Ethylene evolution by rust-infected, detached bean (Phaseolus vulgaris L.) leaves susceptible and hypersensitive to Uromyces phaseoli (Pers.) Wint.

Ethylene production in leaves of susceptible and hypersensitive varieties of beans has been followed after inoculation with Uromyces phaseoli. Four different states of ethylene evolution are distinguishable: (1) 13 h after inoculation and concomitant to the penetration of the fungal mycelium through the stomata, all varieties show an outburst of ethylene with significant differences between the three varieties. (2) After 36 h postinoculation, in all three varieties ethylene evolution is scarcely higher than in noninfected leaves. (3) Starting 59 h after inoculation, only in the hypersensitive variety 765 (which shows the lowest ethylene production after 13 h), a second, very strong ethylene outburst is observed. (4) From 125 h after inoculation, significant ethylene production is not observed in any variety. At this time, characteristic symptoms are expressed in susceptible leaves (differentiation of uredosori) and in the hypersensitive variety 765 (large brown necrotic spots); no macroscopic symptoms are observed in the hypersensitive variety 814, which exhibits the strongest ethylene outburst 13 h after inoculation. The capacity for ethylene formation after mechanical wounding ("point freezing") is almost identical in healthy leaves of all three varieties. This capacity is still preserved after the first ethylene outburst 36 h after infection.