“Two-in-one” stress-tolerant rice: salinity and submergenceE. F. L. Mercado, A. G. Sajise, S. Z. M. Thein, N. A. G. Vispo, M. V. Arceta, M. F. M. Cueto, A. N. Mamiit, M. Q. Esguerra,

G. V. Vergara, A. M. Ismail, D. J. Mackill, R. K. Singh, and G. B. Gregorio*

International Rice Research Institute, DAPO Box 7777, Metro Manila, PhilippinesCorresponding author: g.gregorio@cgiar.org

Breeding for dual stress tolerance• SUB1 (from Swarna-Sub1) and qSALTOL (from Cheriviruppu and IR66946-3R-178-

1-1, FL 478) were transferred to one background using the scheme illustrated in Figure 1.

• 10-d-old F2 progenies were screened for salinity and submergence by completely submerging them in tanks for 10 d in saline water (EC 8 dS m-1).

Fig. 1. Breeding scheme used in the development of the dual stress-tolerant rice.

• Survivors homozygous for SUB1 were selected and advanced to the F6 generation, producing individuals with a wide variety of phenotypic variation, along with tolerance for both salinity and submergence.

Conclusions and future activities•Combining qSALTOL and SUB1 in one genetic background is feasible with no

apparent negative impacts on agronomic traits.•These “two-in-one” Sal1+Sub1 genotypes can lead to the development of

more resilient varieties adapted to the coastal zones. •Sal1+Sub1 lines have been distributed in the Philippines, Bangladesh, India,

Indonesia, Myanmar, and Vietnam, where these will be subjected to on-site and adaptability trials.

Fig. 2. “Two-in-one” Sal1+Sub1 lines (G-I) survived 1 wk after salinization (EC 12 dS m-1), along with their salt-tolerant parents, FL 478 (A and J) and Cheriviruppu (C). Swarna (E), Swarna-Sub1 (F), and IR29 (sensitive check, B) were all sensitive to salinity.

• Under submergence stress, yield of IR84649-81-4-B-B (Sal1+Sub1) was comparable from that of Swarna-Sub1.

• Sal1+Sub1 lines were taller and mature earlier making them better to adopt in stagnant water condition.

• Under salt stress, Swarna-Sub1 will not survive, unlike the new “two-in-one” Sal1+Sub1 lines (Fig. 4).

Screening for salinity stress

Fig 3. Saltol+Sub1 and Sub1 only lines planted in Iloilo, Philippines. Salinity levels in the field ranged from 12 to 16 dS m-1.

Yield trials on submergence stress

Fig. 4. Yield trial under submergence stress of Sal1+Sub1 lines IR84645-34-9-1-B, IR84645-311-22-1-B, and IR84649-81-4-B-B during 2009.

Table 1. Performance under submergence stress of Sal1+Sub1 lines across two seasons (2009 WS and 2010 DS).

wk of flooding, respectively, were transferred to a single background using marker-aided selection (MAS) to develop rice varieties that can tolerate saline and submerged conditions. This study aims to combine salinity and submergence tolerance in at least three genotypes and have these evaluated under field conditions.

Coastal saline areas invariably experience frequent submergence for short periods with saline or freshwater during wet season. The ideal rice genotype for these areas needs dual tolerance for salinity and submergence for better adaptability. qSALTOL and SUB1, a quantitative trait locus conferring vegetative-stage tolerance for salinity and a gene conferring tolerance for 1-2

Sub1 only SalTol + Sub1