# Application of an intensive harvesting system allows identification of tapping panel dryness-susceptible genotypes in Hevea brasiliensis

M Aji, S Ismawanto, A N Cahyo, P Montoro

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M Aji, S Ismawanto, A N Cahyo, P Montoro. Application of an intensive harvesting system allows identification of tapping panel dryness-susceptible genotypes in Hevea brasiliensis. IOP Conference Series: Earth and Environmental Science, 2025, 1526, pp.012002. 10.1088/1755-1315/1526/1/012002. hal-05223728

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# Application of an intensive harvesting system allows identification of tapping panel dryness-susceptible genotypes in *Hevea brasiliensis*

To cite this article: M Aji et al 2025 IOP Conf. Ser.: Earth Environ. Sci. 1526 012002

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# Application of an intensive harvesting system allows identification of tapping panel dryness-susceptible genotypes in *Hevea brasiliensis*

M Aji¹*, S Ismawanto¹, A N Cahyo¹, P Montoro²

¹Indonesian Rubber Research Institute, Jalan Raya Palembang–Pangkalan Balai Km 29, Sembawa, Banyuasin, Sumatera Selatan 30953, Indonesia

²CIRAD, UMR AGAP Institut, F-34398 Montpellier, France

*E-mail: martiniaji.ma@gmail.com

**Abstract.** Rubber (*Hevea brasiliensis*) is natural rubber-producing trees that have a wide range of adaptability to climate conditions. Tapping Panel Dryness (TPD) is a physiological disorder that can affect latex production. The percentage of TPD occurrences in big plantations can reach 7-15%, while in smallholders could be greater. This study aimed to see the distribution of latex production and the occurrence of TPD in a biparental population under an intensive harvesting system. The study used a biparental population from crosses of PB 260 (TPD susceptible clone) and SP 217 (TPD resistance clone) clones planted in a small-scale clone trial plot. The plot consists of 201 genotypes and 8 control clones. Clustering based on production and dry cutting length could reveal the potential analysis of promising TPD-tolerant genotypes. This study suggests that the application of an intensive harvesting system can be considered to discard TPD-susceptible genotypes.

## 1. Introduction

The rubber tree (*Hevea brasiliensis*) is an estate crop that is the main source of natural rubber. It is widely cultivated in tropical areas, such as Indonesia, Malaysia, and Thailand. Indonesia is the world's second largest rubber producer after Thailand (1). Although Indonesia has the most land, rubber productivity remains low in comparison with other producers. Rubber productivity in Indonesia showed a downward trend of 3.61% per year in the period 2017-2021 (2). Most rubber plantations in Indonesia (92%) belong to smallholders (3). Low adoption of cultivation technology is the main reason for the low productivity of smallholder rubber. Some farmers still use seedlings as planting material and carry out tapping with high high-intensity system.

The main product in harvesting rubber is a white sap called latex. Latex is biosynthesized and accumulated in latex cells, which are cambium derivatives, arranged as concentric rings with gaps that connect to each other so that latex can flow from all areas on the bark when a wound occurs. Rubber trees are harvested through tapping activities, a technique for opening latex vessels so that the latex can flow out. For sustainable productivity, rubber tapping needs to pay attention to clone type, plant age, agroecosystem, and local seasonal variations (4).

Rubber has a wide range of adaptability to climatic conditions. One of the limiting factors that significantly affects the production and growth of rubber plants is rainfall. Darmandono (5) stated that the best characteristic of rainfall for rubber was 1,800 – 2,500 mm/year, with 115-150 rainy days, and 5-6 dry months. Excessive rainfall could lead to tapping disorders and increased disease

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intensities. Conversely, drought conditions would inhibit the growth and production of rubber plants.

Increasing rubber productivity can be approached by planting superior clones, optimum agronomical practices, and good tapping management. Superior clones were produced from segregant selection from existing genetic diversity sources from crosses of the selected parents (6). Mistakes in selecting clones will cause losses during one rubber plant cycle. Plant breeding activities in Indonesia have been running for four generations which have produced various clones with higher productivity compared to seed-derived plant production (7). Breeding activities start from crossing selected parents, testing through small-scale clone trials, and testing the agroclimatic adaptation.

In the process of rubber tapping, there is a physiological disorder that affects the production of latex. This syndrome is known as Tapping Panel Dryness (TPD) which is induced by stress, either due to the harvesting system or the environment (8). TPD caused by climate change (environment) may significantly affect world rubber production (9). Lost in production was estimated at 15-20% of annual rubber production in Sri Lanka and India (10,11). The mechanism of TPD is mainly due to the accumulation of reactive oxygen species (ROS) that occurs as stress in plants, either exploitation or stimulants. Over-production of ROS that cannot be countered by the ROS scavenging system will damage the lutoid membrane, which puts its integrity at risk. Decompartmentalization of the lutoid leads to the release of different types of proteins involved in rubber particle agglutination and results in the cessation of latex production(12).

TPD occurs in almost all rubber plantations around the world, both in big plantations and smallholders. The percentage of TPD occurrence in big plantations could reach 7-15%, while in smallholders could be greater, even reaching 30% (13). The higher TPD percentage in smallholder plantations is due to the use of susceptible clones and the application of intensive harvesting practices. Putranto and collaborators (12) found that high metabolism clones had a higher incidence of TPD than low metabolism clones. Herlinawati and collaborators (8) discovered that some clones with high latex metabolism and high sucrose could be TPD tolerant. The emergence of TPD is also triggered by an imbalance between latex regeneration in latex vessels and its uptake through tapping (14). Thus, the application of intensive tapping will increase the risk of TPD.

TPD occurs when rubber is tapped for several years. Symptoms of the attack are usually noticed due to lower production. The level of TPD can be determined by observing dry cut length (DCL) by calculating the percentage of tapping cuts that do not emit latex immediately after tapping. DCL observation is performed visually. Research conducted by Putranto and collaborators (12) using different types of clones followed by stimulant application showed differences in response to DCL levels. The results showed that the d1 tapping plus stimulant application revealed a high level of DCL at five months after treatment, while SP 217 showed a high level of DCL at 2 years during the study. Furthermore, Herlinawati and collaborators (8) conducted research on the induction of intensive harvesting systems using d1 and stimulant applications every month, showing that high DCL levels occurred in the 5th month after treatment and continued until 24 months of the experiment. This shows that the application of an intensive harvesting system (d1 ET 12/y) induces the occurrence of TPD earlier.

In this research, a biparental population from cross-breeding was tested in a small-scale clone trial plot to obtain information on potential prospective clones, and by applying daily tapping on the biparental population, it was expected to obtain information on the potential of clones that are resistant to high-intensity tapping. This study aims to see the distribution of biparental population production through an intensive harvesting system and the effect of tapping panel dryness occurrence.

## 2. Materials and methods
The experiment was carried out from January 2022 to December 2022 at the Indonesian Rubber Research Institute (IRRI) Experimental Garden located in the Sembawa, Banyasin Regency, South Sumatra. IRRI's experimental garden is located at an altitude of ±10m above sea level and the land topography is relatively flat (0-3%). It is dominated by red-yellow podzolic soil, clayey to sandy clay texture, slightly sticky consistency, and fairly good drainage.

The study was conducted using a biparental population derived from crossbreeding PB 260 and SP 217 planted in a small-scale clone trial plot. PB 260 is one of TPD susceptible clone, whereas SP217 tends to be more tolerant (12). The plot consisted of 201 genotypes and 8 control clones. The study used a randomized block design with 5 replicates and each replicate contained all the genotypes tested. The plants used were planted in 2016 with a planting distance of 6 m × 3 m. The tapping system used is half spiral (S/2) with daily tapping (d1) and additional stimulant application with a concentration of 2.5% every month. Stimulants were applied 12 times in a year.

The data obtained through direct observation included production and percentage of dry cut length (DCL). Rubber production was measured as total production in the form of cup lumps. After tapping, the latex was left uncollected until it coagulated in the collection cup to form a cup lump. The lump was collected and weighed before the next tapping. Observations were made every tapping with variable units calculated in dry rubber per tree per tapping (g/p/s). Dry rubber content (DRC) has been calculated using the Chee method. (15): DRC= DW/WW × 100%; where DW= dry weight; WW = wet weight. The DCL is the percentage of tapping cuts that do not emit latex, this parameter is observed every month.

All the observation data obtained were inputted into Microsoft Excel (Microsoft® Excel® 2019 MSO (16.0.14332.20848) 64-bit) and analyzed using XLStat (16). The observation results of each genotype were calculated based on the average trees and the LS-mean calculation was carried out using ANOVA. K-means clustering was performed with XLStat.

### 3. Results and discussion

The pattern of rubber production and percentage of dry cut length showed seasonal variations every month (Figure 1.). In May and September, the average production tended to decrease, while in July the distribution of production tended to increase. This could be caused by less number of rainy days in July than in May and September so tapping days were more optimal. Distribution of DCL percentages showed that there was a tendency for DCL increment, 4 months after intensive harvesting system treatment was applied, even though there was an increase or decrease in rainfall.

In the trial results, it was obtained that the production of SP 217, which was the parent of the genotypes tested, had a high production, while PB 260 was classified as medium. There were 38 genotypes that had high production, and 82 genotypes had medium production along with the control clones PB 260, RRIC 100, IRR 39, and IRR 112. While the others, 81 genotypes and 3 control clones (AVROS 2037, GT1, and PR 261) had low production.
<figure><img src="image_5.png" /><figcaption>Figure 1. Box plots showing monthly yield (A) and DCL (B) distributions within the F1 population in 2022</figcaption></figure>

The K-means method was used to classify the DCL parameters (Figure 2). The genotypes were classified into three classes. The graph shows that the application of an intensive harvesting system could increase the percentage of DCL. However, individuals in cluster 1 showed a dramatic increase in the fourth month after treatment. Clusters 1, 2, and 3 consist of 33, 99, and 77 individuals, respectively. Cluster 1 consists of 33 genotypes, cluster 2 consists of 95 genotypes and some control clones, and cluster 3 consists of 73 genotypes and the rest of the control clones. In this selection, it was necessary to pay attention to cluster 3, where several genotypes had a fairly high DCL percentages. PB 260, a clone that is very popular in smallholders and has a high incidence of tapping panel dryness (TPD) included in cluster 3, while the parent clone SP 217 belonged to cluster 2. So that, the genotypes on cluster 3 must be discarded.

<figure><img src="image_6.png" /><figcaption>Figure 2. K-means clustering on DCL for F1 population and control clones</figcaption></figure>

Selection of a biparental population could be done by comparing phenotypic traits with their parents. The amount of genetic influence on a plant's character can be known from its heritability.
In this study, a high heritability value was obtained in May which reached 86%. In May, it was the peak of DCL after the intensive harvesting system was applied. The level was higher compared to the previous study (16,17). This high heritability may be due to the accuracy of phenotyping or the density of genetic markers.

In rubber, the breeding selection process takes a long time, considering that one rubber plant cycle can reach more than 20 years. Selection that has been done is generally based on production, disease, and environmental stress resistance. Whereas in smallholders' plantations, in addition to complaints against disease attacks, another issue is lost production due to TPD. Generally, TPD is categorized as a physiological disorder due to over-exploitation. Putranto and collaborators (13) showed that TPD-tolerant clones such as SP 217 trigger TPD occurrence after 24 months of intensive harvesting system while TPD-susceptible clones have TPD symptoms only after a few months. This study confirmed that TPD-susceptible genotypes developed TPD under the application of IHS within four months after treatment. This suggests that IHS can be a potential testing parameter to characterize clones that are susceptible or resistant to TPD in conventional breeding.

**4. Conclusion**

The application of an intensive harvesting system (IHS) on plants of a biparental population from the cross between PB 260 and SP 217 showed that there are three classes of intensity of TPD. The genotypes in the class with high TPD occurrence are considered to be TPD-susceptible genotypes that may be excluded from subsequent large-scale clone trials. This shows that the application of IHS in the plant breeding process can be an effective method in identifying genotypes that are susceptible to TPD. The application of IHS in the early selection of clones can be taken into consideration for the selection of TPD-resistant clones. It is planned to continue research on the selected genotypes in order to obtain comprehensive data for the new clones.

**Acknowledgment**

This research was funded by Agropolis Foundation through RUBIS Project in collaboration with CIRAD, IRRI, and UGM.

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