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Responses of Ag1 and Ag2 Qtl Introgression Lines and Seed Pre-treatment on Growth and Physiological Processes During Anaerobic Germination of Rice Under Flooding

Satyen Mondal
Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh.

M Iqbal R Khan
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.

Frederickson Entila
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.

Shalabh Dixit
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.

Pompe C Sta Cruz
University of the Philippines Los Baños, College 4031, Laguna, Philippines.

M Panna Ali
Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh.

Barry Pittendrigh
Michigan State University, East Lansing, MI, USA.

Endang M Septiningsih
Texas A&M University, College Station, TX, USA.

Abdelbagi M Ismail
International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.

Abstract/ Executive Summary:

Rice seeds germinating in flooded soils encounter hypoxia or even anoxia leading to poor seed germination and crop establishment. Introgression of AG1 and AG2 QTLs associated with tolerance of flooding during germination, together with seed pre-treatment via hydro-priming or presoaking can enhance germination and seedling growth in anaerobic soils. This study assessed the performance of elite lines incorporating AG1, AG2 and their combination when directly seeded in flooded soils using dry seeds. The QTLs were in the background of two popular varieties PSB Rc82 and Ciherang-Sub1, evaluated along with the donors Kho Hlan On (AG1) and Ma-Zhan Red (AG2) and recipient parents PSB Rc82 and Ciherang-Sub1. In one set of experiments conducted in the greenhouse, seedling emergence, growth, and carbohydrate mobilization from seeds were assessed. Metabolites associated with reactive oxygen species (ROS) scavenging including malondialdehyde (MDA) as a measure of lipid peroxidation, ascorbate, total phenolic concentration (TPC), and activities of ROS scavenging enzymes were quantified in seeds germinating under control (saturated) and flooded (10 cm) soils. In another set of experiments conducted in a natural field with 3–5 cm flooding depths, control and pretreated seeds of Ciherang-Sub1 introgression lines and checks were used. Flooding reduced seedling
emergence of all genotypes, though emergence of AG1 + AG2 introgression lines was greater than the other AG lines.

Keywords: Anaerobic germination, Flooding, QTLs, Rice

Location: International Rice Research Institute (IRRI) in the Philippines

Start Date: 00-06-2016

End Date:

Program Area: Variety and Species

Commodity: Rice

Objectives:

To assess the performance of elite lines incorporating AG1, AG2 and their combination when directly seeded in flooded soils using dry seeds.

Methodology:

Experiments were conducted in a greenhouse and research field of the International Rice Research Institute (IRRI) in the Philippines. Greenhouse experiments were conducted to determine emergence percentage and physiological responses, while field experiments were conducted to assess agronomic performance of the contrasting genotypes. Greenhouse experiments. Ten rice genotypes with anaerobic germination (AG) QTLs (quantitative trait loci), PSB Rc82-AG1, PSB Rc82-AG2, PSB Rc82-AG1-AG2, Ciherang-Sub1-AG1, Ciherang-Sub1-AG2, Ciherang-Sub1-AG1-AG2, along with their donors Kho Hlan On (AG1), Ma-Zhan Red (AG2) and the intolerant recipients PSB Rc82 and Ciherang-Sub1 were used in this study7,41. The experiment was conducted under control (non-flooded) and flooded condition during June 2016 using seedling trays. Each seedling tray had 34 rows, and each row had 17 cells (1 cm × 1 cm × 1.5 cm), filled with finely ground soil. One dry seed was sown per each of the 578 (34×17) cells half-filled with sterilized dry garden soil, and covered with 1 cm of fine soil. Fifty-one seeds were used per genotype, sown in three rows representing each replication. The trays were then placed in a concrete bench and flooded with tap water to a depth of 10 cm. Another set of trays was maintained under control (non flooded) condition in an adjacent bench1,12. The trial was laid in a randomized complete block design with three replications. Growth parameters (seedling root and shoot length) were measured at 6, 10, 15, and 21 days after sowing (DAS) on 12 seedlings48,66. Seedling emergence percentage was calculated at 21 days after sowing based on the number of seedlings that emerged above the surface of floodwater

Source of Information: Scientific Reports (2020) 10:10214

Article Link (Online Journal): https://doi.org/10.1038/s41598-020-67240-x

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Rice genotypes carrying AG1 and AG2 QTls showed higher seedling emergence and faster elongation when dry seeds are sown in flooded soils, reflecting the important functional role of these QTLs in improving crop establishment under direct seeding. The introgression lines Ciherang-Sub1-AG2 and Ciherang-Sub1-AG1-AG2 had higher emergence and faster seedling growth than the other AG lines. Several traits were identified that are strongly associated with tolerance of anaerobic conditions during germination, including ability to degrade starch through maintenance of high α-amylase activity and subsequent increase in soluble sugars supply to the growing embryo; and maintaining lower MDA concentrations as an indication of cellular membrane integrity. The later was associated with higher concentration of reduced ascorbate, phenolic compounds, and reactive oxygen species (ROS) scavenging enzymes. Seed hydro-priming as well as pre-soaking for 24 h further improved emergence and seedling growth of the AG introgression lines in flooded soils under field conditions. This suggests that combining genetic tolerance with proper seed management before sowing could effectively be used for direct seeding. Moreover, this approach can provide means for weed management, a major constraint for adoption of direct seeded systems in rice.

Knowledge Management: Journal