Reza Partiya - Former master student of horticulture, Department of Horticultural Science, University of Guilan, Rasht, Iran.
Reza Fotouhi Ghazvini - Department of Horticultural Science, Faculty of Agricultural Science, University of Guilan, Rasht, Iran.
Reza Fifaei - Faculty of Citrus and Subtropical Fruits Research Center, Ramsar, Iran.
Mahmood Ghasemnezhad - Department of Horticultural Science, Faculty of Agricultural Science, University of Guilan, Rasht, Iran.

Hypoxia is a potential threat to various horticultural cropsin lands prone to flooding. Citrus is mostly known as a sub-tropical crop that is often exposed to environmental stresses. In order to evaluate response of six different citrus genotypes, including sour orange, rough lemon, Trifoliate orange, Troyer citrange and two local genotypes labeled; CRC1 and CRC2 to flooding conditions, an experiment was carried out in factorial experiment based on a completely randomized design with two treatments including flooded and control plants and three replications. Flooding stress significantly decreased leaf chlorophyll content, and plant total fresh and dry weights (P≤ 0.05). Flooding caused a significant increase in foliar concentration of proline in CRC1 and CRC2 (P≤ 0.05). Guaiacol peroxidase activity was significantly increased in Trifoliate orange. CRC2 and sour orange showed a significant increase in superoxide dismutase activity (P≤ 0.05). The longest survival period in continuous flooding condition was observed in Troyer citrange and Trifoliate orange (more than 60 days); while sour orange was the most sensitive genotype (less than 30 days). The best thriving genotype at the end of recovery period was Troyer citrange, while sour orange showed the least ability to re-establish. The results suggest that among the studied genotypes, Troyer citrange and Trifoliate orange are able to resist for longer periods of flooding exposure. Troyer citrange had the highest capacity to re-establish after being flooded to their critical surviving point. Furthermore, CRC2 tolerated anoxic condition and recovered more successfully than the other sensitive genotypes.

anoxia, biochemical traits, guaiacol peroxidase, Superoxide dismutase, water-logging