Ns

'Different letters in each column indicate significant differences according to the p-value. NS, not significant (P>0.05). Percentage data were previously arc-sin transformed. Duncan test.

'Different letters in each column indicate significant differences according to the p-value. NS, not significant (P>0.05). Percentage data were previously arc-sin transformed. Duncan test.

Deficit Irrigation Effects on Shoot Growth

Shoot growth in control well-irrigated trees fitted a sigmoid pattern (Figure 5). New growth started immediately after harvest and kept a regular pace until early August, when summer rest was imposed in apical buds (August 10th). Plastochron length was very regular during the first weeks, but was greatly enlarged as summer rest approached. Control trees abandoned dormancy in early September forming the terminal panicle. Final length of main shoots in control trees reached 14.3 cm. Seventeen new leaves were formed in these main shoots. DI did not diminish the length or the number of leaves per shoot (Table 1). However, DI profoundly altered the pattern of shoot growth that changed from a single sigmoid to a double sigmoid (Figure 5). This shift was the result of water stress causing an early, but transitory, cease of growth, which was reassumed up to the length of controls when water deficit ended. Modification of shoot growth pattern was more acute in trees where irrigation was completely suspended (W0%) and less noticeable in trees where water irrigation was cut by half (W50%). No new nodes were formed in W0% trees since the beginning of July and summer rest was already established two weeks after water withholding. The onset of summer rest occurred last week of July in W25% trees, while it could be dated at the beginning of August in W50% trees. The release of rest in apical buds was almost immediate in all DI treatments after the resumption of full irrigation. On mid-August just a few days after the end of water deficit, the trees responded forming new leaves below the differentiating terminal panicle (Figure 5). The variations in shoot growth rate along the experimental period expressed in large changes in plastochron length of W0% trees from more than 40 days to scarcely 2, when bud dormancy release and rapid growth occurred. Less marked changes took place in W50% and W25% trees.

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