Effects of load balance on the fruiting-branch growth, fruit bearing and fruit quality of longan

Abstract: 【Objective】This paper aims to verify whether there is an interaction between the FBRT (fruiting-branch rate per tree) and the INFC (initial number of fruits per cluster), and determine the reasonable fruit-loading of longan plant when flower or fruit thinning is applied, as well as estimate the influence of fruit-loading on leaflet growth, fruit- bearing and quality of fruiting branches (FB).【Methods】Using Shixia longan as the material, a one-factor randomized block trial was designed with FBRT as the block (3 levels) and INFC as the treatment (3 levels), and 9 combinations of‘block × treatment’were obtained. The effects of block and treatment were studied on the NRFC (number of remaining fruits in single cluster), FSR (fruit- shedding rate), MSF (mass of single fruit), EPRF (edible portions rate in a single fruit), TSS (total soluble solids) content and CFS (chromaticity of the fruit surface). Besides, the growth covariates affecting FBC (fruit-bearing characteristics) and fruit quality were screened out by multiple stepwise regression analysis. Using the two-factor univariate analysis in the general linear model, the univariate covariance analysis for the FBC and fruit quality was conducted, and the influences of uncontrollable growth factors other than block and treatment based on the analytic results were excluded, and the significance of the difference between block and treatment levels and the estimated marginal means were all obtained.【Results】(1) During the fruit development, the tree vigor gradually decreased, with the leaflets on the FB turning from dark green to yellow green or grey green, and the MSF and FSR gradually increased, while the treated clusters of each combination showed significant or extremely significant differences in LGFB (leaflet growth of the FB), fruit-bearing and quality at mature stage. Within the same block, the NRFC varied significantly among the three levels of treatment, but was similar at the same treatment level among 3 block levels. There was extremely significant difference in MSF between blocks, but not between treatments within the same block. (2) Correlation analysis showed that the block level was significantly related to the LGMB and TVM (tree vigor at mature stage), while the treatment level mainly affected the NRFC and RSLF (ratio of small leaflet to fruit in the single cluster), and TVM was significantly and positively correlated with the DBC (diameter at the base of fruit cluster), LGS (leaf glossiness), numbers of total leaflet and compound leaf, etc., and negatively with leaflet chromaticity index l_ L* , l_ b * and l_ C* . Furthermore, the NRFC and DBC, TVM and FSR were all positively correlated (r=0.357**, 0.329**), respectively. As the covariates, the growth factors such as RSLF, DBC, DBFB (diameter at the base of FB), NCLF (number of compound leaves of single FB) and TNLF (total number of leaflets of single FB) were all significantly and linearly regressed with the FBC and fruit quality of treated clusters. Specifically, the main covariates affecting the fruit-bearing were RSLF, TNLF, DBC and leaf color, and those affecting fruit quality were l_L* , l_h°, l_C* , Rchl, DBFB, RLTB (ratio of the length with leaflets to the total length of FB), and so on. (3) There was no interaction between block and treatment. Among the covariates, the RSLF, RLTB, leaflet l_C* and so on had significant effects on the FBC or fruit quality between the block and treatment levels. The results of ANOVA (analysis of variance) showed that the combined effects of fixed variables (block and treatment) and covariates contributed 40.1%-82.9% (R2 ×100%) to the total differences between the combinations, and all the covariates resulted from the main effect test had a significant impact on the concerned indexes, which meant there was a statistical significance. The NRFC and FSR were mainly affected by block (FBRT), and the FSR was also affected by treatment (INFC); MSF, EPRF and TSS contents were mainly affected by FBRT, and the appearance quality was also significantly affected by the LGMB. In addition, the estimated marginal means showed that as the FBRT and INFC increased, the MSF, EPRF and TSS content decreased, but the changes of FSR between the block and treatment levels showed an opposite trend. Moreover, chromaticity quality of fruit under medium level of FBRT and INFC was the best, showing bright yellow-green.【Conclusion】On the basis of 60- 80 of INFC and 60% of FBRT with medium-strong tree vigor, it is a more scientific practice to adjust the FBRT and INFC according to the actual tree vigor, DBC and TNLF, which can better balance the relationship between LGFB, fruit-bearing and quality of longan. In the aspect of field management during the flowering and fruiting period, especially for the high FBRT of trees, more attention in the aspect of strengthening fertilizer and irrigation management and controlling disease and insect pest should bepaid to maintain the tree and FB growth, prevent leaflet senescence, promote fruit development and ensure that the fruit can obtain the desired external and internal quality.