Abstract:
Among natural disasters, floods cause a 39% annual rice yield loss in Sri Lanka. The development
of submergence tolerant rice cultivars using locally adapted rice accessions is the best solution to
utilize the flood-prone lowlands of Sri Lanka. In the present study, sixteen modern rice cultivars
and sixteen traditional rice accessions were screened at the seedling stage to evaluate their level
of submergence tolerance. The traditional rice accessions used in the study belonged to Heenati,
Suduheenati, Rathuheenati, and Kaluheenati groups. Swarna Sub 1 cultivar was used as the
standard check variety. Two weeks old seedlings were separately subjected to complete
submergence stress for a continuous 9-day period and 14-day followed by two-week recovery in
a randomized complete block design (RCBD). The survival rate of the submerged seedlings and
the mode of seedling elongation during the submergence compared to the control plants. Heenati 3707, Kaluheenati-4991, and Rathuheenati-4992 from the traditional rice accessions and At-354,
and Ld-371 from the modern rice cultivars scored 100% survival rates along with the standard
positive control, Swarna Sub-1 at 9-day submergence stress. Swarna sub-1 had a 100% survival
rate after 14 days of submergence, while Heenati-4935, Kaluheenati-4621, and Kaluheenati-4991
had survival rates of 75%, 71%, and 60%, respectively. Traditional rice accessions scored more
than 50% of survival rates. In modern rice cultivars, Bw-400, At-405, Ld-371, At-354, and Bw-372
scored survival rates of 83.33%, 71%, 66.67%, 50%, and 50% respectively. Modern cultivars aslo
secured more than 50% of survival rates. According to IRRI standard submergence scoring
criteria, traditional rice accession Heenati-4935 (75%) is moderately submergence tolerant, and
Kaluheenati accessions (4621, 4991) are moderately submergence susceptible. Among modern
rice cultivars, Bw-400 is moderately tolerant and At-405, Ld-371, At-354, and Bw-372 accessions
are moderately susceptible to submergence stress. Data analysis revealed the absence of a
significant correlation between tolerant or susceptible rice cultivars and height gain or reduction
under the submergence stress at 9-day or 14-day stresses of the studied rice accessions/cultivars.
This emphasizes the functioning of diverse survival mechanisms in different rice
accessions/cultivars under submergence stress. The identified moderately tolerant and
moderately susceptible rice accessions/cultivars can be further studied at the field conditions for
future breeding purposes.
