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Cassava (Manihot esculenta) provides calories and nutrition for more than half a billion people. It was domesticated by native Amazonian peoples through cultivation of the wild progenitor M. esculenta ssp. flabellifolia and is now grown in tropical regions worldwide. Here we provide a high-quality genome assembly for cassava with improved contiguity, linkage, and completeness; almost 97% of genes are anchored to chromosomes. We find that paleotetraploidy in cassava is shared with the related rubber tree Hevea, providing a resource for comparative studies. We also sequence a global collection of 58 Manihot accessions, including cultivated and wild cassava accessions and related species such as Ceará or India rubber (M. glaziovii), and genotype 268 African cassava varieties. We find widespread interspecific admixture, and detect the genetic signature of past cassava breeding programs. As a clonally propagated crop, cassava is especially vulnerable to pathogens and abiotic stresses. This genomic resource will inform future genome-enabled breeding efforts to improve this staple crop.

Kava (Piper methysticum) is a major cash crop in the Pacific. The aim of this study was to assess genetic variation among 103 accessions of kava using SSRs and DArTs. Genetic structure was determined using clustering analyses (WPGMA) and principal coordinate analyses (PCA). Thirteen SSR primers and 75 DArT markers were found polymorphic, and the two types of markers generated similar clustering patterns. Genetic distances ranged from 0 to 0.65 with an average of 0.24 using SSRs and from 0 to 0.64 with an average of 0.24 using DArT. Eleven genotypes were identified with SSR while 28 genotypes were identified with DArT markers. By combining the two sets of markers, a total of only 30 distinct genotypes were observed. In the Vanuatu archipelago, noble cultivars originating from different islands clustered together within a very narrow genetic base despite their diversity of morphotypes. SSR and DArT fingerprints allowed the identification of kava cultivars unsuitable for consumption, so called two-days, and clearly differentiated the wild types classified as P. methysticum var. wichmannii from the cultivars as var. methysticum. Molecular data reveals that all noble cultivars evolved by the predominance of clonal selection. Although they are represented by clearly distinct morphotypes, these cultivars are genetically vulnerable and their potential to adapt to forthcoming changes is limited. These newly developed markers provide high resolution and will be useful for kava diversity analyses and quality assessment. Key words: kava, clonal selection, kavalactones, genetic variation, SSR, DArT. Le kava (Piper methysticum) est une culture de rente importante dans le Pacifique. L'objectif de cette etude etait d'apprecier la diversite genetique de 103 accessions de kava a l'aide de marqueurs SSR et DArT. La structure genetique a ete determinee a l'aide de classification hierarchique (WPGMA) et par analyse en composantes principales (ACP). Treize amorces SSR et 75 marqueurs DArT se sont reveles etre polymorphes et les deux types de marqueurs ont donne des agregations similaires. Les distances genetiques varient de 0 a 0.65 avec une moyenne de 0.24 pour les SSR et de 0 a 0.64 avec une moyenne de 0.24 pour les DArT. Onze genotypes sont identifies par SSR alors que 28 genotypes sont identifies par DArT. En combinant, les deux types de marqueurs un total de 30 genotypes distincts sont observes. Dans l'archipel du Vanouatou, les cultivars dits nobles et originaires d'iles differentes se regroupent entre eux et presentent une base genetique tres etroite malgre leur variabilite morphologique. Les empreintes SSR et DArT permettent de differencier les formes sauvages identifiees comme P. methysticum var. wichmannii. Les donnees moleculaires revelent que les cultivars nobles ont evolue par selection clonale. Bien que representes par des morphotypes distincts, ces cultivars sont genetiquement vulnerables et leur potentiel d'adaptation aux futurs changements est extremement faible. L'utilisation de ces marqueurs pourrait s'averer fort utile a l'avenir pour les etudes de diversite et le controle de la qualite. Mots-cles: kava, selection clonale, kavalactones, variabilite genetique, SSR, DArT., Introduction Kava is the traditional beverage of the Pacific obtained by cold water extraction of the roots of Piper methysticum Forst. Morphological, chemical, cytological, and genetic evidence indicates that kava [...]

Thermogenesis and heat generating tissues in inflorescences of the giant taro (Alocasia macrorrhizos (L.) G. Don) were studied from December 2005 to February 2006, on the Island of Espiritu Santo, Vanuatu. Temperatures were recorded in the ambient air, in the peduncle tissue, and on 12 positions within spadices during periods of maximum thermogenic activity, in the early morning hours of the female and male phases. The study showed that there were three thermogenic tissues: the sterile appendix, the fertile male part, and the differentiated sterile area below the fertile male part. During the female phase, heat was generated by the sterile appendix and the differentiated sterile area below the fertile male part, the smallest region of the spadix (mean ± SD = 0.86 ± 0.24 cm, 3.17% of the spadix length), and most probably by the fertile male part. Within the spadix, average temperatures gradually increased from the base of the female part and reached the first peak at the midpoint of the differentiated sterile area below the fertile male part (36.11 ± 1.54°C). After that, they gradually decreased towards the midpoint of the fertile male part and increased again, reaching a second (main) peak at 1/4 of the sterile appendix height (44.83 ± 1.87°C). From 1/4 to 1/2 of the appendix height they remained at more or less the same level, and then they decreased towards the tip of the spadix. During the male phase, heat was generated only within the fertile male part. Key words: Alocasia macrorrhizos, Araceae, giant taro, heating tissues, thermogenesis. La thermogenese et les tissus thermogenetiques du taro geant (Alocasia macrorrhizos (L.) G. Don) ont ete etudies de Decembre 2005 a Fevrier 2006 sur File d'Espiritu Santo an Vanuatu. Les temperatures ont ete mesurees dans Fair ambiant, dans le pedoncule ainsi que dans 12 emplacements a l'interieur des spadices pendant les periodes d'activite thermogenetique maximale, an petit matin et pendant les phases femelles et males. L'etude a montre 'existence de trois tissus thermogenetiques : l'appendice sterile, la partie male fertile et la zone sterile differenciee situee sous la partie male fertile. Durant la phase femelle, la chaleur etait generee par l'appendice sterile et par la zone sterile differenciee sous la zone male fertile, soit la plus courte zone (0,86 ± 0,24 cm de long, soit 3,17 % du spadice), enfin tres probablement par la zone male fertile elle-meme. A l'interieur du spadice, les temperatures augmentaient progressivement a partir de la base de la partie femelle et atteignaient leur premier pic a la moitie de la zone sterile differenciee sous la zone male fertile (36,11 ± 1,54°C). Ensuite, elles diminuaient graduellement vers le milieu de la zone male fertile, augmentaient a nouveau avant d'atteindre le second pic (le principal) an quart de la hauteur de l'appendice sterile (44,83 ± 1,87°C). Entre le quart et la moitie de la hauteur de l'appendice, elles conservaient plus on moins le meme degre de temperature, puis decroissaient vers l'apex du spadice. Durant la phase male, la chaleur n'etait generee que par la partie male fertile. Mots-cles : Alocasia macrorrhizos, Araceae, taro geant, tissus thermogenetiques, thermogenese., Introduction The genus Alocasia (Schott) G. Don is a member of the Araceae family, which consists of about 110 genera with over 2500 species, more than half of which occur [...]