Abstract
Seedlings of cherimoya (Annona cherimola Mill.), sugar apple (A. squamosa L.) and soursop (A. muricata L.) were grown at 100, 45, 25, and 5% of full sunlight level to determine the influence of irradiance level on their growth and photosynthesis. For all species the shoot length and dry weight of wholeplant were decreased at 25% sunlight, but there was little difference in them between at 45 and 100% sunlight. Total leaf area tended to increase at 45% sunlight in sugar apple and soursop and to decrease at 25% sunlight in cherimoya and soursop. Leaf area ratio increased with decreasing light intensity in every species, and the degree of increase was the least in cherimoya. With decreasing light intensity, leaves became thinner and the specific leaf weight decreased for all species. Chlorophyll content and photosynthetic rate more decreased at 25% than those at 100 and 45% sunlight in sugar apple and soursop. There were little differences both in the chlorophyll content and photosynthesis among these light intensities in cherimoya. This indicates that cherimoya has higher adaptability to low irradiance than other two species. Under weak light condition the stomatal conductance increased for all species. At 5% sunlight, the plant dry weight was less than about 90% of that of control and photosynthetic rate almost decreased to the light compensation point.
