This document summarizes research on identifying sweet sorghum genotypes tolerant to mid-season moisture stress. Researchers screened improved sweet sorghum genotypes and accessions under irrigation stoppage to simulate drought. Traits like leaf rolling, recovery after stress, stalk yield, juice yield, and sugar yield correlated between stressed and unstressed conditions, indicating their importance in breeding for drought tolerance. Several hybrid parents and varieties showed tolerance, including ICSV 25297, ICSV 25300, and hybrids ICSSH 75 and ICSSH 67. These materials can be further tested and utilized in breeding programs.

1. Identification of Mid-Season Moisture Stress
Tolerant Sweet Sorghum Material
March 2012
Sweet sorghum – Importance
• ICRISAT’s BioPower strategy empowers the dryland poor to benefit from emerging bioenergy
opportunities
• Sweet sorghum is similar to grain sorghum but accumulates sweet juice in the stalk, hence meets
food, fodder, feed and fuel demand.
• It is recognized as an alternate feedstock for bioethanol production by the Govt. of India
(National Biofuel Policy, 2009).
Mid-season moisture stress
• Among biotic and abiotic yield constraints, drought is the primary constraint throughout the
semi-arid tropics (SAT) due to erratic rainfall and monsoon failure. Moisture stress can occur at
any growth stage
i) Germination and seedling emergence,
ii) Early seedling stage (emergence to panicle initiation)
iii) Midseason (panicle differentiation to flowering)
iv) Post-flowering (flowering to grain filling)
• The frequency of occurrence of mid-season drought during rainy season and terminal drought
during postrainy season is high.
• Symptoms of mid-season moisture stress are leaf rolling, leaf erectness, leaf bleaching, leaf tip
and margin burn (leaf firing), delayed flowering, poor panicle exertion, panicle blasting and floret
abortion, reduced panicle size, low biomass and grain yield.
Materials
Improved sweet sorghum genotypes (B-lines and R-lines/ varieties, hybrids) and germplasm
accessions are evaluated in alpha lattice design with two replications along with checks.
Screening method
Irrigation was stopped four weeks after sowing for 28-35 days and data was recorded for the drought
related traits (leaf rolling, wilting, leaf firing and recovery after release of stress). Irrigate the crop after 4-5
weeks of stress and the juice related traits were recorded at physiological maturity. The selected entries
from this screening are also evaluated in the ensuing rainy season for their adaptation in SAT areas.
P Srinivasa Rao, Belum VS Reddy and Team
International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324. AP, India.
• Character associations
♦ The sugar yield was significantly and positively correlated with candidate drought related traits
such as leaf rolling during stress (0.36), recovery after release of stress (0.42), while negatively
associated with leaf firing during stress (-0.45).
♦ The linear regression analysis between summer and rainy season revealed that stalk yield (R2:
0.48), juice yield (R2: 0.62) and sugar yield (R2: 0.56) are dependable traits of selection under stress
condition while the coefficient of determination is low for plant height, days to 50% flowering and
Brix (Fig:1:a-f).
♦ Therefore, selection for leaf rolling, recovery, stalk yield, juice yield and sugar yield need to be
emphasized as these are stable across the seasons while breeding sweet sorghum in the areas
prone to mid-season moisture stress in the SAT.
Severe wilting due to stress. Drought tolerant line with well-filled grains. Leaf firing in susceptible lines. Recovery after release of stress.
For further details, please contact: P Srinivasa Rao (p.srinivasarao@cgiar.org) or Belum VS Reddy (b.reddy@cgiar.org)
Conclusions
♦ Early summer screening can be useful for selecting drought tolerant materials for rainy season
drought prone areas
♦ The hybrid parents (B-/R-lines) such as ICSB 713, ICSB 11002, PBT A2 2, ICSV 25297, ICSV 25300,
ICSV 25316, ICSV93046 and ICSV 25288 can be utilized in the breeding programs for pre-
flowering moisture stress tolerance, while the identified mid-season stress tolerant varieties (ICSV
25297, ICSV 25300, ICSV 25316, ICSV93046 and ICSV 25288) and hybrids (ICSSH 75, ICSSH 67,
ICSSH 39, ICSSH 50 and ICSSH 19) can be deployed for large scale cultivation after conducting
multi-location adaptation trials.
Acknowledgments
Financial support from the European Commission through the grant agreement KBBE 227422
(SWEETFUEL) is gratefully acknowledged.
B-lines (t ha-1
) R-lines (t ha-1
) Hybrids (t ha-1
)
ICSB 11002 (0.7) ICSV 25297 (1.2) ICSSH 75 (1.4)
ICSB 731 (0.5) ICSV 25300 (1.1) ICSSH 67 (1.2)
PBT A2 2 (0.4) ICSV 25316 (1.0) ICSSH 39 (1.1)
ICSV 25288 (1.0) ICSSH 19 (1.1)
ICSV 93046 (0.9) ICSSH 50 (1.0)
Brix (%)-summer
Brix(%)-rainy
20
18
16
14
12
10
8
8.00 10.00 12.00 14.00 16.00 18.00
R2
=0.001d
Stalk yield (t ha-1
) -summer
Stalkyield(tha-1
)-rainy
90
80
70
60
50
40
30
20
10
10 20 30 40 50
R2
=0.48
c
Plant height (m)-summer
Plantheight(m)-rainy
R2
=0.09
1 1.5 2 2.5
2.5
4.5
4.0
3.5
3.0
2.0
1.5
1.0
b
Days 50% flowering-summer
Days50%flowering-rainy
65
68
70
72
74
76
78
80
82
75 85 95 105
R2
=0.09a
Juice yield (t ha-1
)- rainy
Juiceyield(tha-1
)-rainy
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
0.00 5.00 10.00 15.00 20.00
R2
=0.62
e
Sugar yield (t ha-1
) -summer
Sugaryield(tha-1
)-rainy
5
4
3
2
1
0
0.0 0.5 1.0 1.5 2.0
R2
=0.56f
Figure 1. Regression analysis of candidate sugar traits between summer and rainy seasons.
a) Days 50% flowering; b) Plant height; c) Stalk yield; d) Brix; e) Juice yield; f) Sugar yield.
No stress (first 30 days) Under stress (28-35 days) No No stress s
Sowing Maturity
Significant results
The best performing lines/hybrids for the candidate traits of mid-season drought tolerance are given
below.
• Promising genotypes with high sugar yield (t ha-1
)
Mid-season and terminal stress resistant check: E 36-1 (0.7 t ha-1
)
Mid-season and terminal stress susceptible check: R16 (0.2 t ha-1
)