MSc

The present investigation entitled “Identification of microsatellite markers
associated with root traits for drought tolerance in rice (Oryza sativa L.)” was
conducted at Department of Plant Physiology, College of Agriculture, Vellayani
during 2016-17. The objective of the study was to validate the role of root traits in
rice for drought tolerance and to identify the microsatellite markers associated with
root traits for drought tolerance in rice.
The extend of variation for water stress indicators, physio-morphological and
yield components were assessed by evaluating 35 rice genotypes collected from
RARS, Pattambi under water stress and irrigated conditions in the rainout shelter. The
rice accessions grown in polythene tubes of 1 meter height were exposed to water
stress at panicle initiation stage for a period of 15 days along with irrigated control.
The physio-morphological, biochemical and yield components were recorded on
completion of stress period. Significant variation was observed for these traits and ten
drought tolerant and ten drought susceptible genotypes were selected. The genomic
DNA was isolated from these rice genotypes and were pooled into drought tolerant
and susceptible bulks. Bulked line analysis was carried out to identify microsatellite
markers linked to drought tolerance in rice.
The result of the study revealed that physiological parameters such as Relative
Water Content (RWC), photosynthetic rate, transpiration rate and stomatal
conductance decreased where as proline content and leaf temperature increased
significantly in most of the genotypes under water stress condition. Highest leaf
rolling (score – 9) was observed in Ptb–7 and Ptb-13 while the genotypes Ptb–29 and
Ptb-30 showed no leaf rolling symptoms (score – 1). Among the genotypes, the RWC
was recorded to be highest in Ptb–4 while the lowest was recorded in Ptb–13 under
water stress condition. The percentage decrease in RWC compared to irrigated
control was less in Ptb–15. Membrane stability index was more in Ptb–29 (98.5 %)
and Ptb-10 (98.1 %) as compared to other genotypes under water stress condition.
Maximum leaf temperature was observed in Ptb–1(31.70C) and minimum in Ptb–7
(27.80C) under water stress condition. Among the genotypes, stomatal conductance
was recorded to be highest in Ptb–30 (674 m moles m-2 s-1) while the lowest in Ptb–
20 (92 m moles m-2 s-1). The photosynthetic rate decreased significantly under water
stress condition with maximum in Ptb–30 (15.2 μ moles m-2 s-1) and minimum in
Ptb–6 (3.4 μ moles m-2 s-1). Under water stress condition, maximum transpiration rate
was observed in Ptb–4 (1.4 m moles m-2 s-1) and minimum in Ptb–31 (0.05 m moles
m-2 s-1). Proline content increased at 50% flowering stage in water stress condition
with maximum accumulation in Ptb–27 and minimum in Ptb–22.
At flowering stage highest root length was noticed in Ptb-15 and lowest for
Ptb–3 and Ptb-8 under water stress condition. Root volume differed significantly in
several genotypes with maximum in Ptb–21 and minimum in Ptb-31. Root dry weight
decreased in water stress compared to control in most of the genotypes with highest
in Ptb-13 and lowest in Ptb-31. Root shoot ratio was found to be highest in Ptb-29
and Ptb-30 and lowest in Ptb-31.
The plant height at maturity was observed to be highest in Ptb-1 and lowest in
Ptb-34 under water stress condition. Days to 50% flowering reduced in most of the
genotypes under water stress condition compared to irrigated control. Productive
tiller number of most of the genotypes significantly reduced in water stress condition
with maximum reduction in Ptb-28. Maximum yield under water stress was recorded
in Ptb-55 and minimum in Ptb-21. Number of filled grains and unfilled grains were
observed as major attributes affected drastically under water stress condition. The
spikelet fertility percentage was highest in Ptb-25 and lowest in Ptb-1. Ptb-28 had
maximum 1000 grain weight under water stress and minimum was for Ptb-17.
Correlation study revealed that grain yield per plant under water stress
condition was positively correlated with parameters such as relative water content,
membrane stability index, proline content, stomatal conductance, photosynthetic rate,
transpiration rate, root length, root shoot ratio, spikelet fertility % and 1000 grain
weight where as negatively correlated with leaf temperature, leaf rolling score, root
volume, root dry weight, plant height, days to 50% flowering and panicle length.
In Bulked Line Analysis, out of the 150 microsatellite primers screened only
one marker i.e., RM 474 showed polymorphism between the tolerant and susceptible
bulks. The same primer showed similar product size (252bp) among the individual
lines which constituted respective bulks.
In summary, there was significant variation for physio-morphological and
yield components among rice genotypes under water stress condition. Genotypes
having higher root length and root shoot ratio were found to be tolerant to drought.
The genotypes identified as drought tolerant viz Ptb-29, Ptb-30, Ptb-15, Ptb-1, Ptb-55
etc. can be used in breeding programmes to improve drought tolerance in rice.
Microsatellite marker RM 474 which could distinguish drought tolerant and
susceptible bulks can be used for marker assisted selection for drought tolerance in
rice.