Metabolic engineering of cassava to improve carotenoids.

Cassava is a staple food used in many countries around the world, despite deficiencies in micronutrients such as provitamin A carotenoids. Unfortunately, improvement of the cassava nutritional content by use of conventional breeding is slow and difficult. Therefore, there is an urgent need to develop and standardize protocols using biotechnological tools to improve cassava. The Alliance of Biodiversity International and the International Center for Tropical Agriculture (CIAT) have worked on cassava genetic transformation over the last 30 years. Here, we describe, step by step, the procedures used for genetic transformation of cassava variety TMS60444, to improve carotenoids and other traits. This protocol includes stock setup, reagents, media preparation, materials, and equipment, for the genetic transformation of embryogenic tissues. The main expected output in publishing this protocol is to provide the basis for a reproducible and reliable method to genetically modify and/or gene edit Latin American and Asian cassava varieties.

Forests, fields, and the edge of sustainability at the ancient Maya city of Tikal.

Tikal has long been viewed as one of the leading polities of the ancient Maya realm, yet how the city was able to maintain its substantial population in the midst of a tropical forest environment has been a topic of unresolved debate among researchers for decades. We present ecological, paleoethnobotanical, hydraulic, remote sensing, edaphic, and isotopic evidence that reveals how the Late Classic Maya at Tikal practiced intensive forms of agriculture (including irrigation, terrace construction, arboriculture, household gardens, and short fallow swidden) coupled with carefully controlled agroforestry and a complex system of water retention and redistribution. Empirical evidence is presented to demonstrate that this assiduously managed anthropogenic ecosystem of the Classic period Maya was a landscape optimized in a way that provided sustenance to a relatively large population in a preindustrial, low-density urban community. This landscape productivity optimization, however, came with a heavy cost of reduced environmental resiliency and a complete reliance on consistent annual rainfall. Recent speleothem data collected from regional caves showed that persistent episodes of unusually low rainfall were prevalent in the mid-9th century A.D., a time period that coincides strikingly with the abandonment of Tikal and the erection of its last dated monument in A.D. 869. The intensified resource management strategy used at Tikal-already operating at the landscape's carrying capacity-ceased to provide adequate food, fuel, and drinking water for the Late Classic populace in the face of extended periods of drought. As a result, social disorder and abandonment ensued.

Variabilidad morfológica y evaluación agronómica de maukas Mirabilis expansa (Ruiz & Pav.) Standl. del norte peruano

Se estudiaron 40 entradas de mauka, chago o miso, Mirabilis expansa (Nyctaginaceae), para determinar la variabilidad morfológica, la distribución geográfica y el comportamiento agronómico del germoplasma, colectado principalmente en el norte peruano (entre los 2300 y 3400 m de altitud) y mantenido en la Universidad Nacional de Cajamarca (7°2945"S, 78°1012"W, altitud 2670 m, 14 °C de temperatura diaria y 670 mm de lluvia anual). Se usaron 17 descriptores cualitativos de alta heredabilidad y se evaluaron siete componentes de rendimiento, durante tres campañas agrícolas. El fenograma generó cinco grupos o morfotipos (coeficiente de disimilitud de 0,0). Los morfotipos I, III y V se concentran en las provincias de Hualgayoc, San Miguel, Chota y Cajamarca. El morfotipo II probablemente es endémico de la Región La Libertad. La única entrada del sur del Perú (Puno), constituyó un morfotipo independiente (IV). Seis entradas: 15, 17, 24, 25, 28 (morfotipo I) y 16 (morfotipo III), alcanzaron los más altos rendimientos (46 - 76 t. ha-1).

Forty accessions of mauka, chago or miso, Mirabilis expansa (Nyctaginaceae) were studied, in order to determine the morphological variability, geographic distribution and agronomic performance of germplasm collected mainly in northern Peru (between 2300 to 3400 m) and maintained at Universidad Nacional de Cajamarca (7°2945"S, 78°1012"W, 2670 m, 14 °C of daily temperature and 670 mm of rain annually). Seventeen qualitative descriptors of high heritability were used and seven yield components for three crop years were also evaluated. The phenogram generated five groups or morphotypes (dissimilarity coefficient of 0.0), which implies 87.5% of duplicates in the collection. The morphotypes I, III and V are concentrated in the provinces of Hualgayoc, San Miguel, Chota and Cajamarca. The morphotype II is probably endemic to the La Libertad region. The only accession from the south of Peru (Puno) was an independent morphotype (IV). Six accessions: 15, 17, 24, 25, 28 (morphotype I) nad 16 (morphotype III) reached the highest yields (46 - 76 t. ha-1).