Leaflet abscission and phytoalexin production during the response of two faba bean breeding lines to Botrytis infection

Comparisons were made between two breeding lines of faba bean (designated 224 and 335), following inoculation of leaf material with Botrytis cinerea and the more aggressive B. fabae . Line 335 exhibited greater initial resistance to infection, in terms of retarded lesion development and higher rates of phytoalexin production. However, in whole plant inoculation experiments line 335 abscinded its leaflets more readily after infection. The role of the gaseous plant hormone ethylene in this reaction was analysed. Both lines exhibited a similar abscission response to exogenous ethylene, applied at a concentration of 10 μL L^?1. However, there were significant differences in the ability of the lines to produce ethylene. In response to inoculation with B . fabae , line 335 liberated ethylene at a higher concentration and for a longer period. These results suggest that the differential levels of abscission are a consequence of differences in the biosynthesis of ethylene in the two lines rather than in their responses to ethylene.