The Data: Tissue Analysis
Boron analysis confirmed that leaf injury was due primarily to B toxicity. Identical symptoms (dark reddish necrosis on the margins of older leaves) have been observed in pistachio orchards, particularly toward the end of summer.
We observed that more B accumulated in the leaf tissue of the scion (P. vera) as salinity in irrigation waters (i.e., the external solution) increased (Figure 1). We found Boron concentrations in necrotic leaf tissue 3-4 times higher than in healthy tissue. Regarding differences among the rootstocks, leaves on P. atlantica generally contained less B than on P. integerimma and UCB-1 rootstocks.
|Figure 1. Boron in healthy (filled area of column) & injured (total length of column) leaves of scion on 3 rootstocks as influenced by salinity.|
Ion Partitioning between Scion and Rootstock
The concentration of B was about the same in scion as in rootstock tissue. However, this was not true for other ions:
- We measured significantly more sodium in rootstock tissue than in scion tissue for all three rootstocks, with the response strongest for UCB-1 (Figure 2).
- Partitioning of choride followed the same pattern observed for sodium (Figure 3)
|Figure 2. Left: Partitioning of Na between scion (filled area of column) & rootstock (total length of column) on 3 rootstocks as influenced by salinity. Right: Similar Partitioning of Cl. Ions measureed in mmoles/kg (DW). Each column is the mean of 6 trees, vertical line is standard error.
Ion Concentrations in Leaf Tissue
Our leaf tissue measurements indicated that concentrations of both sodium and chloride increased significantly in the leaves with increasing salinity in the irrigation regime. Concentrations of these two ion were also uniformly partitioned between the healthy and necrotic leaf tissue. Pistachio has mechanisms which exclude ions from the tissues, and this was particularly apparent in the exclusion of sodium. For example, the sodium concentration in the external solution was double that of chloride, but substantially lower than chloride in the leaves.
We found that despite up to 10-fold increases in external magnesium, the Mg concentration in healthy scion leaves on UCB-1 or P. atlantica was no different from initial measurements. However, the Mg+2 levels rose significantly in the necrotic leaf tissue on these rootstocks.
This observation was not true for P. integerimma, where we measured a significant decrease in Mg in healthy scion leaves with rising external salinity. The Mg level in necrotic leaf tissue was about the same as in healthy leaves.
The concentration of calcium in healthy leaves, however, decreased for all rooststocks with increasing salinity in the irrigation water. In injured leaf sections, the responses were different: on P. integerimma the calcium level decreased significantly, on P. atlantica rootstock the calcium level increased significantly, and on UCB-1 rootstock, calcuim levels did not change.
Our extensive data on ion content of leaf and woody tissue is available in detail, by contacting Louise Ferguson (see Research Team for contact information).