| The climate in Chongqing of China is characterized by rainy spring, drought and hot summer, high humidity and low solar radiation in late autumn and winter, and annual sunshine mainly focus on xerothermic July and August. This weather condition not only reduces citrus fruit yield, but also affects fruit quality, resulting in bad color, high incidence of disease spots, pest spots and algae stains. Previous studies indicated that rain shelter cultivation could improve fruit growth, yield and quality. To further understand these effects in citrus, in this study, rain shelter cultivation from January to December (RSC1-12), January to March (RSC1-3), April to June (RSC4-6) and September to December (RSC9-12) and open field cultivation (CK) were conducted in24-year-old Skaggs Bonanza navel orange (Citrus sinensis Osbeck cv Skaggs Bonanza) grafted on trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstock in2011and2012in Chongqing, and the trees growth, fruit yield and quality, and photosynthetic characteristics were analyzed. The results are as follows:1. Effects of rain shelter cultivation on phenophase, canopy meteorological factors and shoot-growing in navel orangeThe results indicated that new flushes sprout and growth of Bonanza navel orange was promoted by RSC1-12treatment, and the flowering period was extended about10days than that of CK. Furthermore, fruit color turning period was ahead of7to15days under both RSC1-12and RSC9-12treatments, and the other treatments showed no significant difference. On sunny days, rain shelter cultivation had no obvious effect on canopy temperature and humidity, but on rainy days, the average canopy temperature and relative humidity with rain shelter cultivation were1℃to2℃higher and4% lower than those of CK, respectively. All the rain shelter cultivation treatments had lowered the canopy light intensity. Before August, canopy light intensity with rain shelter cultivation was reduced about30%on average when compared with CK, while there was no significant difference between them after September because of frequent cloudy and rainy weather during this period in Chongqing.2. Effects of rain shelter cultivation on photosynthetic characteristics in navel orangeRain shelter cultivation had significant effects on photosynthesis in new flushes. Compared with CK, rain shelter cultivation decreased net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2concentration (Ci) and transpiration rate (E) of new flushes leaves. Among all the treatments, RSC1-12had lowest Pn, followed by RSC1-3. The Pn of RSC1-12and RSC1-3were3.8μmol·m-2·S-1and2.9μmol·m-2·S-1lower than that of CK, respectively. For the Gs and E, RSC1-12also showed the lowest value, and which were41.5mmol·m-2·S-1and1.3mmol·m-2·S-1less than that of CK, respectively. The Ci was lowest in RSC9-12treatment which was33.1μl·L-1less than that of CK. No significant differences were found in other treatments. For the contents of relative chlorophyll (SPAD), only RSC1-3treatment showed1.0higher than CK, and both RSC1-12and RSC4-6were lower than the CK, and the highest difference between them could reach20.0in May. There was no significant difference between RSC9-12and CK. The chlorophyll fluorescence characteristic of Fv/Fm had no significant differences among all the treatments.3. Effects of rain shelter cultivation on fruit growth and development and yield in navel orangeDifferent seasons of rain shelter cultivation showed no obvious effects on fruit growth and development and split rate, but it had significantly affected the navel yellow rate and fruit yield. The data showed that the vertical and horizontal diameter of fruits in2012were CK>RSC4-6>RSC1-3>RSC9-12>RSC1-12, and there was a10mm difference in vertical and horizontal diameter from early July to fruit maturation between RSC1-12and CK. The navel yellow rate from up to low were RSC1-12, CK, RSC1-3, RSC9-12and RSC4-6. All the treatments had reduced the secondary-fruit yellowing rate as comparing with CK except a16.6%increasing in RSC1-12treatment. Among which, the secondary-fruit yellowing rate of RSC4-6was14.8%which was significant lower than that of CK (50%). For the fruit split rate, the RSC1-12and RSC9-12treatments increased13.7%and21.3%compared with CK, respectively, but there were no statistically different from each other. The fruit yield per plant in2011and2012showed that RSC9-12was34.0kg and1.3kg higher than CK, respectively, while RSC1-12was10.9kg and13.4kg lower than CK, respectively. Compared with CK, no obvious regularity were found for other treatments in2011and2012.4. Effects of rain shelter cultivation on fruit quality of navel orangeThe results showed that the fruit quality under rain shelter cultivation was better than CK. Rain shelter cultivation improved the exterior quality such as surface smooth finish, fruit coloring and fruit shape index of navel orange when compared with CK in the same period. In detail, the sequence of fruit break date was RSC1-12>RSC1-3> RSC9-12>CK> RSC4-6before harvesting (December12th). Fruit break date was brought forward significantly under RSC1-12, RSC9-12and RSC1-3. The data in2011and2012showed that the contents of total soluble solids (TSS) in both RSC1-12and RSC9-12were1%higher than that in CK. The titratable acidity (TA) was no difference in2011while significantly high in2012for both RSC1-12and RSC9-12when compared with CK, because the rainy days are frequent during fruit maturation in2012.In conclusion, RSC9-12in Bonanza navel orange could get the best fruit growth, yield and quality in Chongqing, followed by the RSC1-12, and open field cultivation produced the worst quality of fruits. |
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