Effect of nursery substrate on the growth of Pterocarpus erinaceus Poir. seedlings

Abstract

The high pressures on Pterocarpus erinaceus Poir. severely affect its natural stands in West Africa. The measures taken to reverse this trend are still inefficient due to plantlets production constraints. This study aims to understand the importance of growing substrates on seedlings growth in nursery. Composite soil samples were collected at 20 cm depth from 4 seed trees in 5 different sites in Togo (West Africa). Two batches were made for each site, one of which was sterilized by autoclave and the other has received no treatment. Three growing parameters (length of stem, number of buds and number of leaves) of the plantlets obtained from sterilized seeds were measured during 20 weeks in the nursery. Results show for each site a significantly better growing rate of seedlings on unsterilized substrates, compared to sterilized substrates. At the end of the experiment, plantlets were 8.75 ± 2.32 cm mean height on sterilized substrates when they reach 19.20 ± 5.00 cm on unsterilized substrates. The mean number of buds and leaves per plantlet varies from 2.23 ± 1.71 buds and 3.00 ± 1.86 leaves to 10.73 ± 3.28 buds and 11.09 ± 2.48 leaves at the same date, respectively on sterilized and unsterilized substrates. The low growing rate on sterilized substrates should be linked to the low capacity of plantlets in mobilizing phosphorus, potassium and nitrogen without microorganisms. Negative impacts of sterilization were highlighted on seedlings by necrosis of buds and leaves from the 7th week of growth, demonstrating a positive effect of soil microorganisms on the proper development of the seedlings.