Effects of seed origin, growing medium and mini-plug density on early growth and quality of black locust (Robinia pseudoacacia [L.]) seedlings

The objective of this study was to identify optimal growing conditions for the production of high-quality mini-plug seedlings of black locust (Robinia pseudoacacia [L.].). Two seed origins (Greek and Hungarian), two growing media (enriched peat and stabilized medium) and four mini-plug densities (975; 1,460; 1,820 and 3,500 mini-plugs.m-2) were tested in two phases, in growth chambers and in a nursery after transplanting the mini-plugs into larger containers. Measurements included seedling survival, growth traits (root length, shoot height, leaf area, root dry mass, shoot dry mass, root/shoot ratio) and root growth potential (RGP). In addition, the ratio of variable to maximal fluorescence (Fv/Fm) and the effective quantum yield of photosystem II (ΔF/F'm) were measured. It was found that growing medium produced significant effects mainly in the first phase and seed origin in the second phase while mini-plug density was important in both phases. The Fv/Fm ratio was found to be significantly affected by growing medium while the effective quantum yield was influenced by density. Early survival of seedlings was closely correlated with fluorescence and growth traits (particularly with plant height) suggesting that these parameters might be useful for the grading of black locust seedlings prior to transplanting.