Effect of forchlorfenuron and thidiazuron on kiwifruits' internal qualities, optical properties and their relationship during growth.

Forchlorfenuron (1-(2-chloropyridin-4-yl)-3-phenylurea, CPPU) and thidiazuron (N-Phenyl-N'-1,2,3-thiadiazol-5-ylurea, TDZ) are two widely used plant growth regulators in kiwifruit cultivation. They can promote fruit size, but it is unclear whether they have same effect on internal qualities, optical properties and cell structure of kiwifruit, and whether the kiwifruits treated with CPPU and TDZ can be identified based on optical properties. To answer these questions, the kiwifruits treated with 20 mg/L CPPU and 2 mg/L TDZ solutions were used as samples, and the untreated kiwifruits were used as control to investigate the optical properties (absorption coefficient μ and reduced scattering coefficient μ'), internal qualities (soluble solids content (SSC), firmness and moisture content) and microstructure of pulp tissue during the growth. Moreover, the relationship between the optical properties and internal qualities were analyzed, and the potential for identifying the kiwifruits treated with CPPU and TDZ based on optical properties was evaluated. The results showed that CPPU and TDZ increased the SSC and reduced the firmness of kiwifruits, but had some different effects on the moisture content and cell size. CPPU and TDZ did not influence the change trend of μ and μ' with wavelength, but affected their values and the relationship with internal qualities. In general, the mean μ of the kiwifruits treated with CPPU and with TDZ was the largest and the smallest at the absorption peaks (980 nm, 1190 nm and 1420 nm), respectively. The linear discriminant analysis modeling results showed that the spectra of μ with μ' had greater potential in identifying the kiwifruits treated with CPPU/TDZ with accuracy of 75.76 %.