Bioenergetics, Respiration Cost and Water Relations of Developing Avocado Fruit

Abstract

Avocado fruit of cultivars with different susceptibility to physiological fruit disorders were examinedin 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:o
1. Avocado fruit respired more CO2 in the dark than in the light due to fruit photosynthesis. Respirationrates decreased with fruit ontogeny from 14.5 to 1.5 μmol CO2 m−2 s−1 and increased from 1 to 4.5 μmol 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 66kJoule), with growthrespiration (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 26MJ kg−1 dry matter.

3. Stomatal conductance decreased from 0.17 mmol m−2s−1 at pre-anthesis to 0.01 mmol m−2s−1 at 60gfruit 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 to2 mmol H2O fruict−1 day−1.

5. A 60-g fruit accumulated 51 mL water and transpired 155 mL or 171 mL H2O, resulting in a waterconsumption of 206 mL (Fuerte) or 222 mL (Hass) water with a fruit water use efficiency (FWUE), i.e. mol CO2 respired per mol water transpired, of 9.5 × 10−3.

6. Midday fruit water potentials ranged between −0.4 to −0.9MPa with values obtained for cv. Fuertefruit 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.