Cultivated Sugarcane Research Articles

Illegal occupations in Permanent Preservation Areas: a case study in the city of Campos dos Goytacazes, RJ

Permanent Preservation Areas are constantly and illegally occupied by the population, either to establish residence, or to develop business activities. In Campos dos Goytacazes, RJ, these areas have often been occupied since sugarcane mill suppliers began to use state-owned land to cultivate sugar cane used in ethanol production, molasses and sugar. This article presents aspects of economic development in the city, reviews the history of urban development with the occupation of public spaces, and also presents discussion of regularization in areas of permanent preservation.

The Complex Genetic Structure of Sugarcane Limits Identification of Additional SNP-Defined Simplex Alleles in Microsatellite Loci

Cultivated sugarcane possesses a large number of chromosomes (typically >80) which can be organised into eight homology groups, each containing approximately 12 homo(eo)logous chromosomes. Currently, microsatellite (SSR) markers are the most easily used markers for marker-assisted selection and other genetic applications. However, only SSR alleles that segregate as simplex and duplex markers can be incorporated into sugarcane maps using populations of ∼300 progeny. Consequently only a subset of possible alleles have been mapped for a given SSR locus and are available for subsequent QTL analyses. Three sugarcane SSR loci, mSSCIR8, mSSCIR17 and mSSCIR18, were amplified, cloned and sequenced from the parents of an Australian sugarcane mapping population, IJ76-514 and . The sequences were examined to identify nucleotide sequence polymorphisms in the flanking regions that could provide additional simplex SSR allele markers. Alignment of the sequences revealed SNP, indel and repeat length variation and the pattern of sequence variation suggested multiple alleles for each SSR, including all of the alleles previously scored by fragment length. While the flanking regions of the SSR loci contained numerous SNPs and indels, none defined new simplex alleles within multiplex fragments and no new SSR simplex alleles were mapped. Furthermore, many of the sequence-defined alleles appear to be spurious and may have arisen from PCR-mediated recombination. These results confirm the difficulties associated with characterising allelic diversity in a polyploid species and the complexity of mapping in sugarcane.

Production of bioethanol and other bio-based materials from sugarcane bagasse: Integration to conventional bioethanol production process

Ethanol may be produced using sugarcane bagasse as raw material through the Organosolv process with dilute acid hydrolysis, thus increasing ethanol production with the same cultivated sugarcane area. In this work simulations of bioethanol production from sugarcane juice and bagasse are carried out using software UniSim Design. A typical large scale production plant is considered: 1000 m 3/day of ethanol is produced using sugarcane juice as raw material. A three-step hydrolysis process (pre-hydrolysis of hemicellulose, Organosolv delignification and cellulose hydrolysis) of surplus sugarcane bagasse is considered. Pinch analysis is used to determine the minimum hot utility obtained with thermal integration of the plant, in order to find out the maximum availability of bagasse that can be used in the hydrolysis process, taking into consideration the use of 50% of generated sugarcane trash as fuel for electricity and steam production. Two different cases were analyzed for the product purification step: conventional and double-effect distillation systems. It was found that the double-effect distillation system allows 90% of generated bagasse to be used as raw material in the hydrolysis plant, which accounts for an increase of 26% in bioethanol production, considering exclusively the fermentation of hexoses obtained from the cellulosic fraction.

Molecular Identification of Saccharum spp. × Erianthus fulvus Hybrids Using Sequence‐Characterized Amplified Region Markers

Identification of hybrids derived from crosses between cultivated sugarcane (Saccharum spp.) and its wild relatives, including Erianthus fulvus Nees ex Hack., is important for the development of new sugarcane cultivars. The aim of the present study was to identify true hybrids in 73 F1 progeny obtained from five crosses with cultivated sugarcane as female parents and E. fulvus as male parents. Three random 10mers were used as primers in random amplified polymorphic DNA (RAPD) reactions. A total of 10 E. fulvus–specific RAPD markers were cloned and sequenced, of which four were successfully applied as sequence‐characterized amplified region (SCAR) markers. Based on the four RAPD marker sequences, five SCAR primer pairs were designed for polymerase chain reaction amplifications. Of the 73 progeny examined, 58 produced E. fulvus–specific SCAR bands, thus representing true hybrids of cultivated sugarcane and E. fulvus These results demonstrate the first use of SCAR marker analysis as an effective tool for the identification of intergeneric sugarcane hybrids.

Identification of molecular markers associated with sugar-related traits in a Saccharum interspecific cross

The cultivated sugarcane (Saccharum spp. hybrids, 2n = 100–130) is one crop for which interspecific hybridization involving wild germplasm has provided a major breakthrough in its improvement. Few clones were used in the initial hybridization event leading to a narrow genetic base for continued cultivar development. Molecular breeding would facilitate the identification and introgression of novel alleles/genes from the wild germplasm into cultivated sugarcane. We report the identification of molecular markers associated with sugar-related traits using an F1 population derived from a cross between S. officinarum ‘Louisiana Striped’ × S. spontaneum ‘SES 147B’, the two major progenitor species of cultivated sugarcane. Genetic linkage maps of the S. officinarum and S. spontaneum parents were produced using the AFLP, SRAP and TRAP molecular marker techniques. The mapping population was evaluated for sugar-related traits namely, Brix (B) and pol (P) at the early (E) and late (L) plant growing season in the plant cane (04) and first ratoon (05) crops (04EB, 04LB, 04LP, 05EB and 05EP). For S. officinarum, combined across all the traits, a total of 30 putative QTLs was observed with LOD scores ranging from 2.51 to 7.48. The phenotypic variation (adj. R2) explained by all QTLs per trait ranged from 22.1% (04LP) to 48.4% (04EB). For S. spontaneum, a total of 11 putative QTLs was observed with LOD scores ranging from 2.62 to 4.70 and adj. R2 ranging from 9.3% (04LP) to 43.0% (04LB). Nine digenic interactions (iQTL) were observed in S. officinarum whereas only three were observed in S. spontaneum. About half of the QTLs contributed by both progenitor species were associated with effects on the trait that was contrary to expectations based on the phenotype of the parent contributing the allele. Quantitative trait loci and their associated effects were consistent across crop-years and growing seasons with very few QTLs being unique to the early season. When the data were reanalyzed using the non-parametric discriminant analysis (DA) approach, significant marker-trait associations were detected for markers that were either identical to or in the vicinity of markers previously identified using the traditional QTL approach. Discriminant analysis also pointed to previously unidentified markers some of which remained unlinked on the map. These preliminary results suggest that DA could be used as a complementary approach to traditional QTL analysis in a crop like sugarcane for which saturated linkage maps are unavailable or difficult to obtain.

Temporal dynamics of iron-rich, tropical soil organic carbon pools after land-use change from forest to sugarcane

Background, aim, and scope Land-use change can significantly influence carbon (C) storage and fluxes in terrestrial ecosystems. Soil–plant systems can act as sinks or sources of atmospheric CO2 depending on formation and decomposition rates of soil organic matter. Therefore, changes in tropical soil C pools could have significant impacts on the global C cycle. This study aims to evaluate the impacts of long-term sugarcane cultivation on soil aggregation and organic matter, and to quantify temporal dynamics of soil organic matter in cultivated sugarcane plantation soils previously under a tropical natural secondary forest.

Linkage mapping and genome analysis in a Saccharum interspecific cross using AFLP, SRAP and TRAP markers

Framework genetic linkage maps of two progenitor species of cultivated sugarcane, Saccharum officinarum ‘La Striped’ (2n = 80) and S. spontaneum ‘SES 147B’ (2n = 64) were constructed using amplified fragment length polymorphism (AFLP), sequence related amplified polymorphism (SRAP), and target region amplification polymorphism (TRAP) markers. The mapping population was comprised of 100 F1 progeny derived from the interspecific cross. A total of 344 polymorphic markers were generated from the female (S. officinarum) parent, out of which 247 (72%) were single-dose (segregating in a 1:1 ratio) and 33 (9%) were double-dose (segregating in a 3.3:1 ratio) markers. Sixty-four (19%) markers deviated from Mendelian segregation ratios. In the S. spontaneum genome, out of a total of 306 markers, 221 (72%) were single-dose, 43 (14%) were double-dose, and 42 markers (14%) deviated from Mendelian segregation ratios. Linkage maps with Kosambi map distances were constructed using a LOD score ≥5.0 and a recombination threshold of 0.45. In Saccharum officinarum, 146 markers were linked to form 49 linkage groups (LG) spanning 1732 cM whereas, in S. spontaneum, 121 markers were linked to form 45 LG spanning 1491 cM. The estimated genome size of S. officinarum ‘La Striped’ was 2448 cM whereas that of S. spontaneum ‘SES 147B’ was 3232 cM. Based on the two maps, genome coverage was 69% in S. officinarum and 46% in S. spontaneum. The S. officinarum parent ‘La Striped’ behaved like an auto-allopolyploid whereas S. spontaneum ‘SES 147B’ behaved like a true autopolyploid. Although a large disparity exists between the two genomes, the existence of simple duplex markers, which are heterozygous in both parents and segregate 3:1 in the progeny, indicates that pairing and recombination can occur between the two genomes. The study also revealed that, compared with AFLP, the SRAP and TRAP markers appear less effective at generating a large number of genome-wide markers for linkage mapping in sugarcane. However, SRAP and TRAP markers can be useful for QTL mapping because of their ability to target gene-rich regions of the genome, which is a focus of our future research.

Construction of a genetic linkage map forSaccharum officinarumincorporating both simplex and duplex markers to increase genome coverage

Saccharum officinarum L. is an octoploid with 80 chromosomes and a basic chromosome number of x = 10. It has high stem sucrose and contributes 80% of the chromosomes to the interspecific sugarcane cultivars that are grown commercially for sucrose. A genetic linkage map was developed for S. officinarum (clone IJ76-514) using a segregating population generated from a cross between Q165 (a commercial sugarcane cultivar) and IJ76-514. In total, 40 AFLP and 72 SSR primer pairs were screened across the population, revealing 595 polymorphic bands inherited from IJ76-514. These 595 markers displayed a frequency distribution different from all other sugarcane genetic maps produced, with only 40% being simplex markers (segregated 1:1). Of these 240 simplex markers, 178 were distributed on 47 linkage groups (LGs) and 62 remained unlinked. With the addition of 234 duplex markers and 80 biparental simplex markers (segregating 3:1), 534 markers formed 123 LGs. Using the multi-allelic SSR markers, repulsion phase linkage, and alignment with the Q165 linkage map, 105 of the 123 LGs could be grouped into 10 homology groups (HGs). These 10 HGs were further assigned to the 8 HGs observed in cultivated sugarcane and S. spontaneum. Analysis of repulsion phase linkage indicated that IJ76-514 is neither a complete autopolyploid nor an allopolyploid. Detection of 28 repulsion linkages that occurred between 6 pairs of LGs located in 4 HGs suggested the occurrence of limited preferential chromosome pairing in this species.

AFLP analysis of genetic diversity within Saccharum officinarum and comparison with sugarcane cultivars

Molecular diversity among 421 clones of cultivated sugarcane and wild relatives was analysed using AFLP markers. Of these clones, 270 were Saccharum officinarum and 151 were either cultivars produced by the Australian breeding program or important parents used in the breeding program. The S. officinarum clones were obtained from a collection that contained clones from all the major regions where S. officinarum is grown. Five AFLP primer combinations generated 657 markers of which 614 were polymorphic. All clones contained a large number of markers; a result of the polyploid nature and heterozygosity of the genome. S. officinarum clones from New Guinea displayed greater diversity than S. officinarum clones from other regions. This is in agreement with the hypothesis that New Guinea is the centre of origin of this species. The S. officinarum clones from Hawaii and Fiji formed a separate group and may correspond to clones that have been introgressed with other members of the ‘Saccharum complex’. Greater diversity was found in the cultivars than in the S. officinarum clones due to the introgression of S. spontaneum chromatin. These cultivars clustered as expected based on pedigree. The major contribution of clones QN66-2008 and Nco310 to Australian sugarcane cultivars divided the cultivars into 2 main groups. Although only a few S. officinarum clones are known to have been used in the breeding of current cultivars, about 90% of markers present in the S. officinarum clone collection (2n = 80) were also present in the cultivar collection. This suggests that most of the observed genetic diversity in S. officinarum has been captured in Australian sugarcane germplasm.

Determination of flavonoids in cultivated sugarcane leaves, bagasse, juice and in transgenic sugarcane by liquid chromatography-UV detection

A high-performance liquid chromatography (HPLC) method with photo-diode array (DAD) detection was developed to separate and quantify flavonoids in sugarcane leaves and bagasse (= the crushed sugarcane refuse from juice extraction), and in sugarcane juice. Sugarcane flavonoids consist of a complex mixture of aglycones and glycosides (including flavonolignan glycosides), and the HPLC-UV method herein proposed is suitable for their quantification as total flavonoids. This method was applied to analyze samples of cultivated sugarcane, commercial juice and transgenic sugarcane leaves. Sugarcane leaves proved a promising source of flavonoids: an average of 1.10 mg of total flavonoids/g plant material was found in fresh leaves. Moreover, the flavonoid content of sugarcane juice (0.6 mg/mL) is comparable to other food sources of flavonoids previously reported. Transgenic sugarcane leaves (“Bowman-Birk” and “Kunitz”) were compared with non-modified (“control”) plant samples using the proposed HPLC-UV method, which indicated that the content of total flavonoids in transgenic plants is different from that in non-modified sugarcane.

Species-specific accumulation of interspersed sequences in genus Saccharum

The genus Saccharum consists of two wild and four cultivated species. Novel interspersed sequences were isolated from cultivated sugar cane S. officinarum. These sequences were accumulated in all four cultivated species and their wild ancestral species S. robustum, but were not detected in the other wild species S. spontaneum and the relative Erianthus arundinaceus. The species-specific accumulation of interspersed sequences would correlate to the domestication of sugar canes.

Effects of Water-Logging on Juice Quality and Yield of Sugarcane

Chemical quality and yield performance were studied in six new sugarcane genotypes at normal and water-logging condition. The highest chemical indices, Brix % (22.20) and pol % (20.53) were found in January 2002 in I-93/93 and I-110/93 respectively and the lowest in I-39/94 (Brix %: 14.93; pol %: 12.52) at water-logged cultivated cane in all months. The highest of purity % (95.79) and recovery % (13.05) were found in I-110/93 in the month December 2001 and January 2002 respectively and the lowest in Isd 20 (purity % : 77.44; recovery 6.49 in September 2001) at water- logged and normal cultivated cane respectively. The highest R.S. % (1.51) was found in I-39/94 in all months and the lowest in I-110/93 (0.09) at water-logged cultivated cane. Result showed that the highest tiller (183.3 x 1000 ha-1 in I-110/93), millable cane (117.8x 1000 ha-1 in 1-8/95), Yield (162.8 t ha-1 in I-8/95) and TSH (16.63 ton sugar ha-1 in I- 110/93) were found in normal cultivated and the lowest were found in water- logged cultivated sugarcane (tiller 107.6x 1000 ha-1 in Isd 20; millable cane 73.38x 1000 ha-1 in Isd 30; yield 59.4 t ha-1 in Isd 20 and TSH 6.75 ton sugar ha-1 in Isd 20). It is concluded that the highest percentage in juice quality were found in water-logged condition cultivated cane, on the other hand growth & yield performance were also found in highest in normal cultivated cane. In aspect of sugar production some tested cultivars showed (Isd-20,1-93/93 and 1- 8/95) similar performance in normal and water-logged cultivated sugarcane due to genetic potentiality and environmental adaptation on quality, yield and growth.

Cytological studies of 2n male gamete formation in sugarcane, Saccharum L.

The germplasm for modern sugarcane cultivars (Saccharum spp. hybrids)has been derived principally from S. officinarum (2n = 80), and S. spontaneum (2n = 40 to 128). Diploid gamete formation has been significant in developing cultivated sugarcane, but the cytological basis for the processes involved is not clearly understood. This research investigated microsporogenesis in nine clones of Saccharum spp. Hybrids and in S. officinarum and S. spontaneum. Diploid gamete formation occurred in all 11 lines, but was least frequent in S. spontaneum and S. officinarum which produced 0.5% and 0.8%2n gametes, respectively. In the hybrid lines, 2n gametes were formed infrequencies ranging from 0.9% to 4.4%. Cytological evidence was obtained for dyad and triad formation during microsporogenesis. Detailed analysis of chromosome behaviour at meiosis indicated that 2n male gamete formation is probably attributable to the absence of cytokinesis rather than a combination of asynchrony and non-disjunction. The clones were ranked on the basis of the frequencies with which they formed 4 × 1n microspores and the data were analysed using χ 2 tests for homogeneity. These established that theSaccharum spp. hybrids could be designated as either ‘high’ or ‘low’ frequency haploid gamete producers. Conversely, the latter group, which formed diploid gametes most frequently (2.2%–4.4%), can be described as high frequency diploid gamete producers. The identification of clones most frequently forming diploid gametes may facilitate the more rapid recovery of desirable sugarcane genotypes because such clones could be selected for preferential use in clonal improvement.

Impact of Sugarcane yellow leaf virus on sugarcane yield and juice quality in Réunion Island

Sugarcane yellow leaf virus (SCYLV) was first detected in sugarcane of Reunion Island in 1997. A field experiment was undertaken to assess the potential impact of this virus on sugarcane production. The agronomic characteristics of SCYLV-infected plants were compared to those of virus-free plants of three sugarcane cultivars (R570, R577 and R579) which occupy more than 90% of the cultivated sugarcane area on Reunion Island. In the plant crop, significant losses in stalk weight (28%) and in sugar content (11%) were detected for cultivar R577, but not for either of the two other cultivars. In the first ratoon crop, yield reduction was detected for cultivar R577 (37%), but also for cultivar R579 (19%). Cultivar R577 also showed significant losses in sugar content (12%) due to reduced amount and quality of extracted cane juice. No yield reduction was found for cultivar R570, although stalk height and diameter were reduced in SCYLV-infected canes of this cultivar in the first ratoon crop. Leaf yellowing was observed at harvest of plant and ratoon crops when sugarcane was no longer irrigated, and 10–59% of symptomatic stalks could be attributed to the presence of SCYLV. The most severe yellowing symptoms were related to infection of sugarcane by the virus.

DISTRIBUTION AND OCCURRENCE OF ATRAZINE, DEETHYLATRAZINE, AND AMETRYNE RESIDUES IN GROUNDWATER OF THE TROPICAL ISLAND BARBADOS

The triazine herbicides atrazine (AT) and ametryne (AMET) are used extensively in Barbados to control weeds in sugar cane fields. These pesticides were monitored in groundwater (the primary source of potable water on the island) for the dry seasons of March–June, 1991 and January–May, 1992 and the wet season, July–December, 1992. Residues of either AT or AMET were detected in all 277 groundwater samples collected from 23 wells in three major groundwater catchments underlying heavily cultivated sugar cane fields. The concentration of AT and the metabolite deethylatrazine (DEAT) were in the range 0.11–2.61 μg/l with the highest occurrence in the most heavily cultivated sugar cane area, the Hampton catchment. These measured levels of atrazine in the groundwater, represent a relatively small fraction that may have leached from the annual application, and was estimated to be 0.12, 0.17 and 0.19% of the total amount applied to the Belle, Hampton and Western catchments respectively. These levels, however, are in general higher than those reported for related studies and lower application rates of atrazine in sugar cane plantations should be considered to help preserve the quality of potable water on the island.

Genetic dissection of a modern sugarcane cultivar (Saccharum spp.).II. Detection of QTLs for yield components

The genetics of current sugarcane cultivars ( Saccharum spp.) is outstandingly complex, due to a high ploidy level and an interspecific origin which leads to the presence of numerous chromosomes belonging to two ancestral genomes. In order to analyse the inheritance of quantitative traits, we have undertaken an extensive Quantitative Trait Allele (QTA) mapping study based on a population of 295 progenies derived from the selfing of cultivar R570, using about 1,000 AFLP markers scattered on about half of the genome. The population was evaluated in a replicated trial for four basic yield components, plant height, stalk number, stalk diameter and brix, in two successive crop-cycles. Forty putative QTAs were found for the four traits at P = 5 x 10(-3), of which five appeared in both years. Their individual size ranged between 3 and 7% of the whole variation. The stability across years was improved when limiting threshold stringency. All these results depict the presence in the genome of numerous QTAs, with little effects, fluctuating slightly across cycles, on the verge to being perceptible given the experimental resolution. Epistatic interactions were also explored and 41 independent di-genic interactions were found at P = (5 x 10(-3))(2). Altogether the putative genetic factors revealed here explain from 30 to 55% of the total phenotypic variance depending on the trait. The tentative assignment of some QTAs to the ancestral genomes showed a small majority of contributions as expected from the ancestral phenotypes. This is the first extensive QTL mapping study performed in cultivated sugarcane.

Characterisation of microsatellite markers from sugarcane ( Saccharum sp.), a highly polyploid species

Cultivated sugarcane varieties ( Saccharum spp) are derived from complex interspecific hybridisations between the species S. spontaneum (2 n=40–128) and S. officinarum (2 n=60 or 80). To analyse this complex genome, the potential of microsatellite repeats as genetic markers in sugarcane with respect to their abundance, variability and ability to detect polymorphisms was investigated. A set of microsatellite markers for genome analysis in cultivated sugarcane was identified from an enriched genomic DNA library constructed from Saccharum sp. cv Q124. Sequencing of 798 sugarcane genomic DNA clones from an enriched microsatellite library, yielded 457 inserts containing microsatellite repeat motifs. Just over 84% of the microsatellites contained dinucleotide or trinucleotide repeats averaging 15 and 13 repeat motifs, respectively. Primer sets were designed and synthesised for over 100 microsatellite sequences and tested on a set of five sugarcane cultivars. Both, heterozygosity as witnessed by the number of alleles, and length polymorphisms as seen in the differences in PCR product size for a particular allele were observed. Microsatellite markers are likely to have many applications in sugarcane genetics and breeding including germplasm analysis, cultivar identification, parent evaluation and marker assisted breeding.

Genetic maps of Saccharum officinarum L. and Saccharum robustum Brandes & Jew. ex grassl

Genetic analysis was performed in a population composed of 100 F1 individuals derived from a cross between a cultivated sugarcane (S. officinarum `LA Purple') and its proposed progenitor species (S. robustum `Mol 5829'). Various types (arbitrarily primed-PCR, RFLPs, and AFLPs) of single-dose DNA markers (SDMs) were used to construct genetic linkage maps for both species. The LA Purple map was composed of 341 SDMs, spanning 74 linkage groups and 1,881 cM, while the Mol 5829 map contained 301 SDMs, spanning 65 linkage groups and 1,189 cM. Transmission genetics in these two species showed incomplete polysomy based on the detection of 15% of SDMs linked in repulsion in LA Purple and 13% of these in Mol 5829. Because of this incomplete polysomy, multiple-dose markers could not be mapped for lack of a genetic model for their segregation. Due to inclusion of RFLP anchor probes, conserved in related species, the resulting maps will serve as useful tools for breeding, ecology, evolution, and molecular biology studies within the Andropogoneae.

The capacity of Jamaican mine spoils, agricultural and forest soils to nodulateMyrica cerifera, Leucaena leucocephalaandCasuarina cunninghamiana

Soils from seven sites on the island of Jamaica were assayed for the symbiotic diazotrophsFrankiaandRhizobiumusing serial dilutions. Most probable number and least squares regression methods were used to estimate each soil's capacity to nodulate nativeMyrica cerifera, exoticLeucaena leucocephalaand exoticCasuarina cunninghamiana. The sample sites included a montane forest, a slash‐and‐burn agricultural site, reclaimed bauxite mining areas, abandoned sugar cane fields, and a garden plot. None of the host plants used in the bioassay were present on the sites sampled except for scatteredL.leucocephalaon one site.Frankiacapable of nodulatingM. cerifera, which is native to Jamaican highlands, occurred at all sites sampled. NoC. cunninghamiana‐infective Frankiawas detected in soils sampled. Only soils from one site on the tropical coastal plain harbored rhizobia able to nodulateL. leucocephala(37 nodulation units cm−3 of soil). A subset of nodulatedM. ceriferaandL. leucocephalareduced acetylene to ethylene indicating nitrogenase activity. The slash‐and‐burn agricultural site, which was situated at an elevation of 200 m and possessed both high natural fertility and high soil moisture‐supplying capacity, had significantly greaterMyricainfectious capacity (1 000 nodulation units cm−3of soil) than the other sites (7−207 nodulation units cm−3of soil). A planned, paired comparison revealed that a recently cultivated sugar cane field and a recently reclaimed bauxite mining site together had significantly lessMyrica‐infectiveFrankia(4 nodulation units cm−3of soil) than a corresponding pair of sites consisting of a sugar cane field abandoned for 25 years and a bauxite mining site reclaimed 20 years before sampling (118 nodulation units cm−3of soil). Results indicate that Myrica‐infectiveFrankiais widespread in Jamaica, that the number ofMyrica‐infective Frankiaunits vary from site to site in accordance with soil type and soil history, that Jamaican sites sampled lack soilFrankiapopulations capable of nodulating a casuarina host, that rhizobial symbionts capable of nodulatingL. leucocephalamay be geographically restricted to lowlands in Jamaica, and that the occurrence ofFrankiain these soils is independent of host plant presence.

RFLP mapping in cultivated sugarcane (Saccharum spp.): genome organization in a highly polyploid and aneuploid interspecific hybrid.

Sugarcane cultivars are polyploid, aneuploid, interspecific hybrids between the domesticated species Saccharum officinarum and the wild relative S. spontaneum. Cultivar chromosome numbers range from 100 to 130 with approximately 10% contributed by S. spontaneum. We have undertaken a mapping study on the progeny of a selfed cultivar, R570, to analyze this complex genome structure. A set of 128 restriction fragment length polymorphism probes and one isozyme was used. Four hundred and eight markers were placed onto 96 cosegregation groups, based on linkages in coupling only. These groups could tentatively be assembled into 10 basic linkage groups on the basis of common probes. Origin of markers was investigated for 61 probes and the isozyme, leading to the identification of 80 S. officinarum and 66 S. spontaneum derived markers, respectively. Their distribution in cosegregation groups showed better map coverage for the S. spontaneum than for the S. officinarum genome fraction and occasional recombination between the two genomes. The study of repulsions between markers suggested the prevalence of random pairing between chromosomes, typical of autopolyploids. However, cases of preferential pairing between S. spontaneum chromosomes were also detected. A tentative Saccharum map was constructed by pooling linkage information for each linkage group.