Climbing for nitrogen: symbiotic nitrogen fixation in climbing beans

Research carried out by Lara Ramaekers

Climbing bean varieties are an important component of traditional agriculture in several parts of Latin America, especially in Mexico, Guatemala, Colombia, Ecuador and Peru. Additionally, they have spread to the Great Lakes region of Africa. They are morphologically distinct from bush bean varieties of common beans, being characterized by tall growth, long internodes and climbing ability.
Cultivated climbing beans are found mostly in medium to high altitude (2000 to 2800 m a.s.l.) regions of the Andes and Central America. The International Centre of Tropical Agriculture (CIAT) in Colombia introduced the so-called mid-altitude climbing (MAC) beans to Africa. This has been one of CIAT’s most drastic impact stories, whereby yields of beans were tripled compared to yields of bush beans available at that time.

Common bean is often grown on marginal lands limited in available soil nitrogen (N) and with minimal N-fertilization. Improving the potential of symbiotic nitrogen fixation would reduce N-depletion in such soils (only for crops with a small harvest index), improve grain yield and possibly enhance protein content. The capacity to fix nitrogen is variable among genotypes of common bean, ranging from 4% to 59% of the required nitrogen derived from the atmosphere (Snoeck et al., 2003). In the past, it was shown that climbing common beans are superior to bush beans for nitrogen fixation under different agronomic conditions (Graham and Rosas, 1977; Graham and Temple, 1984; Kipe-Nolt and Giller, 1993). Unravelling the genetic basis and physiological related mechanisms of symbiotic nitrogen fixation (SNF) potential in climbing beans will contribute significantly to improve SNF in bean cultivation.

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