Drought tolerance testing of paddy variety Inpari 4 with PEG-6000 in the germination phase

Paddy (Oryza sativa L.) factors in the importance of life for Indonesians. The challenge that will be faced in the future is global warming which can cause drought in the agricultural sector. Paddy is very susceptible to drought during germination and early growth stages. Such drought can cause crop production to decline. This research aims to provide earlier information on drought-tolerant paddy varieties. The research carried out in the Laboratory of Ecology and Plant Production Management, Sebelas Maret University. It was applied FCRD consisting of the first factor of PEG-6000 concentration (C) which is 0% (C0), 10% (C1), 15% (C2), 20% (C3) and 25% (C4), the second factor of soaking duration (S) is 12 hours (S1), 24 hours (S2) and 36 hours (S3). The data obtained were analyzed using ANOVA and further tested with DMRT 5%. The results of research on seed viability from the application PEG-6000 which can have a drought effect show that at a temperature of 26°C produces germination of 84,30%, C3S3 gave the highest value on germination (90,50%) and growing speed (47,58%/etmal), C0 gives the highest value at lead length (29,05 cm) and C4 gives the highest value at radicle length (35,64 cm).


Introduction
Paddy (Oryza sativa L.) is the main food crop for most of the Indonesian population [1].Paddy is a rice-producing crop that is the staple food source to most Indonesian.Paddy commodities play a very important role in the lives of Indonesian people.Therefore, increasing paddy production needs to be done.
The challenge that will be faced in the future is global warming.Global warming can cause weather changes and climate changes.Weather changes with an increase in temperature will be inversely proportional to paddy production.An increase in temperature can lead to a decrease in yield in paddy [2].
In agriculture, climate change can cause droughts.Drought stress will be the biggest threat to Indonesia because the majority of paddy planted is rainfed rice paddy.During the germination and early growth stages, paddy is very susceptible to drought [3].In addition, lack of water can affect the anatomical, morphological, physiological, and biochemical properties of plants so that the resulting production decreases [4].One of the efforts to increase paddy production that can be done is to plant paddy using superior varieties that are resistant to biotic and abiotic stress.
Paddy variety Inpari 4 is one of the superior widely cultivated paddy varieties.The advantage of this variety is that it is able to produce 8,80 tons/ha of dry grain.Paddy variety Inpari 4 is one of the paddy that is widely cultivated by farmers in Indonesia, so it is necessary to test drought stress resistance in order to overcome climate change that will occur in the future.Drought tolerance testing in the germination phase can provide earlier information on tolerant genotypes.One way that is often used to simulate drought under controlled conditions (laboratory) is by administering PEG (polyethylene glycol) [5].
PEG-6000 is a material that has properties as an osmotic agent, which is a material that can cause the osmosis process [6].PEG can affect chemical and physiological changes in seeds, as they can cause it to experience a lack of water for germination [7] in other words seeds will experience drought.At certain concentrations PEG-6000 can cause drought as occurs on dry land [8].Drought testing in the germination phase is very important to do because this phase is the most critical growth stage and drought stress that occurs in this phase causes plant productivity to be very limited [9].Testing drought tolerance in the germination phase is one of the initial efforts that can increase paddy production yields during drought stress, so this research needs to be carried out for the welfare of farmers and residents of Indonesia.

Materials and methods
The research carried out in February 2023.Seed viability testing was carried out at the Laboratory of Ecology and Plant Production Management, Faculty of Agriculture, Sebelas Maret University.
The materials used are paddy seeds, PEG-6000, aquadest, and CD/opaque paper.The tools used are 1L beaker glass, petridish, tweezers, hand sprayer, and ruler.
The research design used was a Factorial of Completely Randomized Design (FCRD) consisting of 2 factors.The first factor was the concentration of PEG-6000 (C), is 0% (C0), 10% (C1), 15% (C2), 20% (C3), and 25% (C4).The second factor is the soaking duration (S), which is 12 hours (S1), 24 hours (S2), and 36 hours (S3).Each treatment combination was repeat 4 times to total 60 experimental units.The research procedures were carried out as follows:  Seed preparation and growing media : The seeds used were paddy variety Inpari 4 which were given invigoration treatment using aquadest (control) and PEG-6000.Paddy seeds were germinated by the test method on paper (UDK) using 3 sheets of moist CD/opaque paper media in a petridish.The seed viability test using 50 grains for each treatment combination was repeated 4 times. Making of invigoration solution : The solution to be used is prepared in advance.Each PEG-6000 requirement is weighed according to its concentration treatment, namely 0% (0 gram PEG/L solution), 10% (100 gram PEG/L solution), 15% (150 gram PEG/L solution), 20% (200 gram PEG/L solution), and 25% (250 gram PEG/L solution).Then put into beaker glass, and added aquadest until it becomes 1 liter and then homogenized [10]. Seed soaking treatment : The prepared paddy seeds are then soaked in PEG-6000 solution with concentrations of 0%, 10%, 15%, 20%, and 25% and soaked for 12, 24, and 36 hours respectively according to the treatment. Preparation of germination media : Paddy seeds were germinated by the test method on paper (UDK) using 3 sheets of moist CD/opaque paper media in a petridish.Germinated seeds were 50 grains for each treatment combination and each was repeated 4 times. Germination maintenance : Watering using a hand sprayer that is done every day or as needed.

Temperature
Temperature testing is carried out by germinating paddy seeds at various temperatures and observing the percentage of seed germination.

Germination and growth speed
Germination is observed in normally germinated seeds and calculations are carried out on the 5th and 7th days after planting.Growing speed is done by observing seeds germinating daily from 1 -7 days after planting.

Plumule and radicle length
The length of the plumule is observed by measuring sprouts from the stem base to the leaf tips.Observation of radicle length was carried out by measuring the root base to the root tip.Both were performed on normal sprouts at 7 days after planting.

Temperature
Germination carried out at a temperature of 26̊ C gives a germination yield with a percentage of 84,30%.This germination percentage is in accordance with the results of research [11], where in the temperature range of 22̊ C -28̊ C the percentage of germination is 87,31%.Further explains the decrease and increase in temperature from the optimal temperature can decrease the germination percentage.The following data from the research results [11].Based on the table, the results of germination studies conducted at a temperature of 26̊ C indicate suitable temperature conditions for paddy seed germination.[12] states that at very high and very low temperatures, the germination of all seeds will be inhibited.Good germination usually grows at optimum temperatures ranging from 20̊ C -30̊ C.This shows that the research carried out is in accordance with the optimal temperature of paddy seed germination.

Germination and growth speed
Germination testing parameters are carried out to determine how much the seeds can germinate in a certain period of time.Germination observations were made on day 5th (first count) and day 7th (final count).The speed of growth is carried out to determine the number of seeds that can grow every day until day 7.The percentage of germination and growth speed in Inpari 4 variety paddy seeds is shown in Table 2. Based on the results of the 5% DMRT follow-up test on the interaction of 20% concentration treatment and 36 hours soaking duration (C3S3) showed real different results and had the highest germination value and growth speed compared to 25% concentration treatment and 36 hours soaking (C4S3) and others namely 90,50% and 47,58%/etmal.This shows that too high a concentration of PEG-6000 is thought to cause the seed metabolism process to be so slower that the percentage of germination and seed growth speed is low.This is in line with research [13] regarding PEG-6000 concentrations that are too high, causing enzymes and reagent substrates to become runny so that metabolic process in seeds becomes slow.PEG-6000 is an osmotic solution, if the concentration of the osmotic solution is too high, the seeds will no longer absorb water in phase II.The water deficit caused by PEG-6000 can inhibit water molecules entering plant tissue [14].Restriction of water absorption in seeds causes seeds to experience drought as caused by climate change, resulting in a decrease in the percentage of germination and changes in cell metabolism in seeds [15].Climate change has a major impact on plant growth and the development of crops, including paddy seeds.In PEG-6000 with a concentration that is too high makes the osmotic pressure also high.High osmotic pressure causes a decrease in water absorption, resulting in reduced water availability and drought.Lack of water availability (drought) during the germination phase causes a low percentage of germination and growing speed in seeds [16].The higher the percentage of germination and the speed of seed growth in the drought conditions, the higher the vigor of the seed [17].
The duration of soaking seeds is related to the process of imbibition.The imbibition phase (phase II) is a physical process by which water is absorbed.The lag phase (phase II) is associated with low water uptake as dormant seeds transition to a germinating state, and the growth phase (phase III) is mark by a significant increase in water uptake associated with the emergence and growth of the radicle [18].Soaking of duration can also stimulate seed germination metabolism through enzyme activity [19].

Plumule and radicle length
Observation of plumula length was carried out by measuring the normal sprout part from the base root to the leaf tip at 7 days after planting.Observation of radicle length is carried out by measuring the normal sprouted part of the root base and root tip.Observations of each variable were made on day 7.The results of measuring the length of plumula and radicle are presented in Table 3.Based on the results of a 5% DMRT follow-up test on the variable observation of plumula length, PEG-6000 treatment at 0% (C0) concentration showed significantly different results than treatments at other concentrations.C0 treatment also has the highest plumula length value compared to other treatments, which is 29,05 cm.These results showed that the higher the concentration of PEG-6000 given, the shorter the plumula.Plumula growth in drought-choked plants will be shorter than in plants that are not choked by drought [20].This is a sign of adaptation to climate change from drought, plants with drought stress will attach importance to growth on the roots [21].Drought can lead to a greater reduction of above-ground plant organs compared to those in the soil [22].
Based on the results of the 5% DMRT follow-up test on the variable observation of radicule length, PEG-6000 treatment at 25% (C4) showed significantly different results from other concentration treatments and had the highest radicle length value compared to other treatments, namely 35,64 cm.These results indicate that the higher the concentration of PEG-6000 given, the longer the radicle.Higher concentrations of PEG-6000 can reduce the water potential in the media, thereby creating drought conditions such as the impact of climate change [23].In drought conditions, the plants response is to extend the roots to reach the water source [24].

Conclusion
Paddy production in Indonesia is declining, one of the causes is climate change.This causes farmers to be able to adapt by using varieties that are resistant to climate change, especially drought, such as the Inpari 4 variety of paddy.Paddy variety Inpari 4 has fairly good drought tolerance, as evidenced by the fact that the higher the concentration of PEG-6000 and the longer the soaking duration, the higher the germination and growth speed.The highest yield of germination and growth speed was found in C3S3 treatment of 90,50% and 47,58%/etmal.
A single treatment of PEG-6000 concentrations at plumule length and radicle length gave inversely proportional results.At the length of the plumula, the C0 treatment gave the highest result of 29,05 cm.While in radicule length, the treatment that gives the highest result is C4, which is 35,64 cm.The results show how plants adapt to climate change.

Table 1 .
Percentage of germination of paddy seeds at various temperature treatments.

Table 2 .
Further test results of the interaction of concentration treatment and soaking duration of PEG-6000 on germination and growth speed.
Notes: Numbers followed by the same lowercase letter in the same column showed no real difference in the 5% DMRT test.

Table 3 .
Results of further tests of PEG-6000 concentration treatment of plumule and radicle length.