Distinguishing the effects of light and temperature variations on the growth, development, multiplication potential and ex vitro survival rates of invitro cassava

Dissemination of cassava tissue culture plantlets is difficult in the arid tropics due to low ex vitro survival rates. Increased in vitro light intens ity has been reported to induce high ex vitro survival rates. The results f rom earlier experiments suggested that it would be worthwhile to analyse th e separate effects of in vitro light and of temperature on the in vitro gro wth pattern as well as differentiate its relation to ex vitro survival. Acc ordingly, analysis of a range of in vitro light intensities from 0 to 369 m u mol s(-1) m(-2) photosynthetic photon flux density (PPFD) was conducted b oth with and without fans to control the heat. Temperature proved stable at low PPFD levels but increased above 204 mu mol s(-1) m(-2) when no fans we re used. Increased PPFD levels induced larger fresh and dry masses as well as stem thickness. PPFD levels affected the developmental index (senescent leaf numbers) in vitro when it rose above 204 mu mol s(-1) m(-2) PPFD. Rais ed temperature ranges increased the multiplication index (node numbers) in vitro and ay vitro. It increased root number and leaf development (lobe ana tomy). As in vitro temperatures of up to 40 degreesC improve multiplication rates and PPFD levels above 101 mu mol s(-1) m(-2) were detrimental for ex vitro survival (as low as 60%), it is suggested that simpler and less cost ly laboratories with low light levels and a wide range of temperature toler ance could be successfully established in the tropics for in vitro cleaning and rapidly multiplying crops like cassava.