Lateral Stem Development in Tomato according to Rootstock Vigour and Seedling Management Practices

The different vigour expressed by the adopted rootstock might influence the growth of the axillary buds, and thus the uniformity of crops when grown with two stems (i.e. tomato). The aim of this work was to determine whether the rootstock vigour can modify the growth of axillary buds in interaction with seedling management practices. The effects of rootstocks, characterized by different vigour ('Armstrong' - high vigour, 'Interpro' - medium vigour, 'He-Man' - low vigour), were observed in two experiments in relation to i) topping date (5, 9 and 13 days after grafting) and ii) topping (up cotyledon leaves - CL, up two-true leaf - TL, and growing the first lateral stem - LS which appeared the most vigorous after transplant). In both experiments self-grafted plants were used as control. Seedlings characteristics at transplant, shoot length at regular intervals, flowering and numbers of flowers after transplant were monitored. The delay of topping led to an increase in number of leaves and aerial dry weight in seedling at transplant, irrespective of grafting combination. Shoot length measured at different intervals changed according to rootstock and topping date. Flowering was hastened about one week in plants topped at 13 d regardless the rootstock, and the difference between the two shoots increased with the increase of topping delay. Topping at TL enhanced seedling characteristics (collar diameter, aerial DW, chlorophyll index-SPAD) at transplant in all grafting combinations. Shoot length at 30 days after transplant was highest in plants topped at TL irrespective of rootstock. At the same time, the greatest difference in length between the two shoots (δ) was observed in plants with LS treatment of all grafting combinations, but it was reduced in plants grafted onto 'He-Man' and topped at TL and further at CL. Plants grafted onto the vigorous rootstock 'Armstrong' showed a hastening of flowering at LS treatment. Highest difference between the two shoots in flowering occurred in plants with LS treatment but declined with the decrease of vigour.