One of the major abiotic stress which greatly depresses the productivity of barley in the dryland areas of West Asia and North Africa (WANA) is drought. In the WANA region it is not only the inadequate amount of precipitation during the crop growing season, but most of the times it is the erratic distribution of the rainfall which causes reduction in yield or sometimes crop failures. The scientists of ICARDA (International Center for Agricultural research in the Dry Areas) are carrying out considerable amount of research to reduce or minimize the effect of moisture stress at different stages of crop development to enhance the stability in production. The development of improved, moisture stress tolerant barley germplasm is one of the major objectives of research at ICARDA.

The development of drought tolerant barely germplasm is a challenging task, but at the same time it is equally important to understand the adaptability traits in the locally adapted landraces of improved varieties which are associated with high and stable yield under variable moisture stressed environments. Therefore, studies were carried out at ICARDA to identify traits which contribute to high yield in locally adapted cultivars and provide plasticity to tolerate moisture stress.

Materials and Methods

Two landrace varieties (Arabic Aswad and Arabic Abiad) widely cultivated in the moisture stressed areas of Syria; one old winter barely variety Tokak, which is highly adapted to the Central Anatolian Plateau of Turkey, two improved facultative lines (Salmas and Roho/Mazurka); and an improved spring barley cultivar Rihane-03, released by several countries in WANA were employed to study the most important yield component and the major trait(s) contributing to high yield under moisture stressed and non-stressed environments.

The experiments were conducted at Tel Hadya, the main research site for ICARDA with a long term average annual rainfall of 333 mm, and considered to be a non-stressed site; and at Breda-Syria (long term average annual rainfall of 262 mm) a moisture stressed site. The data on a number of agronomic characters were recorded to understand the role of different traits toward yield in genetically diverse genotypes under moisture stress and non-stressed environments. The preliminary results from these studies are reported and discussed here.
 

Table 1. Yield component and yield of barley varieties at Tel Hadya (373 mm rainfall) and Breda (291 mm rainfall).

	Tillers/Plant		Dry matter  per plant (g)					Average  spike				Seed Yield
Cultivars/Lines	Total	Productive	Total	Roots	Straw	Grain	Harvest index	Grain number	Weight (g)	TKW  (g)	Spikes/m2	kg/ha
Tel Hadya
A. Abiad	7.1	4.4	12.73	3.96	3.40	3.44	0.50	18.6	0.78	42.2	550	4333
Rihane-03	4.9	2.6	11.22	5.03	3.20	3.22	0.50	34.7	1.24	36.3	332	4110
Salmas	5.8	3.5	8.82	2.80	3.21	2.82	0.46	19.7	0.81	40.9	510	4110
Tokak	8.8	4.1	11.52	4.06	4.66	2.79	0.37	15.5	0.68	43.8	560	3888
Roho/Mazurka	7.6	5.1	10.68	3.26	3.66	3.66	0.50	18.4	0.72	39.3	590	4250
LSD 0.05												663
Breda
A. Abiad	6.3	4.4	6.25	0.83	2.76	2.66	0.49	17.9	0.67	37.6	416	2788
Rihane-03	3.4	2.6	6.54	1.27	2.78	2.49	0.47	30.5	0.96	31.4	306	2944
Salmas	4.1	3.0	5.26	0.56	2.67	2.07	0.44	18.1	0.69	38.1	325	2244
Tokak	5.6	2.9	5.34	0.75	2.74	1.83	0.40	18.0	0.63	35.0	382	2410
Roho/Mazurk	4.9	3.3	6.41	1.04	2.78	2.58	0.48	21.0	0.78	37.1	363	2833
LSD 0.05												536

Results and Discussion:

The data in Table 1 did not show significant differences in the yield at Tel Hadya (season rainfall 373 mm) whereas at Breda (season rainfall 291 mm) significant differences were observed and Rihan-03 gave the highest yield followed by Roho/Mazurka. The data on yield components show that variety Rihan-03 has higher grain number per spike, and better root dry weight which might have contributed toward its better performance in spite of its lower total as well as productive tillers per plant. This lower tiller number and better developed roots might have helped the productive tillers to better utilize the available moisture. In case of Roho/Mazurka, beside well developed root system and grain number, it had higher TKW (1000-kernel weight) and relatively greater number of productive tillers which contributed towards its better performance under stress conditions. The mechanisms of yield formation in Arabic Abiad, a landrace, and Tokak, a very old Turkish winter barley variety, appear to be very different. Both these cultivars have higher number of total tillers which are reduced drastically under stress situation. However, both these lines have a tendency to respond positively to improved agronomic conditions as their total biomass at Tel Hadya was the highest. Under moisture-stress situation they do not produce large root system, rather a few well developed roots only. Both these varieties, therefore, have a buffering capacity to perform well under variable agroclimatic conditions, hence they are widely adapted.

The correlation coefficients among different agronomic traits of these cultivars given in Table 2 show that yield was positively correlated with productive tillers/plant, total dry matter, grains/plant and harvest index under both the test environments. Significant negative correlation was observed between yield and time to heading, indicating the importance of earliness in areas with terminal moisture stress and high temperature. That is why early maturing variety Rihan-03 gave significantly higher yield than late maturing varieties. Plant height in the better environment (Tel Hayda) is negatively correlated with most of the yield components whereas no relationship was observed under more stressed environment (Breda). High tillering capacity seems to be a highly desirable trait not only for obtaining good yield but also for providing elasticity to perform better under variable stressed environments.

Productive tillers and harvest index had significant positive effect on yield at both the sites. Thus, high harvest index, productive tillers, total biomass, and grains/plant have significantly positive effect on the yield performance of a genotype. The capacity of a genotype to produce high number of total and productive tillers under favorable environments and low productive tillers/plant under moisture stress situation is a highly desirable trait which provides elasticity and buffering capacity to cope up with variable environmental (thermal and moisture) stresses. It is difficult to pin point the role of a single trait in stress tolerance because often more than one trait play interactive role in different genotypes in stress tolerance.
 

Acknowledgement: The authors are thankful to Mr. H. Pashayani and Mr. G. Kashoor for their help in conducting these experiments.

Table 2: Correlation coefficients between yield and yield attributes structure indices in

barley at Tel Hadya (site 1) and Breda (site 2).

Character	Site	1	2	3	4	5	6	7	8
1. Total tillers	1   2	__  __	0.67  0.82	0.33  -0.30	-0.65  -0.62	0.34  0.04	0.11  0.35	0.10  0.31	0.10  0.31
2.Productive tillers	1  2			-0.41  -0.78	-0.94  -0.53	0.60  0.36	0.73  0.71	0.65  0.72	0.68  0.61
3.Days to heading	1  2				0.38  0.30	-0.47  -0.59	-0.76  -0.84	-0.66  -0.89	-0.70  -0.63
4.Plant height	1  2					-0.60  0.24	-0.61  -0.11	-0.64  -0.15	-0.74  0.83
5. Total dry weight/Plant	1  2						0.75   0.83	0.86  0.78	0.78  0.83
6. No. of grain/Plant	1  2							0.91  0.99	0.85  0.96
7.Harvest index	1  2								0.96  0.63
8. Yield (Kg/ha)	1  2								___  ___