Studies on direct and indirect effects at seedling stage stress conditions in early backcross population of rice (Oryza sativa L.)

Introduction

Rice, scientifically known as Oryza sativa L., holds an esteemed position as one of the most indispensable staple crops on a global scale. With its ability to provide nutrition for over half of the world's population, rice serves as a fundamental source of nourishment for billions of individuals (Fanzo et al., 2013) [1] . The potential yield of rice is influenced by various factors, including nutrient availability in the soil. Nutrient stress, particularly deficiencies in essential elements such as nitrogen (N), phosphorus (P), and potassium (K), can significantly limit rice productivity (Dobermann and Fairhurst, 2000) [2] . In regions where soil fertility is compromised or where fertilizer application is limited due to economic constraints, nutrient stress poses a formidable challenge to rice cultivation, jeopardizing food security and livelihoods.

Direct Seeded Rice (DSR) Cultivation

Direct Seeded Rice (DSR) cultivation refers to a method of rice production where seeds are sown directly into the field without the need for nursery raising and subsequent transplantation. DSR is characterized by its simplicity, efficiency, and resource-saving nature, as it eliminates the labor-intensive process of seedling preparation and transplanting, thereby reducing costs and saving water (Pandey et al., 2012) [3] . In DSR, seeds are typically broadcast or drilled into wellprepared fields with adequate soil moisture, facilitating rapid germination and establishment of seedlings (Fischer et al., 2019) [4] . This method offers flexibility in planting time, enabling farmers to synchronize planting with favorable weather conditions and optimize crop establishment. Direct Seeded Rice (DSR) has gained attention as a viable alternative to traditional transplantation methods due to its numerous benefits, including significant water conservation, reduced labor requirements, earlier crop maturity, and lower greenhouse gas emissions. DSR can decrease water use by up to 50%, making it an attractive option in waterscarce regions (Farooq et al., 2011) [5] . It also eliminates the labor-intensive process of transplanting seedlings, thereby cutting labor costs and increasing efficiency (Kumar and Ladha, 2011) [6] . Furthermore, DSR can lead to earlier canopy closure and reduced weed competition, potentially resulting in higher yields (Pandey and Velasco, 2002) [19] , by avoiding continuous field flooding, DSR helps reduce methane emissions, thus contributing to a lower environmental impact (Jain et al., 2019) [20] . Addressing nutrient deficiencies in DSR cultivation requires tailored management strategies to optimize nutrient availability and uptake. Soil testing and nutrient profiling are essential for diagnosing nutrient deficiencies and formulating appropriate fertilizer recommendations based on crop requirements and soil characteristics (Witt et al., 2007) [8] . Furthermore, the timing and placement of fertilizer applications play a crucial role in ensuring nutrient availability during critical growth stages, particularly during the establishment phase in DSR systems (Jat et al., 2019) [7] .

Advantages and challenges of Sand hydroponics compared to traditional transplantation methods

Sand hydroponics, a form of soilless cultivation, offers a sustainable approach to rice farming, presenting unique advantages and challenges compared to traditional transplantation methods. One significant advantage is water conservation, as sand hydroponics allows for efficient water use through recycling and reuse within a controlled environment, minimizing wastage typical of traditional flooding methods (Senthil kumar et al., 2019) [9] . Additionally, the delivery of essential nutrients directly to the plant roots in a dissolved form enhances nutrient uptake efficiency and reduces losses through leaching, contributing to improved crop productivity and reduced environmental pollution (Gupta et al., 2016) [10] . Furthermore, sand hydroponics enables high-density planting and vertical farming techniques, optimizing land use efficiency and facilitating rice cultivation in urban areas with limited land availability (Dawson and Hilton, 2011) [11] . By eliminating soilborne pathogens and pests, sand hydroponics also reduces the need for chemical pesticides, promoting environmentally friendly pest management practices.

Materials and Methods

Materials

The study was initiated with the population BC1F1of improved Lalat x Dular which was obtained from the Crop Improvement Division, ICAR-National Rice Research Institute-Cuttack and advanced to BC1F3 population and screening was done in sand hydroponics.

Sand Hydroponics

A total of 155 BC1F3 population were screened under sand culture hydroponics. In order to ensure high reliability and statistical validity, the screening was carried out using a randomized complete block design coupled with three replications. This study utilized two different check varieties as controls: Improved Lalat, which served as the nutrient-sensitive control, and Dular, which served as the tolerant control. Seeds were sown in acid washed sand containing half strength (N & P) nutrient solution were screened for nutrient stress at seedling stage in greenhouse following the standard protocol of IRRI with some modifications (Al Azzawi et al., 2020) [12] , (Yoshida et al., 1976) [13] .

Recording of Observations

Data on Chlorophyll content (SPAD), shoot length (cm), root length (cm), Leaf number, root number, shoot dry weight (g) and root dry weight (g) were taken for five plants.

Results and Discussion

The ANOVA summary reveals significant insights into the sources of variation among hydroponics conditions (SPAD, SL, RL, LN, RN, SDW, and RDW) across genotypes. Replicates showed variation (p > 0.05) except for RL-Hydro and LN-Hydro, indicating consistent experimental replication.

Direct and Indirect effects among seedling characters at genotypic levels under hydroponics stress conditions

When comparing our genotypic path matrix findings with other studies, several parallels and distinctions emerge. Consistent withour results, research by (Wang et al., 2018) [14] also demonstrates that chlorophyll content (SPAD) can positively influence Root Dry Weight (RDW) aligns with studies indicating trade-offs between early flowering and biomass allocation. Moreover, the strong direct effect of root length on RDW echoes findings that taller plants often allocate more resources to root growth, enhancing overall biomass (Garcia et al., 2018) [15] . Our genotypic path matrix highlights these genetic interrelationships, offering insights into trait co-regulation and informing potential breeding strategies aimed at enhancing crop performance through targeted genetic manipulation. [14] have also identified Shoot Dry Weight (SDW) as a primary direct contributor to RDW (Root Dry Weight) in crop plants, emphasizing the significant role of above-ground biomass in root development. The positive direct effects of Root Length (RL) and Root Number (RN) on RDW, as illustrated in our diagram, align with broader research indicating that root architectural traits play crucial roles in determining overall root biomass (Jones and smith, 2019) [16] . Furthermore, the depiction of indirect effects through multiple variables in our diagram echoes findings that trait interactions and pathways can collectively influence complex traits like RDW (Garcia et al., 2018) [15] . The residual effect in our diagram underscores the portion of variance in RDW that remains unexplained, a concept also explored in studies evaluating the completeness of trait models in crop genetics (Smith et al., 2021) [17] . Overall, Genotypical Path Diagram provides a comprehensive visual representation of genetic influences on RDW, supporting deeper insights into crop trait interdependencies for targeted breeding and management strategies.

Direct and Indirect effects among seedling characters at phenotypic levels under hydroponics stress conditions

In comparing our study's findings with other research, we observe several key similarities and differences. Consistent with previous studies, a strong positive correlation exists between shoot and root biomass, indicating interdependent growth. Root length's positive impact on shoot and root dry weight aligns with past findings, underscoring its role in nutrient and water uptake. However, the negative relationship between chlorophyll content (SPAD) and shoot length contrasts with some studies that report no significant or positive correlations, highlighting variability due to species, growth stages, and conditions. Overall, our study reaffirms the inter connectedness of agronomic traits, emphasizing the need for a multi-trait approach in crop breeding and management to optimize performance and yield. [15] have also highlighted Shoot Dry Weight (SDW) as a major direct contributor to RDW, emphasizing the significant role of above-ground biomass in influencing root development. The negative direct effects of Shoot Length (SL) and Leaf Number (LN) on RDW, as indicated in the diagram, align with research findings that suggest resource allocation trade-offs between shoot and root growth (wang et al., 2018) [14] . Moreover, the residual effect depicted in diagram (0.252) reflects the proportion of variance in RDW not accounted for by the measured factors, akin to findings in studies examining residual effects in complex trait relationships (Garcia et al., 2018) [15] . Overall, our diagram underscores the intricate interplay and indirect effects among these agronomic factors on RDW, supporting the need for comprehensive understanding in crop physiology and breeding.

Conclusion

The integration of phenotypic and genotypic perspectives through matrices such as path diagrams provided critical insights into trait interactions and genetic influences on biomass production and grain yield. Positive correlations observed among biomass-related traits and their impacts on root biomass underscored their synergistic roles in enhancing overall plant productivity. Moreover, environmental factors, particularly chlorophyll content as indicated by SPAD readings, emerged as significant influencers of trait interactions and biomass accumulation.

References

1. Fanzo J, Hunter D, Borelli T, Mattei F. Diversifying Food and Diets: Using Agricultural Biodiversity to Improve Nutrition and Health. In: Issues in Agricultural Biodiversity. Earth scan; 2013.
2. Dobermann A, Fairhurst T. Rice: Nutrient Disorders and Nutrient Management. International Rice Research Institute; 2000.
3. Pandey S, Bhandari H, Hardy B. Economic Costs of Transplanting and Direct Seeding for Rice Production. Int J Agric Sustain. 2012;10(3):202-10.
4. Fischer KS, Fukai S, Kumar A, Leung H, Jongdee B, Kumar V. Defining and measuring crop management alternatives to transplanted flooded rice. Field Crops Res. 2019;235:76-88.
5. Farooq M, Siddique KHM, Rehman H, Aziz T, Lee DJ, Wahid A. Rice direct seeding: Experiences, challenges and opportunities. Soil Tillage Res. 2011;111:87-98.
6. Kumar V, Ladha JK. Direct Seeded Rice: Research Issues and Opportunities. Adv Agron. 2012;115:297-413.
7. Jat HS, Sapkota TB, Yadav AK, Jat ML, Kumar M, Gupta RK, et al. Yield and water productivity of rice (Oryza sativa)-wheat (Triticum aestivum) system as influenced crop establishment and nutrient management practices in are claimed sodic soil. Field Crops Res. 2019;230:1-19.
8. Witt C, Pasuquin JM, Nestel P, Dobermann A. Site-Specific Nutrient Management: Practices for Improving Nutrient Use Efficiency. International Rice Research Institute; 2007.
9. Senthilkumar M, Chandrasekaran R, Sundaramoorthy P, Ganeshamurthy AN, Yu C. Effect of nutrient solution on rice (Oryza sativa L.) grown in sand hydroponics. J Pharmacogn Phytochem. 2019;8(1):402-6.
10. Gupta S, Jha G, Ramesh A, Ravi V. Effect of nutrients and planting density on growth and yield of rice (Oryza sativa L.) grown in sand culture. Int J Agric Environ Biotechnol. 2016;9(3):03-408.
11. Dawson JC, Hilton HW. Sustainable hydroponics and rooftop gardens: a solution to the global food crisis. Int J Environ Cultural Econ Soc Sustain. 2011;7(4):63-74.
12. Al Azzawi TNI, Khan M, Hussain A, Shahid M, Imran QM, Mun BG, et al. Evaluation of Iraqi rice cultivars for their tolerance to drought stress. Agronomy. 2020;10(11):1782.
13. Yoshida S. Routine Procedure for Growing Rice Plants in Culture Solution. In: Yoshida S, Forno DA, Cock JH, editors. Laboratory Manual for Physiological Studies of Rice. International Rice Research Institute; 1976. p. 61-6.
14. Wang Y, Tao H, Hong L, Li X, Li X, Zhao M, et al. A major nitrate transporter and its regulator are involved in the nitrate response and nitrogen use efficiency in rice. Plant Cell. 2018;30(6):1088-104.
15. Garcia CG, Zampieri M, Dentener F, Gumma M, Salamon P, Seguini L, et al. Surface Freshwater Limitation Explains Worst Rice Production Anomaly in India in 2002. Remote Sens. 2018;10(2):244.
16. Jones P, Smith J. Advances in QTL mapping in maize. Mol Breed. 2019;39(3):39.
17. Smith J, Brown T, Johnson R. Advances in stress physiology and genetics of cereals. Crop Sci. 2021;61(2):300-10.
18. Patel V, Kumar A, Gupta R. Advances in genetic studies of stress adaptation in cereals. Mol Breed. 2019;39(6):76.
19. Pandey S, Velasco L. Economics of direct seeding in Asia: Patterns of adoption and research priorities. In: Pandey S, Mortimer M, Wade L, Tuong TP, Lopez K, Hardy B, editors. Direct Seeding: Research Strategies and Opportunities. International Rice Research Institute; 2002. p. 3-14.
20. Jain BT, Aparajita. Effect of different production systems on flowering and maturity duration of basmati rice genotypes. Oryza. 2019;56(1):11-7.