Dynamics and modeling of fruit transverse diameter growth in Guangxi Orah

Abstract：【Objectives】Orah is the most popular citrus variety in Guangxi in recent years because of its beautiful appearance, juicy fruit, crisp taste, early fruiting, high yield, endurable storage and long harvest period. This paper aimed to study the growth dynamics of Guangxi Orah fruit transverse diameter and its mathematical modeling, so as to provide a scientific basis for improving its quality and yield. 【Methods】After Orah fruit set, the data of fruit transverse diameters of Orah from 15 orchards in southern, central and northern Guangxi were measured and recorded until the harvest period by using the method of "fixed an orchard, fixed a point, fixed a fruit and fixed a period" on the 1st and 15th day of each month for two consecutive years, in order to study the variation of transverse diameter growth of Orah, and investigate the correlation between the year-end transverse diameter and each growth stage, monthly transverse diameter growth and main meteorological information for mathematical modeling. 【Results】The final transverse diameters in different orchards were very different, reaching a very significant level, and the transverse diameters in many orchards needed to be improved. In the data of 225 transverse diameters (d) of Orah in 15 orchards during 2021—2022, on January 15, Orah fruit size (d ≥80 mm) accounted for 4.44%; Fruit size (75 mm ≤ d＜80 mm) accounted for 14.22%; Fruit size (70 mm ≤d＜75 mm) accounted for 32.44%; Fruit size (65 mm ≤ d＜70 mm) accounted for 24.00%; Fruit size (60 mm ≤ d＜65 mm) accounted for 12.44%; Fruit size (55 mm ≤ d＜60 mm) accounted for 4.44%; Fruit size (d＜55 mm) accounted for 2.67%, and the minimum transverse diameter was 47.51 mm. In accordance with meteorological data, the transverse diameter data of Orah fruit in 2021— 2022 was selected as the normal year data. On January 15th of the following year, the average fruit transverse diameter was 69.85 mm, and the greatest transverse diameter reached 75.33 mm, followed by 74.71 mm. The trees in the above two orchards in main reasons were healthy as a whole, the prevention and control of diseases and pests were done well, organic fertilizer (more than 30 kg of decomposed organic manure applied to each plant every year) and microbial fertilizer were sufficiently applied, water and fertilizer management were supplied in place, and there was reasonable pruning and thinning. The smallest diameter was only 61.55 mm, significantly smaller than that of the other orchards. As the main reasons, there were citrus Huanglongbing, citrus tristeza virus (CTV) and citrus yellow vein clearing virus (CYVCV) as well as macerating root in this orchard. In the investigation from 2022 to 2023, the transverse diameter of the largest Orah fruit was 78.56 mm, followed by 76.79 mm, mainly because these two orchards strengthened the use of organic manure supplemented with water, beneficial microorganisms, minerals and large plant growth regulators on the basis of selecting reasonable water and fertilizer according to this research method, and reasonably pruned and thinned the fruits. The smallest diameter was only 53.74 mm, significantly smaller than that of the other orchards, mainly because the orchard was affected by citrus Huanglongbing, CTV and CYVCV. According to the grades of 80, 75, 70, 65, 60 and 55 mm, we constructed the growth dynamics comparison table of fruit transverse diameters and the monthly increment of transverse diameter in southern, northern and central Guangxi. The mathematical model of year- end transverse diameter and each growth stage was established (R2 =0.999 98). The year- end transverse diameter was significantly and positively correlated with July 15th, and extremely significantly and positively correlated with the period after August 15th, reaching a very significant level on November 1st (0.934 0). The mathematical model of monthly increment of transverse diameter and main monthly meteorological information was established (R2 =0.845 4). The correlation coefficient between the increment of transverse diameter and rainfall was significant (0.791 8) and the correlation coefficient between the increment of transverse diameter and average temperature was extremely significant (0.879 1), but the correlation coefficient with sunshine hours was only 0.286 6, which indi-cated that the fruit expansion of Orah was closely related to rainfall and temperature, and more rainfall and higher temperature were beneficial to fruit expansion, but other conditions also affected its development. This also showed that strengthening the management of water, fertilizer and pesticide can help the expansion of Orah fruit, thus improving its quality and yield.【Conclusions】There is still much room to improve the quality and yield of Guangxi Orah. In the future, we should vigorously strengthen the virus-free scion and disease-free seedling cultivation. On the basis of deep ploughing, heavy application of organic manure, and paying attention to drainage and reasonable pruning, we can use ampicillin to kill citrus Huanglongbing and canker, strengthen research and explore agricultural chemicals or microorganisms that can effectively cure or prevent CTV and CYVCV. In accordance with the current transverse diameter growth comparison table and the periodic difference comparison table, we can scientifically and reasonably arrange water, fertilizer and pesticide to further accelerate the fruit expansion, thus effectively improving the fruit diameter, yield and economic benefits of Orah and promoting the sustainable growth of the industry.