Tolerância cruzada induzida por choque térmico na germinação de sementes de feijão sob estresse hídrico

Abstract

Stress could be defined as an external factor that could cause some disadvantageous influence over the plant. In tropical regions, crops suffer non biotic stress especially due to water deficit and high temperature. Cross tolerance allow the plants to be acclimated after a short exposition to a specific stress. The objective of this work was to verify the water stress tolerance during bean seed germination influenced by thermal shock induced cross tolerance. Seed of common bean cv IAPAR 81 were submitted to the imbibition in substrate paper with pure water at 20ºC for 24h. One third of the seeds were maintained in that temperature. One third were submitted to cold shock for 24h at 7ºC in the first assay and 13ºC in the second and the final part were submitted to heat shock for 24h at 38ºC and 33ºC as used for the cold shocks; in all experiments there was no change of substrate. Seeds submitted or not to shock were transferred to paper substrate simulating hydric potential of 0; -0.6; -0,9 and -1.2MPa, in the first experiment and 0;-0.3; -0.6; -0.9 and -1.2MPa in the second experiment using mannitol at: 0; 22.29; 44.58; 66.87 e 89.17 g.L-1. Treatments were evaluated by germination percentage, abnormal plants and dead seeds. Seedling evaluation was done with shoot, root and total dry matter and by relation of root/shoot. The best development, in water restriction in the early germination, was of that seeds that passed through a 7ºC or 33ºC during 24h, what allowed the affirmation that induced cross tolerance occurred and that could be induced in the beginning of the imbibition in bean seeds.