ABSTRACT
The 'Okitsu No. 58' citrus variety is highly prone to fruit cracking, which jeopardizes yield and results in economic losses. In this study, we investigated the impacts of spraying 5 distinct concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 g/L) of chelated calcium (Ca) or silicon (Si) fertilizers at the young fruit stage (60-90 days after flowering, DAF) on fruit cracking and quality in the citrus variety 'Okitsu No. 58'. The results showed either Ca or Si fertilizer treatments reduced fruit cracking. We found that all Ca and partial Si treatments (0.4 and 0.5 g/L) significantly promoted the accumulation of Ca content in the peel. Notably, Ca or Si treatments significantly reduced polygalacturonase (PG) activity and inhibited the production of water-soluble pectin (WSP) in the peel. Additionally, Ca or Si treatments elevated the superoxide dismutase (SOD) activity and decreased the malondialdehyde (MDA) content of the peels. Changes in these parameters likely contributed to strengthening the durability of peel cell wall constituents, thus enhancing the fruit's resistance to fruit cracking. Overall, except for the C3 (0.3 g/L of Ca), Ca or Si fertilizers contributed to fruit conventional quality, mainly in terms of higher soluble sugars (SS) and SS/TA (titratable acid). Therefore, our findings will provide a reference for the prevention and control of citrus fruit cracking and the development of new fertilizers.
ABSTRACT
To obtain the compatibility of interstocks crossing with 'Yuanxiaochun', we performed a comparative analysis with five interstocks. From the 60th to 240th day after grafting, there was a significant difference between different treatments. All the new shoot/interstock diameter ratios were <1, indicating that there was no obvious phenomenon of small feet in 'Yuanxiaochun' seedlings of five kinds of interstocks. The density of 'Yuanxiaochun' was significantly different. Chl a, Chl b, T-Chl content of 'Shiranuhi', 'Harumi', 'Tarocco' changed greatly from the 90th to 120th day after grafting. The intercellular CO2 concentration (Ci) of 'Shiranuhi' was significantly higher than the other interstocks. In addition, when 'Yuanxiaochun' was grafted onto 'Shiranuhi', net photosynthetic rate (Pn), stomatal conductance (gs) and tanspiration rate (Tr) were higher. When 'Harumi' were used as the interstocks of 'Yuanxiaochun', the light saturation point (LSP) value was larger, which was conducive to the utilisation of strong light. Moreover, the value of LSP-LCP (LCP, light compensation point) of 'Harumi' and 'Tarocco' were significantly higher than the other three interstocks. The apparent quantum efficiency (AQE), RuBP maximum regeneration rate (Jmax) and maximum carboxylation efficiency of Rubisco (Vcmax) value of 'Shiranuhi' was significantly lower than that of 'Ponkan'. The CO2 compensation point (CCP) of 'Harumi' interstock was lower, but the CO2 saturation point (CSP) of 'Tarocco' interstock was higher than those of other interstocks respectively. There was a small difference in initial fluorescence (F0) of different interstocks. The maximal photochemical efficiency of PSII in the dark (Fv/Fm) of 'Kumquat' was the lowest. In addition, Both Y(II) and ETR values of the 'Yuanxiaochun' leaves of 'Ponkan' interstock was the largest one. However, the non-photochemical quenching (qN) of 'Ponkan' was significantly lower, and that of 'Tarocco' interstock was the highest one. Interstocks have different effect on the growth and development, photosynthetic characteristics related to physiological characteristics of 'Yuanxiaochun' trees. 'Ponkan' and 'Kumquat' as the interstock of 'Yuanxiaochun' was more conducive to the rapid accumulation of photosynthetic products for normal vegetative and reproductive growth of plants.
