Doubled haploids of Coffea canephora: development,fertility and agronomic characteristics

Summary Doubled haploids (DH) of Coffea canephora Pierre were developed using haploid embryos which occur spontaneously in association with polyembryony. The frequencies of polyembryonic seeds and haploid embryos varied according to the parental genotypes. However, production of a large number of DH seemed possible from all genotypes. More than 750 DHs produced from various genotypes were grown under field conditions and evaluated for different characters of agronomic importance. Approximately half of DH genotypes did not survive, suggesting a strong, negative effect of homozygosity. Inbreeding depression is particularly severe on general vigor and reproductive aspects. For several characters studied such as leaf shape, leaf rust resistance and hundred bean weight, considerable genetic variations were observed within and between groups of DHs constituted by the DHs produced from the same clone. Despite their low vigor and reduced fertility, the DHs of C. canephora offer new possibilities in genetic research and coffee breeding.     

A new source of resistance against coffee leaf rust from New-Caledonian natural interspecific hybrids between Coffea arabica and Coffea canephora

The development of cultivars resistant to coffee leaf rust caused by the fungal pathogen Hemileia vastatrix is a priority in coffee breeding. However, only very few descendants of interspecific hybrids between Coffea arabica and diploid relative species have been used as resistance source. Identification of new sources of resistance appeared therefore particularly worthwhile. Hybrid plants derived from interspecific hybridization between C. arabica and Coffea canephora and found in neo‐natural coffee tree populations of New Caledonia were therefore investigated. Amplified Fragment Length Polymorphism and microsatellites amplification were used to evaluate the genetic diversity of 14 hybrid plants, and rust resistance was evaluated by inoculation with a panel of rust races representing a large variability in virulence. An important genetic diversity was characterized in hybrid plants originating from introgressions into C. arabica from various C. canephora progenitors. On the 14 plants tested for leaf rust resistance, eight appeared resistant to all races investigated. Such plant material should represent a highly valuable resource for C. arabica breeding against coffee leaf rust.     

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.     

Detection by simple sequence repeat markers of introgression from Coffea canephora in Coffea arabica cultivars

Microsatellites or simple sequence repeats (SSR) were used to assess polymorphism among 16 Coffea arabica and four Coffea canephora accessions, and to identify DNA introgression fragments from C. canephora in four C. arabica lines. Thirty‐one primer pairs allowed for the identification of 92 polymorphic alleles distributed over 37 loci. The C. arabica accessions derived from the genetic bases ‘Typica’ and ‘Bourbon’ were grouped separately according to their genetic origin. Two genotypes derived from a spontaneous hybrid (C arabica×C. canephora) were classified with the C. canephora accessions from Central Africa. Coffea canephora from West Africa were separated from the other accessions studied. Four alleles related to introgression (i.e. present in C. canephora and introgressed lines, and absent in C. arabica) were identified. The SSR markers were used successfully for characterization of a particular cultivar (‘Veranero’) from Costa Rica, which is known for its late maturity.     

Doubled-haploid versus single-seed descent and S1-family variation for testcross performance in a maize population

Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance. DH and single-seed descent (SSD) lines were produced from random S₁ progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the genetic variance of S₁ families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance of S₁ families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all traits, heritability of SSD or DH lines was higher than heritability of S₁ families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S₁ testcross progenies and DH or SSD testcross progenies, meaning that the S₁ testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation in DH lines appeared to be more in accordance with the observed variation among S₁ families than with the observed variation among SSD lines.     

Antixenosis resistance to leaf miner Leucoptera coffeella in Coffea species

The coffee leaf miner, Leucoptera coffeella, is the most important pest of Coffea arabica plantations in Brazil, and all cultivars are susceptible to the insect. However, distinct reactions have been observed in other species, such as C. congensis and C. canephora. In this work, the occurrence of antixenotic response was surveyed in individuals of Coffea species, selected for resistance to the leaf miner at both field and laboratory conditions. Tests performed on young plants from C. arabica cultivars Icatu Precoce IAC 3282, Mundo Novo IAC 515-20, Tupi IAC 1669-33 and Catuaí Amarelo IAC 62 demonstrated that these were preferred for oviposition when pooled with seedlings from C. canephora cv. Apoat? IAC 2258. Apoat? was also preferred over C. racemosa for oviposition. Similar results were observed in tests using detached leaves, and higher amount of eggs was counted in the cv Obat? IAC 1669-20 and Catuaí Vermelho IAC 81, and lower oviposition frequency was observed in C. canephora cv. Guarini IAC 1598. C. congensis showed an oviposition frequency between C. arabica and C. canephora. Also, the results suggest that the frequency of oviposition is co-related with the plant resistance level, during larvae infection.     

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.     

Resistance to Coffee Berry Disease in Arabica Coffee Variety 'Ruiru 11'

General and specific combining ability effects for resistance to coffee berry disease (Colletotrichum coffeanum Noack sensu Hindorf) in Coffea arabica variety ‘Ruiru 11’ and its parents were estimated according to the North Carolina Design II. A set of nine male parents and eleven females were crossed in all possible combinations to generate ninety-nine single cross hybrids constituting the ‘Ruiru 11’ variety. The parents and their hybrid progenies were screened and the mean score data analyzed for possible genetic variation. The contributions of the parents to the total genetic variance were low hence the low narrow sense heritability (h²= 0.04). The male and female parents accounted for 9.36 % and 0.96 %, respectively, while their interaction effect accounted for 89.68 %. In the analysis of combining ability for resistance, ExB3.96 and Cat.90 exhibited significant negative general combining ability (GCA). Specific combining abilities (SCA) were negative and significant for Cat.86 × ExB3.99, Cat.127 × ExB3.116 and Cat.119 × ExB3.879 crosses. The implications of these results in selection for highly resistant ‘Ruiru 11’ progenies are discussed.     

Genetic analysis of resistance to nematodes in inbred maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) and maize hybrids

Nematodes cause substantial grain yield loss in susceptible maize (Zea mays L.) cultivars. This study was conducted to estimate general combining ability (GCA), specific combining ability (SCA) and genetic effects associated with nematode resistance in maize. The 30 F ₁ hybrids generated from a 6 × 6 diallel and two local checks were evaluated in 2009 at three sites in Uganda. A split plot design was used with nematode treatments serving as whole plots and the hybrids as subplots but arranged in an 8 × 4 spatially adjusted alpha-lattice design. The experiment was replicated three times. Results showed GCA to be important for the reduction of P. zeae and Meloidogyne spp. densities and increase of root mass, with a contribution of 72 to 93% of the phenotypic variance. Inbreds MP709 and CML206 had the highest GCA for Pratylenchus zeae resistance, whereas for grain yield, it was CML444, CML312 and CML395 that were outstanding. The SCA influenced plant height and grain yield under nematode infestation, contributing 43 and 58% of the phenotypic variance, respectively. Observed reciprocal differences due to maternal effects also played a role in influencing the grain yield under nematode infestation. Overdominance genetic effects explained the non-additive variance recorded for the plant height, grain yield, number of root lesions, and P. zeae and Meloidogyne spp. densities under nematode infestation. The parents MP709, CML206, 5057, and CML444 contributed most of the dominant genes for the P. zeae resistance in all their crosses. The parent CML444 contributed most of the dominant genes for improved grain yield in all of its crosses. The high GCA effects among some parents support their utility in breeding of widely adapted nematode-resistant cultivars. The dominant genes and SCA effects would favour pedigree and various sib tests to improve grain yield under nematode pressure.     

Identification of a major QTL for adult plant resistance to coffee leaf rust (Hemileia vastatrix) in the natural Timor hybrid (Coffea arabica x C. canephora)

Most of the commercial varieties of coffee (Coffea arabica L.) derived from the Timor hybrid (TH) have been shown to contain major genes for coffee leaf rust (CLR) resistance. To identify markers tightly linked to such genes, an F₂ mapping population derived from a cross between ‘Caturra’ (susceptible variety) and the TH‐derived DI.200 line (highly resistant) was generated. Using expressed sequence information and a bioinformatics approach, both targeted region amplified polymorphism (TRAPs) markers and simple sequence repeat (SSR) markers were identified. Phenotypic evaluations in the field and under controlled conditions confirmed the existence of one quantitative trait locus for CLR resistance. Four candidate SSR markers were associated with high CLR resistance. They spanning a region of 2.5 cM designated Q_{CLR_4} located within chromosome 4 of the international C. canephora map. The presence of this region was confirmed in a set of elite lines and commercial varieties. The Q_{CLR_4} region corresponds to a new and genetically independent S_H locus that could potentially be useful in gene pyramiding with other genes to enhance rust resistance in TH derivatives.     

Genetic analysis of quantitative traits across environments in linseed (Linum usitatissimum L.)

Summary Fourteen lines of linseed (Linum usitatissimum L.) were evaluated for general and specific combining ability through line × tester cross analysis using five diverse testers in two different environments. Seventy F₁'s and nineteen parental genotypes were raised in completely randomized block design with two replications with respect to yield and yield related traits. Considerable genetic variation was observed for all the traits studied. The additive as well as non-additive gene effects played significant role in the inheritance of yield and related traits with preponderance of non-additive gene effects for all the traits studied. Higher proportion of general combining ability × environment interaction variance as compared to specific combining ability × environment estimates was recorded. Additive genetic variances were more sensitive than non-additive genetic variances to the changing environment. Low estimates of heritability (narrow sense) for primary branches per plant, capsules per plant, seeds per capsule, seed yield per plant, harvest index and oil content and medium heritability for days to 50% flowering, days to maturity, plant height and 1000-seed weight was observed. Among the female parents LCK-9816, Parvati, Himalini, KL-168 were good general combiners for yield and related traits along with oil content, whereas among male parents, Surbhi and KL-224 were good general combiners for yield related traits and oil content but KL-221 was good general combiner for seed yield and related traits.     

Barley mutant heterosis and fixation of'F1-performance'in doubled haploid lines

The phenomenon of mutant heterosis was studied in barley using F₁ hybrids developed from crosses involving two mutants derived from the same parent variety (067AR× 032AR), or from crosses of mutants with their parent varieties (Diva × 228DV; 437MG × Mg 4170). The agronomic performance (plant height, tillers per plant, kernel number and weight per plant) of F₁ hybrids was evaluated in relation to the corresponding parent variety used for mutant development. Wide-space sowing (0.O6 m²/plant) was applied to allow the full expression of hybrid vigour. The hybrids significantly exceeded their parent varieties in various yield parameters in each year of the experiment, Depending on the cross, the level of heterosis ranged from 39.45% to 82.1% for kernel number and from 44.45% to 91.2% for kernel weight, as an average of observations over three years. The increased yield of hybrids was accompanied by an increase in spikes/plant, without significant changes, in most cases, in yield components such as kernels/spike and 1000 kernel weight. The height of F₁ plants remained similar to the corresponding parent variety. Doubled haploicls (DH) were developed through anther culture from three F₁ hybrids to determine whether the heterotic effect could be fixed, even partly, in homozygous lines. Twenty-eight, 42 and 68 DH lines per cross were produced, and evaluated in the field, space-planted at 0.06 m²/plant, together with hybrids and parent varieties. The best-performing DH lines were evaluated again the following season in a conventional field trial. We were able to select 1.5 -14.3% of‘F₁,-performing’DH lines per hetorotic cross combination, which, in two years of studies, reached the yield of heterotic hybrids and significantly out-yielded the parent variety in plot. The yield potential of DH lines was better expressed under a wide sowing density, but even under normal growing conditions, the yield of the best selected DH lines surpassed their corresponding parent varieties by 17.77ndash;30.1%.     

Doubled haploids in tropical maize: <Emphasis Type="SmallCaps">II</Emphasis>. Quantitative genetic parameters for testcross performance

Single crosses (SC) of elite inbreds and open-pollinated populations (OP) are suitable source germplasm for doubled haploid (DH) line development in hybrid maize breeding, given that they combine a high population mean ([`(x)] \overline{x} ) for testcross performance with adequate response to selection ( \Updelta G \Updelta G ). This is the first study reporting testcross grain yield (TCGY) and dry matter content (TCDMC) evaluations of 131 DH lines developed from ten tropical source germplasm comprising five OP (OP1–OP5) and five SC (SC1–SC5). Gene diversity (d) and the average number of alleles (a <sub>r</sub> ) per locus was estimated for DH lines based on 24 simple sequence repeat markers. Analysis across three environments revealed no significant differences between [`(x)] \overline{x} of OP- and SC-derived DH lines for TCGY and TCDMC. Significant genetic variance for both traits was only detected among OP-derived DH lines which may be explained by a larger number of segregating quantitative trait loci (QTL) as suggested by higher d and a _r values than in SC-derived DH lines. The usefulness criterion ( U = [`(x)] + \Updelta G U = \overline{x} + \Updelta G ) was higher for OP-derived DH lines for TCDMC, but higher for SC-derived DH lines for TCGY. DH lines from OP1, OP2, and OP3 showed high TCGY, suggesting that they may be useful in tropical hybrid breeding. We conclude that tropical OP represent a valuable source of untapped genetic variation that can efficiently be exploited with DH technology for hybrid maize breeding.     

Study of genetic parameters and heterotic effects in crosses of maize (Zea mays L.) varieties with varying chromosome knob numbers

Summary Sibbed and selfed populations of ten maize varieties of geographically diverse origin and with chromosome knob number varying from 6–12, and their F₁ crosses in all possible combinations were studied at two agro-climatically different locations to find out general and specific combining ability, gene action and hybrid vigour in the varietal crosses of maize. The general and specific combining ability and their interaction with locations were highly significant. The magnitude of variance due to interaction of locations with specific combining ability were much more than with general combining ability. The estimates for non-additive component were higher for yield per plant, plant height, and ear placement, whereas for days to silking, ear length, ear diameter and 100-grain weight, the additive as well as non-additive components were of the same order. The magnitude of heterosis over the better parent and the mid parent indicated absence of epistasis and prevalence of partial or complete dominance of genes for yield and days to flowering.In the light of gene action and the magnitude of heterosis, utility and feasibility of varietal crosses in the maize improvement work in India has been discussed.Part of the thesis submitted by H. S. Kalsy in partial fulfilment of the requirement for Ph.D. degree.Present address: Pau Cotton Research Sub-Station, Faridkot, Distr. Bhatinda (Panjab), India.     

Combining ability for seed yield traits of Chenopodium quinoa breeding lines

For a better understanding of the inheritance of seed yield traits in Quinoa (Chenopodium quinoa) Willd., a half-diallelic crossing experiment with six diverse but uniform breeding lines was conducted. True hybrid plants were detected by means of differences in panicle colour in 14 out of the 15 crosses performed. The agronomic performance of 14 F₂ populations and six parental lines was evaluated in field trials on fertile clay soil. General and specific combining ability of the lines (GCA and SCA) were estimated. Highly significant differences in GCA effects were found between the lines for plant height at maturity, early flowering, early maturity, seed yield and thousand seed weight. Significant SCA effects were only found for plant height at maturity. However, SCA effects were rather small and accounted for 7% of the total variance. The finding of large GCA effects and low SCA effects suggests that best selection results could be expected from crosses between the agronomic best performing genotypes. This revised version was published online in August 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.     

Genetic analysis of partial resistance to coffee leaf rust ( Hemileia vastatrix Berk & Br.) introgressed into the cultivated Coffea arabica L. from the diploid C. canephora species

The objective of this study was to identify polymorphic molecular markers associated with partial resistance to coffee leaf rust, Hemileia vastarix. A segregating F ₂ population derived from a cross between the susceptible Coffea arabica cv. Caturra and a C. canephora-introgressed Arabica line exhibiting high partial resistance was analyzed. Rust resistance measured as rust incidence (RI) and defoliation (DEF) was evaluated in field conditions in three consecutive years (2003–2005). During the 2003 season, which was characterized by favorable conditions for a rust epidemic, the F ₂ plants exhibited different levels of resistance ranging from very susceptible (50.1% for DEF and 49.5% for RI) to highly partial resistance (9.1% for DEF and 3.7% for RI). Molecular analysis enabled identification of seven polymorphic markers (5 AFLP and 2 SSR) exhibiting significant association with partial resistance. Coexistence of resistance homozygous alleles (RR) at codominant SSR loci was correlated with high resistance. This study is the first attempt to develop PCR-based sequence specific markers linked to partial rust resistance in coffee.     

Studies on a diallel cross and double-cross hybrids among various Brassica oleracea types

Summary Three unrelated pairs of inbred lines from marrow-stem kale (A), thousand headed kale (B), and Scotch curled kale (C), together with 3 lines from Chou Fourrager Jaune (D), Brussels sprouts (E), and January King cabbage (F) were used to produce a diallel cross.Study of the F₁ generation revealed that general combining ability was highly significant for all yield components studied and specific combining ability was also significant for all but at a much lower level. Greater heterosis for leaf yield, but not for stem yield, was indicated in the inter-type hybrids as compared with intra-type hybrids.Double-crosses made among F₁ from the paired inbred lines did not reveal consistent effects of order of combining the inbred lines on yield characters, but the large differences in plant-to-plant uniformity showed that only the (X₁×X₂)×(Y₁×Y₂) combination is likely to be of practical significance.     

Pleiotropic effects of male sterility genes in hybrid tomatoes (Lycopersicon esculentum Mill.)

Summary The influence of seven recessive male-sterile alleles on early marketable yield, total marketable yield and average fruit weight in heterozygous F1 hybrid tomatoes was studied. Differences were found between nearisogenic F1 hybrid pairs, in the mutants ms-14, ms-17 and ms-18 for percentage of early marketable yield; in the mutants ms-17, ms-31 and ms-47 for average fruit weight; and in the mutants ms-14, ms-17 and ms-33 for total marketable yield. These differences may be attributed to pleiotropic effects of male-sterility alleles or genes highly linked to these alleles. The direction and the magnitude of the pleiotropic effect on a specific characteristic were found to be dependent on the general genetic background of the parental lines and the specific combining ability of the F1 hybrid. Interactions found in crosses between male-sterile and male-fertile female lines and parental lines suggest that male-sterility alleles affect the general combining ability of female lines. Such differences were demonstrated to be statistically significant for percentage of early marketable yield with mutant ms-18, for average fruit weight with mutants ms-47, and for total marketable yield with mutant ms-17 and ms-33. The absence of uniformity with respect to the pleiotropic effects and occasional deviations in the general combining ability are discussed.     

Heterosis and Genetic Variances and their Implications for Breeding Improved Varieties of Spring Beans (Vicia faba L.)*

Handcrosses were made in a factorial manner with 24 Vicia faba inbred lines m three sets, each between four male and four female parents. The resulting 48 hybrids, their parental inbreds and three commercial varieties were grown in performance trials during the years 1985—87 with three replications at one location. Yield and yield components were recorded on single plant basis. The average superiority of the hybrids above the control varieties was 26 % in plant yield. The best crosses outyielded the controls by more than 50 %. However, a few inbred lines also reached, the yield level of the controls. The average heterosis was significant for all characters except for maturity date. In plant yield the average heterosis was 75%, ranging between 34% and 148% in the various cross combinations. The highest average heterosis of 110 % was observed in yield at the lateral stems. In all characters the best inbreds were superior to the lower hybrids and in some characters even equal to the average of the hybrids. A strong positive relationship was found for all characters between hybrid performance and mid-parent value and between the per se performance of the inbreds and their general combining ability. Genotypic differences between the hybrids as well as between the inbreds were highly significant. Most of the variability between the hybrids in all characters were attributed to general combining, ability with only little evidence for specific combining ability. In the discussion the results are evaluated according to the choice of the breeding category of the partial allogamous faba bean species.