EDITORIAL

The reports in this issue of Agronomía Colombiana in the "Plant breeding, genetic resources and molecular biology" section are directly related to the environment in cotton and corn transgenic crops; knowledge of the biodiversity of medicinal and aromatic species as a valuable resource for development of pharmaceuticals, cosmetics, agriculture and food because they possess phytochemical components. Also, the use of molecular biology microsatellite methodologies to identify diversity of genotypes of rubber in clonal gardens and association mapping studies as a tool for identification and localization of quantitative traits in crops are addressed.

In the "Propagation and tissue culture" section, histological and morphological studies were performed with covered passion fruit seeds (Passiflora ligularis Juss.), to determine the value in the differentiation of accessions; from the portfolio of aromatic herbs offered for export in Colombia tarragon was selected (Artemisia dracunculus Linn.), and it was determined that cultures grown with micropropagation are more efficient at growing and using light than crops with traditional propagation. In the conservation of natural habitats of wetlands of the country, a scheme of propagation of the native bamboo (Chusquea tessellata) was developed using basal culm sections and different concentrations of rooting (ANA), this alternative is useful for repopulating areas with species losses due to intensive production practices.

Advances in the area of "Crop physiology" contribute to the development of horticulture in the highland tropics with the use of padded plastic of different colors on the quality of strawberry fruit crops, with red padding improving performance, size and quality of flavor and sweetness of the fruit. While in vegetables, using biofertilizers is a viable alternative to improve the profitability of crops, particularly in lettuce and cabbage with an increase in the diameter of the head and yield due to the mineral content and microbial action of the biofertilizers. Another alternative for improving crop productivity is the use of thermal screens in tomato crops under plastic cover, which achieved nighttime heat retention.

"Crop protection" reviews the Radopholus similis (Cobb) Thorne nematode pathogen of Musa, analyzing the intraspecific and pathogenic variability and control measures. In addition, "Physiology and postharvest technology" shows the effects of sucrose as a stabilizer in arazá pulp (Eugenia stipitata Mc. Vaugth) before a freezing and slow thawing. Importantly, "Soil, fertility and water management" presents the evaluation the effect of foliar and soil applications of manganese on the yield of potato crops. Moreover, in the coffee ecoregion, soil microbial communities responsible for the cycling of nitrogen were studied, which are essential for maintaining and improving soil fertility, productivity and functionality in natural and agricultural ecosystems. Also, under greenhouse conditions, the potential of the association and biological nitrogen fixation of strains of Rhizobium sp. isolated from nodules of the tree legume "matarratón" (Gliricidia sepium) and the commercial strain Rhizobiol® was quantified. The results of this research allow the optimal use of native strains of Rhizobium in growth and fixation of N used as biofertilizer in the cultivation of matarratón for feeding cattle in the Colombian Caribbean region; presenting an overview of the relationship between mineral nutrition and disease development and discussing the beneficial effects of silicon in crops, its mobility in soil, assimilation process and influence on resistance to diseases caused by fungi.

Finally, this issue presents two scientific reports with significant contributions to plant propagation and entomology: the first report is about the in vitro formation of multiple shoots induced in nodal sections of adult plants of "palo gordo" Vasconcellea chilensis, the second report records the presence of Diaphorina citri Kuwayama (Hemiptera: Psyllidae) and the parasitoid Tamarixia radiata (Waterson) in citrus crops in Cundinamarca, Colombia.

It is hoped that the contents of this journal will lend considerable support to the scientific and academic communities and the production sector. The collaboration of the present issue has been guided by the contributions of the guest editors during the year 2011 on their respective disciplines: Luis Ernesto Rodriguez, Plant breeding, genetic resources and molecular biology; Stanislav Magnitskiy, Propagation and tissue culture; Gerhard Fischer, Crop physiology and Post-harvest technology; Liliana Hoyos, Crop protection; Alia Rodriguez, Soils, plant nutrition and water management and Fabio Pachon, Economy and rural development. Thanks to the editors, translators and designers for the work done to produce this issue.

Gustavo A. Ligarreto M.

Editor