Impact of the rootstock genotype on the performance of grafted common bean (Phaseolus vulgaris L.) cultivars

Grafting is an excellent tool to investigate shoot/root interactions involved in root nodulation by rhizobia and biological nitrogen fixation (BNF) in legumes of high economic and nutritional importance, such as common bean (Phaseolus vulgaris L.). Considering this, three landraces and one commercial cultivar of common bean were grafted onto eight different legume genotypes to identify possible rootstock x scion combinations that increase yield, and to study the impact of the root genotype on nitrogen fixation. The genotypes were three Greek landraces of Phaseolus vulgaris L. (namely 'Chandres Therines', 'Pyrgetos' and 'Tsaoulia'), and one commercial cultivar (cv. 'Helda'). These were grafted onto six different Greek landraces of Phaseolus vulgaris L., particularly 'Chandres', 'Papouda', 'Pastalia', 'Vanilla', 'Zargana Chryssoupolis' and 'Zargana Kavalas', one Phaseolus cocci-neus L. landrace originating from the Greek province Feneos, and one cowpea (Vigna unguiculata (L.) Walp) landrace originating from Arta, Greece. Grafting success was mainly determined by the rootstock genotype. The best rootstock/scion combination, attaining 100% success, was 'Tsaoulia' grafted onto 'Zargana Kavalas'. Moreover, the use of P. coccineus L. as rootstock enhanced appreciably the fresh pod yield by increasing the number of fresh pods. In contrast, cowpea was an incompatible rootstock for grafting P. vulgaris, as all plants grafted on it failed to survive. Most grafting combinations reduced the% of N derived from the atmosphere (% Ndfa) through BNF. Despite the decreased%Ndfa, some rootstocks increased the biologically fixed N per culti-vated area unit due to higher total biomass production, which indicates involvement of mechanisms causing rootstock/scion interactions.