MODIFICATION OF LEAF GAS EXCHANGES IN WHEAT SEEDLINGS SUBJECTED TO WATER STRESS AND/OR LEAF RUST ATTACK
O BETHENOD, L HUBER and H SLIMI
INRA, Thiverval-Grignon, France
Background and objectives
Materials and methods
Disease severity was assessed by the number of lesions per unit area of leaf. The water stress intensity was characterized by measuring pre-dawn water potential (PWP). Leaf gas exchanges were measured using an open circuit chamber (Li-6400, Li-Cor, USA) for (1) seven radiation levels between 0 and 1500 Ámol/m2.s under external CO2 concentration of 330 Ámol/mol, and (ii) seven external CO2 concentrations between 330 and 0 Ámol/mol under a PAR value of 1500 Ámol/m2.s. Variables calculated were net CO2 assimilation, stomatal conductance for CO2 and CO2 concentration in the air spaces of a leaf.
Results and conclusions
On the fifth leaf, area reduction reached 37% on WSXFS treatment, and 19% and 14% on independent WS and FS treatments. The influence of both stresses was also shown to be cumulative on leaf 7.
In the control treatment (NS), there was no time change in dark respiration, maximal radiation-use efficiency (MRUE) and net assimilation under saturating PAR (Anmax). In the WS treatment, with an increasing water stress, net assimilation and stomatal conductance for CO2 decreased with constant CO2 concentration in the leaf air spaces. On FS and WSXFS treatments MRUE and Anmax decreased over time in relation to growing fungal attack; stomatal conductance for water decreased before sporulation and then increased with concomitant increase of CO2 concentration in the leaf air spaces.
The relationship between Anmax and PWP suggested that plant water loss caused by fungal lesions could explain the net assimilation reduction, which is consistent with the cumulative influence of both water stress and fungal constraint on leaf area expansion.