Avocado fruit of cultivars with different susceptibility to physiological fruit disorders were examined in situ for respiration, stomatal conductance, transpiration and xylem water potential. Therein, attached fruit of cv. Fuerte (susceptible to mesocarp discolouration) were compared with Hass (susceptible to small fruit) over the 3-month period from anthesis until the fruit reached 60 g fresh matter: 1. Avocado fruit respired more CO2 in the dark than in the light due to fruit photosynthesis. Respiration rates decreased with fruit ontogeny from 14.5 to 1.5 mu mol CO2 m(-2) s(-1) and increased from 1 to 4.5 mu mol CO2 fruit(-1) h(-1), reflecting the higher energy requirement of the avocado relative to other fruits and of cv. Hass relative to Fuerte fruit. 2. Fruit respiration accumulated to 4.8 g (Fuerte) or 5.1 g (Hass) CO2 (= 63 or 66 kJoule), with growth respiration (Fuerte) of 0.324 kg CO2 (7.35 MJ) kg(-1) dry matter twice as large as found in fruits of other species and maintenance respiration of 1.98 kg CO2 or 26 MJ kg(-1) dry matter. 3. Stomatal conductance decreased from 0.17 mmol m(-2) s(-1) at pre-anthesis to 0.01 mmol m(-2) s(-1) at 60 g fruit weight. 4. Fruit of cv. Hass transpired more water than those of Fuerte, i.e. 0.2 to 1 mmol H2O m(-2) s(-1) or 0.2 to 2 mmol H2O fruit(-1)day(-1) 5. A 60-g fruit accumulated 51 mL water and transpired 155 mt or 171 mL H2O, resulting in a water consumption of 206 mt (Fuerte) or 222 mt (Hass) water with a fruit water use efficiency (FWUE), i.e. mol CO2 respired per mol water transpired, of 9.5 x 10(-3). 6. Midday fruit water potentials ranged between -0.4 to -0.9 MPa with values obtained for cv. Fuerte fruit exceeding those of the respective leaf. These results present the first data on energy requirement, maintenance and growth respiration, transpiration, water use and water potential of developing avocado fruit, which are discussed with respect to physiological fruit disorders.
