INTRODUCTION. Papaya is often grown in areas that are prone to flooding from poor soil drainage or as a consequence of hurricanes or other storms.
Effect of flooding duration and percentage of roots submerged on physiology, growth, survival and recovery of papaya (Carica papaya L.) Gustavo Rodríguez1, Bruce Schaffer2, Ana I. Vargas2, Carmen Basso1 1Faculty of Agriculture, Central University of Venezuela, Maracay, Venezuela 2Tropical Research and Education Center, University of Florida, Homestead, Florida, USA
INTRODUCTION Papaya is often grown in areas that are prone to flooding from poor soil drainage or as a consequence of hurricanes or other storms. These flooding events are expected to increase worldwide as a result of climate change (IPCC, 2014). In the agricultural area of south Florida, a high watertable coupled with heavy rains can lead to water remaining above the soil surface for several days (Fig. 1a). Additionally, plans to elevate the watertable as part of the Everglades Restoration Plan will increase the potential for partial or total root submergence of crops grown in the area (Schaffer, 1998). Papaya is very sensitive to flooding stress (Fig. 1b; Marler et al., 1994). Flooding for only one day caused a decline in leaf gas exchange in potted papaya (Marler, 1995). However, the ability of plants to recover from different short-term flooding durations or the percentage of root submergence necessary to cause flooding damage to papaya has not been reported.
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The objectives of this study were to: 1) further elucidate the effects of short-term flooding duration (days) on physiology, survival, and recovery of papaya plants; and 2) test the effects of differing percentages of root submergence on papaya physiology, survival and recovery.
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Figure 1. Flooded agricultural area (a) and papaya plant (b) in south Florida.
MATERIALS AND METHODS
10-month-old 'Red Lady' papaya plants in 11.3-L containers in Pro-Mix® potting medium were subjected to 0, 1, 2, 3, 4, or 5 days of total root submergence. The study was conducted in a greenhouse (mean air temperature 26.1oC) with 6 single plant replications per treatment in a completely randomized design (Fig. 2). Soil redox potential of flooded plants was determined during the flooding period. Net CO2 assimilation (A), transpiration (E), 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 all plants over a 10-day period. Measurements began 1 day before plants were flooded and concluded 4 days after plants in the longest flooding treatment were unflooded. At the end of the study period, plant survival was recorded. In a subsequent experiment in the same greenhouse with the same number of replications per treatment, 10-month-old ‘Red Lady’ papaya plants were flooded by submerging 0%, 50%, 75% or 100% of the root system in water for 3 days. Data were collected for the same variables as described for the first experiment. Figure 2. ‘Red Lady’ papaya plants in flooded and non-flooded treatments in the greenhouse.
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In the second experiment, Fv/Fm, leaf chlorophyll index (Fig. 5), A, E, and gs (Fig. 6) were significantly lower for plants with 100% of the roots submerged compared to plants with 0, 50, or 75% of the roots submerged. Only plants with 100% of the roots submerged did not survive 3 days of flooding.
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Figure 3. Effects of flooding duration on net CO2 assimilation (A), transpiration (E), and stomatal conductance (gs).
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Soil redox potential measurements indicated that the soil became anaerobic after 1 day of flooding (data not shown). After 1 day of flooding, A, E and gs, (Fig. 3) of flooded plants declined compared to the non-flooded controls. By the end of the experiment, leaf gas exchange variables were significantly higher for plants flooded for 0 or 1 day compared to all of the other treatments. For plants flooded for 2 or more days, leaf gas exchange variables continued to decline until the end of the study period. By day 6, Fv/Fm and leaf chlorophyll index (Fig. 4) were lower for plants flooded for 2 or more days compared to plants flooded for 0 or 1 day. All plants flooded for 0 or 1 day survived, whereas plants flooded for more than one day did not survive.
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RESULTS
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Figure 4. Effects of flooding duration on the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and leaf chlorophyll index.
Figure 5. Effects of percentage of root submergence on the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and leaf chlorophyll index.
Figure 6. Effects of percentage of root submergence on net CO2 assimilation (A), transpiration (E), and stomatal conductance (gs).
REFERENCES IPCC. 2014, IPPC (Intergovernmental Panel on Climate Change). Climate Change 2014: Impacts, Adaptation, and Vulnerability. http://www.ipcc.ch/report/ar5/wg2/. Marler, T.E., et al. 1994. Miscellaneous tropical fruit. In: Handbook of Environmental Physiology of Fruit Crops, Vol. 2, Subtropical and Tropical Crops. B. Schaffer and P.C. Andersen (eds.). CRC Press, Boca Raton, FL, pp. 199-224. Marler, T.E. 1995. Leaf gas exchange and ion content of papaya plants simultaneously exposed to salinity and flooding. HortScience 30:780 (abstract). Schaffer, B. 1998. Flooding responses and water-use efficiency of subtropical and tropical fruit trees in an environmentally-sensitive wetland. Annals of Botany 81:475-481.
