This study evaluated the low-temperature tolerance of rice seedlings by measuring root depth after pruning and exposing plants to 15/13°C for 7 days. Root depth was found to differ significantly among accessions. Desvauxii and Kon Suito showed exceptional root growth under low temperatures, with root depths comparable to local varieties grown under normal temperatures. Crosses were initiated between the two tolerant accessions and local varieties to develop populations for mapping quantitative trait loci associated with root development under low temperatures.

1. Abstract
Materials & Methods
Results & Discussions
Measurement of root system
Root depth measured by the end of low temperature treatment is mostly
contributed by the elongation of preexisting roots shorter that 5 cm, and
thus their growth points were not removed by the pruning process, at the
beginning of treatment. A more detailed measuring system, which include
the number of roots, length of each root, and total root growth after pruning
should be used for further study, in order to fully reflect the tolerance to low
temperature for rice seedlings.
Significant differences of root depth among accessions
Fig. 2 Root depth of rice seedling for 7 days after pruning, at (C) 30/25ºC and (T)
15/13ºC. The root depth are significantly different among accessions within
each treatment. Space between each white line is 1 cm.
Fig.1 Roots were pruned to 5 cm at the 3-leaf
stage to simulates damage caused by
mechanical transplanting.
Fig. 6
The number of newly grown roots,
illustrated by the white, short and
thick ones in the picture, is also a
good indicator for the vigor of root
system but is not covered by the
measurement of root depth.
Seedlings were grown to 3-leaf
stage hydroponically in phytotron at
normal (30/25ºC) temperature before
pruning the roots and transferred to
15/13 ºC for 7 days. Root depth
(cm) was measured at the end of
low-temperature treatment.
LT-tolerance Evaluation
RD (cm)
Density
RD(cm)
GN number
Fig. 3 Root depth (a) distribution and (b) variation of rice accessions and varieties under
control (30/25ºC, Pink) and low temperature treatment (15/13ºC, Blue). The dashed
lines in (b) are the sample means of root depth within control and low temperature
treatment.Accessions are presented as GN number, which is listed in Table.1.
a. b.
Table.1 Twenty accessions originated from
high-latitude or altitude areas were
selected from a Rice Diversity (44k)
panel (Zhao et al., 2011), and evaluated
with two local varieties Taiken 2 (TK2)
and Taichung Sen 10 (TCS10).
Assessment of Low-Temperature Tolerance
of Rice (Oryza sativa) at Seedling Stage
Chun-Peng Chen1, Dong-Hong Wu2, Kae-kang Hwu1
1Department of Agronomy, National Taiwan University, Taipei, Taiwan (ROC)
2Crop Science Division of Agricultural Research Institute of Council of Agriculture, Taichung, Taiwan (ROC)
Fig. 4
For most of the rice accessions,
including two local varieties (TCS10
and TK2), the root depth of seedlings
under low temperature is related to
the root depth under normal
(control) temperature. However, both
Kon Suito and Desvauxii shows
exceptionally root growth under low
temperature, while the root depth of
Sundensis was severely retarded by
low temperature.
Fig.5
The root depth of both Desvauxii and
Kon Suito under low temperature
treatment are comparable to that of
local check varieties, TK2 and TCS10,
under normal temperature. Space
between each white line on the
pictures is 1 cm.
In Taiwan, rice grown in the first season, from spring to summer, typically has greater yield production. However, the cold streams occurred during the seedling
stage often hindered the development of root systems recovering from mechanical damage caused by transplanting, resulting prolonged growth period and a
higher risk to encounter typhoon before harvest. The objectives of the study are center on the establishing a phenotyping system to assess the low temperature
tolerance among rice accessions, and identifying superior genotypes for further breeding and genetic study. A set of 20 varieties from a rice diversity panel were
used in this study, along with two Taiwanese rice cultivars which have been both deemed to low temperature sensitive in a pilot study. The results indicated that
root depth (RD) under 15/13 ºC for 7 days after pruning may be used to assess the low temperature tolerance among rice accessions. Furthermore, accessions
Desvauxii and Kon Suito had shown outstanding root growth then the other 18 varieties and 2 local varieties under the treatment condition. Crosses between the
two low temperature tolerant accessions and local varieties has been initiated to develop segregation populations that may be used for mapping quantitative trait
loci (QTL) associated with root development under low temperature.