NIRS (Near Infrared Reflectance Spectroscopy) potential for breeding aroids

Aroids corms and cormels are chemically very variable and there is significant variation of their major constituents (starch, sugars, cellulose, proteins, minerals) between genotypes. A fairly common difficulty for breeding programmes is to assess precisely these compounds as chemical analyses are too expensive for routine screening. These programmes are often based on mass recurrent selection and great numbers of hybrids have to be screened to achieve some progress. However, the wrong selection of a parent can cause a serious constraint to the development of new varieties for processing purposes. Likewise, if the table quality is not acceptable for consumers, years of intense and expensive breeding efforts can lead to complete failure. Low-cost methods for rapid evaluation of numerous hybrids are urgently needed. The present paper, assess the potential of NIRS (Near Infrared Reflectance Spectroscopy) as an alternative method for predicting these major constituents and evaluating corms and cormels quality. Models have been developed using data from 642 root crops accessions and their predictive potential has been tested on 100 varieties and hybrid lines of taro, Colocasia esculenta. The NIRS calibration results for major constituents, and their practical applications for aroids breeding and genetic improvement of quality traits, are discussed. (Résumé d'auteur

Conservation of tropical root and tuber crops agrobiodiversity : on farm true seeds production and use as a mean for geographic distribution of allelic diversity

The tropical root and tuber crops (cassava, sweet potato, taro and yam) are cultivated throughout the tropics where they play a major role for food security. In Vanuatu, anarchipelago of 81 islands situated in the South West Pacific, traditional food gardens are at the basis of self-sufficiency with tuber and root crops as the main source of carbohydratesfor smallholders. Emerging environmental changes such as climatic ones, the introduction of new plant diseases and/or changing diets are now endangering the local agrobiodiversity and the country's food security. As several molecular genetic studies have shown, the local tuber and root crops diversity of Vanuatu is narrow and in the course of genetic erosion, its resilience to changes is thus quite limited. To enlarge this genetic pool, introduction of exotic varieties has been conducted through in vitro genotypes but excessive distribution costs and the limited success of the operation, mainly due to the high fragmentation of the country, pointed up the need for other means of allelic dispersion. True botanical seeds production and use seems to be a promising way since it is easier to distribute and because it enables efficient protection of local allelic pool by crossing it with introduced one. However, the adoption of this innovative practice by traditional smallholders raises numerous problems since they are practicing exclusively clonal propagation and are not aware of tuber and root crops sexual reproduction. Our project aims at evaluating the potential for on-farm true seeds production and use through participatory methods. This study will focus on mains environmental, economical, social and cultural constraints to the development of this practice in on-farm conditions. Since the sexual reproduction of these plants is poorly documented, this study will also assess the efficiency of this method through the characterization of reproductive biology and estimation of the percentage of new cultivars created during a cycle. We will finally evaluate the possible practical improvements by building on farmer's own experiments and analysis of their difficulties. As most of the work on tropical tuber and root crops true seed of has been limited to scientific research stations, it is of interest to develop this technique for on farm activities. (Résumé de l'auteur

La caractérisation et l'évaluation des plantes à racines et tubercules et des bananes plantains

L'agriculture des plantes à racines et tubercules et des bananes plantains (Musa spp.) s'appuie essentiellement sur la multiplication végétative. La plupart des cultivars ne bénéficient donc pas des recombinaisons génétiques fournies par la sexualité. Leurs potentialités adaptatives sont quasi nulles par rapport à des espèces à multiplication sexuée. Les ressources génétiques sont par conséquent de très grande valeur et doivent être soigneusement conservées et protégées. La caractérisation et l'évaluation des cultivars sont des étapes fondamentales dans le processus d'amélioration et de développement de ces cultures. Une méthodologie commune à ces espèces peut être utilisée, elle procède par étapes successives dans l'identification des morphotypes, zymotypes, chimiotypes, cytotypes et génotypes. Elle vise essentiellement à établir des concordances ou à révéler des discordances qui sont utilisées pour expliquer la structure de la variabilité. Les résultats obtenus pour les ignames, le taro, les plantains et le kava sont succintement exposés et concordent pour révéler que, compte tenu des difficultés que rencontre l'amélioration génétique de ces plantes, il est urgent de caractériser et d'évaluer les ressources génétiques existantes car des cultivars d'intérêt potentiel méritent certainement d'être sélectionnés et multiplié

Domestication history of a hexaploid, the sweet potato (Ipomoea batatas (L.) Lam.)

Despite the importance of sweet potato as a food crop, its evolutionary history has been poorly investigated. The geographical and botanical origins of sweet potato remain unclear. Sweet potato is in the section Batatas of the genus, which also includes 13 wild relatives, almost all endemic to the Americas. I. batatas is not known in the wild state. Morphological and genetic analyses indicate that I. trifida is sweet potato¿s closest wild relative, but the genomic composition of I. batatas is still debated. It is still unclear whether this hexaploid is auto-, allo- or auto-allopolyploid. The range of I. trifida extends from northern Peru to Mexico, and the assumed region of origin of I. batatas is somewhere within this vast geographical area. I. trifida forms a complex of ecotypes of differing ploidy levels (diploids to hexaploids), but the distribution and origin of populations of varying ploidy levels are not documented. Morever, no genetic studies have been conducted to determine the relationships between different wild populations of I. trifida and the cultivated I. batatas, which could allow inference of sweet potato¿s region(s) of origin. Finally, a major domesticated trait of I. batatas is its capacity to produce edible storage roots. Some I. trifida are known to form small tuberous roots, but these have not been studied in any depth. The purpose of our study is to investigate the origin of sweet potato and particularly the role of polyploidization in its domestication history. A set of 180 I. trifida populations and 450 sweet potato landraces, distributed from Peru to Mexico, were chosen from the collection of the International Potato Center (CIP, Lima, Peru). Morphological characterisation of these plants is in progress, as well as genetic analyses using neutral chloroplast markers. We plan to evaluate ploidy levels of these different wild and cultivated samples by flow cytometry and study the genome composition of representatives of ploidy groups by genomic in situ hybridization. These analyses should lead to advances in the reconstruction of sweet potato¿s evolutionary history. (Texte intégral

Descriptors for Colocasia esculenta

Descriptors for Taro (Colocasia esculenta) is a revision of the original IBPGR publication Descriptors for Colocasia (AGP:IBPGR/79/52, 1980). The 1980 list was based upon the work of the Regional Committee in Southeast Asia and its descriptor numbers are given in parentheses beside the present descriptors for cross-referencing purposes. This descriptor list includes modifications for the Solomon Islands, Papua New Guinea, Indonesia, New Caledonia and Vanuatu developed during 1989 to 1997 by Dr Anton Ivancic and Dr Vincent Lebot. However, the list is suitable for Asian, Pacific and Caribbean taros. A draft version prepared in the internationally accepted IPGRI format for descriptor lists was subsequently sent to a number of experts for their comments and amendments. Later it was revised by taro experts as part of the AusAID/SPC Taro Genetic Resources Project - Taro Collection Strategy Workshop, during 7-11 December 1998, at NARI, Lae, Papua New Guinea. The names and addresses of those involved are given in ‘Contributors’. IPGRI encourages the collecting of data for all five types of descriptors (see page 1, Definition sand Use of Descriptors), whereby data from the first four categories - Passport, Management, Environment and Site, and Characterization - should be available for any accession. The number of descriptors selected in each of the categories will depend on the crop and their importance to the crop’s description. Descriptors listed under Evaluation allow for a more extensive description of the accession, but generally require replicated trials over a period of time. Although the suggested coding should not be regarded as the definitive scheme, this format represents an important tool for a standardized characterization system and it is promoted by IPGRI throughout the world. This descriptor list provides an international format and thereby produces a universally understood ‘language’ for plant genetic resources data. The adoption of this scheme for data encoding, or at least the production of a transformation method to convert other schemes into the IPGRI format, will produce a rapid, reliable and efficient means for information storage, retrieval and communication, and will assist with the utilization of germplasm. It is recommended, therefore, that information should be produced by closely following the descriptor list with regard to ordering and numbering descriptors, using the descriptors specified, and using the descriptor states recommended. This descriptor list is intended to be comprehensive for the descriptors that it contains. This approach assists with the standardization of descriptor definitions. IPGRI does not, however, assume that each curator will characterize accessions of their collection utilizing all descriptors given. Descriptors should be used when they are useful to the curator for the management and maintenance of the collection and/or to the users of the plant genetic resources. However, highly discriminating descriptors are marked as highlighted text to facilitate selection of descriptors. Multicrop passport descriptors (see Annex I) were developed jointly by IPGRI and FAO, to provide consistent coding schemes for common passport descriptors across crops. They are marked in the text as [MCPD]. Please note that owing to the generic nature of the multicrop passport descriptors, not all descriptor states for a particular descriptor will be relevant to a specific crop. In Annex II, the reader will find a Collecting form for taro that will facilitate data collecting. Any suggestions for improvement on the Descriptors for Taro will be highly appreciated by IPGRI. (Résumé d'auteur