THE EFFECT OF PLUG SIZE AND GRAFTING METHOD ON THE DRY MATTER PARTITIONING AND STAND ESTABLISHMENT RATE OF GRAFTED CUCUMBER SEEDLINGS UNDER SALINE CONDITIONS

A commercial cucumber (Cucumis sativum L.) cultivar ‘Ekron F₁’ was grafted onto a commercial rootstocks (Cucurbita maxima × C. moschata). Graded rootstock seeds were sown in three different trays (40, 84 and 104 plugs per tray) with respectively (100, 43, 32 cm3 per plant. Splice grafting (SG) and root pruning splice grafting (RPSG) were simultaneously applied. Additionally, non grafted seedlings were grown in similar trays. Two weeks after grafting, an equal number of each experimental unit was transplanted into 200 cm3 plastic pots filled with vermiculite. The plants of each group were split in three equal subgroups and irrigated several times with equal amounts of the same nutrient solution, but differing by each other by the amount of NaCl added in the nutrient solution (0, 50 and 100 mM). Stem diameter of rootstock and scion was measured prior to grafting and the respective ratios were calculated. Root, stem and leaf dry matter was weighted, and leaf area of plants was measured successively for randomly selected plants of each experimental plot. The relative growth rate (RGR), root relative growth rate (RRGR), net assimilation rate (NAR), leaf area ratio (LAR), root-shoot allometry coefficients, and growth response coefficients (GRC) were calculated. The grafting method showed a significant effect on the dry matter partitioning of grafted seedlings. Compared to SG, RPSG seedlings addressed a much large amount of assimilates to the formation of new roots, but no clear evidences were found regarding the effects of plug size on the dry matter partitioning of grafted seedlings. RPSG seedlings showed a significantly higher root relative growth versus SG seedlings, which in turn whichprovided to them a higher stand establishment rate after transplanting. Also, a better rootstock-scion diameter proportion demonstrated a significantly higher plant relative growth rate, as well as a significantly higher root relative growth rate. The increased root relative growth rate/stand establishment rate of root pruned seedlings under saline conditions was due to their enhanced physiological efficiency.