An overview of genetic diversity within Italian common bean germplasm

Historical documents fixed the first half of XVI century as the period of common bean introduction in Italy. Adaptation to different soil type, climatic conditions and peculiar agrotechniques, in addition to geographic isolation of growing areas and selective pressure operated by farmers, provided the prerequisites for the selection toward a myriad of landraces. This process resulted in the selection of a different group of landraces in each Italian region. Nowadays, common bean is widely cultivated in intensive agricultural systems and, in this frame, the new cultivars displaced completely the local varieties. Conversely, in the areas where traditional or low input agricultural systems are present, farmers still grow autochthonous varieties. The analysis of the most recent scientific literature show that on farm survival of common bean landraces is a relevant phenomenon in Italy. The knowledge about the levels of diversity present in this germplasm is an important goal in planning the most adequate strategies for ex situ conservation, as well as for the management and utilisation of collections. In the lack of specific financial resources, any systematic cataloguing of Italian common bean landraces has been attempted. This contribution resumes the present status of knowledge on the diversity within common bean germplsm as assessed by phenotypic, biochemical and molecular markers. Phenotypic variation - A considerable variation has been described for seed morphological traits. In regard to the plant habit climbing types are widely preponderant. Similarly, large seeded types are predominant in consequence of their high appreciation by consumers. Biochemical markers - The prevalence of the Andean gene pool within the Italian germplasm has been evidenced by several studies. The highest polymorphism of phaseolin pattern has been detected in populations from Central Italy. The existence of non small-seeded populations showing S phaseolin type has been evidenced in some authors. Molecular markers - Several PCR-based molecular markers can be used for the assessment of genetic diversity. Studies based on SSR markers have confirmed the predominance of Andean gene pool in the Italian peninsula. Moreover, it has been evidenced that the level of heterogeneity within the landraces is variable and generally strictly related to the history of each locally variety. Seed quality - Still today, the nutritional and nutraceutical value of Italian common bean landraces has been the object of a low number of studies. However, there are reasonable evidences that some of them have compositional traits comparable to those of modern cultivars. Results relative to the assessment of genetic variation at regional level are presented as case studies.