Abstract
Background: Soil salinity is an abiotic stress wide spread in rice producing areas, limiting both plant growth and
yield. The development of salt-tolerant rice requires efficient and high-throughput screening techniques to identify
promising lines for salt affected areas. Advances made in image-based phenotyping techniques provide an
opportunity to use non-destructive imaging to screen for salinity tolerance traits in a wide range of germplasm in a
reliable, quantitative and efficient way. However, the application of image-based phenotyping in the development
of salt-tolerant rice remains limited.
Results: A non-destructive image-based phenotyping protocol to assess salinity tolerance traits of two rice cultivars
(IR64 and Fatmawati) has been established in this study. The response of rice to different levels of salt stress was
quantified over time based on total shoot area and senescent shoot area, calculated from visible red-green-blue
(RGB) and fluorescence images. The response of rice to salt stress (50, 75 and 100 mM NaCl) could be clearly
distinguished from the control as indicated by the reduced increase of shoot area. The salt concentrations used
had only a small effect on the growth of rice during the initial phase of stress, the shoot Na+ accumulation
independent phase termed the ‘osmotic stress’ phase. However, after 20 d of treatment, the shoot area of salt
stressed plants was reduced compared with non-stressed plants. This was accompanied by a significant increase
in the concentration of Na+ in the shoot. Variation in the senescent area of the cultivars IR64 and Fatmawati in
response to a high concentration of Na+ in the shoot indicates variation in tissue tolerance mechanisms between
the cultivars.
Conclusions: Image analysis has the potential to be used for high-throughput screening procedures in the
development of salt-tolerant rice. The ability of image analysis to discriminate between the different aspects of
salt stress (shoot ion-independent stress and shoot ion dependent stress) makes it a useful tool for genetic and
physiological studies to elucidate processes that contribute to salinity tolerance in rice. The technique has the
potential for identifying the genetic basis of these mechanisms and assisting in pyramiding different tolerance
mechanisms into breeding lines.
Keywords: Rice (Oryza sativa L.); Salinity tolerance; Phenotyping; Image analysis; Growth; Senescence
* Correspondence: