Dessert and cooking bananas are vegetatively propagated crops of great importance for both the subsistence and the livelihood of people in developing countries. A wide diversity of diploid and ...triploid cultivars including AA, AB, AS, AT, AAA, AAB, ABB, AAS and AAT genomic constitutions exists. Within each of this genome groups, cultivars are classified into subgroups that are reported to correspond to varieties clonally derived from each other after a single sexual event. The number of those founding events at the basis of the diversity of bananas is a matter of debate.
We analysed a large panel of 575 accessions, 94 wild relatives and 481 cultivated accessions belonging to the section Musa with a set of 498 DArT markers previously developed.
DArT appeared successful and accurate to describe Musa diversity and help in the resolution of cultivated banana genome constitution and taxonomy, and highlighted discrepancies in the acknowledged classification of some accessions. This study also argues for at least two centres of domestication corresponding to South-East Asia and New Guinea, respectively. Banana domestication in New Guinea probably followed different schemes that those previously reported where hybridization underpins the emergence of edible banana. In addition, our results suggest that not all wild ancestors of bananas are known, especially in M. acuminata subspecies. We also estimate the extent of the two consecutive bottlenecks in edible bananas by evaluating the number of sexual founding events underlying our sets of edible diploids and triploids, respectively.
The attribution of clone identity to each sample of the sets allowed the detection of subgroups represented by several sets of clones. Although morphological characterization of some of the accessions is needed to correct potentially erroneous classifications, some of the subgroups seem polyclonal.
So Close Yet So Different: Cultural Differences among Farmers in Central Kenya Affect Their Knowledge of Sorghum (Sorghum bicolor L. Moench) Landrace Identification
. Whether knowledge of landrace ...identification is shared among farmers in rural societies is a matter of debate in crop diversity research, and the influence of culture on knowledge heterogeneity remains largely misunderstood. This study analyzes the heterogeneity of farmers’ knowledge of crop landrace identification, and investigates factors involved in its patterns. It especially explores the effect of cultural differences by comparing how three ethnolinguistic groups identify and name sorghum diversity in the Mount Kenya region. A set of 293 panicles representing sorghum diversity in the study area was presented for identification to 96 farmers randomly selected in the three groups. A subset of 287 panicles was scored for morphological characteristics using 16 qualitative descriptors, and neutral genetic diversity of 170 of them was described using 18 SSR genetic markers. Distance-based analyses were applied to analyze knowledge patterns within and between groups and to describe the structure of sorghum morphological and genetic diversity. Results show that the degree of heterogeneity of knowledge among farmers varies strongly according to both their ethnolinguistic membership and panicle characteristics, despite their high geographic proximity. The effect of farmers’ experience of landraces and of pathways for social learning on inter-individual variations of knowledge is discussed.
• Background and Aims The production of triploid banana and plantain (Musa spp.) cultivars with improved characteristics (e.g. greater disease resistance or higher yield), while still preserving the ...main features of current popular cultivars (e. g. taste and cooking quality), remains a major challenge for Musa breeders. In this regard, breeders require a sound knowledge of the lineage of the current sterile triploid cultivars, to select diploid parents that are able to transmit desirable traits, together with a breeding strategy ensuring final triploidization and sterility. Highly polymorphic single sequence repeats (SSRs) are valuable markers for investigating phylogenetic relationships. • Methods Here, the allelic distribution of each of 22 SSR loci across 561 Musa accessions is analysed. • Key Results and Conclusions We determine the closest diploid progenitors of the triploid 'Cavendish' and 'Gros Michel' subgroups, valuable information for breeding programmes. Nevertheless, in establishing the likely monoclonal origin of the main edible triploid banana subgroups (i.e. 'Cavendish', 'Plantain' and 'Mutika-Lujugira'), we postulated that the huge phenotypic diversity observed within these subgroups did not result from gamete recombination, but rather from epigenetic regulations. This emphasizes the need to investigate the regulatory mechanisms of genome expression on a unique model in the plant kingdom. We also propose experimental standards to compare additional and independent genotyping data for reference.
Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), a noncachexia variant of Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) were co-inoculated as ...two-, three-, four-, and five-viroid mixtures to Clementine trees grafted on trifoliate orange to evaluate their effect on symptom expression, tree growth, and fruit yield. Most trees infected with CEVd-containing viroid mixtures developed exocortis scaling symptoms, as did CEVd alone, whereas most trees infected with HSVd- or CVd-IV-containing mixtures developed bark-cracking symptoms. Trees infected with mixtures containing both CEVd and CVd-IV revealed the existence of antagonism between these two viroids in terms of the expected bark-scaling and cracking symptoms. Synergistic interactions also were identified in trees infected with certain viroid combinations that, in spite of lacking CEVd, expressed exocortis-like scaling symptoms. Viroid interactions also affected the expected response of trees in terms of vegetative growth and fruit yield. Trees infected with viroid combinations containing CEVd or CVd-III were smaller and produced less fruit than trees infected with mixtures not containing these viroids. Viroid interactions on scion circumference and cumulative fruit yield, in terms of additivity of their effects, were statistically confirmed using a factorial analysis of variance model with two mean estimation approaches. In single-viroid infections, CEVd, CVd-III, and, to a lesser extent, CBLVd consistently and significantly reduced tree size and fruit yield. Conversely, HSVd and CVd-IV slightly increased fruit yield and reduced scion circumference. Rare and not consistent significant interactions were detected with the five-, four-, and three-viroid combinations. Antagonistic interactions between CEVd and CVd-III or CBLVd and CVd-III were revealed over the years with consistent significance. The antagonistic interaction between CEVd and CVd-IV was highly significant over the years when additional viroids were present; however, this antagonism appeared much later in the case of an exclusive interaction. HSVd and CVd-IV showed a consistent and significant synergistic interaction on yield only when both viroids were exclusively present. These results demonstrate antagonistic or synergistic relationships between citrus viroids depending on the viroid mixtures present in the host.
Sorghum has shown the adaptability necessary to sustain its improvement during time and geographical extension despite a genetic foundation constricted by domestication bottlenecks. Initially ...domesticated in the northeastern part of sub-Saharan Africa several millenia ago, sorghum quickly spread throughout Africa, and to Asia. We performed phylogeographic analysis of sequence diversity for six candidate genes for grain quality (Shrunken2, Brittle2, Soluble starch synthaseI, Waxy, Amylose extender1, and Opaque2) in a representative sample of sorghum cultivars. Haplotypes along 1-kb segments appeared little affected by recombination. Sequence similarity enabled clustering of closely related alleles and discrimination of two or three distantly related groups depending on the gene. This scheme indicated that sorghum domestication involved structured founder populations, while confirming a specific status for the guinea margaritiferum subrace. Allele rooted genealogy revealed derivation relationships by mutation or, less frequently, by recombination. Comparison of germplasm compartments revealed contrasts between genes. Sh2, Bt2, and SssI displayed a loss of diversity outside the area of origin of sorghum, whereas O2 and, to some extent, Wx and Ae1 displayed novel variation, derived from postdomestication mutations. These are likely to have been conserved under the effect of human selection, thus releasing valuable neodiversity whose extent will influence germplasm management strategies.
Citrus are natural hosts of five viroid species: Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV). ...CEVd and specific sequence variants of HSVd are the causal agents of the well-known diseases of citrus, exocortis and cachexia. Other viroids have been found to induce different degrees of stunting. Since commercial citrus trees are commonly infected with mixtures of these viroids, only limited information is available on their effect in species other than Etrog citron. A field assay was conducted to establish the effect of each viroid on Commune clementine trees grafted on Pomeroy trifoliate orange. Infected trees were periodically monitored over a 12-year period (1990 to 2002) for symptom expression, growth, and fruit yield. Only CEVd caused bark scaling on the trifoliate orange rootstock and marked dwarfing, both characteristic of exocortis disease as initially described. In addition, very conspicuous bumps were observed in the wood of the rootstock after removing the bark. Only those HSVd variants, previously characterized as pathogenic in several cachexia-sensitive species, induced pits and gum deposits characteristic of this disease in the clementine scion. Bark cracking symptoms on the trifoliate orange rootstock were also observed. They were associated with CVd-IV, HSVd, or CEVd infection, but in the latter, they were only clearly observed in trees that showed mild scaling. Other abnormalities (deep pits, crests, and gummy pits) were not associated with viroid infection. No specific symptoms resulted from infection with CBLVd and CVd-III. HSVd, CVd-IV, and CBLVd had little or no effect in growth and yield, whereas CEVd and CVd-III caused a significant reduction of growth and yield, which became more pronounced over time with CEVd infection. Yield reduction was associated mainly with loss of production of large fruits. In general, there was a good correlation between reduction in vegetative growth and yield.
The genetic diversity of sugarcane yellow leaf virus (SCYLV) was analyzed with 43 virus isolates from Réunion Island and 17 isolates from world-wide locations. We attempted to amplify by ...reverse-transcription polymerase chain reaction (RT-PCR), clone, and sequence four different fragments covering 72% of the genome of these virus isolates. The number of amplified isolates and useful sequence information varied according to each fragment, whereas an amplicon was obtained with diagnostic primers for 59 out of 60 isolates (98%). Phylogenetic analyses of the sequences determined here and additional sequences of 11 other SCYLV isolates available from GenBank showed that SCYLV isolates were distributed in different phylogenetic groups or belonged to single genotypes. The majority of isolates from Réunion Island were grouped in phylogenetic clusters that did not contain any isolates from other origins. The complete six ORFs (5612 bp) of five SCYLV isolates (two from Réunion Island, one from Brazil, one from China, and one from Peru) were amplified, cloned, and sequenced. The existence of at least three distinct genotypes of SCYLV was shown by phylogenetic analysis of the sequences of these isolates and additional published sequences of three SCYLV isolates (GenBank accessions). The biological significance of these genotypes and of the origin of the distinct lineage of SCYLV in Réunion Island remains to be determined.
This paper presents a simple and practical method for stratifying taro germplasm based on morpho-agronomical characters. More than 450 accessions of taro collected throughout Vanuatu and established ...in a field collection were described using 19 descriptors. A hierarchical approach was used to stratify the agro-morphological variation. Three sampling strategies were tested and the variation captured within each sample was compared for the frequencies of characters. The first sample (S1) was randomly selected; the second sample (S2) was conducted within the subgroups produced by the stratification method, and the third sample (S3) was based on UPGMA clustering within each subgroup. AFLP markers were used to compare the diversity between S3 and a fourth sample (S4) that included the parents of the Vanuatu breeding programme, and more diversity was found in S3. AFLPs were found to be useful to validate the hierarchical approach used for stratification. These studies have confirmed the narrow genetic base of the Vanuatu taro germplasm. They have been useful for detecting duplicates and fingerprinting of accessions.PUBLICATION ABSTRACT
The Dioscorea cayenensis - Dioscorea rotundata species complex is the most widely cultivated yam in West Africa. This species complex has been described as deriving from wild yams belonging to the ...Enanthiophyllum section through domestication by African farmers. To study patterns of yam evolution and to establish phylogenetic relationships existing between wild and cultivated species sampled in Benin, we investigated changes in chloroplast DNA simple sequence repeats (cpSSR) in 148 yam accessions selected to cover the wider possible genetic diversity existing in the country. Dioscorea cayenensis and D. rotundata share the same haplotype. The morphotype "abyssinica" appeared to be subdivided into 2 haplotypes. One of these haplotypes shares the same haplotype with the Dioscorea cayenensis - Dioscorea rotundata species complex and with morphotypes praehensilis, suggesting that they might belong to the same species. Relationships among sections Lasiophyton, Macrocapaea, Opsophyton, and Enanthiophyllum were clarified, and some taxonomic changes within the Enanthiophyllum section were suggested. Dioscorea minutiflora, D. smilacifolia, and D. burkilliana might be considered as 1 single genetic group, and they are suspected of belonging to the same species.Key words: chloroplast genome, microsatellite, Dioscorea, Enanthiophyllum, taxonomy.
We conducted this study to assess the impact of the bait station used in the Carambola fruit fly eradication program on non-target insects indigenous to French Guiana. A sampling device was developed ...based on the bait station, using four treatments: fiberboard blocks impregnated with methyl eugenol (ME) and malathion (MA), ME only, MA only, and a non-impregnated block. A total of only 149 non-target insects were captured during the 52 weeks of the experiment. The non-target taxa captured included representatives of nine orders and 26 families. Analysis based on a Poisson model of captures indicated no difference in the taxa or number of specimens captured among the treatments, providing evidence that the bait stations used by the regional program had no greater impact on non-target insect populations than the non-impregnated blocks. Our results indicate that captures of non-target insects could be related to accidental exposure to the sampling device and as such can be considered random events. The results of this experiment support the hypothesis that bait stations made with ME and MA can be used in an area-wide program without risk to non-target insect populations.
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