The inicial growth of Lotus glaber affected by the cotyledon removal and shading.

The objective of this study was to determine in Lotus glaber (= Lotus tenuis) seedlings: I) The effect of removal and shading of cotyledons on seedling vigor determination and on other characters that could conditionated the establishment, and II) The evolution of the cotyledon growth during the experimental period. The experiment was performed in a glasshouse. Seeds from a natural population were sown in pots with homogeneus soil. The treatments consisted in the cotyledon removal when the seedlings showed the stages of: unfolded cotyledons, and 1st and 2nd unfolded leaves, and the shading at the same stages until the end of the experiment, 35 days after sowing. The control kept cotyledon untouched and exposed to the full daylight. Darkness in the unfolded cotyledon stages had a negative effect over total, aereal and radical dry weights; foliar area; principal axe and root lenght; number of stems in the crown; number of unfolded leaves, and foliar area/root lenght ratio. In addition, darkness determined a greater number of leaves with less than 5 leaflets and an increase in the lenght of the hypocotyl. The most affected character was root length. Cotyledon removal in the three stages strongly affected the total dry weight and the other evaluated characters. From their unfolded until to unfolded 1st leaf stage, the cotyledon increased 74, 108, and 28% in their dry weight, area and thickness, respectively. Starting from that moment their growth stopped. The results stand out the direct and indirect roleplaying of the cotyledons in the establishment of L. glaber, not only in relation to the seedling vigor but also in the capacity to explore the substratum.

Key words: seedling vigor, hypocotyl lengthening, cotyledon growth, cotyledon shading, cotyledon removal.