The germination of milkweedvine (Morrenia odorata Lindl. ♯3 MONOD) seed at 20 or 25 C was unaffected by a 12-h photoperiod. The 12-h photoperiod, however, decreased germination by 50% at 15 C. No germination occurred at 35 C regardless of photoperiod. By alternating 35 C for 12 h with 20 C for 12 h, the germination percentage was 57%. Seedling growth was maximum at alternating temperatures of 30/20 C. Optimum pH for germination and seedling growth was 7 and germination did not occur at pH levels below 6. Seed germination declined steadily at osmotic stress below −0.12 MPa; no germination occurred at −0.5 MPa. Seedling growth was not influenced by osmotic stress down to −0.18 MPa. Germination percentages of seeds kept under aerated water and nonaerated water were similar, but the seedling growth was greater in aerated water. Seedling emergence was maximum from depths of 0.5 to 2.5 cm, but no seedling emerged from 0 or 10 cm. Planting depth was negatively correlated (r = −0.7) with shoot growth but positively correlated (r = +0.98) to root growth.

Laboratory studies were conducted to determine the effect of various factors on germination of tropical soda apple. Tropical soda apple seed were found to be moderately photoblastic with 30% germination occurring in the dark. Germination increased in response to green (545 nm) and red light (650 nm) to 75 and 66%, respectively, indicating phytochrome regulation. No germination occurred in response to blue (450 nm) and far-red light (750 nm). Germination increased from 4 to 64% between 10 to 30 C, but no germination was found at 5 and 40 C. Maximum germination occurred at 30 C. A second degree polynomial (Y= −48.7 + 7.9X – 0.2X2, R2 = 0.76) best fit the data. Seed germinated over a broad range of pH (2 to 14) with the highest germination occurring at pH 8 and no germination occurring at pH 2 and 14 (Y = −63.3 + 30.5X – 1.9X2, R2 = 0.95). Seed germination declined as osmotic potential increased from 0 to −1.0 MPa (Y = 76.7 – 12.9X + 5.2X2, R2 = 0.87). Seedling emergence was maximum from depth of 3 to 6 cm, but no seedling emergence occurred when seed were planted below 12 cm (Y = 10.2 + 17.8X – 1.6X2, R2 = 0.93). Optimum germination occurred at a depth of 5.6 cm. Mechanical and sulfuric acid scarification increased the rate of germination but not the overall percentage. Tap water or hot water increased the rate of germination 26% and KNO3, GA3, or ethephon increased it 53%. Tropical soda apple seed germinated in response to variable environmental and edaphic conditions which could allow establishment in diverse ecosystems.