The Cassava Genome: Current Progress, Future Directions

The starchy swollen roots of cassava provide an essential food source for nearly a billion people, as well as possibilities for bioenergy, yet improvements to nutritional content and resistance to threatening diseases are currently impeded. A 454-based whole genome shotgun sequence has been assembled, which covers 69% of the predicted genome size and 96% of protein-coding gene space, with genome finishing underway. The predicted 30,666 genes and 3,485 alternate splice forms are supported by 1.4 M expressed sequence tags (ESTs). Maps based on simple sequence repeat (SSR)-, and EST-derived single nucleotide polymorphisms (SNPs) already exist. Thanks to the genome sequence, a high-density linkage map is currently being developed from a cross between two diverse cassava cultivars: one susceptible to cassava brown streak disease; the other resistant. An efficient genotyping-by-sequencing (GBS) approach is being developed to catalog SNPs both within the mapping population and among diverse African farmer-preferred varieties of cassava. These resources will accelerate marker-assisted breeding programs, allowing improvements in disease-resistance and nutrition, and will help us understand the genetic basis for disease resistance

High genetic diversity among and within bitter manioc varieties cultivated in different soil types in Central Amazonia

Although manioc is well adapted to nutrient-poor Oxisols of Amazonia, ethnobotanical observations show that bitter manioc is also frequently cultivated in the highly fertile soils of the floodplains and Amazonian dark earths (ADE) along the middle Madeira River. Because different sets of varieties are grown in each soil type, and there are agronomic similarities between ADE and floodplain varieties, it was hypothesized that varieties grown in ADE and floodplain were more closely related to each other than either is to varieties grown in Oxisols. We tested this hypothesis evaluating the intra-varietal genetic diversity and the genetic relationships among manioc varieties commonly cultivated in Oxisols, ADE and floodplain soils. Genetic results did not agree with ethnobotanical expectation, since the relationships between varieties were variable and most individuals of varieties with the same vernacular name, but grown in ADE and floodplain, were distinct. Although the same vernacular name could not always be associated with genetic similarities, there is still a great amount of variation among the varieties. Many ecological and genetic processes may explain the high genetic diversity and differentiation found for bitter manioc varieties, but all contribute to the maintenance and amplification of genetic diversity within the manioc in Central Amazonia. © 2017, Sociedade Brasileira de Genética

Grain yield potential and associated traits in maize (Zea mays L.) varieties in the forest zone of Nigeria

Grain yield and 15 associated traits were studied in 10 maize varieties (DMR-L-SR-W, SUWAN 1, EV 9043-DMR, TZPB-SR, TZSR-Y, 8321-18, 8535-23, 8644-27, 8644-31 and 8805-4) from 1995 to 1997 at Ibadan, Nigeria. Varietal differences and the relationship between grain yield and associated traits were determined. Variety 8321-18 with the highest grain yield had a 27 per cent yield advantage over the lowest-yielding variety TZSR-Y. Crop growth rates at vegetative and reproductive stages were highest in TZSR-Y whilst its harvest index was lowest when compared to other varieties. 8321-18 had longer ear and kernel growth duration than most varieties evaluated, and its harvest index was higher than TZSR-Y. Kernels per plant were more in 8321-18, 8805-4, and EV 9043-DMR than in the other varieties. Positive correlations were found between grain yield and Kernels per ear (r=0.70***), kernel rows (r=0.30***) and kernels per row (r=0.63***), harvest index (r= 0.53**), total dry matter (r=0.50***), ear growth duration (r=0.36***), kernel growth duration (r=0.30***), and crop growth rate at reproductive stage (r=0.17**), except days to 50 per silking (r=0.19*). To improve grain yield, the biological traits that are significantly associated with grain yield could be incorporated into a model for developing improved maize genotypes for the forest zone in Nigeria. Potentialité de rendement de grain et les traits associés dans les variétés de maïs (Zea mays L.) dans la zone forestière du Nigiria Résumé Le rendement de grain et 15 traits associés étaient étudiés en 10 variétés de maïs (DMR-L-SR-W, SUWAN 1, EV 9043-DMR, TZPB-SR, TZSR-Y, 8321-18, 8535-23, 8644-27, 8644-31 et 8805-4) de 1995 à 1997 à Ibadan, au Nigéria. Les différences variétales et le rapport entre le rendement de grain et les traits associés étaient déterminés. La variété 8321-18 avec le rendement de grain le plus élevé avait un avantage de rendement de 27 pour cent par rapport à la variété TZSR-Y ayant de rendement le plus bas. Les proportions de la croissance de culture aux stades végétatifs et reproductifs étaient les plus élevées en TZSR-Y alors que son indice de moisson était le plus bas lorsqu'il est comparé aux autres variétés. 8321-18 avait une durée de croissance d'épi et de grain plus long que les autres variétés évaluées et son indice de moisson était plus élevé que celui de TZSR-Y. Les grains par plante étaient plus nombreux en 8321-18, 8805-4 et EV 9043-DMR que dans les autres variétés. Des corrélations positives étaient découvertes entre le rendement de grain et les grains par épi (r = 0.70 ***), les rayons de grain (r = 0.30 ***) et les grains par rayon (r = 0.63 ***), indice de moisson (r = 0.53 **), le total de matière sèche (r = 0.50 ***), la durée de croissance d' épi (r = 0.36 ***), la durée de croissance de grain (r = 0.30 ***), la proportion de croissance au stade reproductif (r = 0. 17 **) excepté les jour à 50 pour cent de l'apparition des soies (r = -0.19 *). Pour améliorer le rendement de grain les traits biologiques qui sont considérablement associés au rendement de grain pourraient être incorporé dans un modèle pour le développement des génotypes de maïs amélioré pour la zone forestière au Nigéria. Ghana Jnl agric. Sci. Vol.33(2) 2000: 191-19