Differential Flood Stress Resistance of Two Tomato Genotypes

Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (L. esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to root-zone flooding, respectively. A comparative study of these accessions was undertaken to examine adaptive responses to inundation. Root and shoot growth of both accessions were inhibited by 120 hr of flooding. Aerobic respiratory capacity of secondary roots of both accessions decreased to a similar extent after 24 hr of inundation. Flooding did not significantly affect anaerobic root respiration rate of either accession. Stomatal conductance decreased after 24 hr of flooding for both accessions, with some recovery by PI 406966 after 168 hr of treatment, coinciding with development of adventitious roots on lower stems. Few adventitious roots formed on flooded PI 128644 plants. Leaf water potential of both accessions initially increased as a result of flooding, but declined to near control level by 120 hr of treatment. Total phenol content of PI 128644 roots decreased with 72 hr of flooding, while that of PI 406966 roots was not significantly affected. Factors underlying the greater resistance of PI 406966 to flooding remain unclear, but may include a lower root respiratory requirement for O2 and greater ability to sequester or eliminate toxic substances during inundation.