ability (GSA)). Varietal ability and value in test are to be considered as any quantitative characters for which it is possible to define additive effects, dominance effects and epistasis. For diploids in recurrent selection, only additive effects and additive× additive epistasis for varietal value contribute to genetic advance. Genetic advance depends on the covariance between the testing value of the parents and the test value of the progeny by intercrossing. Such a parent-offspring covariance is, in the absence of epistasis and inbreeding, one half of the covariance between additive effects in test of the parents and additive effects in test of their progenies. This allows one to express directly the genetic advance in varietal value according to the type of variety and to the testing system used in recurrent selection. The case of biallelic populations is considered; it allows some discussions on the relative values of components of variance of varietal and test values.     

Correlated responses of fatty acid composition, grain quality, and agronomic traits to nine cycles of recurrent selection for increased oil content in oat

Increases in the groat-oil content of oat (Avena sativa L.) increase the energy value of the grain and improve the feasibility of extracting oat oil for use as a vegetable oil. Nine cycles of recurrent selection for greater groat-oil content conducted in a genetically broad-based oat population resulted in dramatic increases in groat-oil content. Our objectives were todetermine if selection for greater groat-oil content affected fatty acid composition, grain quality traits (test weight and seed weight), or agronomic traits (straw yield, biomass, harvest index, heading date, and height). We evaluated 100 random lines from the base (C0) population and each of the nine selection cycle populations in three environments in order to estimate means, genetic variances, heritabilities, and genotypic and phenotypic correlations of grain quality and agronomic traits. We also evaluated 20 random lines from each population to estimate changes in fatty acid contents. Oleate and stearate contents increased over cycles of selection, as did the ratio of unsaturated to saturated fatty acids. Palmitate, linoleate, and linolenate contents and all grain quality and agronomic traits except harvest index decreased over cycles of selection. There was no evidence for reduced genetic variance or heritability in C9 for any trait, but the genotypic and phenotypic correlations between agronomic traits and oil content fluctuated over cycles. Selection for increased groat-oil content improved oil quality but reduced grain quality and agronomic performance of the population. This revised version was published online in August 2006 with corrections to the Cover Date.