Genetic Dissection of Epistatic Interactions Contributing Grain Yield Variability
in Rice under Drought
Authors: Majumder Ratna Rani , Sandhu Nitika , Yadav Shailesh , Catolos Margaret , Cruz Ma. Teresa Sta. , Maturan Paul Cornelio , Hassan Lutful , Hossain Mohammad Amir , Kumar Arvind 
Published: July 2021

Aims:
The aim of the present study was to evaluate the performance of ‘high’-‘low’
yielding pyramided lines (PLs), having the same combinations of qDTYs in Samba Mahsuri,
MR219 and IR64-Sub1 genetic backgrounds, and to understand the genetic interactions among
QTL and/with genetic background affecting grain yield.

Background:
Epistasis regulates the expression of traits governed by several major/minor genes/
QTL. Multiple pyramided lines (PLs) with the same grain yield QTL (qDTYs) combinations
but possessing grain yield variability under different levels of reproductive stage drought stress
were identified in different rice genetic backgrounds at International Rice Research Institute (IRRI).

Objectives:
The objectives of the present study were to evaluate the performance pyramided lines
(PLs) with drought QTL in the backgrounds of Samba Mahsuri, MR219 and IR64-Sub1 under reproductive
stage drought stress (RS) and NS (non-stress) conditions, to understand the effect of
epistatic interactions among qDTYs and with genetic background on GY under the differential level
of stress and to identify the promising drought-tolerant lines with high yield under drought and
higher background recovery in different genetic backgrounds.

Methods:
The experiments were conducted in 2015 DS (dry season), 2015 WS (wet season) and
2017 DS at IRRI, Los Baños, Philippines, in a transplanted lowland ecosystem under lowland severe
stress (LSS), lowland moderate stress (LMS) and lowland non-stress (LNS). The experiments
were laid out in alpha lattice design with two replications.

Results:
Several digenic interactions were found in different genetic backgrounds, 13 interactions
in Samba Mahsuri, 11 in MR219 and 20 in IR64-Sub1 backgrounds. Among all digenic interactions,
one QTL × QTL interaction, 17 QTL × background and 26 background × background interactions
resulted in GY reduction in low yielding PLs in different genetic backgrounds under LSS or
LMS. Negative interaction of qDTY3.1, qDTY4.1 and qDTY9.1 with background markers and background
× background interactions caused up to 15% GY reduction compared to the high yielding
PLs under LMS in the Samba Mahsuri PLs. In MR219 PLs, the negative interaction of qDTY2.2,
qDTY3.2, qDTY4.1 and qDTY12.1 with the background marker interval RM314-RM539, RM273-RM349
and RM445-RM346, RM473D-RM16, respectively resulted 52% GY reduction compared to
the high yielding PLs under LSS. In IR64-Sub1 PLs, qDTY6.1 interacted with background loci at
RM16-RM135, RM228-RM333, RM202-RM287 and RM415-RM558A marker interval under
LSS and at RM475-RM525 marker interval under LMS, causing GY reduction to 58% compared
to the high yielding PLs.

Conclusion:
High yielding PLs in Samba Mahsuri (IR 99734:1-33-69-1-22-6), MR219 (IR
99784-156-87-2-4-1) and IR64-Sub1 (IR 102784:2-89-632-2-1-2) backgrounds without any negative
interactions were identified. The identified selected promising PLs may be used as potential
drought-tolerant donors or may be released as varieties for drought-prone ecosystems in different
countries.