Gas exchange and growth of zucchini crop subjected to salt and water stress¹

Trocas gasosas e crescimento da cultura da abobrinha submetida aos estresses salino e hídrico

HIGHLIGHTS:

The combination of salt and water stresses increased the accumulation of CO₂ in the leaf mesophyll of zucchini cv. Caserta.

Photosynthesis and water use efficiency were affected by salinity, but to a lesser degree under 100% irrigation depth.

Irrigation with water of electrical conductivity above 1 dS m^-1 negatively affected gas exchange and zucchini crop growth.

ABSTRACT

Semi-arid regions present the inherent problem of accumulation of salts in the soil due to the use of brackish water for irrigation, and water deficit compromises the growth and physiological indices of crops. This study evaluated the effect of salt and water stress on growth and gas exchange in the zucchini cv. Caserta crop. The study was conducted at the University of International Integration of Afro-Brazilian Lusophony, Redenção, Ceará State, Brazil. The experimental design was completely randomized, in a 5 × 2 factorial scheme with five levels of electrical conductivity of the irrigation water - ECw (0.5, 1.0, 1.5, 2.0, and 2.5 dS m^-1) and two water regimes (50 and 100% of the potential crop evapotranspiration - ETc), with five replicates. At 36 days after sowing, the following traits were evaluated: CO₂ assimilation rate, transpiration, stomatal conductance, internal carbon concentration, leaf temperature, relative chlorophyll index, and water use efficiency. At 45 days after sowing, the plant height, stem diameter, number of leaves, and leaf area were also evaluated. The use of brackish water (1 to 2.5 dS m^-1) reduced the growth parameters of zucchini cv. Caserta. The increase in ECw caused a decline in the physiological traits. Under 100% ETc, higher values of CO₂ assimilation rate, transpiration, and instantaneous water use efficiency were recorded, and there was 50% ETc for internal carbon concentration, even with the increase in ECw.

Key words:
Cucurbita pepo L.; water deficit; salinity; combined stress