Analysis of Genetic and Nutritional Diversity Among Selected Accessions of Dry Beans and Nuña Beans (Phaseolus vulgaris L.) from the USDA-ARS National Plant Germplasm System

Beans (Phaseolus spp.) are one of the most economically and nutritionally important crops world-wide, with a value of over $17 billion harvested annually.  They are one of the most ancient crops of the New World, having been cultivated for thousands of years. They are an environmentally diverse crop, growing in temperate and sub-tropical environments from sea level to more than 3000 m above sea level, and are consumed as either fresh pods or as a dry bean, making them an ideal nutritional food legume in areas where storage without refrigeration is necessary. They are the most important legume for direct human consumption with more than 23 million metric tons produced in 2013. Of the more than 20,000 Phaseolus accessions held at the Western Regional Plant Introduction Station (WRPIS), the most abundant species by far is P. vulgaris L. with over 17,000 accessions. Of these, 177 are described as “snap” varieties, grown for harvest as fresh vegetable, while the remainder are described as “dry beans.” Among these, 90 are classified as nuña beans, or the Peruvian “popping” bean. These beans have been selected and raised among the Andean natives in the high mountains for millennia and have the unique characteristic of bursting when subjected to heat, making them a high protein food in conditions where boiling would consume scarce fuel. This property also makes these beans a potential nutritious snack food, both in and of themselves, as well as in the form of an extruded product. We analyzed the molecular diversity of 35 nuña and 8 common dry bean accessions and compared a range of nutritional factors, including protein, starch, sugars, phytate, and antioxidant activity. Genetic analysis using AFLP markers showed nuñas were distinct from the common dry beans analyzed, and there were two distinct groups within the nuñas. There was a similar wide range of nutritional characteristics within both the common dry beans and the nuñas. Values for nuñas and common bean respectively were: protein (18% to 25% and 17% to 27%), extractable polyphenols (50–350 and 50–450 mg/100 g GAE), non-extractable polyphenols (50–220 and 70–175 mg/100 g  GAE), phytate (0.45% to 1.2% and 0.6% to 1.0%), and total antioxidant activity (8–52 and 7–48 mg TE). There is enough genetic variation in both nuña and common dry beans to breed popping beans adapted to a temperate, long-day environment and to develop a highly nutritious snack food for America.