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. This revised version was published online in July 2006 with corrections to the Cover Date.     

2n gametes in potato species and their function in sexual polyploidization

Summary The extent and pattern of polyploidy in the tuber-bearing Solanums varies among the many taxanomic series that have been identified in this subsection of Solanum. While several series appear to be entirely diploid, others exhibit a range of ploidy levels from 2x to 6x, and some contain only polyploid species.In many diploid, triploid and tetraploid species 2n gametes (gametes or gametophytes with the sporophytic chromosome number) have been detected. Both 2n eggs and 2n pollen occur. 2n gametes provide the opportunity for unilateral and bilateral sexual polyploidization. The genetic determination and consequences of sexual polyploidization strongly suggest that 2n gametes have been the major instrument in the polyploid evolution of the tuber-bearing Solanums. Somatic doubling of species and interspecific hybrids appears to be of very limited importance.New evidence for the occurrence of 2n eggs and 2n pollen in many species is reported, and data from the literature are added to illustrate the widespread distribution of 2n gametes throughout the subsection. A very high correlation is found between polyploidy and 2n gametes, and its significance is discussed. Proof is presented for the occurrence of alleles governing 2n pollen production in the cultivated tetraploids, providing additional evidence for the hypothesis that 2n gametes have been involved in their origin.Multiple unilateral and bilateral sexual polyploidizations are proposed for the origin of the cultivated tetraploids: this accounts for the large variability encountered in this group, which closely resembles that of the related diploids. Similar evolutionary pathways are hypothesized for the other polyploid complexes in the subsection.A scheme is proposed in which participation of both 2n and n gametes link together all ploidy levels in the tuber-bearing Solanums, thus overcoming the ploidy barriers and providing for gene flow throughout the sympatric species of the subsection.Paper No. 2093 from the Laboratory of Genetics. Research supported by the College of Agricultural and Life Sciences, a gift from Frito-Lay, Inc., and grants from NIH (GM 15422) and The International Potato Center. Plant materials, unpublished chromosome counts and technical help of IR-1 are gratefully acknowledged.     

Screening for and heritability of flood-tolerance in the Florida (CP) sugarcane breeding population

Summary An experiment screening for flood-tolerance and estimating the heritability of flood-tolerance was conducted on 160 sugarcane clones in the Canal Point, Florida, USA sugarcane breeding population. Clones were grown in two environments, a drained control and a continuous, five-month flood. The test ran for two crop years, plant-cane and first ratoon. A wide range of production was observed, with some clones dying out after the first year. Several clones had two-year mean cane production in flood that was 70% of their production in control. Heritabilities calculated by parent-offspring regression ranged from 0.29 to 0.51.     

Polyploidy in tulips (Tulipa L.). The occurrence of diploid gametes

Summary From data available in the literature and supplemented by information from private tulip breeders, it appeared that triploid and tetraploid varieties raised in the past, resulted from crosses between diploid tulips and between diploids and tetraploids. This can only be explained by the occurrence of diploid gametes in diploid (2n=24) cultivars. This phenomenon which may affect both female and male gametes, appears to be specific for certain varieties. Consequences for practical breeding are discussed.     

In tergeneric crosses with Fragaria and Potentilla. II. Crosses between the progeny of Fragaria moschata x Potentilla fruticosa and the original parents

Summary An aneuploid hybrid (2n=23) of Fragaria moschata (2n=42) and Potentilla fruticosa (2n=14) was backcrossed with pollen of both parents, separately and combined in a pollen mixture. Seven vigorous progeny were obtained. The origin of the exeptional chromosome numbers, 2n=44, 49, 63, 63, 65, 67, 67, is discussed, and it is shown that each of the numbers could be produced by the fertilisation of unreduced and double unreduced gametes of the hybrid by normally reduced gametes of one of the parental species.     

Discovery of 2n gametes in tetraploid oat Avena vaviloviana

Summary Sexual polyploidization via the action of 2n gametes (gametes with the sporophytic chromosome number) has been identified as the most important evolutionary mode of polyploidization among plant genera. This study was conducted to determine whether 2n gametes are present in the tetraploid level of the genus Avena (2n=4×=28) Twenty tetraploid Avena lines, representing four species and one interspecific hybrid, were screened for pollen grain size in order to differentiate between n and 2n pollen. Avena vaviloviana (Malz.) Mordv. line PI 412767 was observed to contain large pollen grains at a 1.0% frequency. Cytogenetic analyses of pollen mother cells of PI 412767 revealed cells with double the normal chromosome number (i.e., 56 chromosomes at metaphase I and anaphase I). The mode of chromosome doubling was found to be failure of cell wall formation during the last mitotic division that preceded meiosis. The resulting binucleate cells underwent normal meiotic divisions and formed pollen grains with 28 chromosomes. Based on the formation and function of 2n gametes, three models involving diploid and tetraploid oat lines are proposed to describe possible evolutionary pathways for hexaploid oats. If stable synthetic hexaploid oat lines could be developed by utilizing 2n gametes from diploid and tetraploid oat species through bilateral sexual polyploidization, the resulting hexaploids could be used in breeding programs for transferring genes from diploids and tetraploids to cultivated hexaploids.     

Stability and potential use of RAPD markers in a sugarcane genealogy

Summary A complete ancestral history of the recently developed and closely related South African commercial sugarcane varieties N11 and NCo376, which differ markedly in their response to sugarcane mosaic virus (SCMV), was elucidated from archival records. The genealogy spans seven generations, starting with early intraspecific crosses between varieties of Saccharum officinarum and interspecific crosses between S. officinarum and either S. spontaneum or S. barberi. In total, the genealogy comprises 38 different varieties. Genomic DNA samples from N11 and NCo376 respectively were screened for polymorphisms using the PCR-RAPD technique. Ten polymorphic fragments ranging in molecular size from 317 to 1263bp were identified from a total of 1159 loci amplified with 100 random decamer primers. Two of the 10 polymorphic fragments were shown to be consistently present in N11 (resistant) and absent in NCo376 (susceptible), while 8 showed the reverse occurrence. The primers producing the polymorphisms were used to screen genomic DNA samples from all 19 varieties representing the genealogy. Results have indicated that (1) specific PCR-RAPD generated polymorphic fragments can indeed be identified across the seven generations; (2) certain fragments are sufficiently definitive to be used as markers to trace parentage; (3) the validity of documented crosses and/or the authenticity of germplasm material may be questioned using this technique, and (4) there is the potential to subject the markers to linkage analysis once a full and accurate assessment of the SCMV resistance phenotype is obtained.     

Molecular diversity and genome structure in modern sugarcane varieties

Summary RFLP analysis was performed on 40 sugarcane cultivated varieties. Twenty-two maize low copy DNA clones located on different regions of the 10 maize chromosomes were used as probes to survey variability among the sugarcane varieties. A total of 425 fragments, 411 of which were polymorphic, were identified for 22 probe/enzyme combinations. Each variety displayed an average of 7.28 fragments per combination, revealing the complex polyploid origin of modern sugarcane varieties. The average genetic similarity between sugarcane varieties was 0.61. Although cultivated varieties appear closely related to S. officinarum clones, the genes of S. spontaneum seem to constitute the principal component of varietal diversity. A very weak global structuring among the 40 varieties is observed, in agreement with the profuse exchanges of parental materials between sugarcane breeding stations. Traces of linkage disequilibrium can be attributed to the distribution of S. spontaneum chromosomes among sugarcane varieties. The possibility of using modern varieties as a population for detecting associations between molecular markers and agronomic traits is suggested.     

Transmission of resistance to common scab from the diploid to the tetraploid level via 4x-2x crosses in potatoes

Summary Diploid potato clones selected for their reaction to common scab and their ability to produce 2n male gametes were used in a series of crosses to a susceptible tetraploid female parent (cv. Shepody). In addition, two tetraploid clones were also selected for their reaction to common scab and crossed with Shepody as a female parent. Results indicated that resistance to common scab can be effectively transmitted from the diploid to the tetraploid level via 4x-2x crosses. Diploid parents producing 2n pollen via either first division or second division restitution can be used to transmit scab resistance. A relatively small proportion of resistant individuals could be recovered from susceptible x susceptible crosses in both 4x-2x and 4x-4x combinations. The data support a previously developed hypothesis that scab resistance is relatively simply inherited.     

Isolation,fusion and multiplication of sugarcane protoplasts and comparison of sexual and parasexual hybridization

Summary The problems associated with the isolation of leaf protoplasts in sugarcanes have been overcome by the choice of spindle tissue as source material. It is now possible to isolate, fuse, regenerate and multiply sugarcane protoplasts. However, the usefulness is limited due to the shortlived chromosomal stability during the callus stage. Nevertheless, preliminary results are promising and the method should prove feasible with refinement in technique. Two breeding systems for using parasexual hybridization are discussed.     

Relationships among ancestral species of sugarcane revealed with RFLP using single copy maize nuclear probes

Summary DNA restriction fragment length polymorphism (RFLP) analysis was performed on 50 wild and old cultivated sugarcane accessions. Ninety-four maize low copy nuclear DNA sequences of known chromosomal position were screened for hybridization to digested sugarcane genomic DNA blots. Seventy-five (80%) gave very strong hybridization signals and usually yielded many bands and detected profuse polymorphism. Twenty-nine probes and 36 probe/enzyme combinations were selected on the basis of the scorability of the banding profiles. A total of 1110 fragments were separately identified among the 50 genotypes. Multivariate analyses of the data allowed the separation of the three basic species, Saccharum spontaneum, S. robustum and S. officinarum, showed that S. spontaneum had structure which could be related to the geographic origin of the clones and supported current hypotheses on the origin of secondary species S. barberi and S. sinense. The use of more probes did not improve the resolution between the various species examined but identified a few key polymorphisms which were not accounted for by current phylogenetic hypotheses and can guide future analyses. RFLPs in sugarcane will be useful essentially for depicting the genomic constitution of modern varieties of interspecific origin.     

Effect of tissue culture explant source on sugarcane yield components

Clonal propagation of sugarcane(interspecific hybrids of Saccharum)is conducive to spread of systemicdiseases, such as ratoon stunting disease,caused by Leifsonia xyli subsp. xyli. This important disease iscontrolled by obtaining and plantinghealthy seed-cane. In Louisiana, commercialseed-cane initially produced through tissueculture is available to sugarcane farmersand is being widely planted. Long-termacceptability of this seed-cane productionmethod depends on the production of healthyplants that do not differ significantly inphenotypic and yield characteristics fromthe clones originally selected and releasedas commercial cultivars. To determinewhether tissue culture affects yield or itscomponents, three cultivars, CP 70-321, LCP85-384, and HoCP 85-845, were compared inthree successive crops initially plantedwith stalks from three sources: plantsderived from callus culture of the leafroll above the apical meristem, directregeneration from the apical meristem, andconventional bud propagation. Stalks ofplants derived from both explant sourceswere typical of seed-cane farmers wouldpurchase for planting that had beenpreviously rogued for phenotypic variantsand increased by bud propagation.Differences in yield components amongtissue culture explant sources and budpropagated cane only occurred in CP 70-321.Stalk diameter and stalk weight were lowerand stalk population was higher for plantsderived from leaf roll callus compared tobud propagated cane. Yield components weresimilar for plants derived from an apicalmeristem and bud propagation. Individualplant phenotypic variants resulting fromsomaclonal variation were not observed inany of the cultivars derived from eitherexplant source. In summary, genotype andexplant source affected persistent, uniformphenotypic variation resulting from tissueculture that changed some yield components. However, apical meristem culture wassuitable for production of seed-cane, assugarcane derived by meristem culture ofthree cultivars did not differsignificantly from the original germplasmfor any measured yield trait.     

Assignment of Endosperm Balance Numbers to the tuber-bearing Solanums and their close non-tuber-bearing relatives

The Endosperm Balance Number (EBN) of over 80 species and subspecies of the tuber-bearing Solanums and their close non-tuber-bearing relatives representing 13 taxonomic series has been determined, with no species assigned to more than one EBN level. Among North American species, most diploids are 1EBN, most tetraploids are 2EBN and all hexaploids are 4EBN; however, among South American species most diploids are 2EBN, most tetraploids are 4EBN and again all hexaploids are 4EBN. Thus species may be isolated from others of the same ploidy level by EBN differences, e.g., 4×(2EBN) from 4×(4EBN), while other species differing in ploidy but having the same EBN may be intercrossed, e.g., 4×(2EBN) and 2×(2EBN). Chromosome doubling or 2n gametes can be used to make a lower EBN species compatible with a higher EBN species. These findings also explain the major crossing difficulties previously inherent in the use of North American species in potato improvement. They also have direct implications for potato improvement, barring the occurrence of other incompatibility barriers. Any 4×(4EBN) cultivar is endosperm compatible and thus will cross with 4×(4EBN) and 6×(4EBN) species. The 2×(2EBN) haploids of 4×(4EBN) cultivars likewise will hybridize with 2×(2EBN) and 4×(4EBN) species. All 2×(1EBN) species are crossable with 2×(2EBN) haploids through 2n gametes or chromosome doubling.Cooperative investigation of the U.S. Department of Agriculture, Agriculture Research Service, and the Wisconsin Experiment Station.     

Selection indices for sugarcane improvement at three stages of selection

Summary Selection indices at different stages of selection were estimated for a biparental mating population of sugarcane (Saccharum officinarum L.). At the seedling stage indices constructed from primary characters are better than selection for yield alone. At the clonal stage the superiority of index selection over direct selection was marginal. In the seedling stage, selection based on index can lead to better selection efficiency in succeeding clonal stages. This was confirmed by a sample study.     

Occurrence of numerically unreduced (2n) gametes in Alstroemeria interspecific hybrids and their significance for sexual polyploidisation

The F1 hybrids of seven diploid Alstroemeria species (2n=2x=16) were investigated for the production of numerically unreduced (2n) gametes and their mode of origin. Based on a survey of 17 interspecific hybrid combinations,consisting of 119 genotypes, it was found that the F1 hybrids of Chilean-Brazilian species mostly produced first division restitution (FDR) 2n gametes. These F1 hybrids were self-pollinated in order to obtain F2 seeds, which was an indication that the F1 plants also produced 2neggs simultaneously. All the F2 progeny plants were typical allotetraploids, most of which formed 16 bivalents and a small proportion formed multivalents during metaphase I stages of meiosis. Through genomic in situ hybridisation (GISH) it was proved that multivalent formation in F2plants, derived from A. inodora ×A. pelegrina hybrid, was due to homoeologous recombination but not from reciprocal translocations. In order to test the segregation pattern of the recombinant chromosomes, an F3 population from one genotype, P6C49-6, was investigated. The recombinant chromosomes assorted independently from each other supporting the hypothesis that the segregation of chromosomes in ring quadrivalents did not behave like those in translocation heterozygotes. It was concluded that in allopolyploids of Alstroemeria,bilateral sexual polyploidisation could accomplish genetic recombination by both homoeologous crossing-over as well as through the assortment of chromosomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic relationships between attributes in sugarcane clones closely related to Saccharum spontaneum

Summary Saccharum spontaneum is being used in sugarcane breeding programs in attempt to improve characteristics such as ratooning ability and stress tolerance. A population of F₁ (Saccharum officinarum or commercial variety x S. spontaneum) and F₁ x F₁ sugarcane clones was evaluated for sugar yield and a range of yield components in a plant and two ratoon crops. The aim was to determine genetic correlations between attributes in clones with a large component of S. spontaneum, that could be used to help derive appropriate selection indices in such populations.There were close associations between the same attributes measured in different crop-years and the associations between different attributes were generally similar across crop-years. Stalk number and fibre content were positively correlated, as were stalk weight and CCS. The latter two attributes (which are low in S. spontaneum but high in S. officinarum) were negatively correlated with the former two (high in S. spontaneum, low in S. officinarum). Sugar yield was more closely associated with stalk weight and CCS than with stalk number but became more closely associated with stalk number with successive ratoon crops.CCS was positively correlated (r_g=0.55) with cane yield in the plant crop but showed a small negative correlation with cane yield (r_g=–0.20) in the second ratoon crop. CCS (measured in any crop) also had a negative correlation with cane yield in the ratoon crops expressed as a percentage of plant cane yield. This suggests that CCS is negatively correlated with levels of traits contributing to ratooning ability. Intensive selection among such populations for CCS without consideration of ratooning performance may reduce the frequency of favourable specific ratooning characteristics.Abbreviations CCS commercial cane sugar     

The use of the topiary gene in adapting Solanum germplasm for potato improvement

Summary The topiary gene, a single recessive conditioning very short stolons and early tuber initiation, may provide a tool for selecting wild species for tuberization. Topiary segregants may be recognized at the seedling stage, and there is good expression in interspecific hybrids. A genetically diverse diploid population, composed of accessions of 22 species selected for disease resistance and 2n gametes and crossed with sources of the topiary gene, is being developed. Recurrent phenotypic selection for yield and carliness of tuberization will be facilitated by the topiary trait, insect pollination and the self-incompatibility system. Standard varietal evaluation techniques including yield trials, sequential harvests, and tuber quality assessments can be applied to the population to alter gene frequencies or identify suitable parents for crossing to Tuberosum. Selected clones may be maintained in the field without clonal mixture. The population should retain most of the simply inherited disease resistance characteristics present in the original introductions. Adapted germplasm produced by this method should be especially valuable where the number of backcrosses to Tuberosum is to be minimized, as in the improvement of potatoes for quantitative traits such as yield, polygenic disease resistance, and environmental tolerance. Well-adapted clones may contribute a maximum input of genetic diversity through hybridization with Tuberosum haploids and subsequent polyploidization via 2n gametes.Paper No. 2486 from the Laboratory of Genetics. Research supported by the College of Agricultural and Life Sciences; International Potato Center; SEA, USDA, CRGO5901-0410-8-0180-0; and Frito-Lay, Inc.     

Tissue and cell culture as AIDS to sugarcane breeding. I. Creation of genetic variation through callus culture

Summary Four-hundred and seventeen plants from 8 sugarcane varieties were selected among the 4600 plants that had been generated from calluses of shoot-apices, rolled young leaves and young inflorescences of 58 varieties. They were planted in the field (Field Test-II stage) in December, 1971 and examined for morphology, sugar content and chromosome number in the summer of 1972 and thereafter. The callus derivatives of the 8 varieties differed from their donors in the frequency of morphological changes: F146 (1.8%), N:Co310 (2.4%), F161 (4.8%), F164 (6.7%), F162 (7.4%), 56–2080 (15.8%), F170 (27.6%), and F156 (34.0%). Auricle length showed the greatest frequency of difference (8.6%); dewlap shape ranked next (6.5%); followed by hair group (6.2%); attitude of top leaves (1.9%). The sucrose content of callus derivative was increased over their donors by 2% to 12%. Chromosome number (2n) varied from 86 to 126 in the F156 derivatives in contrast with the donor's 114 whereas those of F164 varied from 88 to 108 as compared with the donor's 108. The derivatives of F146 generally centred around the original chromosome number of 110 and it is considered to be the most genetically stable cultivar. The cause of the occurrence of chromosome mosaicism in sugarcane is discussed. There was no apparent correlation between morphological modifications and changes in chromosome number.     

气象因子对广西新植蔗和宿根蔗茎伸长的影响

利用2000－2011年广西4个农业气象试验站的甘蔗旬茎伸长量和气象资料, 分析宿根蔗和新植蔗在气象因子影响下茎伸长的差异。结果表明, 新植蔗和宿根蔗茎生长具有明显差异, 新植蔗茎伸长期茎高明显大于宿根蔗, 进入茎生长期时的茎高本底值较小, 茎总伸长量较大但其伸长期较短。多数气象因子与新植蔗、宿根蔗旬茎伸长量极显著相关(P<0.05), 且对新植蔗的影响大于宿根蔗。对新植蔗、宿根蔗茎伸长起直接正作用的主要因子均为最低气温、相对湿度、最高气温, 起直接负作用的主要因子为平均气温、气压, 积温、降雨量则通过其他气象因子起明显的间接作用。旬茎伸长量对降雨量存在较明显的滞后性, 新植蔗滞后期多为2旬, 宿根蔗多为1旬, 新植蔗对日照时数的响应也存在滞后现象, 两者对温度类气象因子及相对湿度均无滞后。     

Relevance of sexual polyploidization for crop improvement – A review

Colchicine induced polyploids have not directly contributed for crop improvement in the past. On the other hand, the so-called natural polyploids, derived from the functioning of numerically unreduced(2n) gametes have been shown to be more relevant for crop improvement in many cases. Different types of cytological abnormalities during meiosis can give rise to 2n gametes and the genetic composition of these gametes is variable. Depending on the type meiotic abnormalities, various types of 2ngametes, such as first division restitution(FDR), second division restitution (SDR),indeterminate meiotic restitution (IMR) and post meiotic restitution (PMR) gametes,among others, have been described in recent years. For the improvement of autopolyploids such as potato, alfalfa,Vaccinium spp., and some of the fodder grasses, FDR gametes have been proved to be highly useful. However, the use of 2n gametes for the improvement of allopolyploid crops has received much less attention so far. Some of the investigations on allopolyploids, derived from Festuca-Lolium, Alstroemeria and Lilium species hybrids, have revealed that 2ngametes can be most useful for the introgression of alien genes and chromosomes into cultivars. An important feature of using sexual polyploidization in the case of allopolyploids is that introgression can be achieved through recombination due to genetic crossing-over between alien chromosomes as well as addition of alien chromosomes, which is extremely difficult or impossible to achieve in the case of colchicine induced allopolyploids. Because of the recent developments in the field of plant molecular biology, methods have become available for the analysis of 2ngametes and sexual polyploid progenies more accurately and to develop systematic breeding approaches. The methods include DNA in situ hybridization (GISH and FISH)and molecular mapping (AFLP, RFLP, RAPDs).In addition to providing basic information on the genetic and genome composition of the polyploid progenies, these methods can be potentially useful for a more efficient creation of desirable breeding material and cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.