Developing determination of gamma irradiation dose to increase sugarcane growth and yield

. Application of low radiation doses to seeds and plants can produce biostimulants so that they can increase plant growth and production. The study aimed to obtain the optimum radiation dose to obtain high sucrose content. The research was conducted at the Karangploso Research Station, Malang from October 2021 – October 2022. The research material was obtained from the first ratoon cane Bululawang variety whose seeds were irradiated in 2019. The treatments consisted of 4 radiation doses (30, 40, 50, and 60 Gy) and 1 treatment without radiation (control treatment) arranged in a randomized block design with 6 replications. The result of the study shows that plant growth (stem length and diameter, cane weight, cane per clump number) and yield component (sucrose content, sugar yield) are affected by radiation dose. The radiation dose required for the Bululawang variety to produce the highest sugar yield or increase of 0.3% without radiation is 4.7 Gy. The radiation dose required to obtain the highest sucrose content or increase of 0.45% without radiation is 5.7 Gy.


Introduction
Sugarcane is the primary commodity for sugar in Indonesia.However, the sugar yield of sugarcane in Indonesia is low, around 4.98 t/ha [1].Therefore, efforts have been made to increase yield by creating new superior clones for dry land conventionally and unconventionally.The engineering of superior clones has resulted in new clones with a yield potential of 10.35 t/ha [2,3].However, the potential yield has not been able to increase the average yield, so the engineering of new varieties is indispensable.
One way to create new superior varieties is through gen mutation by applying radiation.Low radiation doses applied to seeds and plants can result in biostimulants increasing growth and production [4].In addition, biostimulants present in plants will trigger faster growth to produce higher stover weight [5].If this happens to sugarcane, high cane productivity will be achieved.
The optimal radiation dose to increase productivity, sucrose content, and sugar yield is determined by the clones used.For example, NIA 0819 clone produces the highest cane productivity at a 10 Gy radiation level, while NIA 98 clone and BL 4 need 20 GY for the optimal result, and all clones produce the highest sugar yield at 40 Gy [6].A similar result, confirms that each cane clone responds differently to radiation dose [7].
The most dominant cane clone used in Indonesia is the Bululawang clone.The clone has high adaptability to the environment, so farmers like it very much.However, the clone is experiencing a degradation in its ability to produce high productivity, so it needs improvement.Moreover, there has been no information on its optimal radiation dose to produce the best growth, productivity, sucrose content, and sugar yield.Thus, we are interested in conducting this study to reveal the optimal radiation dose for the Bululawang clone to produce the highest sugar yield.

Methodology
The study took place in an experimental garden in Karangploso, Malang, from October 2020 to October 2021.We used the RC-1 sugarcane of the Bululawang variety, and radiation was done to the seed in 2019 as research material.We also used inorganic and organic fertilizers and pesticides.The materials used included hand refractometers, meters, scales, calipers, and other supporting tools.Treatments were arranged in a randomized block design with 6 replications.Treatments consisted of 4 radiation doses (30, 40, 50, and 60 Gy) and 1 control group without radiation.Each treatment in 1 replication consisted of 10 clumps.
First, the PC canes were harvested.After that, the remaining sugarcane stump was cut.A week after the stump was cut, irrigation was done.Irrigation was then done continuously once a month for the next 6 months.Next, weeding and earthing-up were done simultaneously in 3 stages.Stage I was done when the cane was 2-2.5 months, Stage II when the cane was 3-4.5 months, and Stage when the cane was 4-4.5 months.Next, NPK fertilizer was applied 1 month after stump cutting, while ZA fertilizer was applied 3 months after stump cutting.Finally, leaf stripping (of dry leaves) was done in stages: Stage I before the last earthing-up, Stage II when the cane was 7 months, and Stage III when the cane was 11 months.
Observations were made on growth, productivity, sucrose content, and sugar yield.Growth was observed before harvest by measuring the number of stalks per row, stalk height, stalk diameter, and cane weight when the cane was 8 months.Productivity, sucrose content, and sugar yield were observed when the cane was 12 months.Productivity was measured by weighing the weight of harvested stalk per block.Sucrose content was measured by taking 3 samples of harvested stalks per row and analyzing them in the laboratory.Sugar yield was calculated based on the productivity and sucrose content obtained.The data were analyzed using variance and followed by a 5% BNT test if the values differed significantly.Regression analysis was conducted to determine the response of the observed variables to radiation dose.If the response is a closed quadratic curve, the optimal radiation dose is determined by the equation 1.

The effect of radiation dose on growth
Growth parameters, including the number of stalks per row, stalk height, stalk diameter, and cane weight, were affected by radiation dose (Tables 1 and 2).A radiation dose of 30-40 Gy resulted in a stalk height not different from the control group (without radiation), while other  [8] shows that the cane height was affected by the radiation dose applied.Similar results were on Dianthus caryophyllus [9], tulips [10], and Andrographis paniculata [11].
Regression analysis showed that stalk height responded to an increase in radiation dose by forming a closed quadratic curve (Figure 1).These results show that the best radiation dose for stalk height is 16.2 Gy.Therefore, increasing the radiation dose above that dose causes a decrease in the obtained stalk height.Increasing the radiation dose above the optimal dose in maize causes a decrease in plant height [12].The obtained stalk diameter was influenced by the radiation dose applied (Table 1).The radiation dose of 30 Gy resulted in a stalk diameter that was not different from the control group (without radiation), while other radiation doses produced a smaller stalk diameter than the control group.A similar result on peanuts of the JL24 variety, that is stem diameter is affected by the radiation dose applied [13].
The regression analysis shows that the stalk diameter responded to an increase in radiation dose by forming a closed quadratic curve (Figure 1).The largest stalk diameter was obtained by the control group (without radiation).Radiation causes a decrease in the stalk diameter.
The cane weight was influenced by the radiation dose applied (Table 2).The radiation dose of 30 Gy resulted in a cane weight that was not different from the control group (without radiation), while other radiation doses produced a lower cane weight than the control group.Previous studies on Foeniculum vulgare [14] and Pterocarpus santalinus [15] show that plant weight is affected by the radiation dose applied.
The regression analysis shows that cane weight responded to an increase in radiation dose by forming a closed quadratic curve (Figure 2).The largest cane weight was obtained on the 1.2 Gy radiation dose.Increasing the radiation dose above that dose causes a decrease in the obtained cane weight.Low radiation doses can increase the weight of sorghum plants [16].The weight of an object is composed of its volume and the gravitational constant.Assuming the gravitational constant of sugarcane stalks is not affected by radiation treatments, the cane weight is affected by the stalk volume.The stalk volume is determined by the height and diameter of the cane stalk.In this study, the relationship between cane weight (BBAT) with height (PB) and diameter (DB) was obtained by forming the equation BBAT = 3.0721 PB** + 944.67 DB** -1821.297with a correlation coefficient (r) of 0.995**.The obtained correlation coefficient value (r) shows the total effect of stalk height and diameter on cane weight, it was 99.5%, in which stalk height affected 48.32% and diameter affected 51.18% of the cane weight.Thus, it can be concluded that the weight loss of sugarcane stalks due to radiation treatments occurred through a decrease in the obtained stalk height and diameter.
The number of stalks per clump was influenced by the radiation dose applied (Table 2).The radiation dose of 30-50 Gy resulted in a number of stalks per clump that was not different from the control group (without radiation), while the radiation dose of 60 Gy resulted in a lower number of stalks per clump.The regression analysis shows that the number of stalks per clump responded to an increase in radiation dose by forming a closed quadratic curve (Figure 2).Based on the obtained equation, the radiation dose needed to get the highest number of stalks per clump was 11.9 Gy.Increasing the radiation dose above that dose causes a decrease in the obtained number of stalks per clump.Increasing the radiation dose above the optimal dose causes a decrease in the obtained tillers of Digitaria exilis [17].

The effect of radiation dose on productivity
Production components of sugarcane affected by radiation dose are productivity and sugar yield, while sucrose content is not affected by radiation dose (Table 1).The radiation dose of 30-40 Gy resulted in productivity that was not different from the control group (without radiation), while other radiation doses resulted in lower productivity.The regression analysis shows that productivity responded to an increase in radiation dose by forming a closed quadratic curve (Figure 3).The results show that the best radiation dose to produce the highest productivity was 4.7 Gy.Increasing the radiation dose above that dose causes a decrease in the obtained productivity.Increasing the radiation dose above the optimal dose causes a decrease in the obtained productivity of tomatoes [18].The obtained correlation coefficient value (r) shows the total effect of cane weight and the number of stalks on cane productivity was 100%, in which cane weight affected 50.82%% and the number of stalks affected 49.18% of productivity.Thus, it can be concluded that decreased productivity due to radiation treatments occurred through a decrease in the obtained cane weight and the number of stalks.
A radiation dose of 30-60 Gy could not affect the sugar yield of the Bululawang clone.A similar result using the NIA 2004 clone [7].However, a different finding with the NIA 0819, NIA 98, and BL 4 clones [6].The radiation dose of 30 Gy resulted in a sugar yield that was not different from the control group (without radiation), while higher radiation doses resulted in lower sugar yield (Table 3); Khan et al. [7] and Yasmeen et al. [6] confirm the same finding.The regression analysis shows that sugar yield responded to an increase in radiation dose by forming a closed quadratic curve (Figure 3).Based on the obtained equation, the radiation dose needed to get the highest sugar yield was 5.7 Gy.Increasing the radiation dose above that dose causes a decrease in the obtained sugar yield.
Cane productivity and sucrose content are the components forming sugar yield.Since sucrose content was not affected by radiation dose, sugar yield was only affected by cane productivity.The regression analysis shows the relationship between sugar yield (HABLUR) and cane productivity (PROTAS).The relationship can be written using the formula HABLUR = 0.098186 PROTAS -17.69092 with a correlation coefficient (r) of 1.000**.Thus, it can be concluded that decreased sugar yield due to radiation treatments occurred through a decrease in the obtained productivity.

Conclusion
The findings and discussion show that growth (stalk height and diameter, cane weight, and the number of stalks per clump) and production components (productivity and sugar yield) were affected by radiation dose.The radiation dose by the Bululawang sugarcane variety to produce the highest cane productivity or an increase of 0.3% from the control treatment (without radiation), was 4.7 Gy.The radiation dose needed to achieve the highest sugar yield, or an increase of 0.45% from the control treatment (without radiation), was 5.7 Gy.

Fig. 1 .
Fig. 1.Responses on stalk height and stalk diameter of the Bululawang clone to an increase in radiation dose.

Fig. 2 .
Fig. 2. Responses on cane weight and number of stalks per clump of the Bululawang clone to an increase in radiation dose.

Fig. 3 .
Fig. 3. Responses on cane productivity and sugar yield of the Bululawang clone to an increase in radiation dose.Cane weight and the number of stalks are the two components affecting cane productivity.In this study, the relationship between cane productivity (PROTAS) with cane weight (BBAT) and the number of stalks (JBAT) was obtained by forming the equation PROTAS = 6.8139BBAT** + 912.53 JBAT** -6221.974with a correlation coefficient (r) of 1.000**.The obtained correlation coefficient value (r) shows the total effect of cane weight and the number of stalks on cane productivity was 100%, in which cane weight affected 50.82%% and the number of stalks affected 49.18% of productivity.Thus, it can be concluded that decreased productivity due to radiation treatments occurred through a decrease in the obtained cane weight and the number of stalks.A radiation dose of 30-60 Gy could not affect the sugar yield of the Bululawang clone.A similar result using the NIA 2004 clone[7].However, a different finding with the NIA 0819, NIA 98, and BL 4 clones[6].The radiation dose of 30 Gy resulted in a sugar yield that was not different from the control group (without radiation), while higher radiation doses resulted in lower sugar yield (Table3); Khan et al.[7] and Yasmeen et al.[6] confirm the same finding.The regression analysis shows that sugar yield responded to an increase in radiation dose by forming a closed quadratic curve (Figure3).Based on the obtained equation, the radiation dose needed to get the highest sugar yield was 5.7 Gy.Increasing the radiation dose above that dose causes a decrease in the obtained sugar yield.Cane productivity and sucrose content are the components forming sugar yield.Since sucrose content was not affected by radiation dose, sugar yield was only affected by cane productivity.The regression analysis shows the relationship between sugar yield (HABLUR) and cane productivity (PROTAS).The relationship can be written using the formula HABLUR = 0.098186 PROTAS -17.69092 with a correlation coefficient (r) of 1.000**.Thus, it can be concluded that decreased sugar yield due to radiation treatments occurred through a decrease in the obtained productivity.

Table 1 .
Obtained stalk height and diameter after treatments (radiation).Numbers accompanied by the same letter in one column are not significantly different in the 5% BNT test.

Table 2 .
Cane weight and the number of stalks per clump after treatments (radiation).Numbers accompanied by the same letter in one column are not significantly different in the 5% BNT test.

Table 3 .
Productivity, sucrose content, and sugar yield after treatments (radiation).Numbers accompanied by the same letter in one column are not significantly different in the 5% BNT test.