Botany and Genetics of New Caledonian Wild Taro, Colocasia esculenta

Taro, Colocasia esculenta (L.) Schott, is considered to be an introduced crop in New Caledonia and has been cultivated since its introduction by Melanesian farmers. Wild germplasm exists on the main (continental) island and is represented by three easily distinguished morphotypes: a morphotype with purple leaves, another with green leaves, and a third with green leaves and a purple vein junction on the lamina. All three morphotypes are diploids (2n = 2x = 28) and have well-established wild populations in many valleys and gulches of the main island. The morphotype with purple leaves has all typical traits of a wild genotype (inedible corms; long, thin stolons); the other two produce edible corms. The purple and the green morphotypes flower and produce fertile pollen. The spathes of the green morphotype can be more than 40 cm long and the spadix is characterized by an extremely long appendix atypical for Pacific taros. Isozyme analysis conducted using four enzyme systems (EST, PGM, PGI, SkDH) indicated that New Caledonian wild taros differ from most widely grown local cultivars and Pacific cultivated and wild genotypes. Evidence presented in this study suggests that C. esculenta is an endemic species to New Caledonia. Cultivars were probably introduced as clones from what is now Vanuatu by early Melanesian migrants and were not domesticated locally from existing wild forms, which appear to be genetically distant from other Melanesian wild taros

Effect of Alomae-Bobone Virus Complex on Young Taro Seedlings and Other Aroid Species in Controlled Conditions

The effect of Alomae-Bobone Virus Complex (ABVC), the lethal disease of taro Colocasia esculenta in the Solomon Islands, on young taro seedlings and on other aroid species has been studied. Young taro seedlings are very sensitive to the disease. The symptoms of the disease are not uniform. Other aroid species can also be affected by ABVC in controlled conditions

Genetic Resistance to Alomae-Bobone Virus Complex, the Lethal Disease of Taro (Colocasia Esculenta (L.) Schott)

Alomae-Bobone Virus Complex (ABVC) ,remains the most destructive and the most serious disease of taro (Colocasia esculenta (L.) Schott) in the Solomon Islands, and its spread could be a major threat to taro cultivation in the South Pacific region, especially for countries where taro is a major export crop. To create resistant varieties, a recurrent selection method was chosen and 350 genetic recombinations were performed. The offspring generation was tested for resistance. The performance and reaction of the genotypes to the lethal viral disease was observed during a period covering ten months. The genotypes showed great differences in resistance/susceptibility. Plants with higher levels of resistance were selected for further recombinations. The selected materials (genotypes with higher levels of field resistance) were predominantly those where one of the grandparents was wild taro from areas affected by ABVC

Cleavage of a model DNA replication fork by a methyl-specific endonuclease

Epigenetic DNA methylation is involved in many biological processes. An epigenetic status can be altered by gain or loss of a DNA methyltransferase gene or its activity. Repair of DNA damage can also remove DNA methylation. In response to such alterations, DNA endonucleases that sense DNA methylation can act and may cause cell death. Here, we explored the possibility that McrBC, a methylation-dependent DNase of Escherichia coli, cleaves DNA at a replication fork. First, we found that in vivo restriction by McrBC of bacteriophage carrying a foreign DNA methyltransferase gene is increased in the absence of homologous recombination. This suggests that some cleavage events are repaired by recombination and must take place during or after replication. Next, we demonstrated that the enzyme can cleave a model DNA replication fork in vitro. Cleavage of a fork required methylation on both arms and removed one, the other or both of the arms. Most cleavage events removed the methylated sites from the fork. This result suggests that acquisition of even rarely occurring modification patterns will be recognized and rejected efficiently by modification-dependent restriction systems that recognize two sites. This process might serve to maintain an epigenetic status along the genome through programmed cell death

The genetics and breeding of taro

Le taro Colocasia esculenta (L.) Schott est une plante amylacée ancienne et importante, consommée par plus de 400 millions de personnes. Il est cultivé dans des environnements très diversifiés pour son corme riche en amidon, pour ses pétioles et ses feuilles consommées en épinards et parfois comme plante ornementale. En raison de leur multiplication végétative exclusive, les cultivars ne peuvent s'adapter aux rapides changements environnementaux. De nos jours, et du fait de l'accroissement des échanges, de nouveaux pathogènes sont introduits dans les systèmes de culture traditionnels. C'est le cas de Phytophthora colocasiae responsable du flétrissement, qui tend à se développer inexorablement vers de nouvelles zones. L'intensification des cultures s'accompagne d'une amélioration génétique et donc de la caractérisation des ressources existantes. Bien que le taro soit multiplié par voie asexuée, la variabilité morphoagronomique des cultivars est remarquable. Elle est actuellement exploitée par des programmes nationaux qu'il convient d'encourager. Cet ouvrage tente de synthétiser les informations disponibles sur Colocasia esculenta et les espèces apparentées. Il traite de la taxonomie, de la botanique, de l'origine et de la distribution des ressources génétiques ainsi que de l'amélioration proprement dite. Il aborde essentiellement les aspects pratiques de la caractérisation et de l'amélioration génétique et s'appuie sur les données scientifiques les plus récentes ; l'objectif étant de revitaliser la production, non seulement du taro, mais aussi des espèces apparentées. (Résumé d'auteur