IntroductionIn Sudan, wheat is grown at low latitudes under irrigation. Heat stress is the main constraint, affecting the crop at all stages of growth and development – with even greater impacts in the future, as a result of global warming. It is important to identify genotypes that give adequate yields under heat stress and high yield under normal conditions. This study sought to characterize physiological traits that are associated with yield performance under heat stress.

Materials and Methods161 F8 recombinant inbred lines (RILs) derived from the cross between Cham-6 (drought tolerant) and Cham-8 (heat tolerant), along with 13 check cultivars, were grown under field conditions at the ARC experimental farm at Wad Medani, Sudan (14°N, 33°E, 414 m asl), with surface irrigation. •Conditions during growing season: mean

max. and min. temperatures 36.1˚C and 17.6˚C, mean relative humidity 25.8%

•Experimental design: Alpha lattice with three replicates.

•Measurements: Emergence % (E), early vigor (EV), ground cover (GC), flag leaf characteristics, days to heading (DTH), days to physiological maturity (DTPM), grain filling period (GFP), glaucousness, plant height, biomass, yield and its components.

Results and DiscussionTables 1 and 2 summarizes the results. The RILs displayed transgressive segregation for all investigated traits. Only 3 RILs gave higher yield than the adaptive heat tolerant parent Cham-8: predicted mean yield 3.64-3.39 t ha-1, increase of 7.4% (Fig. 1).

• 49 RILs gave higher yield than Cham-6, 3.35-2.93 t ha-1.

• RILs were superior to Cham-6 with regard to E1, E3, E4, E5, GC4, GC5, and GC6, FLL (cm), DTPM, Duration of GL, GFP, peduncle length (cm) and TKW (g).

• RILs were superior to Cham-8 with regard to E6, E7, GC3, FLW (cm), DTH, glaucousness, plant height (cm), biomass (g), head length (cm), threshing %, HI and grain yield (t ha-1).

• Cham-6 was superior to the RILs in E1 and number of heads per m2, Cham-8 was superior to the RILs for GC1 and GC2.

There were significant differences amongst the traits (pr<0.001) except for EV, number of heads per m2, threshing % and harvest index (Table 1). Grain yield was positively and highly significantly correlated with ground cover (GC1 to GC5) (Fig. 2), number of heads per m2, biomass and harvest index. Yield was non-significantly (p<0.001) and

negatively correlated with flag leaf length (cm), days to heading and kernel weight (g).There was no correlation between yield and the other traits investigated. The linear regression of yield and harvest index was the most positive and highly significant amongst the traits under study (Fig. 3).

These results suggest that ground cover, number of heads per m2, biomass and harvest index could play an important role in yield stability of bread wheat in heat stress environments. Ground cover is important at all stages of crop growth; it shades the soil surface, reducing evaporation. This ensures that the developing grains are provided with assimilates from current photosynthesis which translates into increased biomass. Emergence, early vigor and flag leaf characteristics were non-significantly correlated with yield. It is likely these traits have limited physiological role in heat tolerance in the environment studied.

Further physiological characterizations in multi-environmental trials are ongoing.

ReferencesBlake, N. K., Lanning, J. M., Martin, J. M., Sherman,

J. D. and Talbert, L. E. 2007. Relationship of flag leaf characteristics to economically important traits in two spring wheat crosses. Crop Sci., 47:492-496.

Margreet W. ter Steege, Franka M. den Ouden, Hans Lambers, Piet Stam , and Anton J.M. Peeters. 2005. Genetic and Physiological Architecture of Early Vigor in Aegilops tauschii, the D-Genome Donor of Hexaploid Wheat. A Quantitative Trait Loci Analysis. Plant Physiology. 139(2):1078-1094.

Steege, M. W., Ouden, F. M., Lambers, H., Stam, P., Peeters, A. J. M. 2005. Genetic and physiological Architecture of Early Vigor in Aegilops tauschii, the D-Genome Donor of Hexpaploid Wheat. A Quantitative Trait Loci Analysis. Plant Physiology. 139(2): 1078-1094.

Xun-Li Lu, Ao-Lei Niu, Hai-Ya Cai, Yong Zhao, Jun-Wei Liu, Ying-Gau Zhu, Zhi-Hong Zhang. 2007. Genetic

dissection of seedling and early vigor in the recombinant inbred line population of rice. Plant Sci., 172:212-220.

AcknowledgmentsMinistry of Higher Education, University of Juba and ARC, Sudan.

Physiological Characterization of Heat AdaptiveTraits in Bread Wheat (Triticum aestivum L.)

A. Farag Alla*,1,2 FC Ogbonnaya,2 M. Ahmed3 and O. Abdalla2

1 University of Juba, Khartoum Center, Sudan. E-mail awatif9@gmail.com2 ICARDA, PO Box 5466, Aleppo, Syria

3 University of Khartoum, Sudan

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Table 1. Phenotypic traits measured in RILs and two parents, 2009/10 season, Wad Medani, Sudan.

TraitParents RILs Fpr

(<0.001)LSD

(0.05) CV SECham 6 Cham 8 Max MinE1 26.86 16.87 31.77 4.03 1.71*** 0.16 24.20 0.09E2 37.21 23.94 36.69 9.45 1.76*** 0.17 19.53 0.09E3 46.00 42.32 52.89 13.86 1.33ns 4.66 20.05 1.51E4 65.48 54.20 74.69 23.87 1.66*** 23.06 26.23 13.07E5 72.56 67.04 82.39 33.33 1.84*** 20.44 19.97 11.58E6 77.93 78.94 87.98 43.66 1.97*** 17.51 14.82 9.92E7 86.96 87.90 92.66 62.94 1.78*** 13.02 9.44 7.38Early vigor 2.77 1.90 3.47 0.90 1.06ns 0.51 13.02 0.29GC1 11.73 13.72 13.09 3.33 1.56*** 0.09 18.72 0.05GC2 39.18 46.42 45.99 13.90 1.69*** 13.80 25.19 7.77GC3 76.83 83.50 92.61 50.63 2.08*** 16.48 13.08 9.27GC4 86.13 84.79 96.71 53.51 2.47*** 13.82 9.81 7.83GC5 83.82 81.31 95.41 56.62 3.29*** 12.04 8.52 6.78GC6 74.94 73.46 89.97 47.07 3.20*** 11.39 9.37 6.40Flag leaf length (cm) 18.46 16.33 26.17 15.67 2.54*** 3.34 9.09 1.88Flag leaf width (cm) 1.26 1.32 1.62 1.19 2.99*** 0.15 6.28 0.09Days to heading 57.12 59.14 68.40 41.50 8.28*** 4.33 4.21 2.45Glaucousness 2.62 3.85 4.16 1.58 4.26*** 0.75 10.58 0.42No. of heads m2 559.00 384.10 533.50 303.00 1.40ns 120.30 17.11 67.65Plant height (cm) 61.70 64.36 83.71 53.05 7.24*** 5.08 4.60 2.86Days to physiological maturity 91.29 89.62 104.31 82.06 4.68*** 4.99 3.10 2.81Duration of green leaf (days) 36.09 31.83 48.15 24.79 1.85*** 6.09 9.83 3.43Extended grain filling (days) 34.31 30.54 41.91 26.53 1.59*** 6.21 10.67 3.50Biomass (g) 1.52 1.57 1.88 1.11 1.75*** 0.31 11.98 0.18Peduncle length (cm) 30.35 20.33 32.78 17.49 2.32*** 4.03 8.97 2.27Head length (cm) 6.82 7.81 15.83 5.22 1.52*** 2.35 17.39 1.32Threshing % 0.63 0.77 0.80 0.44 1.32ns 0.19 17.06 0.11Harvest Index 0.31 0.35 0.38 0.23 1.39ns 0.07 12.13 0.041000-kernel wt. (g) 29.42 26.23 37.55 22.94 2.99*** 4.33 8.03 2.43Yield (t ha-1) 2.93 3.39 3.64 1.59 1.79*** 0.73 14.96 0.42

Trait r2

Early Vigor 0.002ns

Flag Leaf Length (cm) (-)ve 0.08ns

Flag Leaf Width (cm) 0.1ns

Days to Heading (Days) (-)ve 0.15ns

Glaucuones 0.07ns

Number of heads m-2 0.65***

Plant height (cm) 0.32ns

Days to Physiological Maturity (Days) 0.06ns

Duration of Green Leaf (Days) 0.04ns

Extended Grain Filling (Days) 0.01ns

Dry Wt. (g) 0.32***

Peduncle length (cm) 0.005ns

Head Length (cm) (-)ve 0.05ns

Threshing % 0.08ns

Harvest Index 0.28***

1000 Kernel Wt. (g) (-)ve 0.005ns

Table 2. Correlation coefficient between grain yield (t ha-1) and investigated traits.

RILmax C_8 C_6 PopulationAverage

RILmin0

0.5

1

1.5

2

2.5

3

3.5

4

Yiel

d (T

on h

a-1 )

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

GC1 GC2 GC3 GC4 GC5 GC6

r2

Ground Cover (GC)

Figure 1. Yields of RILs compared to parents, showing trangressive segregation.

Figure 2. Correlation coefficient of grain yield(t ha-1) and ground cover.

Figure 3. Regression analysis of harvest index with grain yield (t ha-1)

Manual weeding before irrigation

The Crop two weeks before maturity Crop at Maturity