ICRISAT Archival Report 2006 - The seedlings of success in the ...

performed. Subsequently the molecular diversity data together with the trait diversity data will be analyzed and the
candidate genotypes with a greater TE and genetic diversities will be identified to develop new populations for TE.
Vincent Vadez, Rajeev Varshney and L Krishnamurthy
Milestone: Range of variations for root traits assessed in groundnut germplasm (VV/SNN/RA/HDU) 2008
Measurement of root traits, though better and more easily done in a controlled cylinder system, remains a time
consuming exercice, with large error component, using destructive sampling, and providing “static” data that does
provide little information about the actual activity of roots and the kinetics of this activity. In the end, more than the
roots, water uptake and the kinetics of water uptake to cope with terminal drought are important. We used 4
groundnut genotypes and grew them in 1.2 m PVC cylinders with 16 cm diameter. Plants were grown for 30 days.
Fifteen plants per genotype were grown. At 30 DAS, 5 plants per genotype were harvested to assess root depth and
root dry weight in 15-cm layers. The other 10 cylinders were saturated with water, and 5 plants maintained under
well-watered conditions (WW) and the other 5 left with no further irrigation (water stressed, WS). Cylinder weight
was recorded on a regular basis, usually every 3 days. Water loss in WW plants was adjusted to the cylinder weight
3 days after imposing the treatment. The process of weighing the cylinders was relatively simple and rapid. Data
showed that 5 days after stress imposition, normalized TR (NTR) was about 50% of controls. Thereafter, and until
harvest at 17 days after treatment imposition, NTR of TMV 2, a genotype known to be drought-susceptible, was 20
% lower than TAG 24 and ICGS 44 (these 2 genotypes are known for deep and profuse rooting). At 17 days after
stress imposition, TMV 2 plants were permanently wilted whereas TAG 24 and ICGS 44 were not. Total
transpiration values from the time of treatment imposition were similar in TAG 24 and TMV 2, but the total TR
value from 5 to 17 days after stress imposition were about 20% higher in TAG 24 than in TMV 2, showing that
TAG 44 was able to manage better its water uptake compared to TMV 2, which allowed it to maintain higher NTR
later during the stress. At harvest, root depth was measured after washing the roots and stretching. The root were cut
in 15 cm portions, which were dried and weighted. We found that there was no significant correlation between either
root dry weights, or with root dry weight in each of the 15-cm portion and TR. By contrast, total TR between 5 and
17 days after stress imposition was related to root depth. These data show that there is variation for the pattern of
water extraction, and that root dry weight, which is usually well correlated to root length density, appears to be a
poor proxy for water uptake.
Vincent Vadez
Milestone: Molecular markers ready for validation and use in introgression studies for abiotic and biotic stresses
(VV/RA/SNN/RKV) 2009
The set of polymorphic markers suitable to map QTLs in groundnut is being built up.
Rajeev Varshney and Vincent Vadez
Milestone: QTLs for root traits identified (VV/SNN/RA) 2011
In the experiment reported above, we showed that though root traits displayed variation between genotypes. Only
the differences in root depth were related to differences in water uptake, whereas differences in dry weight at
different soil depth were not. Furthermore, differences in water extraction in the last 10 days of the experiment were
relatively larger than the differences in root depth. This shows that water uptake is probably a better estimator of
“root” traits than root traits (such as root length density, depth, dW, etc.) traditionally measured.
Vincent Vadez
Output target 6B.2: High throughput molecular genetic and phenotyping platforms for drought and salinity
stress and promising transgenic events of groundnut for tolerance to drought stress available for
commercialization and introgression in locally adapted germplasm
Activity 6B.2.1: Develop groundnut transgenic events for enhanced tolerance to drought
Milestone: 50 transgenic events of groundnut with DREB1A gene screened for drought tolerance in the contained
greenhouse (KKS/VV/RA) 2007
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