The Effect of NAA and BA on Carbon Dioxide Assimilation by Shoot Leaves of Spur-type `Delicious' and `Empire' Apple Trees

Abstract

The effects of NAA, BA, or Accel on CO2 assimilation of shoot leaves of mature bearing Redchief `Delicious' and `Empire' apple (Malus ×domestica Borkh.) trees were evaluated over two seasons. BA at 50 mg·L-1 did not significantly affect any of the gas-exchange parameters measured. NAA (15 mg·L-1) consistently suppressed CO2 assimilation rate (from ≈10% to 24% below that of the control). This suppression was NAA-concentration dependent, continued for >15 days after treatment, and was completely overcome in `Empire', but only partially or not at all in `Delicious' when BA was combined with NAA. These results are discussed in relation to fruit thinning and NAA-induced inhibition of fruit growth in spur-type `Delicious'. Chemical names used: 2-(1-napthyl) acetic acid (NAA); N-(phenyl)-1H-purine-6-amine (BA); BA + gibberellin A (GA)4+7 (Accel).