Genotypic Differences in the Effect of Temperature on CO2 Assimilation and Water Use Efficiency in Blueberry

Abstract

To determine if the net CO 2 assimilation and water use efficiency (WUE) of highbush blueberry under high temperature can be improved genetically, gas exchange determinations were made for a selection of Vaccinium darrowi Camp (Florida 4B), a highbush cultivar (Bluecrop) ( V. corymbosum L.), their F 1 hybrid (US75), and two crosses of the F 1 hybrid to another improved genotype (US239 and US245). All genotypes responded parabolically to increasing temperature at vapor pressure deficits <1 kPa. Maximum CO 2 assimilation of US75 (15 µmol·s –1 ·m –2 ) was 30% to 40% higher than either parent. Carbon dioxide assimilation of US75 and Florida 4B was optimum at 30°C and that of ‘Bluecrop’ at 20°. The optimum for US239 was similar to ‘Bluecrop’, and that of US245 to Florida 4B. Florida 4B had higher WUEs than ‘Bluecrop’ at both 20° (5.64 µmol CO 2 /mmol H 2 O to 4.01) and 30° (3.73 to 2.53). US239 and US245 had significantly ( P < 0.05) higher WUEs at 30° than did ‘Bluecrop’. Residual conductance to CO 2 (g r ) decreased in ‘Bluecrop’ when temperature was raised from 20° to 30°, but increased in all other genotypes. Due to the favorable gas exchange properties of US75 and US245 at 30°, we suggest that the high temperature tolerance of V. darrowi may be heritable and that US245 may be used to improve the heat tolerance of highbush blueberry.