Effect of seed size on field survival and growth of Eucalyptus in KwaZulu-Natal, South Africa

Abstract

This study was established to determine the effect of seed size on nursery performance, field survival and growth. Results indicated that germination was greater for larger seed whereas the smallest seeds germinated poorly. In addition, seedling survival in the nursery was also lower for Grade 4 Eucalyptus grandis but not for E. smithii. Grade 4 seeds produced the shortest seedlings. This was attributed to a slower rate of germination within a tray of seedlings produced from Grade 4 seed. The Grade 4 seeds, however, produced seedlings with larger root collar diameters due to a greater amount of empty spaces within a tray (a function of poor germination). Field results indicated good survival irrespective of species or seed grade. At 12 months, only seed orchard source was significant for all response variates for E. grandis, whereas there were no significant inter-treatment differences for E. smithii. This study showed that Eucalyptus seed size effects were transitory, only apparent in the nursery and not perceptible one year after planting in the field. Smaller seeds can therefore be used in a commercial nursery as long as they are sown with similar-sized seeds to allow for management of poor germination and crop uniformity. Seed orchard source proved to be very important in predicting field growth.