Why Harvest Timing Matters for Siam Orange
Siam orange is an important citrus commodity cultivated in Bali, with Kintamani in Bangli Regency recognized as one of the production areas. Fruit quality can vary depending on growing conditions and the stage at which fruit is harvested.
Harvest maturity is particularly important because citrus is classified as a non-climacteric fruit. Unlike some fruits that can continue substantial ripening after harvest, citrus quality development is more closely associated with conditions before harvest and the maturity stage when the fruit is picked. This makes appropriate harvest timing relevant to characteristics such as sweetness, acidity, vitamin C content, juice content, and water retention.
The researchers also examined KHP as a potential plant biostimulant. Protein hydrolysates contain peptides and amino acids produced through the breakdown of proteins and can influence physiological processes in plants, including nutrient utilization, water balance, photosynthetic characteristics, and responses to environmental stress.
However, higher concentrations do not necessarily produce stronger responses. Plant species, product composition, environmental conditions, application timing, and dosage can all affect how plants respond to protein hydrolysates.
Testing KHP on Siam Orange Trees in Kintamani
The research was conducted in a farmer's Siam orange orchard in Bayung Gede Village, Kintamani District, Bangli Regency, Bali. The researchers used approximately 12-year-old Siam orange trees growing within the same orchard area and under relatively uniform management conditions.
Three KHP concentrations were tested: 0, 2, and 4 mL per liter. The 0 mL per liter treatment served as the control.
The researchers also compared three harvest maturity stages: fruit harvested before physiological maturity, characterized by glossy green skin; fruit at physiological maturity, characterized by green skin beginning to develop a yellowish tint; and fruit harvested after physiological maturity, when the skin had become uniformly yellow.
The experiment therefore included nine treatment combinations, with four biological replications for each combination and 36 trees in total. KHP was applied by spraying the plant canopy four times, beginning at flowering and continuing through fruit development.
The researchers measured physiological indicators including leaf water content, chlorophyll, canopy light transmission, leaf sugar, phosphorus, and potassium. Fruit quality was evaluated through fruit weight, vitamin C, total soluble solids (TSS), titratable acidity, the TSS-to-acidity ratio, juice content, water content, and weight loss during storage for up to 21 days.
KHP at 2 mL per Liter Produced Notable Plant Responses
The results showed that KHP concentration significantly affected several physiological characteristics of the plants.
The 2 mL per liter treatment produced a relative leaf water content of 80.91 percent and chlorophyll content of 65.30 SPAD. At the same concentration, light transmission into the lower part of the canopy was the lowest, at 26.94 percent.
KHP concentration did not significantly affect total leaf sugar or the phosphorus and potassium content measured in the study. Increasing the concentration from 2 to 4 mL per liter also did not produce a further increase in relative leaf water content or chlorophyll.
The researchers therefore identified 2 mL per liter as a concentration associated with favorable responses for several measured parameters under the conditions of the experiment. However, the findings do not demonstrate that KHP directly increased photosynthetic rate because photosynthesis and leaf area index were not directly measured.
Harvest Maturity Changed Sweetness, Acidity, and Vitamin C
Harvest maturity had a clear relationship with several aspects of fruit quality.
Fruit harvested at physiological maturity contained 161.33 mg of vitamin C per 100 grams. Total soluble solids increased from 8.31 °Brix before physiological maturity to 8.86 °Brix at physiological maturity and 9.38 °Brix after physiological maturity.
At the same time, titratable acidity decreased from 1.77 percent before physiological maturity to 1.00 percent at physiological maturity and 0.60 percent after physiological maturity.
As a result, the TSS-to-acidity ratio increased substantially from 6.51 to 10.99 and then 15.61 across the three maturity stages.
These results indicate that fruit maturity is associated not only with changes in sweetness but also with acidity and vitamin C. Physiologically mature fruit showed a combination of characteristics including relatively high vitamin C, high fruit weight, moderate TSS, and lower acidity compared with fruit harvested before physiological maturity.
The 2 mL-per-Liter KHP Treatment Also Affected Fruit Water and Juice Content
The interaction between KHP concentration and harvest maturity affected juice content, total fruit water content, and weight loss after 21 days of storage.
The combination of 2 mL per liter KHP and physiological maturity produced the highest fruit water content, at 88.72 percent, while juice content reached 44.13 percent.
Meanwhile, fruit receiving 2 mL per liter KHP and harvested after physiological maturity recorded the highest juice content, at 47.43 percent.
For weight loss during 21 days of storage, fruit harvested at physiological maturity without KHP showed the lowest numerical value, at 13.02 percent. The corresponding value for the 2 mL per liter KHP treatment was 14.24 percent. However, the statistical results placed these values in overlapping groups, meaning the difference could not be considered statistically significant.
Implications for Siam Orange Production
The findings provide practical information for growers and researchers working with Siam orange in Kintamani. KHP at 2 mL per liter was associated with favorable responses in several plant and fruit characteristics, while harvest maturity strongly influenced fruit quality.
According to Putu Bujangga Wahyu Kharisma Putra, I Nyoman Rai, and Ni Nyoman Ari Mayadewi of Udayana University, the combination of KHP concentration and harvest maturity should be considered together because different quality characteristics responded differently to the treatments. The researchers reported that 2 mL per liter KHP and physiological maturity produced several favorable characteristics, but they did not designate the combination as universally optimal for every measured parameter.
For farmers, the findings may contribute to more informed decisions about biostimulant application and harvest timing. For the broader horticultural sector, the results provide a basis for further research into improving fruit quality while maintaining appropriate harvest practices.
The researchers recommend additional trials across different seasons, orchards, and environmental conditions before the findings are broadly applied at the commercial level. Further research could also examine narrower KHP concentrations around 2 mL per liter and directly measure photosynthetic rate and leaf area index. Additional postharvest measurements, including respiration, consumer acceptance, fruit damage, and microbiological characteristics, could provide a more comprehensive picture of fruit quality and storage performance.
Author Profile
Putu Bujangga Wahyu Kharisma Putra is affiliated with the Master's Program in Agrotechnology, Faculty of Agriculture, Udayana University. I Nyoman Rai and Ni Nyoman Ari Mayadewi are affiliated with the Laboratory of Agronomy and Horticulture, Faculty of Agriculture, Udayana University. Their work in this article focuses on plant physiological responses, horticultural production, harvest maturity, and the physicochemical quality of Siam orange fruit.
.jpg)
0 Komentar