Effect of dry heat on germination and viability of Cryptostegia grandiflora seeds

Abstract

The present study described the effect of six dry heat intensities (28, 40, 60, 80, 100, and 200°C) and eight heat durations (0.5, 1, 2, 3, 6, 12, 24, and 36 min) on
germination, viability, and germination rate of one-year-old seeds of the invasive weed rubber vine (Cryptostegia grandiflora R.Br.). Heat induced seed mortality is of significance to land managers, especially in pastoral areas, where prescribed burning is used to control rubber vine. There was a highly significant interaction between heat intensity and heat duration on germination, viability and germination rate of rubber vine seed. Seed germination was reduced once temperatures reached 80°C for more than 24 min. Raising the temperature to 100°C completely inhibited germination at 6 min and induced a total kill of seeds at 24 min. Further increases in dry heat to 200°C advanced inhibition of germination to 1 min and induced total kill of seeds at 3 min. Germination rate at 80, 100, and 200°C slowed down by 42, 65 and 91% of the original rate respectively. Above 80°C a negative correlation was detected between (i) germination response and heat duration, (ii) seed viability and heat duration, and (iii) germination rate and heat duration whereas seed viability was positively correlated with seed germination. The apparent tolerance to high temperature in rubber vine seeds indicates that high-intensity fires may be a requirement for maintenance of an effective seed management strategy in rubber vine infested habitats.