Fast track participatory approach to release of elite cassava genotypes for various uses in Nigeria’s cassava economy

The aim of the Integrated Cassava Project (ICP) of the International Institute of Tropical Agriculture was to pre-emptively manage the cassava mosaic disease (CMD) to avert an imminent and increasing possible threat of the Ugandan strain of the CMD virus of the pathogen from doing damage to the Nigerian cassava economy. The strategy was to engage in activities that would lead to cultivar-substitution by replacing the susceptible varieties on farmers’ fields with superior genotypes that are not only CMD resistant or tolerant but also high yielding with good dry matter content. A fast track participatory selection approach was used in 2 years to release nine new lines in Nigeria. It was intensive and several lessons were learnt. The varieties released after 2 years were TMS 98/0510, TMS 98/0581, TMS 97/2205, TMS 98/0505, TME 419, TMS 92/0326, TMS 96/1632, TMS 98/0002, and TMS 92/0057.     

Bulked segregant analysis identifies molecular markers associated with early bulking in cassava (Manihot esculenta Crantz)

Late root bulking is a major factor leading to rejection and abandoning of improved cassava genotypes in sub-Saharan Africa. Early bulking (EB) varieties shorten the growth period from planting to harvesting, better fit into environments with short rainy season, and reduce exposure to biotic and abiotic stresses thereby increasing productivity. This study was carried out to identify molecular markers linked to EB in cassava. Nine cassava hybrid populations (COB-1–COB-9) were developed using six elite varieties (TMS 30572, TMS 97/2205, TMS 98/0505, TMS 30555, NR 8212 and NR 8083) from the African cassava germplasm as parents. The progeny in each of the nine populations (101–272 genotypes per population) were evaluated for EB at 7 months after planting at seedling, clonal, and preliminary stages of breeding evaluation at Umudike. The parameters measured are fresh root yield, harvest index, fresh shoot weight and number of storage roots per plant. The progeny in each of the nine populations were genotyped at 542 simple sequence repeat (SSR) marker loci. Bulked segregant analysis was used to identify the SSR markers associated with EB in the populations. Nine SSR markers (SSRY 106, (ESTs)SSRY 292, SSRY 239, (ESTs)SSRY 7, NS 194, (ESTs)SSRY 47, SSRY 63, SSRY 250, and NS 323) were found to be closely linked (r = 0.3–0.5; p < 0.05) to EB in six of the nine hybrid populations. Seven of the markers with 10 % or more coefficient of determination (R²) were linked to major quantitative trait loci associated with EB in cassava. The molecular markers identified in this study provide useful materials to select for EB in cassava and for further target-traits-improvement by pyramiding.     

Breeding cassava for resistance to cassava mosaic disease

Summary Cassava mosaic disease (CMD) is one of the most serious and widespread diseases throughout cassava growing areas in Africa, causing yield reductions of up to 90%. Early research on breeding of cassava (Manihot esculenta Crantz) for resistance to CMD in Africa is reviewed. Changes in population size and in activity of the white-fly vector to CMD (Bemisia tabaci Genn.) in relation to changes in environmental conditions such as amount and distribution of rainfall, light intensity and temperature are discussed in relation to screening for resistance to CMD. Over the past eight years, significant progress has been made at the International Institute of Tropical Agriculture (IITA). Resistance to CMD has been successfully incorporated into high yielding cultivars of acceptable quality. The CMD resistant material has been evaluated and many promising clones have been selected in various countries in tropical Africa and India. The resistance has been effective in those countries.     

Identification of markers associated with bacterial blight resistance loci in cowpea [Vigna unguiculata (L.) Walp.]

Cowpea bacterial blight (CoBB), caused by Xanthomonas axonopodis pv. vignicola (Xav), is a worldwide major disease of cowpea [Vigna unguiculata (L.) Walp.]. Among different strategies to control the disease including cultural practices, intercropping, application of chemicals, and sowing pathogen-free seeds, planting of cowpea genotypes with resistance to the pathogen would be the most attractive option to the resource poor cowpea farmers in sub-Saharan Africa. Breeding resistance cultivars would be facilitated by marker-assisted selection (MAS). In order to identify loci with effects on resistance to this pathogen and map QTLs controlling resistance to CoBB, eleven cowpea genotypes were screened for resistance to bacterial blight using 2 virulent Xav18 and Xav19 strains isolated from Kano (Nigeria). Two cowpea genotypes Danila and Tvu7778 were identified to contrast in their responses to foliar disease expression following leaf infection with pathogen. A set of recombinant inbred lines (RILs) comprising 113 individuals derived from Danila (resistant parent) and Tvu7778 (susceptible parent) were infected with CoBB using leaf inoculation method. The experiments were conducted under greenhouse conditions (2007 and 2008) and disease severity was visually assessed using a scale where 0 = no disease and 4 = maximum susceptibility with leaf drop. A single nucleotide polymorphism (SNP) genetic map with 282 SNP markers constructed from the same RIL population was used to perform QTL analysis. Using Kruskall-Wallis and Multiple-QTL model of MapQTL 5, three QTLs, CoBB-1, CoBB-2 and CoBB-3 were identified on linkage group LG3, LG5 and LG9 respectively showing that potential resistance candidate genes cosegregated with CoBB resistance phenotypes. Two of the QTLs CoBB-1, CoBB-2 were consistently confirmed in the two experiments accounting for up to 22.1 and to 17.4% respectively for the first and second experiments. Whereas CoBB-3 was only discovered for the first experiment (2007) with less phenotypic variation explained of about 10%. Our results represent a resource for molecular marker development that can be used for marker assisted selection of bacterial blight resistance in cowpea.     

Selection of cassava accessions with multiple resistance to pathogens associated with root rot disease

Cassava root rot disease (CRRD) severely affects productivity in several countries. The objective of this study was to estimate genetic parameters and to identify multiple resistance sources against pathogens associated with CRRD. The symptoms caused by Fusarium spp., Phytophthora spp., and Botryosphaeriaceae species in peel and pulp from the roots were evaluated in 277 accessions using a whole tuberous root inoculation method. The resistance data were obtained by REML/BLUP (restricted maximum likelihood/best linear unbiased predictor). The classic selection index (CI), multiplicative (MI), and sum of ranks (SRI) were used to identify the accessions with multiple resistance. For all pathogens, the environmental variance (\(\sigma_{e}^{2}\)) was the most important component. Individual heritability \(\left( {h_{g}^{2} } \right)\) was of low magnitude for resistance to most pathogens (0.16 ± 0.02—peel and 0.31 ± 0.03—pulp for Fusarium spp.; 0.26 ± 0.03—peel and 0.30 ± 0.03—pulp for Phytophthora spp.; and 0.28 ± 0.03—peel and 0.27 ± 0.03—pulp for Botryosphaereacea species). The distribution of CRRD symptoms indicated the presence of quantitative inheritance. The direct selection of the 15 more resistant accessions based on the genotypic predicted values result in high reductions of disease (>50%). However, there was a low matching rate of the most resistant accessions for each pathogen and the different parts of the tuberous roots (peel and pulp). The CI and MI were the most promising compared to the SRI to ensure high and balanced resistance for each pathogen. Understanding the genetic basis of resistance to CRRD and the identification of sources with multiple resistance may be useful in various management strategies to control the disease.     

Creating cold resistant strawberry via interploidy hybridization between octoploid and dodecaploid

Strawberry cultivars showed limited cold resistance in the Northeast of China, while we obtained a synthetic dodecaploid strawberry hybrid ‘YH15-10’ (2n = 12x = 84) which showed sufficient cold resistance in this area. The reciprocal crosses between F. × ananassa cv. ‘Allstar’ (2n = 8x = 56) and ‘YH15-10’ (2n = 12x = 84) were carried out to select cold resistant strawberry in this study. The 134 seedlings were obtained from the cross of Allstar × YH15-10, while failed in its reciprocal cross. The 30 randomly selected seedlings were examined in terms of morphological characters, chromosome numbers and cold resistance. Most morphological characters were widely separated among F1 progeny with a high broad-sense heritability, which showed that these variations mainly resulted from genetic effect. Some hybrids exhibited heterosis, especially in growth vigor and runner production. Among the 30 tested hybrids, 28 decaploids (2n = 10x = 70), one octoploid (2n = 8x = 56) and one enneaploid (2n = 9x = 63) were observed. The 63.3% hybrids demonstrated higher cold resistance than that of ‘Allstar’ at P < 0.05. These high polyploidy strawberries have potential values in commercial production and modern cultivar improvement.     

Standardizing resistance screening to Pseudomonas fuscovaginae and evaluation of rice germplasm at seedling and adult plant growth stages

Sheath lesions, grain sterility and grain discolouration of rice caused by Pseudomonas fuscovaginae can cause yield losses of up to 100 %. The most sustainable method of managing this disease is the use of host plant resistance. To identify sources of resistance an inoculation method that is practical, rapid and reliable is needed. We compare three different inoculation methods. Results showed that the pin-prick method is appropriate for identifying sources of resistance to P. fuscovaginae, while the spray method could be useful for mass screening of rice genotypes. The seed-soaking method was also evaluated and has showed potential in detection of early disease resistance. A total of 16 Multiparent Advanced Generation Inter-Crosses and 20 OryzaSNP set varieties from the International Rice Research Institute were evaluated using the pin-prick and seed-soaking methods. All growth stages were susceptible to the pathogen and the 10⁷ cfu mL^?1 inoculum concentration was optimal for discriminating between resistant and susceptible genotypes. For the pin-prick method, a single point assessment of disease severity at 14 days post-inoculation could be used instead of the AUDPC values to classify genotypes. An index of reduction in seedling height 10 days after seed soaking was established for the classification of the genotypes reaction to the disease. Resistant varieties identified using both the pin-prick and seed-soaking methods could be verified for use in disease resistance breeding programs. Of the 36 genotypes evaluated 22 were found to be resistant at the late booting or early panicle exsertion stage by pin-prick method, while 25 were resistant at the seed to germination stage. No correlation was found between the resistance classification of varieties between the two inoculation methods, indicating that there could be different mechanisms of resistance to P. fuscovaginae in rice.     

Ploidy manipulation and introgression breeding in Darwin hybrid tulips

Meiotic polyploidisation via crossing with 2n gamete producing genotypes and interploidy crosses are two of the main methods currently used to obtain polyploid tulips. In our study diploid 2n gamete producing F₁ hybrids of Darwin hybrids (Tulipa gesneriana × Tulipa fosteriana) and triploid hybrid resulting from ‘Rhodos’ × ‘Princeps’ cross were used as pollen donor and crossed with cultivars of T. gesneriana in the following combination: 2x × 2x, 3x × 2x, 2x × 3x, and 3x × 3x. The progenies resulting from crosses at diploid level were mostly diploid, whereas a few seedlings were triploid. In 3x × 2x crosses aneuploids with chromosome constitution in between triploid and tetraploid (43–45 chromosomes) were predominant, but also one tetraploid (2n = 4x = 48) and four pentaploids (2n = 5x = 60) were obtained. In 2x × 3x crosses most progenies were triploid with the exception of a few aneuploids (3x + 1 and 3x ? 1), whereas in 3x × 3x cross diploid and aneuploid genotypes were recorded with chromosome number varied from 27 to 34. These results indicate that triploid parents produced aneuploid as well as euploid (x, 2x, 3x) gametes and that success in ploidy manipulation in tulip depends to a large degree on the ploidy level of the parental genotypes used for hybridization. Genome constitution of selected population of F1 and BC1 hybrids was analyzed through genomic in situ hybridization (GISH). GISH analysis of the BC1 showed a considerable amount of intergenomic recombination which is desirable for introgression breeding.     

Combining ability of cassava genotypes for cassava mosaic disease and cassava bacterial blight, yield and its related components in two ecological zones in Ghana

Breeding for resistant genotypes is the best strategy to offset the destructive effects of cassava mosaic disease (CMD) and cassava bacterial blight (CBB). Two sets of diallel parents were selected for the forest and the savannah ecological zones in Ghana based on good levels of resistance to CMD and CBB. Both sets were crossed in a half-diallel design. The first set of seven progenitors and their 21 F1 progenies were planted in a randomised complete block design (RCBD) with three replications in two different locations for two seasons in the forest ecology. The second set of five progenitors and their 10 F1 progenies were planted in a RCBD with three replications in two locations in the coastal savannah ecological zone of Ghana. Both experiments were evaluated for CMD and CBB resistance, fresh root yield, dry root yield, root number, harvest index, dry matter content, plant height at maturity and height at first branching, levels of branching and plant vigour. Results of the combined analysis of variance revealed that the environment effect was significant for all the traits. General combining ability and specific combining ability effects were significant for most of the traits. Narrow sense heritability was significant for plant vigour, root number, CMD and CBB in both the zones. CMD and root number also had a predictability ratio of close to one, indicating the importance of additive gene effects.     

Sources of resistance to Fusarium head blight in VIR oat collection

Fusarium head blight (FBH) is a serious disease of cultivated oats (Avena sativa L.). The objective of this study was to screen a set of oat genotypes from the VIR Avena sativa germplasm collection for the FHB resistance. Of the 155 screened genotypes 42 % belonged to both hulled and naked cultivars, 55 % were landraces and the rest were breeding lines. Screening nurseries were planted at two locations: in the Northwestern Russia in 2007–2008 with artificial inoculation by F. sporotrichioides strains and in the Russian Far East in 2009 (natural infections). The resistance data were based on three different parameters: (a) percentage of grain showing evidence of Fusarium damage, (b) the DNA content of the trichothecene-producing Fusarium species and (c) the trichothecene mycotoxin accumulation; the sum of which permitted identification of genotypes with multicomponent resistance to FHB. The highest degrees of resistance were observed in the naked cvs. Iymay (k-11014, China) and Numbat (k-14851, Australia) and by the hulled cv. Kuromi (к-11632, Japan). The most resistant landraces were the hulled oats originating from the Asian region (k-2513, k-6963, k-7766, and k-8479). Considerable similarity was observed between the resistance reactions of oat genotypes to the Fusarium disease under different environmental conditions. The identified resistant accessions may serve as crossing partners in oat breeding efforts.     

Inheritance of resistance to Fusarium oxysporum f. sp. cubense race 1 in bananas

Fusarium wilt of bananas (also known as Panama disease), caused by the soil-borne fungus Fusarium oxysporum f. sp cubense (Foc), is a serious problem to banana production worldwide. Genetic resistance offers the most promising means to the control of Fusarium wilt of bananas. In this study, the inheritance of resistance in Musa to Foc race 1 was investigated in three F₂ populations derived from a cross between ‘Sukali Ndizi’ and ‘TMB2X8075-7’. A total of 163 F₂ progenies were evaluated for their response to Fusarium wilt in a screen house experiment. One hundred and fifteen progenies were susceptible and 48 were resistant. Mendelian segregation analysis for susceptible versus resistant progenies fits the segregation ratio of 3:1 (χ² = 1.72, P = 0.81), suggesting that resistance to Fusarium wilt in Musa is conditioned by a single recessive gene. We propose panama disease 1 to be the name of the recessive gene conditioning resistance to Fusarium wilt in the diploid banana ‘TMB2X8075-7’.     

A SNP mutation affects rhizomania-virus content of sugar beets grown on resistance-breaking soils

Rhizomania is one of the most devastating biotic stresses affecting sugar beet (Beta vulgaris L.). It is caused by Beet necrotic yellow vein virus (BNYVV) vectored by the plasmodiophorid Polymyxa betae K. The only means available to control the disease is the use of genetically resistant varieties. “Rizor” or “Holly” (Rz1) and WB42 (Rz2) have been the most widely used resistance sources in the commercial varieties. Recently, naturally occurring resistance-breaking (RB) rhizomania strains have been identified causing major concerns. The aim of this study was to identify SNP mutations that show associations with resistance to rhizomania in sugar beet plants grown under resistance-breaking (RB)-BNYVV soils. Rhizomania virus content was evaluated by indirect triple-antibody sandwich-ELISA within two F ₂ segregating populations respectively grown on an AYPR and IV-BNYVV strain infected soils. Bulked segregant analysis (BSA) was performed. The resistant and susceptible plants were genotyped with a 384-SNPs panel. Of the 384 SNPs, SNP249 was found to associate with the resistance both to the AYPR strain (R ² = 0.37; P = 0.0004) and to the IV-BNYVV (R ² = 0.09; P = 0.0074). Our results suggested that the SNP249 could be readily applicable for marker-assisted breeding of resistance to AYPR strain of rhizomania.     

Number of involved genes and heritability of clover rot (Sclerotinia trifoliorum) resistance in red clover (Trifolium pratense)

European red clover (Trifolium pratense) crops are challenged by clover rot, a devastating disease caused by Sclerotinia trifoliorum or, in some cases by S. sclerotiorum. No completely resistant cultivars are available and resistance breeding is hampered by the lack of knowledge on the number of involved resistance genes and the heritability of clover rot resistance. In this study, we estimated the number of major genes contributing to clover rot resistance by analysing 15 F₁ progeny populations from pair crosses between ramets of resistant and susceptible genotypes. Parent plants were chosen from diverse, diploid populations, including wild material, landraces and cultivars. Young progeny plants were inoculated with ascospores, evaluated phenotypically and the segregation of disease scores was studied. Our results indicated that clover rot resistance may be conferred by three major effect genes, although segregation patterns suggested that there may be numerous minor effect genes involved as well. No proof was found for a maternal inheritance of clover rot resistance. To get insight in the heritability of clover rot resistance, we applied divergent selection by our high-throughput bio-test on an experimental diploid population: the original population (70.5 %), the first generation after selection for susceptibility (79.2 %) and the first generation after selection for resistance (62.3 %) differed significantly in susceptibility (p < 0.001). The second generation after selection for resistance (60.0 %) was not more resistant than the first generation after selection for resistance. In the first generation of selection the heritability (h²) was on average 0.34. In the second generation of selection h² was 0.07. These findings have important implications for resistance breeding.     

Interspecific hybridization in <Emphasis Type="Italic">Sarcococca</Emphasis> supported by analysis of ploidy level,genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.     

Characterization of resistance of cassava genotypes to bacterial blight by evaluation of leaf and systemic symptoms in relation to yield in different ecozones

Twenty-two improved and local cassava genotypes were evaluated for their bacterial blight symptom types in reaction to infection by Xanthomonas axonopodis pv. manihotis under field conditions in the forest, forest savanna transition and wet savanna zones of Togo. High genotype × environment interactions in development of each symptom type were observed. Combining data on environments and genotypes, spot, blight and wilt symptoms were positively correlated. Analysing genotype reactions across environments, indications for independent mechanisms of resistance on leaf and stem level, varying by genotype, were found. Genotypes Main27 with resistance to spot and blight symptoms and TMS4(2)1425 with resistance to wilt symptoms are recommended to breeders to introgress their resistance characteristics. Significant negative correlations were generally observed between blight and wilt symptom development and root yield across ecozones, with blight being more important under lower, and wilt under higher inoculum pressure. Genotypes TMS30572, CVTM4, TMS92/0429 and TMS91/02316 showed low spot, blight and wilt symptoms combined with high root yield across ecozones.     

Phenotypic and genotypic screening for rust resistance in common bean germplasm in Uganda

Rust caused by Uromyces appendiculatus (Pers., Pers.) Unger is one of the major foliar diseases of common bean (Phaseolus vulgaris) in Uganda. The use of host resistance remains the best option in managing this disease. The objective of this study was to identify sources of broad-spectrum rust resistance in common bean germplasm including landraces, commercial cultivars and introduced genotypes using a combination of phenotypic and genotypic screening with 22 simple sequence repeat (SSR) markers located on chromosome Pv04. A total of 138 genotypes were field screened from 2014 and 2015 using an alpha lattice design. The variance and correlation of disease incidence, area under the disease progression curve (AUDPC) and total grain yield were computed using GenStat. The polymorphism information content of the genotypes was determined, and the association of the markers and the disease resistance traits were analyzed using PowerMarker and TASSEL respectively. Resistance of each genotype was compared to the presence and absence of amplified markers. There were highly significant differences (P < 0.001) among the genotypes for disease incidence, AUDPC and total grain yield and a strong correlation (P < 0.001) between disease incidence and AUDPC in both years. The SSR markers, BARC_PV_SSR04725, bean_ssr_0778 and bean_ssr_2892 were associated (P ≤ 0.05) with rust resistance. Fifteen 15 genotypes which included the landraces Nabufumbo, and Kapchorwa white, and the commercial cultivar NABE 2 were identified as new sources of rust resistance that would be useful in future bean breeding programmes in Uganda.     

Bru1 gene and potential alternative sources of resistance to sugarcane brown rust disease

Brown rust, caused by the fungus Puccinia melanocephala, is responsible for important yield losses in sugarcane production globally and it is therefore an important objective to introduce resistance to this disease in breeding programs. A major gene, Bru1, has been shown to confer resistance to P. melanocephala strains from different parts of the world and two molecular markers, R12H16 and 9O20-F4, closely associated to this gene have been previously reported. The usefulness of these molecular diagnostic markers in order to predict a rust resistant phenotype under natural high pressure inoculums conditions was analyzed. A total of 129 sugarcane accessions were evaluated under field infection for resistance or susceptibility to brown rust and subsequently screened for presence or absence of the two Bru1 diagnostic markers. A total of 49 genotypes (38 %) were phenotyped as resistant to brown rust but only eight (16.3 %) of them were harboring the Bru1 gene. To determine overall frequency of the Bru1 in the local sugarcane germplasm collection, 190 additional genotypes were examined. Presence of Bru1, as determined by the diagnostic markers, was detected in only 7 % of the genotypes evaluated. In conclusion, Bru1 diagnostic markers enable positive selection for brown rust resistance in sugarcane and moreover allowed detecting at least one additional source(s) of resistance. Interestingly, whilst only little genetic variability of rust resistance independent of Bru1 has been reported previously, this alternative genetic resource(s) found in our local germplasm constitutes the predominant one and should be helpful in order to amplify the narrow genetic basis for brown rust resistance in sugarcane.     

Performance of cowpea varieties under <Emphasis Type="Italic">Striga gesnerioides</Emphasis> (Willd.) Vatke infestation using biplot analysis

Striga gesnerioides (Willd) Vatke, is a major destructive parasitic weed of cowpea (Vigna unguiculata (L.) Walp.) which causes substantial yield reduction in West and Central Africa. The presence of different virulent races within the parasite population contributes to significant genotype × environment interaction, and complicates breeding for durable resistance to Striga. A 3-year study was conducted at three locations in the dry savanna agro-ecology of Nigeria, where Striga gesnerioides is endemic. The primary objective of the study was to identify cowpea genotypes with high yield under Striga infestation and yield stability across test environments and to access suitability of the test environment. Data collected on grain yield and yield components were subjected to analysis of variance (ANOVA). Means from ANOVA were subjected to the genotype main effect plus genotype × environment (GGE) biplot analysis to examine the multi-environment trial data and rank genotypes according to the environments. Genotypes, environment, and genotypes × environment interaction mean squares were significant for grain yield and yield components, and number of emerged Striga plants. The environment accounted for 35.01%, whereas the genotype × environment interaction accounted for 9.10% of the variation in grain yield. The GGE biplot identified UAM09 1046-6-1 (V7), and UAM09 1046-6-2 (V8), as ideal genotypes suggesting that these genotypes performed relatively well in all study environments and could be regarded as adapted to a wide range of locations. Tilla was the most repeatable and ideal location for selecting widely adapted genotypes for resistance to S. gesnerioides.     

Meiotic chromosome pairing in intergeneric hybrids of colchicaceous ornamentals revealed by genomic in situ hybridization (GISH)

Diploid and triploid intergeneric hybrids obtained by crosses among Gloriosa superba ‘Lutea’ (2n = 2x = 22), G. ‘Marron Gold’ (2n = 4x = 44), Littonia modesta (2n = 2x = 22), and Sandersonia aurantiaca (2n = 2x = 24) were analyzed for their meiotic chromosome pairing in pollen mother cells by genomic in situ hybridization (GISH) with digoxigenin-labeled total DNA of one parent as probe. Chromosomes from each parent could be clearly distinguished in pollen mother cells of all the five intergeneric hybrids by GISH. For three diploid hybrids, L. modesta × G. superba ‘Lutea’ (2n = 2x = 22), L. modesta × S. aurantiaca (2n = 2x = 23) and S. aurantiaca × G. superba ‘Lutea’ (2n = 2x = 23), 0.04?0.27 autosyndetic bivalents (intragenomic pairing of non-homologous chromosomes) and 0.13?0.36 allosyndetic bivalents (intergenomic chromosome pairing) were observed per pollen mother cell, indicating that there are some homologous chromosomal regions within each genome and among the genomes of Gloriosa, Littonia and Sandersonia. Differences in the average number of allosyndetic bivalents per pollen mother cell among different genome combinations may reflect the evolutionary distances among the three genera, and Gloriosa and Littonia may be closely related to each other, while Sandersonia may have relatively distant relationships with Gloriosa and Littonia. For two triploid hybrids, L. modesta × G. ‘Marron Gold’ (2n = 3x = 33) and S. aurantiaca × G. ‘Marron Gold’ (2n = 3x = 34), no allosyndetic bivalents were observed. Based on the results obtained in the present study, possible utilization of the diploid and triploid intergeneric hybrids for further breeding of colchicaceous ornamentals is discussed.     

Genomic in situ hybridization (GISH) analysis of intergeneric hybrids in Colchicaceae

Some intergeneric hybrids produced by the crosses among several colchicaceous ornamentals, Gloriosa superba ??Lutea?? (2n = 2x = 22), G. ??Marron Gold?? (2n = 4x = 44), G. ??Verschild?? (2n = 7x = 77), Littonia modesta Hook. (2n = 2x = 22), and Sandersonia aurantiaca Hook. (2n = 2x = 24), were subjected to genomic in situ hybridization (GISH) analysis in order to clarify their genome constitutions. Chromosome preparation was made from root tip cells of L. modesta × G. superba ??Lutea??, L. modesta × S. aurantiaca, S. aurantiaca × G. superba ??Lutea??, L. modesta × G. ??Marron Gold??, S. aurantiaca × G. ??Marron Gold?? and G. ??Verschild?? × S. aurantiaca. Total DNA of one parent was labeled with digoxigenin or biotin and used as probe, and chromosomes were counterstained with 4??-6-diamidono-2-phenylindole (DAPI). For all the nine intergeneric hybrids, chromosomes from each parent could be clearly distinguished by GISH analysis. Thus GISH analysis is a powerful tool for identifying the genome constitution of intergeneric hybrids in colchicaceous ornamentals. The results obtained by GISH analysis study may be important for further progress in breeding of colchicaceous ornamentals.