Character Selection and Tolerance Screening Efectivity on Static Hydroponic Method Under Drought Stress in Rice

This research was aimed to evaluate the efectivity of screening method and identification of tolerance screening selection character in statis hydroponic system towards drough stress. The research was carried out in Hydroponic Screenhouse Perdos Unhas, Tamalanrea, Makassar which throughout February-April 2020. This research was conducted in factorial design in nested patterns, where environment was the nested replication. Environments used were normal (0% PEG) and drought stress (10% PEG). Five rice varieties were used: Inpari 34, Ciherang, IR29 and Jeliteng. Research result showed that canopy height and fresh weight were the suitable selection character in drought tolerance screening through statis hydroponic cultivation. Grouping consistency was found between drought and salinity stress. Inpari 34, Ciherang, Jeliteng and Inpari 29 was considered to be have drought tolerance, whilst IR29 was examined to be responsive to drough stress in hydroponic culture. From the overall result, it can be concluded that hydroponic screening and PEG application was quite effective in rice drought stress tolerance screening

lines germinating phase screening under drought stress had been reported by Akbar et al (2018a). The solution is able to be used as an alternative to drought stress selection in hydroponic culture. The determination was necessary to be conducted on a number of released varieties to examine their effectivities. The research aimed to evaluate screening method and identify selection character tolerance screening in static hydroponic system under drought stress.
The experiment was done with hydroponic system according to modified IRRI Standard Evaluation System (SES) (IRRI, 2013). Seeds from each variety were firstly germinated in germinating containers. Seeds that grew well were transplanted in treatment container seven days after sowing with Abmix volume 8 L per container. AB mix concentration used was 5 mL/L water each stock solution. Seedlings then were transplanted in foam container and inserted in styrofoam holes. Each hole was 2 cm in diameter with 4 cm x 3 cm spacing. PEG applicatipn was done as osmotic stress induction on 14 days after sowing gradually to prevent osmotic shock (Swapna & Shylaraj, 2017). 5% PEG 6000 was given in the first stage of concentration application, equal to 500 g PEG per liter. PEG concentration was optimalized to 10% after three days. On contrary, plants with PEG 0% treatment (control) were planted in normal condition with AB mix hydroponic solution. Maintenance included nutrient application, pH value checking and water checking and nutrient container cleaning. Solution pH was maintained at 5,0-5,1 with NaOH 1N and HCl 1N.
Tolerance characterand biomass harvest was observed at 14 days after application. Observed parameters included canopy height (cm), number of tillers, number of leaves, root length (cm), fresh root weight (g) and fresh canopy weight (g). Obtained data were then analysis with ANOVA. Characters that indicated significant interaction will be proceeded with relative derivation analysis and tolerance mapping from five tested varieties. Software used for analysis was STAR 2.1.

C. Result and Discussion
Analysis of variance showed variety influenced significantly towards number of leaves, canopy height and fresh canopy weight. Significant effect was also shown in varied PEG concentration towards number of tussels, number of leaves, canopy height and fresh canopy weight. Even so, interactions between varieties and PEG concentration only presented significant value on canopy height and fresh weight. According to the result, these two characters are recommended as selection characters. Analysis of variance is one of determining indicator on tolerance screening effectivity under a certain stress (Al-Amin, Islam, Begum, Alam, Moniruzzaman, & Patwary. 2013; Al-Naggar, Sabry, Atta & El-Aleem, 2015; Safitri, Purwoko, Dewi, & Ardie, 2016). Effectivity evaluation was weighed on the significant influence of the interactions. Significant interaction effects between genotypes and environment will deliver varied respon pattern of genotype on different growing environment (Akҫura & Ҫeri, 2011;Safitri et al. 2016;Anshori et al., 2019). If this was related with drought stress tolerance, significant interactions of a character would show different adaptability respond of genotypes under drought stress. For this reason, canopy height and fresh weight can be used in tolerance screening evaluation. This was also supported by research conducted by Anshori et al. (2020) that delivered significant interactions of canopy height and fresh weight in rice tolerance screening through hydroponic culture. Despite the fact that salinity was used in the research, the stress was relatively similar to drought in terms of osmotic stress (Ghosh, Ali, & Saikat, 2016;Reddy, Kim, Yoon, Kim, & Kwon, 2017), thus making them tolerance screening indicator to osmotic stress. Therefore, both characters were the base for the next analysis in this research.
Canopy height and fresh weight as selection characters in static hydroponic system also indicated that drought stress or osmotic effected more on canopy compared to the roots. Generally, when plants experience drought stress, the growth will be focused on root development. This is to optimize water and nutrient absorbtion width for fulfilling both of needs in plants (Mohamadi, Bagheri, Kiani, & Jelodar, 2017). However, relatively tolerant tenotype are able to make efficient water balance for plant growth, resulting in more adaptable cell division or canopy growth compared to responsive genotypes (Anshori et al., 2020). Osmotic stress will induce a number of osmoticum regulator compounds. Relatively responsive plants will produce large amount of osmoticum compound. The similar result was also discovered by Anshori et al. (2019) on dihaploid rice towards salinity stress. The occurance caused minimal canopy growth due to decreased energy and photosintate, influencing some of canopy characters. Inhibited canopy growth was also supported with absisic acid hormone induced during the occurred drought stress (Chaturvedi, Singh, Bahadur, 2012;Sah, Reddy, & Li, 2016). Thus, canopy growth was more considered as selection character compared to root characters.
Relative reduction from canopy height and fresh weight is shown in Table 2. The relative reduction from canopy height averaged in 31.02%, while the average relative reduction from canopy fresh weight was 65%. V3 was the most impacted variety, indicated in plant height (41.01%) and fresh canopy weight (79.38%). Varieties with low relative reduction were V1 (26.66%), V2 (27.36%), and V5 (26.74%) on canopy height as well as V4 (58.20%) for fresh canopy weight. Relative reduction is an approach in order to evaluate tolerance of a genotype. This variable using has been widely reported in researches related to environmental stress screening in various plants (Ali, Yeasmin, Gantait, Goswami, & Chakraborty, 2014;Krishnamurthy, Sharma, Gautama, & Kumar, 2014;Souleymane, Nartey, Manneh, Danquah & Ofori, 2016;Safitri et al. 2016). Based on this analysis, fresh canopy weight gave more relative reduction value compared to canopy height in drought stress. Commonly, fresh canopy weight is a character directly related to canopy water content. On the other hand, plant height indirectly related to water content in the plant (Anshori et al, 2020). Based on the statement, Fresh canopy weight gave more negative impact result compared to plant height under salinity through hydroponic screening. Similarly, it was also reported by Anshori et al. (2020) on rice salinity screening and Kumar, Binodh, Saravanan, Senthil, & Kumar, (2019) on rice drough screening. Therefore, fresh canopy weight screening was more prioritized as selection character.
Tolerance mapping result of five rice varieties under drought stress was shown in Picture 1. V3 is shown in the first quadrant with high relative reduction in canopy height and fresh weight. V1, V2, and V5 is found in third quadrant with below average relative reduction values both on canopy height and fresh weight. V4 found in fourth quadran indicated low relative reduction towards canopy fresh weight yet with above average canopy height relative reduction.

Figure 1. Tolerance mapping of five characters according to selection character
According to the mapping in Picture 1., canopy height and fresh weight was shown having the same tolerance, excluding Inpari 29. This indicated that the drought tolerance character evaluation based on the two characters had high precision. Based on the previous discussion, however, canopy fresh weight was more prioritized in genotype evaluation compared to canopy height. Thus, Inpari 29 was considered having moderate tolerance under drought stress. This was caused due to high amount of absisic acid and cell resistency in order to maintain its turgor (Munns & Tester, 2008), therefore pushing lower canopy weight reduction and inhibit relative plant growth. Despite the stated fact, the two characters can be recommended as a pair of drought tolerance selection criteria in hydroponic culture.
Mapping result can be used to illustrated consistency between drought stress and salinity according to the mapping result in this research. Inpari Agritan 34 as salinity tolerant also has good tolerance in PEG induced drought stress. Toxicity is also a primary stress besides osmotic. However, relative salinity tolerance plants have good drought tolerance. The overall result can be concluded that static hydroponic with PEG selection had good effectivity in drought stress genotype selection.

D. Conclusion
Hydroponic screening and PEG 6000 application was considered quite effective in rice tolerance screening towards drought stress. Canopy height and fresh weight were good selection characters in drought stress tolerance screening. Grouping consistency was found between drought and salinity stress. Inpari 34, Ciherang, Jebbliteng and Inpari 29 was considered having good tolerance under drought stress, whilst IR29 was considered as responsive variety under drought stress in hydroponic culture.