Rubber Trees Affected by Necrotic Tapping Panel Dryness Exhibit Poor Transpiration Regulation under Atmospheric Drought

Abstract

The objective was to study the responses in water status and transpiration regulation of rubber trees affected by the necrotic Tapping Panel Dryness (N) by comparison with healthy trees (H). The experiment was done with 5 N trees and 5 H trees of clone RRIM600 during well soil watered periods differing in evaporative demand intensity, May and August 2007. The study compared predawn leaf water potential (ψpd), midday leaf water potential (ψmid), whole tree hydraulic conductance (K), midday sapflow density (Js) and tree transpiration (ET) with the average girth size 51.54 cm of H tree and 52.66 cm of N tree. These variables, investigated in the high evaporative demand day (ETO = 3.71 mm day-1) on 23 May 2007 and low evaporative demand day (ETO = 1.75 mm day-1) on 22 Aug 2007, did not significantly differ between tree types. However, over a long period, in high evaporative demand, ET tended to be higher in N trees. Expression of ET versus ETO confirmed different relationships between the two tree types with a higher plateau of maximum transpiration for N trees. Our results suggested that individuals with relatively poor transpiration regulation could be more sensitive to necrotic Tapping Panel Dryness syndrome.