Assessing Flood Tolerance Potential of Papaya Germplasm at the Juvenile Stage

Aims: To assess flood tolerance potential of papaya germplasm and determine physiological basis of observed tolerance. Study Design: Both Experiment 1 and 2 were in RCBD with 2 and 3 treatments respectively. Place and Duration of Study: Experiments were conducted in a screen-house at the Kwadaso Station of Crops Research Institute, Ghana between February and September 2014. Methodology: Six weeks old seedlings of 30 papaya accessions were subjected to 90% partial flooding (F90) by standing planting bags with seedlings in 15 L bucket filled with water up to 90% of height of soil level in bags. Control (non-stressed: NS) plants were watered regularly for 1 week. Post flooding recovery of seedlings was monitored for 1 week. In Experiment 2, seedlings of 6 papaya accessions were subjected to 100% flooding (F100) or 50% partial flooding (F50) for 5 weeks, and a post flood recovery period of 6 weeks. Plant height, girth and biomass were measured together with leaf SPAD chlorophyll content, chlorophyll fluorescence, RWC and senescence. Results: None of the 30 papaya accessions had high flood tolerance potential, with 60% of accessions studied having low flood tolerance. F90 plants had reduced height and girth relative to control (p<.001). Leaf senescence was high in F90 plants (p<.001). All six accessions used in Experiment 2 could not withstand 100% flooding longer than 3 days. F50 treatment increased lateral root biomass (p<.001), although controls had higher tap root (p<.001), total root (p=.02) and total plant biomass (p=.002) than F50 plants. Leaf RWC (p=.89), SPAD chlorophyll content (p=.05) and chlorophyll fluorescence (p=.24) were not negatively affected by F50 treatment. Conclusion: None of the papaya accessions studied was able to withstand complete flooding. However, most could tolerate partial flooding of roots for 5 weeks and resume normal growth after release from flood stress