Interspecific Progenies Research Articles

Transfert à des Blés marocains, à la suite de croisement avec Aegilops squarrosa, de gènes de résistance à la mouche de Hesse

Hessian fly (Mayetiola destructor (Say) is probably the most serious pest on wheat crops (Triticum sp.) in many countries. Interspecific crosses were carried out between durum wheat cultivars and different Ae. squarrosa accessions that are resistant to the Hessian fly. The low viability and the sterility of the interspecific hybrids F1 and its progenies 1st, 2nd and 3rd generations have a determinant impact on seed set and percentages of the interspecific hybrid produced. The rate of univalent percentages decreased clearly in the second generation, in connection with spontaneous chromosomal doubling. Most interspecific offspring were resistant to the Hessian fly. At F4 and F5 they still showed a segregation of resistance. Few interspecific progenies showed higher resistance, especially at the 5th generation.

Pollen donor impact on progenies of pseudogamous blackberries (Rubus subgen. Rubus)

A series of intra- and interspecific crosses in Rubus was evaluated with DNA markers to assess the proportion of apomictically vs. sexually derived progeny plants. The species were well separated from each other with these markers and the interspecific hybrids were easy to ascertain. Ten plants each were derived by selfing of R. hartmanni, R. polyanthemus and R. vestitus, and evaluated with RFLP. Of these plants, only one R. hartmanni plant appeared to be sexually derived, whereas the remainder appeared to have arisen by apomixis. Between 10 and 19 progeny plants, derived by open pollination of R. Hartmanni, R. infestus, R. laciniatus and R. vestitus, respectively (total of 63plants), were evaluated with RFLP. Of these, 6 plants (approx. 10%) showed as lightly deviating band pattern, which may indicate sexual seed set but could also result from experimental artefacts. The three species combinations 1) R. hartmanni and R. sprengelii, 2) R. infestus and R. vestitus, and 3)R. laciniatus and R. polyanthemus were cross-pollinated reciprocally and the resulting progenies evaluated with RAPD (combinations 1 and 2)and leaf shape (combination 3). Combination1 produced 20% (3 out of 15 progenies)sexually derived progenies, combination 2produced 100% (26 progenies) and combination 3 produced 64% (16 out of 26progenies), respectively. The hybrid progenies appeared to have been derived through pollination of unreduced as well as reduced egg cells. The ability to produce interspecific hybrid progenies is most probably dependent upon the species combination.

Increasing biodiversity of irrigated rice in Africa by interspecific crossing of Oryza glaberrima (Steud.) × O. sativa indica (L.)

The African rice Oryza glaberrima, traditionally cultivated since more than 3.500 years, is of poor agronomic performance but resistant/tolerant to various stresses and diseases. The introduction of these characters into O. sativa cultivars is difficult since crossing barriers cause spikelet sterility in F1. Backcrossing can restore fertility and recently facilitated the development of fertile O. glaberrima × O. sativa ssp. japonica hybrid progenies for rain fed systems. With the objective to gain access to African rice germplasm for improvement of irrigated rice, crosses were performed with eighteen O. glaberrima and twenty O. sativa ssp. indica accessions. In total about one hundred F1-hybrid grains were obtained. The F1 plants were all completely sterile and backcrossing (BC) to O. sativa was performed in order to restore spikelet fertility. Monitoring of Tog5681 × IR64 hybrid progenies under field conditions revealed a broad genetic diversity within the BC1 and BC2 populations. Some BC1 and BC2 progeny plants outperformed the O. sativa parent, indicating that the heterozygocity level and complementary gene action after two backcrosses are still sufficient to positively influence plant vigor. Spikelet fertility of progenies was highly variable, but almost complete fertility was already observed within the BC1F2 population. High spikelet fertility was preserved in one out of two analyzed BC1F3 families and inmost of the BC2F3 families. The ability to restore spikelet fertility within few generations and the potential of the genetic diversity present in interspecific progenies facilitates the development of plant types specifically designed for the African irrigated and lowland environment.

MARKER-ASSISTED SELECTION OF THE MA GENE FROM MYROBALAN PLUM FOR A COMPLETE-SPECTRUM ROOT-KNOT NEMATODE (RKN) RESISTANCE IN PRUNUS ROOTSTOCKS

In Myrobalan plum (Prunus cerasifera; subgenus Prunophora), the clones P.2175, P.1079 and P.2980 are highly resistant to all tested RKN nematodes including Meloidogyne arenaria, M. incognita, M. javanica and also an unclassified isolate Meloidogyne sp. Florida (FL) that overcomes the resistance in other commonly used Prunus sources from the Amygdalus subgenus. All three clones carry a single major dominant gene (alleles respectively designated Ma1, Ma2 and Ma3) that confers a high-level and complete-spectrum resistance (including at least M. arenaria, M. incognita, M. javanica, the Florida isolate and M. mayaguensis). Bulked segregant analysis associated with the RAPD or AFLP techniques were performed to detect markers linked to Ma1 using segregating intra- and interspecific progenies from P.2175 (Ma1ma1) crossed by several host parents (ma ma). Three RAPD, one AFLP and three SSR markers were obtained. From these, one RAPD and one AFLP markers, converted into reliable SCAR (sequence characterized amplified region) markers, were located at less than 1 cM from the gene. One of them (SCAL19) has been evaluated for MAS in an European rootstock program based on Myrobalan plum x Amygdalus (peach, almond or almond-peach) hybrids and proved to be usable reliably in particular to detect the Ma alleles in segregating progenies involving Amygdalus resistance sources such as the peach Nemared, the wild peach P. davidiana, the almond Alnem or the almond-peach hybrids GF.557 and Garfi x Nemared. Data from RFLP and SSR markers, from a reference Prunus map initiated by a European mapping group, indicate that Ma1 is located on the linkage group 7.

Recessive resistance genes against potyviruses are localized in colinear genomic regions of the tomato ( Lycopersicon spp.) and pepper ( Capsicum spp.) genomes.

Resistance against both Potato virus Y (PVY) and Tobacco etch virus (TEV) was identified in the wild tomato relative Lycopersicon hirsutum PI247087. Analysis of the segregation ratio in F(2)/F(3) and BC(1) interspecific progenies indicated that a single recessive gene, or two very tightly linked recessive loci, are involved in resistance to both potyviruses. This locus was named pot-1. Using amplified fragment length polymorphism markers and a set of L. hirsutum introgression lines, pot-1 was mapped to the short arm of tomato chromosome 3, in the vicinity of the recessive py-1 locus for resistance to corky root rot. Because of the occurrence of phenotypically similar genes in pepper ( Capsicum spp.), the comparative genetics of resistance to potyviruses between tomato and pepper was investigated. Unlike most of the comparative genetic studies on resistance genes, pot-1 was tightly flanked by the same restriction fragment length polymorphism (RFLP) markers than the pvr2/pvr5 locus for resistance to PVY and TEV from pepper. These results may indicate that recessive resistance genes against potyviruses evolve less rapidly than the majority of the dominant genes cloned so far, and consequently may belong to a different family of resistance genes.

IDENTIFICATION OF PARENTAL CHROMOSOMES AND DETECTION OF RIBOSOMAL DNA SEQUENCES IN INTERSPECIFIC HYBRIDS OF LILIUM REVEALED BY MULTICOLOR IN SITU HYBRIDIZATION

IDENTIFICATION OF PARENTAL CHROMOSOMES AND DETECTION OF RIBOSOMAL DNA SEQUENCES IN INTERSPECIFIC HYBRIDS OF LILIUM REVEALED BY MULTICOLOR IN SITU HYBRIDIZATION

Essai d'introgression, chez des Blés marocains, de gènes de résistance à la Mouche de Hesse présents chez quatre Aegilops

Interspecific crosses between the two cultivated wheat (Triticum durum, T. aestivum) and four species of Aegilops (Ae. triaristata, Ae. ovata, Ae. ventricosa and Ae. squarrosa) have been made. Comparative study of the crossing capability of the four species of Aegilops with cultivated wheat showed that both seed set and plant hybrids produced are variable and not related to the yield interspecific progeny. The crosses giving the best seed set were not those who produced a viable interspecific progeny. The viability and fertility of F1 hybrids and their progeny are better criteria to evaluate the success of the introgressed lines.

Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus

The African horned cucumber (Cucumis metuliferus Naud.; 2x = 2n = 24) contains genes that can confer resistance to many important cucumber (C. sativus L.; 2x = 2n = 14) pests [e.g., root-knotnematode, Meloidogyne incognita (Kofoid & White) Chitwood]. Cucumber is highly susceptible to this root-knot nematode species, and a recent screening of C. sativus accessions in the U.S. National Plant Germplasm collection did not identify sources of resistance. Thus,autotetraploids of Cucumis sativus and C. metuliferus were created to recover fertile resistant interspecific progeny. Autotetraploids were obtained at the highest rate when seeds were immersed in 0.5% colchicine for a period of 6 to 8 hrs. Treatment durations less than 6 hrs produced few tetraploids, and durations of 10 hrs or more were lethal to seeds or developing seedlings. Crosses between C. sativus and C. metuliferus were made using diploid and tetraploid lines in all possible combinations, including reciprocals. Fruit development occurred in crosses when diploid and tetraploid C. sativus were used as the female parent. However, seeds developed only in fruit of C. sativus (4n) ×C. metuliferus (2n) crossings. Seeds from these crosses, however,were flat and not viable. No fruit development occurred in crosses whereC. metuliferus was used as the female parent.

Fertilization Fitness and Relation to Chromosome Number in Interspecific Progeny between <I>Brassica napus</I> and <I>B. rapa</I>: A Comparative Study using Natural and Resynthesized <I>B. napus</I>

The variation of the chromosome number in interspecific progeny is difficult to predict. We defined the terms “fertilization fitness” and “relative fitness” as the parameters of competitive ability of the gametes and attempted to use them in a study on the variation of the chromosome number in the progeny between Brassica napus and B. rapa. Fertilization fitness was defined as the ratio of the actual frequency of the gametes with a specific chromosome number to the theoretical frequency based on binomial distribution. Relative fitness was defined as the ratio of fertilization fitness of the gametes with a specific chromosome number to fertilization fitness of the gametes with n=10. A resynthesized accession and a natural accession of B. napus were used in this experiment to produce sesquidiploids AAC-S and AAC-N, respectively. A comparative study on these two sesquidiploid populations was carried out to reveal differences in the pattern of variation in the chromosome number. Fitness analysis showed that gamete competition was conspicuous and closely related to the chromosome number. Gamete competition occurred predominantly during the embryo developmental stage. In both sesquidiploid populations, fertilization fitness decreased abruptly when the chromosome number varied in the range from n=10 to n=12 or in the range from n=19 to n=17. However, in the range from n=13 to n=16, the effect of the chromosome number on fertilization fitness was more pronounced in the AAC-N population than in the AAC-S one. The AAC-N population showed stronger tendency in keeping its gametes toward euploid number. Fertilization fitness and relative fitness was found to be efficient parameters for the study of variation of the chromosome number in interspecific hybridization. The use of the Relative fitness parameter may enable to predict the frequency of a specific chromosome number in interspecific progenies.

Male accessory gland secretory proteins in a few members of the Drosophila nasuta subgroup.

Male accessory gland secretory proteins in seven members of the Drosophila nasuta subgroup have been analyzed by SDS-PAGE. The study revealed remarkable simplicity in the patterns. The protein fractions, which migrate in three groups, could be categorized as "major" and "minor." The number of major fractions varies from a maximum of eight to a minimum of four. Group I consists of high molecular weight fractions, and group III, low molecular weight fractions. Among different members analyzed, the variation with respect to pattern and the number of fractions are confined largely to group III protein fractions, while group I and II fractions are found to be conserved to a greater extent. These proteins are PAS positive and group III fractions are not sensitive to silver staining. Analysis of these tissue specific proteins in the F1 and F2 of interspecific crosses and backcross progeny as well as volume analysis revealed that a 26-kD fraction in D. n. nasuta follows an autosomal pattern of inheritance, while a 55-kD and a 25-kD fraction in D. n. albomicans and a 24-kD fraction in D. n. kepulauana follow an X-linked pattern of inheritance.

Red rot resistance in interspecific protoplast fusion product progeny of Porphyra yezoensis and P. tenuipedalis (Bangiales, Rhodophyta)

SUMMARY Nine primary regenerants were recovered by interspecific protoplast fusion of Porphyra yezoensis Ueda T-14 (Py) (cultivated Porphyra) and Porphyra tenuipedalis Miura (Pt). This combination is difficult to achieve with conventional sexual hybridization, yet is important in that non-cultivated P. tenuipedalis is partially resistant (PR) to red rot disease, caused by the microbial pathogen, Pythium porphyrae Takahashi et Sasaki. Out of the nine primary regenerants, two strains (Py-Pt-4 and Py-Pt-7) were like the parent, P. tenuipedalis, while the rest were like the other cultivated parent P. yezoensis T-14 in their life cycle. Red rot resistance was assessed in parents and interspecific fusion product progeny (FPP) by exposing the foliose thalli to equivalent infection and measuring two parameters of the host-pathogen interactions: supported fungal biomass and amount of disease produced. Intermediate resistance between P. yezoensis T-14 (1.00) and P. tenuipedalis (0.13) was observed in two of the Py-type FPP, Py-Pt-2F2 (0.25) and Py-Pt-5F2 (0.23). Stable inheritance of resistance was observed through two subsequent generations. The morphologic and reproductive characteristics of the regenerated foliose thalli, and nature of host-pathogen interactions were used to further verify the hybrid origin of the FPP. Host-pathogen interactions were followed using epi-fluorescence and scanning electron microscopy (SEM). The zoospores encysted at higher rates on the susceptible cultivated parent (P. yezoensis T-14) germinated immediately and the short germ tubes formed appres-soria and penetrated the algal cells near the site of encystment. While on the PR parental (P. tenuipedalis) and partially resistant FPP (PRFPP) progeny (Py-Pt-2F2 and Py-Pt-5F2) the low rate of zoospore encystment was followed by cyst germination, but only a few of the germ tubes formed appressoria and penetrated the thallus surface. Long germ tubes (with no appressoria) were seen growing on the thallus surface without host penetration. The minimal rate of encystment concomitant with low rate of appressorium formation on the PR parent and PRFPP was observed as the major factor responsible for the partial resistance in these thalli.

High regeneration potential in vitro of sunflower (Helianthus annuus L.) lines derived from interspecific hybridization.

Successful selection of interspecific hybrid progenies with superior ability to regenerate shoots from apical meristems was performed in sunflower which now allows for the development of lines for improved biotechnological applications. Early generations of interspecific hybrids originating from crosses between the two H. annuus CMS lines ‘HA89’ and ‘Baso’, and 9 wild species were screened for their ability to regenerate in vitro. Evaluation of 36 progenies allowed to identify seven progenies from crosses involving H. mollis, H. giganteus, H. strumosus, and H. decapetalus which showed a significantly higher regeneration potential than the commercial hybrid ‘Albena’ regarding the number of shoots per explant. Among these progenies, 47.2 to 62.4% of explants produced shoots with an average of 2.3 to 3.5 shoots per cultured explant. Regeneration in vitro was significantly determined by the genotype. More than half of the investigated interspecific hybrids performed better than the inbred ‘HA89’ demonstrating that the high regeneration potential available in the wild species can be efficiently transferred to cultivated sunflower. The seven progenies with high regeneration potential in vitro were characterised by agronomic performance in the field. Two of the interspecific hybrids derived from H. strumosus and H. decapetalus not only showed a superior regeneration potential but also proved to be competitive to commercial hybrids with regard to important agronomic traits, e.g. fat content and TGW.

The Genetic Basis of High Resistance to Rice Yellow Mottle Virus (RYMV) in Cultivars of Two Cultivated Rice Species.

Three cultivars of Oryza sativa (IR64, Azucena, and Gigante) and four cultivars of O. glaberrima (Tog5681, Tog5673, CG14, and SG329) were evaluated for their resistance to two isolates of rice yellow mottle virus (RYMV) by enzyme-linked immunosorbent assay (ELISA) and symptomatology. Cultivars Tog5681 and Gigante were highly resistant, and no symptoms were observed when either virus isolate was inoculated at 10 or 20 days postgermination and assayed by ELISA at 7, 14, 22, 35, 50, or 64 days postinoculation. Azucena showed a partial resistance, whereas the other cultivars were susceptible. Symptom appearance was associated with increase in ELISA absorbance in the systemically infected leaves. The best discrimination among the cultivars occurred when the plants were inoculated at 10 days postgermination. Crosses were made between the highly resistant (Gigante and Tog5681) and the susceptible (IR64) cultivars to determine the genetic basis of resistance to RYMV. Evaluation of F1 hybrids and interspecific progenies, as well as the segregation of resistance in F2 and F3 lines of the IR64 × Gigante cross, provided results consistent with the presence of a single recessive resistance gene common to Tog5681 and Gigante.

Reserve mobilization, dry matter partitioning and specific leaf area in seedlings of African rice cultivars differing in early vigor

Rice breeding for weed competitiveness requires improved screening tools. An ongoing breeding program uses O. glaberrima as genetic donor for growth vigor and weed competitiveness. This study investigates morphophysiological characteristics relevant to seedling vigor, namely, the kinetics of reserve mobilization, dry matter partitioning among organs, and specific leaf area (SLA). Five diverse cultivars ( O. glaberrima upland rice, improved and traditional tropical O. sativa japonica upland rices, an improved O. sativa indica cultivar and an interspecific progeny) were grown in the screenhouse for 18 days on wet soil. Dry matter fractions of plant organs were measured daily, leaf area (LA) and SLA were measured 9, 14 and 18 days after seed soaking (DAS). SLA measurements were repeated using crowded populations simulating farmers' seedbed nurseries. Seedlings achieved photo-autotrophic growth between 7.6 and 9.3 DAS, and had compensated for respiration losses during heterotrophic growth at 10.3–12.4 DAS, with O. glaberrima and improved indica cultivars requiring shorter periods than tropical japonica cultivars. For all cultivars, dry matter partitioning coefficients (PC) for roots were initially large but dropped temporarily to near zero during the transition from heterotrophic to autotrophic growth. The O. glaberrima cultivar had the largest PC for laminae and the largest SLA among the cultivars. It is concluded that the superior early growth vigor of the O. glaberrima cultivar, as documented in previous studies, is partly due to (1) early onset of autotrophic growth, (2) high PC for leaves, and (3) large SLA. Based on the previous observation that SLA is correlated with weed competitiveness, it appears that SLA measured at about 14 days after germination might be employed as a rapid screen for weed competitiveness.

Relationships between upland rice canopy characteristics and weed competitiveness

Weed-competitive upland rices with an acceptable yield potential are needed for labor-limited systems in Africa, particularly where shortened fallow periods have increased weed pressure. Crosses between weed-competitive but low-yielding African rice, Oryza glaberrima, and improved Oryza sativa tropical-japonica rices, might reduce tradeoffs between competitiveness and yield potential. Parallel field studies under moist upland conditions were conducted during the 1996 and 1997 wet seasons at Mbe in Cote d'Ivoire to (1) characterize canopy properties, growth vigor and yield for O. glaberrima, O. sativa and interspecific progenies under monoculture, and (2) determine their competitiveness when grown in single rows in competition with natural weed growth, maize (removed 50 days after sowing [DAS]), the highly weed-competitive O. glaberrima IG10, and with themselves. In the monoculture study with 21 lines, dry matter, leaf area index (LAI), PAR extinction coefficient ( K df), mean tip elevation angle (MTA) and specific leaf area (SLA) were measured 31, 46 and 64 DAS. Across lines, LAI was positively correlated with SLA, dry matter partitioning to leaves (31 and 46 DAS) and K df (46 DAS); and negatively with MTA (46 and 64 DAS). Plant height was negatively correlated with tiller number. In the competition study with 16 lines, the O. glaberrima landraces had superior relative yield (yield under interspecific competition/yield under intraspecific competition). Some breeding lines were competitive with specific competitors. Correlations between canopy characteristics under monoculture and competition indicated that LAI, SLA and tillering ability were predictive of competitiveness regardless of the competing species, whereas partitioning, K df and MTA were correlated with competitiveness only for specific growth stages and/or competitors. Competitiveness was negatively but weakly correlated with yield potential, and positively, with crop duration. The authors conclude that SLA and tillering ability, which are major determinants of vegetative vigor, and crop duration, which affects the ability to recover from early competition, are useful traits in the selection of weed-competitive rices, particularly in breeding programs that use O. glaberrima. The traits are compatible with high yield potential if cultivars have large SLA during early developmental stages and small SLA during advanced stages. Major knowledge gaps remain on weed competitiveness under drought- and flood-prone conditions, which are frequently associated with weed problems.

Phenological responses of Oryza sativa, O. glaberrima and inter-specific rice cultivars on a toposquence in West Africa

Phenological properties of rice cultivars, particularly crop duration, determine their yield potential, local agronomic suitability and ability to escape from drought. Crop duration of a given cultivar depends mainly on photoperiod (PP) and temperature, but is also affected by the crop establishment practice and environmental stresses. A sample of 84 ecologically and genetically diverse rice cultivars was sown on five dates between May and September 1997 on the flooded-lowland (transplant), hydromorphic and upland levels of a toposequence at 7° 52′ N in Cote d'Ivoire, in order to characterize the cultivars' phenological responses. In the upland, life-saving sprinkler irrigation was applied when drought symptoms were visible. A non-replicated design augmented with four replicated checks (four replications per ecosystem) was used. Phenology was characterized by date of emergence, first heading, 50% flowering and maturity. The period from emergence to flowering was subdivided into three phases following a simple model used at IRRI to characterize germplasm for photoperiodism. For each ecosystem and cultivar, the basic vegetative period (BVP) was estimated by subtracting 30 d from the duration to flowering at the sowing date associated with the shortest duration, and expressed in degree-days (dd), assuming a base temperature of 10 °C. The PP-sensitive phase (PSP) was estimated by subtracting BVP+30 d from the time to flowering. PP-sensitivity (PS) was calculated from the apparent change in PSP between 12.0 and 12.5 h mean astronomic daylength during the PSP, by regression across dates. Cultivars differed strongly in BVP (300 to 1200 dd) and PS (0 to 1000 dd). The BVP was generally longer in the lowland than in the hydromorph, and mostly longer in the upland than in the hydromorph, possibly due to transplanting shock (lowland) and drought (upland). Many cultivars, particularly upland-adapted japonicas, had a greater PS in the lowland than in the upland. Principal-component and cluster analyses based on BVP and PS in each of the three ecosystems established three large and three small groups of cultivars having common phenological responses. The linkage groups were associated with ecotypes (lowland vs upland, traditional vs improved) and genetic groups (O. sativa japonica and indica, O. glaberrima, inter-specific progenies). The groups were seen to represent past selection strategies by farmers and recent breeding strategies, with respect to achieving yield stability in the various ecosystems. For example, indigenous selection strategies for O. sativa upland rices seem to have favored a long BVP, whereas from O. glaberrima, which generally has a superior initial vigor, cultivars with a short BVP have been selected. The authors conclude that the modern upland rice breeding strategy for the region on the basis O. sativa, which aims at drought escape using a short BVP, is paralleled by existing indigenous O. glaberrima materials. Efforts to utilize these materials for breeding are ongoing.

Growth and yield potential of Oryza sativa and O. glaberrima upland rice cultivars and their interspecific progenies

A recent breakthrough in generating fertile progeny from Oryza sativa× O. glaberrima crosses gives rice breeders access to a broader range of germplasm. Interspecific crosses might provide new solutions to the low productivity of upland rice systems prone to weed competition. Two field and one pot experiments conducted during 1995 and 1996 served to characterize growth and yield potential of CG14 ( O. glaberrima), WAB56-104 ( O. sativa) and their progeny. During the 1995 wet season and the 1996 dry and wet seasons, the lines were seeded in a well-drained upland field in Ivory Coast with supplemental sprinkler irrigation. A randomized complete-block design with three replications was used, with cultivar and nitrogen levels as sub-plots. Specific leaf area (SLA), leaf area index (LAI), leaf chlorophyll content (SPAD method) and tiller number were measured at 2-week intervals until flowering. Grain yield and yield components were measured at maturity. In all environments, CG14 produced two to three times the LAI and tiller numbers as WAB56-104. This was associated with a high SLA and low leaf chlorophyll content. Grain yields of CG14 did not respond to N inputs, although the sink potential did. The difference was mainly caused by grain shattering. The progenies had intermediate LAI, SLA and leaf chlorophyll content, but their grain yields, tiller numbers and resistance to lodging and grain shattering were similar to WAB56-104. Across lines, LAI and SLA were significantly correlated. A paddy field experiment confirmed the relationship between LAI and SLA for a wider range of rice cultivars and interspecific progenies. A pot experiment demonstrated that leaf net CO 2 assimilation rates ( A max) followed a common linear function of areal leaf chlorophyll content across cultivars. The main common cause of differential LAI and A max appeared to have been genotypic patterns of SLA, which might be an important determinant of growth vigor and competitiveness with weeds. The possibility is discussed of combining, in a single line, high SLA during vegetative growth (for weed competitiveness) with low SLA during the reproductive growth phase (for high yield potential), to produce an efficient plant type for low-management conditions.

Inheritance and linkage relationships of isoenzymes in two interspecific cherry progenies

Two interspecific cherry progenies, Prunus avium ‘Napoleon’ × P. incisa E621 and ‘Napoleon’ × P. nipponica F1292, were analysed with polyacrylamide gel electrophoresis for 19 enzyme systems: alanine aminopeptidase (AAP), aldolase (ALD), alkaline phosphatase (AKP), arginine aminopeptidase (ARA), catechol oxidase (CO), diaphorase (DIA), endopeptidase (ENP), esterase (EST), formate dehydrogenase (FDH), fructose-bisphosphatase (FBP), β-galactosidase (GAL), glucose-6-phosphate dehydrogenase (G6PDH), β-glucosidase (GLU), glutamate dehydrogenase (GDH), glyceraldehyde-3-phosphate dehydrogenase (G3PDH), hexokinase (HEX), peroxidase (PRX), phosphorylase (PHO) and triose-phosphate isomerase (TPI). Activity for GAL was identical with GLU, and CO with PRX. In addition, activity for AKP was identical with some regions detected previously as acid phosphatase; and most of the PRX activity was identical with regions detected previously as superoxide dismutase. In all, 16 new segregating loci were identified, Ara-1, Dia-2, Est-1, Est-2, -6, -7 and -9, Glu-1 to -4, Hex-1, Pho-1 and -2, and Prx-8 and -9, together with 10 polymorphic putative loci. Analysis of cosegregations of the segregating loci with each other, and with loci established previously, resulted in 19 more loci being added to the cherry linkage map. Fifteen of these were new, and four had been described previously, but were hitherto unlinked. The additional linkages are: Ara-1– Dia-2– Mdh-2–Est-2; Glu-3/Prx-8–Glu-1/-2/-4–Prx-1/-9; Pgd-2–Pho-1/-2; Idh-2–Est-7–Est-6; (Amy-2)–Est-1–(Adh-4/-6); and (Acp-1/-2/-3)–Hex-1–(Gpi-2). (The bracketed loci had been mapped already). Several cherry linkages resemble linkages reported in apple. Analysis of 14 cultivars of P. avium for the same enzyme systems revealed polymorphism for just four of the 15 loci, and for an additional putative locus that was monomorphic in the interspecific material. This lack of isoenzyme polymorphism among cherry cultivars reduces the utility of these markers for linkage analysis and mapping in progenies of P. avium.

Inheritance of isoenzymes and their linkage relationships in two interspecific cherry progenies

Two interspecific cherry progenies, Prunus avium 'Napoleon' × P. incisa E621 and × P. nipponica F1292, were analysed by polyacrylamide gel electrophoresis for 14 enzyme systems: aconitase (ACO), acid phosphatase (ACP), alcohol dehydrogenase (ADH), amylase (AMY), glutamate oxaloacetate transaminase (GOT), glucose–6-phosphate isomerase (GPI), isocitrate dehydrogenase (IDH), leucine aminopeptidase (LAP), malate dehydrogenase (MDH), malic enzyme (ME), phosphogluconate dehydrogenase (PGD), phosphoglucomutase (PGM), shikimate dehydrogenase (SKD) and superoxide dismutase (SOD). Thirty-one loci were deduced from segregating banding patterns, Aco–2, Acp–1 to –5, Acp–8, –9, Adh–1 to –6, Amy–2, –3, Got–1 to –3, Gpi–2, Idh–1 to –4, Lap–1, Me–1, –2, Mdh–2, Pgd–1, –2 and Sod–2. Only ten of these had previously been established. Seven putative loci were polymorphic but did not segregate in the progenies. Analysis of cosegregations and calculation of recombination fractions revealed that 15 loci could be grouped into four linkage groups: Acp–1/–2/–3–-Acp–5; Gpi–2–- Got–2–-Got–1–-Lap–1; Adh–4/–6– -Amy–2; and Adh–1–-Adh–5–-Adh–2–- Me–2. These consolidate two previously reported linkage groups and establish three new groups. The previously reported linkage of Lap–1 with Me–1 was not confirmed. Fourteen cultivars of P. avium were analysed for the same 14 enzyme systems and showed polymorphism for just 17 of the established loci and for none of the putative loci, indicating far less scope for linkage analysis in intraspecific progenies from crosses among these cultivars.

Interspecific Oryza Sativa L. X O. Glaberrima Steud. progenies in upland rice improvement

Fertile interspecific progenies between Oryza sativa L. and O. glaberrima Steud. were produced through backcrossing and doubled haploid breeding (DHB). Backcrossing with the O. sativa parents increased fertility and helped combine the O. sativa and O. glaberrima features. The use of DHB to generate a large proportion of doubled haploids from interspecific F2 hybrids, helped overcome constraints associated with the conventional breeding of these species, such as: (1) slow fixation of the lines, (2) frequent partial sterility of the progenies and (3) low recovery of useful recombinants. Although true interspecific progenies between O. sativa and O. glaberrima were generally rare, their occurrence in some populations was as high as 30%. Some progenies combined the high yield potential of O. sativa, a result of high spikelet number caused by secondary branches on the panicle, with useful traits of O. glaberrima such as rapid leaf canopy establishment and high N responsiveness. The progenies partly inherited the O. glaberrima parents' high specific leaf area (SLA) during early growth, theoretically improving competitiveness with weeds, and from the O. sativa parents the rapid decrease in SLA towards the reproductive stage, theoretically allowing for high leaf photosynthetic rates and high grain yield. Research is in progress to develop new interspecific plant type concepts for resource poor, weed prone upland rice environments in West Africa.