Tropical root and tuber crops (cassava, sweet potato, taro, and yam) are staples in developing countries where rapid urbanization is strengthening the demand for flour based foods. Quality control techniques are still under development, and when available, laboratory analyses are too expensive. The objectives of this study were to calibrate Near-infrared spectroscopy (NIRS) for routine analysis of flours and to test its reliability to determine their major constituents. Flours prepared from 472 accessions (traditional varieties and breeding lines) were analyzed for their starch, total sugars, cellulose, total nitrogen, and ash (total minerals) contents. The near-infrared (350-2500 nm) spectra of all samples were measured. Calibration equations with cross and independent validation for all analytical characteristics were computed using the partial least squares method. Models were developed separately for each of the four crop species and by combining data from all spp. to predict values within each of them. The quality of prediction was evaluated on a test set of 94 accessions (20%) by standard error of prediction (SEP) and r2 parameters between the measured and the predicted values from cross-validation. Starch, sugar, and total nitrogen content could be predicted, respectively, with 87%, 86%, and 93% confidence, whereas ash (minerals) could be predicted with 71%, and cellulose was not predictable (r2=0.31). The statistical parameters obtained for starch, sugars, and total nitrogen are of special interest for flour quality control. These constituents are quantitatively the most important in the chemical composition of flours, and starch content is negatively correlated with sugars and total nitrogen. NIRS is a low cost technique well adapted to the conditions in developing countries and can be used for the high-throughput screening of a great number of samples. Possible applications are discussed.

Genetic diversity of the greater yam (Dioscorea alata L.) and relatedness to D. nummularia Lam. and D. transversa Br. as revealed with AFLP markers Abstract Amplified fragment length polymorphism markers were used to assess the genetic relatedness between Dioscorea alata and nine other edible Dioscorea. These species include D. abyssinica Hoch., D. bulbifera L., D. cayenensis-rotundata Lamk. et Poir., D. esculenta Burk., D. nummularia Lam., D. pentaphylla L., D. persimilis Prain. et Burk., D. transversa Br. and D. trifida L. Four successive studies were conducted with emphasis on the genetic relationship within D. alata and among species of the Enantiophyllum section from Vanuatu. Study 1 was carried out to select a set of polymorphic primer pairs using 11 combinations and eight species belonging to five distinct sections. The four most polymorphic primer pairs were used in study 2 among six species of the Enantiophyllum section. Study 3 focussed mainly on the genetic relationship among 83 accessions of D. alata, mostly from Vanuatu (78 acc.) but also from Benin, Guadeloupe, New Caledonia and Vietnam. The ploidy level of 53 accessions was determined and results indicated the presence of tetraploid, hexaploid and octoploid cultivars. Study 4, included 35 accessions of D. alata, D. nummularia and D. transversa and was conducted using two primer pairs to verify the taxonomical identity of the cultivars 'langlang', 'maro' and 'netsar' from Vanuatu. The overall results indicated that each accession can be fingerprinted uniquely with AFLP. D. alata is an heterogeneous species which shares a common genetic background with D. nummularia and 'langlang', 'maro' and 'netsar'. UPGMA cluster analysis revealed the existence of three major groups of genotypes within D. alata, each assembling accessions from distant geographical origins and different ploidy levels. The analysis also revealed that 'langlang', 'maro' and 'netsar' clustered together with the cultivar 'wael' (D. transversa) from New Caledonia. Results are discussed in the paper.

The objectives of this study were: (1) to analyse the physico-chemical characteristics of 48 Dioscorea alata varieties representing a core sample of the Vanuatu national germplasm collection; (2) to relate those characteristics with the varieties eating quality; and (3) to assess the possibility of selecting varieties according to their chemotype. Overall, 331 accessions were collected from 15 different islands of Vanuatu, planted in an ex situ germplasm collection and described during 3 years. The 48 varieties included in the core sample were selected according to their island of origin, eating quality, tuber shape, tuber flesh colour and morphotype. Analyses of their tubers were made for percentage dry matter, starch, amylose, lipids, minerals, proteins, sugars and gelatinisation temperature range. Significant variation exists for each of these characteristics except for gelatinisation temperature. Varieties with good eating quality are characterised with high dry matter, starch and amylose contents. Chemotypes appear to be genetically controlled and further screening of germplasm and/or breeding will have to take into consideration these characteristics, important for farmers' adoption.

Yams (Dioscorea sp.) are staple food crops for millions of people in tropical and subtropical regions. Dioscorea alata, also known as greater yam, is one of the major cultivated species and most widely distributed throughout the tropics. Despite its economic and cultural importance, very little is known about its origin, diversity and genetics. As a consequence, breeding efforts for resistance to its main disease, anthracnose, have been fairly limited. The objective of this study was to contribute to the understanding of D. alata genetic diversity by genotyping 384 accessions from different geographical regions (South Pacific, Asia, Africa and the Caribbean), using 24 microsatellite markers. Diversity structuration was assessed via Principal Coordinate Analysis, UPGMA analysis and the Bayesian approach implemented in STRUCTURE. Our results revealed the existence of a wide genetic diversity and a significant structuring associated with geographic origin, ploidy levels and morpho-agronomic characteristics. Seventeen major groups of genetically close cultivars have been identified, including eleven groups of diploid cultivars, four groups of triploids and two groups of tetraploids. STRUCTURE revealed the existence of six populations in the diploid genetic pool and a few admixed cultivars. These results will be very useful for rationalizing D. alata genetic resources in breeding programs across different regions and for improving germplasm conservation methods.

Cassava (Manihot esculenta Crantz) is a clonally propagated crop that was introduced into the South Pacific archipelago of Vanuatu in the 1850s. Based on a survey conducted in 10 different villages throughout the archipelago, we present here a study of its diversity. Farmers' knowledge about cultivation cycle and sexual reproduction of cassava was recorded during group interviews in each village. Using a set of 11 SSR markers, we genotyped the 104 landraces collected and 60 supplementary accessions from a within-landrace study (12 landraces x 5 plants). Out of the 104 landraces collected, we discovered 77 different multilocus genotypes and the within-landrace study identified several polyclonal landraces. Our data suggest a number of hypotheses about the dynamics of diversity of cassava in Vanuatu.

The aim of the present study is to develop a methodology for the rapid estimation of taro (Colocasia esculenta) quality. Chemical analyses were conducted on 315 accessions for major constituents (starch, total sugars, cellulose, proteins, and minerals). NIRS calibration equations, developed on a calibration set composed of 243 accessions, showed high explained variances in cross-validation (r(2)(cv)) for starch (0.89), sugars (0.90), proteins (0.89), and minerals (0.90) but poor response for amylose (0.44) and cellulose (0.61). The predictions were tested on an independent set of 58 randomly selected accessions. The r(2)(pred) values for starch, sugars, proteins, and minerals were, respectively, of 0.76, 0.74, 0.85, and 0.85 with ratios of performance to deviation (RPD) of 3.41, 4.01, 3.78, and 3.64. New calibration equations developed on 303 accessions confirmed good RPD values for starch (3.30), sugars (4.13), proteins (3.61), and minerals (3.74). NIRS could be used to predict starch, sugars, proteins, and minerals contents in taro corms with reasonably high confidence.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699In Vanuatu, an oceanic archipelago located in south-west Pacific, taro ( (L.) Schott) is one of the staple crops. An eco-geographical survey of its genetic resources was conducted in ten villages, each located on a different island. A sample of 344 landraces referred as the National Sample (NS) was collected. Its genetic diversity was assessed using nine microsatellites markers and then was compared with an International Core Sample (ICS) that was previously distributed in the ten villages of the study in order to test the geographical distribution of allelic diversity as an effective mean for the on-farm conservation of root crops. The ICS was composed of 41 accessions, including 23 originating from South-East Asia. The molecular dataset revealed in the NS (1) 324 distinct multilocus genotypes, (2) six genetic clusters mainly differentiated by rare alleles, (3) a geographical structure of the genetic resources of taro based, within each village, on the dominance of one or two of these clusters rather that their exclusivity, and (4) an analogy between the patterns of dominant clusters between villages and the past and present social networks. In addition, accessions from the ICS revealed 52 new alleles. Based on these findings, we formulate hypotheses regarding the processes involved in the genetic diversification of taro in Vanuatu. We also discuss the use of this set of microsatellite markers along with the molecular dataset obtained from this study as effective tools to monitor the diversity and evolution of taro in the future

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