R. Santilocchi

Molecular analysis of the parallel domestication of the common bean (Phaseolus vulgaris) in Mesoamerica and the Andes.

We have studied the nucleotide diversity of common bean, Phaseolus vulgaris, which is characterized by two independent domestications in two geographically distinct areas: Mesoamerica and the Andes. This provides an important model, as domestication can be studied as a replicate experiment. We used nucleotide data from five gene fragments characterized by large introns to analyse 214 accessions (102 wild and 112 domesticated). The wild accessions represent a cross-section of the entire geographical distribution of P. vulgaris. A reduction in genetic diversity in both of these gene pools was found, which was three-fold greater in Mesoamerica compared with the Andes. This appears to be a result of a bottleneck that occurred before domestication in the Andes, which strongly impoverished this wild germplasm, leading to the minor effect of the subsequent domestication bottleneck (i.e. sequential bottleneck). These findings show the importance of considering the evolutionary history of crop species as a major factor that influences their current level and structure of genetic diversity. Furthermore, these data highlight a single domestication event within each gene pool. Although the findings should be interpreted with caution, this evidence indicates the Oaxaca valley in Mesoamerica, and southern Bolivia and northern Argentina in South America, as the origins of common bean domestication.

Effect of rotation, nitrogen fertilization and management of crop residues on some chemical, microbiological and biochemical properties of soil

Abstract A long-term experiment, which started in 1971 near Perugia, central Italy, was performed to investigate the effect of different crop residue management practices and rotation systems on some soil properties. Twenty years after the beginning of the experiment, chemical (organic C, total N, humified organic C, humic and fulvic acids), microbiological and biochemical parameters (microbial biomass, global hydrolase activity, dehydrogenase and catalase activities) were investigated. Two crop residue management practices were used in the experiment, i.e. removal (RCR soils) and burial (BCR soils). These treatments were factorially combined with eight rotation systems, i.e. five maize-wheat rotations of different lengths (M-1W, M-2W, M-3W, M-4W and M-5W) and three continuous wheat systems with different fertilization inputs, from 150 to 250 kg N ha–1. Soil samples were collected in the spring of 1991 for chemical determinations, and in the spring and autumn of 1992, 1993 and 1994, for microbiological and biochemical determinations. All soil chemical, microbiological and biochemical parameters investigated showed significant differences depending on the management of the crop residues. The BCR soils showed more favourable characteristics. In contrast, few significant effects were observed in relation to rotation and N-fertilization treatment. Significant correlations were found between organic-C content and all microbiological and biochemical parameters, as well as between the microbiological and biochemical parameters themselves, indicating that organic-C content plays an important role in determining the level of soil enzyme activity and, consequently, of soil fertility. This experiment showed that burying crop residues in soil can be considered good agronomic practice, which may help limit the gradual depletion of soil organic matter and improve the chemical properties of the soil.

Variazioni del paesaggio agricolo italiano in relazione all'evoluzione delle tecniche agronomiche

Abstract Variation of the Italian agricultural landscape in relation to the evolution of the agronomic techniques.- The agricultural activity and the practices that are connected with it more or less directly, have been transformed during the history of mankind according to the evolution of the various societies and policies. These variations are with no doubt the most “responsible” of the evolution of the agricultural landscape. The agronomic techniques that were used in the ancient agricultural societies were initially rough, the land being used temporarly by nomadic people and then abandoned when fertility or weather were not favourable to crop growth and replaced with new fertile areas. Therefore the impact of ancient agriculture on the landscape was very limited, also because of the low population density. The permanent agriculture developed with the beginning of the great civilisations when the rural environment begun to assume a more stable aspect. During the Reinassance the diversification of agri...