Effect of Flooding Duration and Portion of the Roots Submerged on Physiology, Growth, and Survival of Papaya (Carica papaya L.)

Flooding for as little as 1 day has been shown to cause a dramatic decline in leaf gas exchange of potted papaya (Carica papaya L.) plants. However, the ability of papaya to recover from different durations of short-term flooding has not been reported. Therefore, a study was conducted to determine the effects of flooding duration on physiology, survival and recovery of 10-month-old 'Red Lady' papaya plants. During a 7-day period, plants in 11.3-L containers in Pro-Mix^® potting medium were subjected to one of 6 different flooding durations: 0, 1, 2, 3, 4, or 5 days of root submersion in a completely randomized design with 6 single-plant replications per treatment. The study was conducted in a greenhouse where the mean air temperature was 26.1^oC (range19.4 to 33.4^oC).  Plants were unflooded immediately after treatment. Soil redox potential in flooded pots was measured daily; these measurements indicated that the soil became anaerobic after 24 hours of flooding. Leaf gas exchange [net CO₂ assimilation (A), transpiration (E), and stomatal conductance (gs)], the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), and leaf chlorophyll index (determined with a SPAD meter) were determined daily for 10 days for all plants. These measurements began 1 day before plants were flooded, continued until 1 day after plants in the 5-day flooding treatment were unflooded, and concluded 4 days later. At the end of the study period, plant survival was recorded. All plants flooded for 0 or 1 day survived. After 1 day of flooding, A, E, gs, Fv/Fm and leaf chlorophyll index of flooded plants began to decline compared to the non-flooded controls, but values for these variables recovered to those of the non-flooded controls 9 days after unflooding. For plants flooded for 2 or more days, A, E, gs, Fv/Fm and leaf chlorophyll index continued to decline during flooding. Nearly all plants flooded for 2 or more days permanently wilted by day 11. In a subsequent experiment where plants were flooded by inundating 100%, 75%, 50% or 0% (control) of the root system for 3 days, only plants with the root system totally submerged did not recover after unflooding. The data indicate that, under the conditions of this study, papaya plants are very intolerant of total root submersion, but can tolerate up to 75% of the root system continuously submerged for at least 3 days.