Effects of the Diphenylurea Cytokinin CPPU and the Auxin 3,5,6-TPA on 'Washington' Navel Orange Yield,Fruit Size and Quality

摘要

California produces picture perfect navel oranges (Citrus sinensis) for the fresh fruit market. A high yield of commercially valuable large size fruit of good quality is required yearly to sustain the California citrus industry. N-2-chloro-4pyridinyl-N-phenylurea (CPPU), a diphenylurea-type cytokinin, and 3,5,6-trichloro-2-pyridyloxyacetic acid (3,5,6-TPA), an auxin, were tested for their ability to increase yield of commercially valuable large size navel orange fruit (6. 9 -8. 8cm transverse diameter). Commercially bearing 24-yearold ' Washington' navel orange scion on ' Carrizo' citrange rootstock (C. sinensis X Poncirus trifoliata) was used in the research. CPPU [20 and 25g active ingredient (a. i.)per ha] and 3,5,6-TPA (18.5,28,and 37g a. i./ha) were applied in 1869L of water (pH 5.5)per ha with a high pressure (2.76MPa) handgun sprayer to the foliage of 15 individual trees per treatment at 10% anthesis in the southwest tree quadrant,75% petal fall in the northeast tree quadrant or maximum peel thickness (MPT) (CPPU) and when fruit averaged 24mm transverse diameter or at MPT (3,5,6-TPA) in a randomized complete block design, including untreated trees that served as the control. Averaged across the 2 years of the experiment,all CPPU treatments,except 20g/ha applied at MPT, reduced total yield and yield of commercially valuable large size fruit. Leaf phytotoxicity was observed on 20% to 30% of the canopy of all trees treated with CPPU before MPT. CPPU applied at 25g/ha at 10% anthesis or at 20 and 25 g/ha at 75% petal fall increased juice weight and juice volume per fruit by December, but decreased total soluble solids. Averaged across the 2 years of the experiment,3,5,6-TPA had no effect on total yield or yield of commercially valuable large size fruit,with the exception that 3,5,6-TPA (18. 5g/ha) applied when fruit averaged 24mm in diameter reduced the yield of fruit with transverse diameters less than 6. 9cm and increased the yield of fruit 6.9 to 7. 4cm in diameter both as fruit weight and number of fruit per tree. Application of 3,5,6-TPA (37 g/ha) when fruit averaged 24mm in diameter increased juice weight and juice volume per fruit by November,without decreasing total soluble solids.