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Evaluation of arid and semi-arid ecotypes of guar (Cyamopsis tetragonoloba L.) for salinity (NaCl) tolerance
Journal of Arid Environments (2002) 52: 473–482 doi:10.1006/jare.2002.1017, available online at http://www.idealibrary.com on
Evaluation of arid and semi-arid ecotypes of guar (Cyamopsis tetragonoloba L.) for salinity (NaCl) tolerance
M. Yasin Ashraf% , Kalsoom Akhtarw, G. Sarwar% and M. Ashrafw %
Nuclear Institute for Agriculture and Biology, P.O. Box No. 128, Jhang Road, Faisalabad, Pakistan wDepartment of Botany,University of Agriculture, Faisalabad, Pakistan (Received 18 May 2001, accepted 27 February 2002) The germplasm of 15 guar (Cyamopsis tetragonoloba L.) ecotypes was collected from different stressed ecozones of Pakistan to study the morphogenetic parameters under various levels of salt stress. The experiment was laid out in completely randomized design with three repeats and three treatments, i.e. 3, 9 and 15 dS m 1 in 135 pots lined with polythene bags. The results showed that salt stress had considerable effect on plant height, root length, roof fresh and dry weights, shoot fresh and dry weights and seed yield per plant. However, ecotype/accession 281/3 and 239/2 performed better than others at higher salinity levels. # 2002 Elsevier Science Ltd.
Introduction In saline soils, the high ionic concentration results in lowering the osmotic potential and thus hindering the normal development of plants. The problem of salinity is enormous in arid and semi-arid regions of Pakistan. It poses a serious threat to the national economy because a major portion of foreign exchange is being earned through the agriculture sector. Many curative and management practices have been adopted by soil scientists to overcome the salinity problem but most of these methods are highly expensive. One of the possible solutions is development of crop cultivars tolerant to higher concentrations of salinity. This biological approach, to overcome the salinity problem, has received considerable attention in the last few decades (Ashraf et al., 1999b). Guar (Cyamopsis tetragonoloba L.) is an annual summer legume crop. It is drought tolerant and is grown as a vegetable for human consumption, forage for cattle, green manure for corps, and as a grain crop. The endosperm of guar seed contains galactomannan which is gaining importance as a food and non-food item. It is an important ingredient of pharmaceutics, cosmetics, textile, and paper industry. In Pakistan, its maximum yield was 987 kg h 1 during the year 1996–97 (Anonymous, 2000). *Corresponding author. E-mail: [email protected] 0140-1963/02/040473 + 10 $35.00/0
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Guar is a short duration and fast growing crop, hence it fits well into most of the prevailing summer cropping system. The endemic germplasm of guar appears to be diverse in nature, and has good adaptability for a wide range of environmental conditions of the country including some cooler parts too. In Pakistan, guar is grown under irrigation, primarily in Punjab with limited cultivation in Bahawalpur, Sind, NWFP and Balochistan areas of Pakistan (Whistler & Hymowitz, 1979). Because of its increasing uses, U.S.A. imports substantial quantity of guar every year from the Indo-Pak subcontinent (Anonymous, 2000). By virtue of a large number of its desirable agrobotanical, biochemical and ecological characters, this under-utilized crop is in sharp focus. Efforts are underway to grow or introduce this crop in several areas of Pakistan. As salinity is becoming a major constraint for agriculture, the possibility of growing alternative plants and crops suited to moderately saline conditions is being vigorously explored. The first step in this direction is to introduce new agricultural crops which are under exploited and salt-tolerant plants (Asharf et al., 1999b). Approximately, 6?3 million hectares of Pakistan are affected to various degrees of salinity and sodicity problems (Anonymous, 2000). Osmotic stress under saline conditions termed as physiological drought, subjects plants to dehydration. Ionic toxicity resulting from the accumulation of specific ions such as Na and Cl, in the cytoplasm or apoplast, interferes with plant metabolic functions (Subbarao & Johansen, 1994; Ashraf & Ali, 1998; Ashraf et al., 1999a). An understanding of genotypic differences to salt tolerance can aid in identifying cultivars which have the potential to produce a reasonably high seed yield. This study was, therefore, undertaken to assess the performance of 15 guar genotypes to salt stress and to determine their response to different salinity levels. Materials and Methods The experiment was conducted in the net house, in earthen pots (dia 30 cm, length 45 cm) containing 10 kg of air-dried soil (60% river sand and 40% field soil). Pots were lined with polythene bags for study of root system and nodulation. This
Table 1. Guar germplasm collected from south-western Pakistan
S.no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Accession no.
Sites of collection/district/ province of Pakistan
Altitude (m)
BR-90 83/5 (a) 83/5(b) 290/3 286/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
Bahawalpur/Punjab Hathilangar/Baluchistan Hathilangar/Baluchistan Tank/Khuzdar Katagiri/Baluchistan Shadikaur/Guadar Dera Pandwa/Baluchistan Dhobricast/Baluchistan Tajaban/Baluchistan Dash-e-Khudan/Baluchistan Chalani/Baluchistan Naloot/Turbat Naal/Khuzdar Guttay Duff/Khuzdar Chalani/Turbat
F F F 570 F 1000 F F 440 60 60 45 1000 585 F
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experiment consisted of 15 guar accessions (collected from different agroclimatic zones of Pakistan, Table 1), three salinity treatments with three replications. The soil analyses showed that it had pH 7?49, ECe 3?0 dS m 1 and saturation percentage 29?85. The salinity levels 3 (T1), 9 (T2) and 15 (T3) dS m 1 were maintained with NaCl. Seeds of each accession of guar in each pot were down and tap water of 1 dS m 1 was used for irrigation and three plants in each pot were maintained upto harvesting. At maturity, plants were harvested and fresh and dry weights of roots and shoots, root length, and yield per plant were recorded. The data were statistically analysed and DMRT test (Steel & Torrey, 1980) was used to compare the treatments and varietal means. Results Maximum plant height (88?07 cm) was attained by accession 281/3 and minimum (57?90 cm) by 83/5 (a) at 3 dSm 1 (Table 2). In T2, the accession 242/3 exhibited the top most value (78?03 cm) while the lowest (47?00cm) was recorded in accession 272/ 4. In T3, the most tolerant accession was 281/3 having a plant height of 70?10 cm and the least tolerant was accession 260/6 having a plant height of 26?63 cm. Accession means indicated a maximum plant height (77?30 cm) in accession 281/3 followed by accessions 242/3 and 239/2 having a value of 76?66 and 75?61 cm, respectively. From statistical analysis, it was evident that plant height was significantly restrained by a progressive increase in salinity in all accessions. Accession 281/3 was observed to be tolerant having a decrease of 20?40% over control in plant height. Root length of guar germplasm (Table 3) at different salinity levels revealed that plants attained greater root length at low salinity levels as compared to high Table 2. Effect of different levels of NaCl salinity on plant height of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
64?23 57?90 71?07 66?80 60?00 88?07 87?87 86?90 71?63 80?73 77?80 70?57 75?17 76?70 61?17
53?97 50?03 53?83 57?00 49?97 73?73 70?87 78?03 47?00 48?00 65?83 65?07 60?53 55?57 52?87
38?60 41?03 41?60 49?13 41?30 70?10 68?10 65?05 40?60 37?83 30?50 44?53 26?63 46?53 42?27
Mean percent decrease
73?10 a
58?82 b 19?53
47?61 c 34?88
Percent decrease over control
Mean
39?90 29?13 41?46 26?45 31?16 20?40 22?49 25?16 44?15 53?14 60?79 36?89 64?57 39?33 30?08
52?27 i 49?27 k 55?50 f 57?64 e 50?42 j 77?30 a 75?61 b 76?66 b 53?09 h 55?52 f 58?04 e 60?60 d 54?11 g 59?60 d 52?10 i
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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Table 3. Effect of different levels of NaCl salinity on root length of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
16?63 18?67 14?37 23?10 9?40 14?93 10?50 30?14 8?50 9?40 11?67 11?90 9?00 10?87 7?47
10?30 9?70 9?13 10?17 6?47 10?83 9?07 10?70 4?80 7?47 3?60 7?33 7?37 7?50 7?07
5?90 5?10 6?43 5?50 4?53 9?90 6?90 7?73 1?47 5?40 4?33 6?33 5?30 6?93 4?20
Mean percent decrease
13?77 a
8?10 b 41?17
Percent decrease over control
Mean
64?52 72?68 55?25 76?19 51?80 33?69 13?61 74?35 43?52 42?55 62?89 46?80 41?11 36?32 43?77
10?94 c 11?16 c 9?98 d 12?92 b 6?80 k 11?88 c 8?82 g 16?19 a 4?92 m 7?42 i 6?53 k 8?52 f 7?22 g 8?43 f 6?24 k
5?73 c 58?38
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
Table 4. Effect of different levels of NaCl salinity on root fresh weight of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
3?95 5?03 3?83 4?32 4?67 5?11 4?95 4?96 4?03 3?87 4?14 3?91 4?69 4?61 4?27
2?79 2?83 2?55 3?55 2?53 4?21 2?57 4?09 3?49 3?00 3?82 2?86 2?93 2?36 3?04
2?45 2?69 2?43 2?35 2?42 3?51 3?31 3?71 2?30 2?45 2?47 2?30 2?63 2?24 2?62
Mean percent decrease
4?42 a
3?10 b 29?86
2?65 c 40?04
Percent decrease over control
Mean
37?97 46?52 36?55 46?60 48?17 31?31 33?13 25?20 42?92 35?23 40?33 42?35 46?97 51?40 38?64
3?06 s 3?52 c 2?94 h 3?41 d 3?21 f 4?27 a 3?61 b 4?25 a 3?27 ef 3?11 g 3?48 cd 2?72 i 3?42 d 3?07 s 3?31 f
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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Table 5. Effect of different levels of NaCl salinity on root dry weight in different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
0?53 1?08 0?45 0?84 0?79 1?21 1?09 1?06 0?66 0?52 0?77 0?27 0?82 0?19 0?70
0?25 0?24 0?24 0?53 0?51 0?89 0?66 0?38 0?33 0?47 0?73 0?29 0?24 0?16 0?39
0?11 0?19 0?18 0?13 0?41 0?87 0?50 0?22 0?12 0?22 0?21 0?11 0?34 0?06 0?21
Mean percent decrease
0?73 a
0?39 b 46?57
0?42c 67?12
Percent decrease over control
Mean
79?24 82?40 60?00 84?52 48?10 28?09 54?12 79?24 81?81 57?69 72?72 59?25 58?53 68?42 70?00
0?30 i 0?50 de 0?29 i 0?50 de 0?38 gh 0?97 a 0?62 b 0?55 cd 0?37 h 0?40 fgh 0?57 bc 0?22 j 0?46 ef 0?13 k 0?44 fg
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
counterparts. The difference in root length at different salinity levels was highly significant. Treatment means indicated that maximum (13?77 cm) was recorded in T1 (control) while minimum (5?73 cm) in T3, thus indicating a decrease with progressive increase in salinity levels. Treatment accession interaction indicated that in T1, a maximum value of 30?14 cm was observed in accession 242/3 while only 7?47 cm root length was noted in accession 279/2. In T2, accessions 281/3 and 242/3 exhibited maximum root lengths of 10?83 and 10?70 cm, respectively, while minimum (3?60 cm) was recorded in accession 279/1. In T3, accession 281/3 outyielded the others by exhibiting a root length of 9?90 cm while accession 271/4 was the most sensitive exhibiting a root length of 1?47 cm. The accessions 239/2 and 281/3 proved to be tolerant exhibiting a decrease of nearly 31?61% and 33?69% over control. Maximum root fresh weight under T1 (5?11 and 5?03 g, respectively) was observed in accessions 281/3 and 83/5 (a), respectively, while minimum (3?83 g) was recorded in accessions 83/5. Similarly, in T2 highest root fresh weight was recorded in ecotype 281/3 (4?21 g) and lowest in ecotype 291/3 (2?36 g). In T3, accession 242/3 proved to be salt tolerant having a value of 3?71 g followed by a value of 3?51 g exhibited by accession 281/3 (Table 4). From accessions means, it is clear that maximum fresh weight of root (4?27 g) was recorded in accession 281/3 followed by a value of 4?25 g by accession 242/3. Treatment means indicated that control had a maximum value (4?42 g) while T3 showed minimum (2?65 g) fresh weight of root. Accessions 242/3 and 281/3 were found to be salt tolerant having a mere reduction of 25?20% and 31?31% over control, respectively. Accessions 281/3 and 239/2 in T1 exhibited maximum root dry weight values of 1?21 and 1?09 g, respectively, while minimum value (0?19 g) was recorded in accession 291/3 (Table 5). In T2, accession 281/3 exhibited the maximum (0?89 g) while minimum (0?16 g) was recorded in accession 291/3. In T3, maximum (0?87 g) was recorded in accession 281/3 while minimum (0?06 g) was observed in accession 291/3.
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Table 6. Effect of different levels of NaCl salinity on shoot fresh weight of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
19?91 12?20 25?26 22?20 18?96 33?96 28?33 25?60 18?70 22?20 19?23 19?00 15?70 19?00 15?70
15?03 9?10 18?70 17?10 15?20 30?50 24?30 20?93 15?20 17?03 16?96 18?93 14?10 16?93 10?06
12?13 6?53 13?30 11?30 8?93 26?40 19?86 14?13 12?80 12?80 13?20 10?03 7?06 10?66 6?07
Mean percent decrease
21?73a
17?34b 20?20
12?34 c 40?91
Percent decrease over control
Mean
35?45 46?47 47?34 49?09 52?90 22?26 29?89 44?80 31?55 42?34 39?72 56?20 63?28 43?89 61?33
15?69 i 9?27 j 19?08 c 16?86 c 14?36 g 30?28 a 24?16 b 20?22 c 15?56 f 17?34 a 17?35 d 17?28 d 13?46 h 15?53 f 10?61 i
15?0
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
Table 7. Effect of different levels of NaCl salinity on shoot dry weight of different guar accessions
Accession no.
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2 Mean percent decrease
Salinity levels (dS m 1) 3?0
9?0
15?0
5?92 3?66 7?71 6?65 4?97 8?17 5?28 11?09 8?13 7?07 8?40 7?21 5?03 7?28 5?42
4?24 2?66 5?27 4?71 4?59 6?99 4?47 9?92 6?14 5?28 6?51 5?85 4?61 5?03 4?00
3?51 1?51 3?15 3?06 2?47 5?96 3?84 7?78 5?00 3?79 5?99 3?03 3?52 2?59 6?07
5?35 b 21?20
4?01 c 40?94
6?79 a
Percent decrease over control
Mean
40?70 58?74 59?14 53?98 50?30 27?05 27?27 38?49 45?40 28?69 30?09 39?76 51?64 53?13 61?33
4?55 f 2?61 j 5?37 c 4?80 e 4?01 g 7?04 a 4?53 b 9?59 c 6?42 f 5?38 a 6?96 d 6?03 d 4?22 h 5?27 f 3?98 i
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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Accession means showed that accession 281/3 outyielded the others by producing 0?97 g dry weight of root. From data it is clear that accession 281/3 was salt tolerant showing a decrease of 28?09% over control. Maximum shoot fresh weight (Table 6) under T1 of 33?96 g was attained by accession 281/3 and minimum (3?33 g) was observed in accession 279/2. At 9 dS m 1 (T2), maximum (30?50 g) was recorded in accession 281/3 while minimum (9?10 g) in accession 83/5 (a). At higher salinity level (15 dS m 1) a minimum shoot fresh weight (6?07 g) was observed in accession 279/2 and a maximum (26?40 g) in accession 281/3. Treatment means revealed that fresh weight of shoot decreased with progressive increase in salinity levels. In T3, 49?91% reduction over control was observed. Accession means showed that accession 281/3 appeared to be tolerant having fresh weight of shoot equal to 30?28 g while least tolerant was accession 85/3 (a) having a value of 9?27 g. Accession 281/3 had a decrease of 22?26% over control (tolerant accession) while accession 279/2 had 61?33% decrease over control (most sensitive accession). The average shoot dry weights were 6?79, 5?35 and 4?01 g in T1, T2 and T3, respectively. These differences were statistically highly significant (Table 7). For mean shoot dry weights of accessions, a maximum of 9?59 g was exhibited by accession 242/3 while minimum (2?61 g) by accession 83/5 (a). The results showed that accessions 281/3 and 239/2 were the most tolerant exhibiting decrease of 27?05% and 27?27% over control. Accession 279/2 proved to be salt sensitive as its shoot dry weight was reduced 61?33% over control. Maximum (3?23 g) yield per plant was attained by accession 281/3 while minimum (1?87 g) was recorded for accession 268/8 (Table 8). All others were in between these two peaks. Treatments accession interaction showed highly significant difference between accessions in relation to different treatments. In T1 (control), maximum Table 8. Effect of different levels of NaCl salinity on seed yield per plant of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
2?56 2?65 2?68 2?85 2?02 3?71 3?33 3?18 2?98 3?39 3?04 2?88 2?84 2?96 2?79
2?50 2?03 2?49 2?72 1?98 3?18 2?93 2?98 2?82 3?06 2?68 2?34 1?96 2?10 1?81
1?22 1?83 1?97 2?11 1?63 2?82 2?32 1?85 1?92 1?87 1?93 1?90 1?26 1?56 1?22
Mean percent decrease
2?94 a
2?43 b 16?89
1?82 c 37?75
Percent decrease over control
Mean
52?34 30?94 26?49 25?96 39?00 23?98 30?33 41?82 35?57 44?83 36?51 34?02 55?63 62?83 56?27
2?09 hi 2?17 gh 2?38 f 2?56 eg 1?87 k 3?23 a 2?86 d 3?00 c 2?57 e 2?77 de 2?55 e 2?37 f 2?02 ij 2?21 g 1?94j k
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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M.Y. ASHRAF ET AL.
values 3?71, 3?39 and 3?33 g were recorded for accessions 281/3, 274/6 and 239/2, respectively, while accession 268/8 exhibited a minimum of 2?02 g. In T2 and T3, same accession (281/3) showed maximum values 3?18 and 2?82 g, respectively. The least-tolerant accession in T2 and T3 was 279/2 exhibiting values 1?81 and 1?22 g, respectively. Treatment means revealed that at high salinity level 37?75% reduction occurred in this character. From the above results, it can be said that increase in salinity level progressively decreased yield per plant. Accession 281/3 proved to be the most tolerant with a mere reduction of 23?98% over control. Accession 291/3 appeared to be the most sensitive having a reduction of 62?83% over control.
Discussion Plant height is an important character in determining the competitive ability of a plant for capturing the sunlight. It depends upon both genetic and environmental factors. The least reduction (20?40% and 22?49%) in plant height under 15 dS m 1 was recorded in accessions 281/3 and 239/2, respectively, indicating best tolerance among accessions under study. Osmotic stress results from lowering of soil water potential as salt content of soil rises. This leads to a water deficit or a state of dehydration in plants. Specific ion toxicity results due to penetration of injurious concentrations of Na+ and Cl in the protoplast, which may lead to an inactivation of enzymes, inhibition of protein synthesis, change in membrane permeability, and damage to cell organelles. Ionic imbalance or nutritional imbalance results in salt-stressed plants due to the competition of salt ions with nutrients (Ashraf & Khan, 1994, 1999a; Dubey, 1997; Khan & Ashraf, 1988). All these changes affect extension growth of plant which is turgor dependent (Khan et al., 1992;; Ashraf & Khan, 1994; Shalhevet et al., 1995) leading to decreased plant height. The salt-tolerant accessions may develop an osmotic adjustment mechanism which allows cell enlargement and plant growth at low water availability caused by the presence of ions, especially Na+ and Cl ions (Khan et al., 1995). The accessions sensitive to salt stress fail to operate the dehydration-avoidance mechanisms (Ludlow & Muchow, 1990), thus cannot withstand high salt stress. Our results are in accord with the findings of Ashraf & Khan (1993), Ashraf & Bhatti (2000) noted a decrease in shoot length under high salinity stress. Visual observations indicated that root length decreased under stress conditions. Roots are directly in contact with salinity and are potentially the first line of defence, i.e. salinity inhibits the long-term root growth and disturbs the mineral nutrition of plants (Khan et al., 1990; Cramer, 1994). Under saline conditions, depletion of O2 deprives the plants of its primary energy source, and root growth declines. Accumulation of high levels of internal ethylene under stressed conditions can inhibit root elongation (Koning & Jackson, 1979). Decreased root length may lead to yield losses in legumes (Noble & Rogers, 1994). The accessions of salt-tolerant guar germplasm (281/3 and 239/2) might have developed osmo-regulatory mechanisms, hormonal balance and ion exchange to minimize the adverse effects of salinity on root length. Our data for guar are consistent with those Kumar et al. (1988), who observed a decrease in root length of guar with progressive increase in salt stress. Our data disagree with the results of Datta & Dayal (1988) who reported an increase in root length of guar under saline conditions. NaCl stress significantly reduced total dry matter yield for all cultivars but ecotype 281/3 was the least affected at all salinity levels. The degree of reduction in dry matter yield increased with increasing salt stress level. Other investigators have reported similar findings, with various bean cultivars and a number of other crops (Pessarakli & Huber, 1991; Al-Rawahy et al., 1992). The negative response of dry weight of
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increasing salinity stress may be attributed to decreased leaf area expansion, smaller amounts of radiation intercepted, and hence decreased photosynthesis. These results are in accord with those of Ashraf & Khan (1993), Ashraf et al. (1991), Sharma (1991), Ullah et al. (1993) and Cachorro et al. (1994). Seed yield of all the cultivars was significantly reduced at salinity levels above 8 dS m 1. As salinity levels increased the associated seed reduction of all cultivars was attributed primarily to a reduction in number of pods per plant and the number of seeds per pod. Some reduction in 100-seed weight occurred but its contribution to reduced seed yield was relatively small. These results are identical to those of Kumar et al. (1988), Sharma (1991), and Ullah et al. (1993). In the germplasm under study, exposure to salinity resulted in low pod set, reducing greatly the number of pods per plant and consequently the grain yield. Seed yield showed a highly variable pattern under salt stress with regard to different characters. At 15 dS m 1 accessions 281/3 and 239/2 (both from Balochistan province of Pakistan) were the heaviest yielders under Faisalabad environment. The success of these accessions may be due to their inherent genetic potential which conferred salt resistance through osmotic adjustment and hormonal control thus minimizing the adverse effect of salinity.
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Khan, A.H., Ashraf, M.Y. & Azmi, A.R. (1992). Osmotic adjustment in sorghum under sodium chloride stress. Acta Physiologica Plantarum, 14(3): 159–162. Khan, A.H., Ashraf, M.Y. & Azmi, A.R. (1990). Effect of NaCl on growth and nitrogen metabolism of sorghum. Acta Physiologica Plantarum, 12(3): 233–238. Khan, A.H., & Ashraf, M.Y. (1988). Effect of sodium chloride on growth and mineral composition of sorghum. Acta Physiologica Plantarum, 10(3): 259–264. Konings, H. & Jackson, M. B. (1979). A relationship between rates of ethylene production by root and the promoting or inhibiting effects of endogenous ethylene and water on root elongation. Zeitschrift fu¨r Pflanzenphysiologie, 92: 385–379. Kumar, A.B., Bahadur, B. & Sharma, B.K. (1988). Effects of salinity on germination, seedling growth and some quantitive characters of Cyamoposis tetragonoloba (L) Taub. New Botanist, 15(1): 23–27. Ludlow, M.M. & Muchow, R.C. (1990). A critical evaluation of trait for improving crop yields in water limited environments. Advances in Agronomy, 43: 107–153. Noble, C.L. & Rogers, M.E. (1994). Response of temperate forage legumes to water logging and salinity. In: Pessarakli, M. (Ed.), Handbook of Plant and Crop Stress, pp. 472–496. Tucson, AZ: University of Arizona. Pessarakli, M. & Huber, J.T. (1991). Biomass production and protein synthesis by alfalfa under salt stress. Journal of Plant Nutrition, 14(3): 283–293. Shalhevet, J., Huck, M.G. & Schroader, B.P. (1995). Root and shoot growth response to salinity in maize and soybean. Agronomy Journal, 87: 512–516. Sharma, S.K. (1991). Role of ionic distribution in growth and salt tolerance to Vicia faba L. Plant Physiology and Biochemistry, 18(2): 75–79. Steel, R.G.D. & Torrey, J.H. (1980). Principles and Procedures of Statistics. New York: McGrawHill. Subbarao, G.V. & Johansen, C. (1994). Potential for genetic improvement of salinity tolerance in legumes: Pigeon Pea. In: Pessarakli, M. (Ed.), Handbook of plant and Crop Stress. pp. 581–598. Ullah, S.M., Soja, G. & Gertzabek, M.H. (1993). Ion uptake, osmoregulation and plant water relations in faba bean (Vicia faba L.) under salt stress. Bodenkultur, 44(4): 291–301. Whistle, R.L. & Hymowitz, T. (1979). Guar agronomy, production, industrial use and nutrition. West Lafayette, In: Purdue University Press.
Evaluation of arid and semi-arid ecotypes of guar (Cyamopsis tetragonoloba L.) for salinity (NaCl) tolerance
M. Yasin Ashraf% , Kalsoom Akhtarw, G. Sarwar% and M. Ashrafw %
Nuclear Institute for Agriculture and Biology, P.O. Box No. 128, Jhang Road, Faisalabad, Pakistan wDepartment of Botany,University of Agriculture, Faisalabad, Pakistan (Received 18 May 2001, accepted 27 February 2002) The germplasm of 15 guar (Cyamopsis tetragonoloba L.) ecotypes was collected from different stressed ecozones of Pakistan to study the morphogenetic parameters under various levels of salt stress. The experiment was laid out in completely randomized design with three repeats and three treatments, i.e. 3, 9 and 15 dS m 1 in 135 pots lined with polythene bags. The results showed that salt stress had considerable effect on plant height, root length, roof fresh and dry weights, shoot fresh and dry weights and seed yield per plant. However, ecotype/accession 281/3 and 239/2 performed better than others at higher salinity levels. # 2002 Elsevier Science Ltd.
Introduction In saline soils, the high ionic concentration results in lowering the osmotic potential and thus hindering the normal development of plants. The problem of salinity is enormous in arid and semi-arid regions of Pakistan. It poses a serious threat to the national economy because a major portion of foreign exchange is being earned through the agriculture sector. Many curative and management practices have been adopted by soil scientists to overcome the salinity problem but most of these methods are highly expensive. One of the possible solutions is development of crop cultivars tolerant to higher concentrations of salinity. This biological approach, to overcome the salinity problem, has received considerable attention in the last few decades (Ashraf et al., 1999b). Guar (Cyamopsis tetragonoloba L.) is an annual summer legume crop. It is drought tolerant and is grown as a vegetable for human consumption, forage for cattle, green manure for corps, and as a grain crop. The endosperm of guar seed contains galactomannan which is gaining importance as a food and non-food item. It is an important ingredient of pharmaceutics, cosmetics, textile, and paper industry. In Pakistan, its maximum yield was 987 kg h 1 during the year 1996–97 (Anonymous, 2000). *Corresponding author. E-mail: [email protected] 0140-1963/02/040473 + 10 $35.00/0
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Guar is a short duration and fast growing crop, hence it fits well into most of the prevailing summer cropping system. The endemic germplasm of guar appears to be diverse in nature, and has good adaptability for a wide range of environmental conditions of the country including some cooler parts too. In Pakistan, guar is grown under irrigation, primarily in Punjab with limited cultivation in Bahawalpur, Sind, NWFP and Balochistan areas of Pakistan (Whistler & Hymowitz, 1979). Because of its increasing uses, U.S.A. imports substantial quantity of guar every year from the Indo-Pak subcontinent (Anonymous, 2000). By virtue of a large number of its desirable agrobotanical, biochemical and ecological characters, this under-utilized crop is in sharp focus. Efforts are underway to grow or introduce this crop in several areas of Pakistan. As salinity is becoming a major constraint for agriculture, the possibility of growing alternative plants and crops suited to moderately saline conditions is being vigorously explored. The first step in this direction is to introduce new agricultural crops which are under exploited and salt-tolerant plants (Asharf et al., 1999b). Approximately, 6?3 million hectares of Pakistan are affected to various degrees of salinity and sodicity problems (Anonymous, 2000). Osmotic stress under saline conditions termed as physiological drought, subjects plants to dehydration. Ionic toxicity resulting from the accumulation of specific ions such as Na and Cl, in the cytoplasm or apoplast, interferes with plant metabolic functions (Subbarao & Johansen, 1994; Ashraf & Ali, 1998; Ashraf et al., 1999a). An understanding of genotypic differences to salt tolerance can aid in identifying cultivars which have the potential to produce a reasonably high seed yield. This study was, therefore, undertaken to assess the performance of 15 guar genotypes to salt stress and to determine their response to different salinity levels. Materials and Methods The experiment was conducted in the net house, in earthen pots (dia 30 cm, length 45 cm) containing 10 kg of air-dried soil (60% river sand and 40% field soil). Pots were lined with polythene bags for study of root system and nodulation. This
Table 1. Guar germplasm collected from south-western Pakistan
S.no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Accession no.
Sites of collection/district/ province of Pakistan
Altitude (m)
BR-90 83/5 (a) 83/5(b) 290/3 286/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
Bahawalpur/Punjab Hathilangar/Baluchistan Hathilangar/Baluchistan Tank/Khuzdar Katagiri/Baluchistan Shadikaur/Guadar Dera Pandwa/Baluchistan Dhobricast/Baluchistan Tajaban/Baluchistan Dash-e-Khudan/Baluchistan Chalani/Baluchistan Naloot/Turbat Naal/Khuzdar Guttay Duff/Khuzdar Chalani/Turbat
F F F 570 F 1000 F F 440 60 60 45 1000 585 F
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experiment consisted of 15 guar accessions (collected from different agroclimatic zones of Pakistan, Table 1), three salinity treatments with three replications. The soil analyses showed that it had pH 7?49, ECe 3?0 dS m 1 and saturation percentage 29?85. The salinity levels 3 (T1), 9 (T2) and 15 (T3) dS m 1 were maintained with NaCl. Seeds of each accession of guar in each pot were down and tap water of 1 dS m 1 was used for irrigation and three plants in each pot were maintained upto harvesting. At maturity, plants were harvested and fresh and dry weights of roots and shoots, root length, and yield per plant were recorded. The data were statistically analysed and DMRT test (Steel & Torrey, 1980) was used to compare the treatments and varietal means. Results Maximum plant height (88?07 cm) was attained by accession 281/3 and minimum (57?90 cm) by 83/5 (a) at 3 dSm 1 (Table 2). In T2, the accession 242/3 exhibited the top most value (78?03 cm) while the lowest (47?00cm) was recorded in accession 272/ 4. In T3, the most tolerant accession was 281/3 having a plant height of 70?10 cm and the least tolerant was accession 260/6 having a plant height of 26?63 cm. Accession means indicated a maximum plant height (77?30 cm) in accession 281/3 followed by accessions 242/3 and 239/2 having a value of 76?66 and 75?61 cm, respectively. From statistical analysis, it was evident that plant height was significantly restrained by a progressive increase in salinity in all accessions. Accession 281/3 was observed to be tolerant having a decrease of 20?40% over control in plant height. Root length of guar germplasm (Table 3) at different salinity levels revealed that plants attained greater root length at low salinity levels as compared to high Table 2. Effect of different levels of NaCl salinity on plant height of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
64?23 57?90 71?07 66?80 60?00 88?07 87?87 86?90 71?63 80?73 77?80 70?57 75?17 76?70 61?17
53?97 50?03 53?83 57?00 49?97 73?73 70?87 78?03 47?00 48?00 65?83 65?07 60?53 55?57 52?87
38?60 41?03 41?60 49?13 41?30 70?10 68?10 65?05 40?60 37?83 30?50 44?53 26?63 46?53 42?27
Mean percent decrease
73?10 a
58?82 b 19?53
47?61 c 34?88
Percent decrease over control
Mean
39?90 29?13 41?46 26?45 31?16 20?40 22?49 25?16 44?15 53?14 60?79 36?89 64?57 39?33 30?08
52?27 i 49?27 k 55?50 f 57?64 e 50?42 j 77?30 a 75?61 b 76?66 b 53?09 h 55?52 f 58?04 e 60?60 d 54?11 g 59?60 d 52?10 i
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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Table 3. Effect of different levels of NaCl salinity on root length of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
16?63 18?67 14?37 23?10 9?40 14?93 10?50 30?14 8?50 9?40 11?67 11?90 9?00 10?87 7?47
10?30 9?70 9?13 10?17 6?47 10?83 9?07 10?70 4?80 7?47 3?60 7?33 7?37 7?50 7?07
5?90 5?10 6?43 5?50 4?53 9?90 6?90 7?73 1?47 5?40 4?33 6?33 5?30 6?93 4?20
Mean percent decrease
13?77 a
8?10 b 41?17
Percent decrease over control
Mean
64?52 72?68 55?25 76?19 51?80 33?69 13?61 74?35 43?52 42?55 62?89 46?80 41?11 36?32 43?77
10?94 c 11?16 c 9?98 d 12?92 b 6?80 k 11?88 c 8?82 g 16?19 a 4?92 m 7?42 i 6?53 k 8?52 f 7?22 g 8?43 f 6?24 k
5?73 c 58?38
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
Table 4. Effect of different levels of NaCl salinity on root fresh weight of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
3?95 5?03 3?83 4?32 4?67 5?11 4?95 4?96 4?03 3?87 4?14 3?91 4?69 4?61 4?27
2?79 2?83 2?55 3?55 2?53 4?21 2?57 4?09 3?49 3?00 3?82 2?86 2?93 2?36 3?04
2?45 2?69 2?43 2?35 2?42 3?51 3?31 3?71 2?30 2?45 2?47 2?30 2?63 2?24 2?62
Mean percent decrease
4?42 a
3?10 b 29?86
2?65 c 40?04
Percent decrease over control
Mean
37?97 46?52 36?55 46?60 48?17 31?31 33?13 25?20 42?92 35?23 40?33 42?35 46?97 51?40 38?64
3?06 s 3?52 c 2?94 h 3?41 d 3?21 f 4?27 a 3?61 b 4?25 a 3?27 ef 3?11 g 3?48 cd 2?72 i 3?42 d 3?07 s 3?31 f
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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Table 5. Effect of different levels of NaCl salinity on root dry weight in different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
0?53 1?08 0?45 0?84 0?79 1?21 1?09 1?06 0?66 0?52 0?77 0?27 0?82 0?19 0?70
0?25 0?24 0?24 0?53 0?51 0?89 0?66 0?38 0?33 0?47 0?73 0?29 0?24 0?16 0?39
0?11 0?19 0?18 0?13 0?41 0?87 0?50 0?22 0?12 0?22 0?21 0?11 0?34 0?06 0?21
Mean percent decrease
0?73 a
0?39 b 46?57
0?42c 67?12
Percent decrease over control
Mean
79?24 82?40 60?00 84?52 48?10 28?09 54?12 79?24 81?81 57?69 72?72 59?25 58?53 68?42 70?00
0?30 i 0?50 de 0?29 i 0?50 de 0?38 gh 0?97 a 0?62 b 0?55 cd 0?37 h 0?40 fgh 0?57 bc 0?22 j 0?46 ef 0?13 k 0?44 fg
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
counterparts. The difference in root length at different salinity levels was highly significant. Treatment means indicated that maximum (13?77 cm) was recorded in T1 (control) while minimum (5?73 cm) in T3, thus indicating a decrease with progressive increase in salinity levels. Treatment accession interaction indicated that in T1, a maximum value of 30?14 cm was observed in accession 242/3 while only 7?47 cm root length was noted in accession 279/2. In T2, accessions 281/3 and 242/3 exhibited maximum root lengths of 10?83 and 10?70 cm, respectively, while minimum (3?60 cm) was recorded in accession 279/1. In T3, accession 281/3 outyielded the others by exhibiting a root length of 9?90 cm while accession 271/4 was the most sensitive exhibiting a root length of 1?47 cm. The accessions 239/2 and 281/3 proved to be tolerant exhibiting a decrease of nearly 31?61% and 33?69% over control. Maximum root fresh weight under T1 (5?11 and 5?03 g, respectively) was observed in accessions 281/3 and 83/5 (a), respectively, while minimum (3?83 g) was recorded in accessions 83/5. Similarly, in T2 highest root fresh weight was recorded in ecotype 281/3 (4?21 g) and lowest in ecotype 291/3 (2?36 g). In T3, accession 242/3 proved to be salt tolerant having a value of 3?71 g followed by a value of 3?51 g exhibited by accession 281/3 (Table 4). From accessions means, it is clear that maximum fresh weight of root (4?27 g) was recorded in accession 281/3 followed by a value of 4?25 g by accession 242/3. Treatment means indicated that control had a maximum value (4?42 g) while T3 showed minimum (2?65 g) fresh weight of root. Accessions 242/3 and 281/3 were found to be salt tolerant having a mere reduction of 25?20% and 31?31% over control, respectively. Accessions 281/3 and 239/2 in T1 exhibited maximum root dry weight values of 1?21 and 1?09 g, respectively, while minimum value (0?19 g) was recorded in accession 291/3 (Table 5). In T2, accession 281/3 exhibited the maximum (0?89 g) while minimum (0?16 g) was recorded in accession 291/3. In T3, maximum (0?87 g) was recorded in accession 281/3 while minimum (0?06 g) was observed in accession 291/3.
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M.Y. ASHRAF ET AL.
Table 6. Effect of different levels of NaCl salinity on shoot fresh weight of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
19?91 12?20 25?26 22?20 18?96 33?96 28?33 25?60 18?70 22?20 19?23 19?00 15?70 19?00 15?70
15?03 9?10 18?70 17?10 15?20 30?50 24?30 20?93 15?20 17?03 16?96 18?93 14?10 16?93 10?06
12?13 6?53 13?30 11?30 8?93 26?40 19?86 14?13 12?80 12?80 13?20 10?03 7?06 10?66 6?07
Mean percent decrease
21?73a
17?34b 20?20
12?34 c 40?91
Percent decrease over control
Mean
35?45 46?47 47?34 49?09 52?90 22?26 29?89 44?80 31?55 42?34 39?72 56?20 63?28 43?89 61?33
15?69 i 9?27 j 19?08 c 16?86 c 14?36 g 30?28 a 24?16 b 20?22 c 15?56 f 17?34 a 17?35 d 17?28 d 13?46 h 15?53 f 10?61 i
15?0
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
Table 7. Effect of different levels of NaCl salinity on shoot dry weight of different guar accessions
Accession no.
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2 Mean percent decrease
Salinity levels (dS m 1) 3?0
9?0
15?0
5?92 3?66 7?71 6?65 4?97 8?17 5?28 11?09 8?13 7?07 8?40 7?21 5?03 7?28 5?42
4?24 2?66 5?27 4?71 4?59 6?99 4?47 9?92 6?14 5?28 6?51 5?85 4?61 5?03 4?00
3?51 1?51 3?15 3?06 2?47 5?96 3?84 7?78 5?00 3?79 5?99 3?03 3?52 2?59 6?07
5?35 b 21?20
4?01 c 40?94
6?79 a
Percent decrease over control
Mean
40?70 58?74 59?14 53?98 50?30 27?05 27?27 38?49 45?40 28?69 30?09 39?76 51?64 53?13 61?33
4?55 f 2?61 j 5?37 c 4?80 e 4?01 g 7?04 a 4?53 b 9?59 c 6?42 f 5?38 a 6?96 d 6?03 d 4?22 h 5?27 f 3?98 i
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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479
Accession means showed that accession 281/3 outyielded the others by producing 0?97 g dry weight of root. From data it is clear that accession 281/3 was salt tolerant showing a decrease of 28?09% over control. Maximum shoot fresh weight (Table 6) under T1 of 33?96 g was attained by accession 281/3 and minimum (3?33 g) was observed in accession 279/2. At 9 dS m 1 (T2), maximum (30?50 g) was recorded in accession 281/3 while minimum (9?10 g) in accession 83/5 (a). At higher salinity level (15 dS m 1) a minimum shoot fresh weight (6?07 g) was observed in accession 279/2 and a maximum (26?40 g) in accession 281/3. Treatment means revealed that fresh weight of shoot decreased with progressive increase in salinity levels. In T3, 49?91% reduction over control was observed. Accession means showed that accession 281/3 appeared to be tolerant having fresh weight of shoot equal to 30?28 g while least tolerant was accession 85/3 (a) having a value of 9?27 g. Accession 281/3 had a decrease of 22?26% over control (tolerant accession) while accession 279/2 had 61?33% decrease over control (most sensitive accession). The average shoot dry weights were 6?79, 5?35 and 4?01 g in T1, T2 and T3, respectively. These differences were statistically highly significant (Table 7). For mean shoot dry weights of accessions, a maximum of 9?59 g was exhibited by accession 242/3 while minimum (2?61 g) by accession 83/5 (a). The results showed that accessions 281/3 and 239/2 were the most tolerant exhibiting decrease of 27?05% and 27?27% over control. Accession 279/2 proved to be salt sensitive as its shoot dry weight was reduced 61?33% over control. Maximum (3?23 g) yield per plant was attained by accession 281/3 while minimum (1?87 g) was recorded for accession 268/8 (Table 8). All others were in between these two peaks. Treatments accession interaction showed highly significant difference between accessions in relation to different treatments. In T1 (control), maximum Table 8. Effect of different levels of NaCl salinity on seed yield per plant of different guar accessions
Accession no.
Salinity levels (dS m 1) 3?0
9?0
15?0
BR-90 83/5 (a) 83/5 (b) 290/3 268/8 281/3 239/2 242/3 272/4 274/6 279/1 277/2 260/6 291/3 279/2
2?56 2?65 2?68 2?85 2?02 3?71 3?33 3?18 2?98 3?39 3?04 2?88 2?84 2?96 2?79
2?50 2?03 2?49 2?72 1?98 3?18 2?93 2?98 2?82 3?06 2?68 2?34 1?96 2?10 1?81
1?22 1?83 1?97 2?11 1?63 2?82 2?32 1?85 1?92 1?87 1?93 1?90 1?26 1?56 1?22
Mean percent decrease
2?94 a
2?43 b 16?89
1?82 c 37?75
Percent decrease over control
Mean
52?34 30?94 26?49 25?96 39?00 23?98 30?33 41?82 35?57 44?83 36?51 34?02 55?63 62?83 56?27
2?09 hi 2?17 gh 2?38 f 2?56 eg 1?87 k 3?23 a 2?86 d 3?00 c 2?57 e 2?77 de 2?55 e 2?37 f 2?02 ij 2?21 g 1?94j k
Means sharing the same letter did not differ significantly at the 5% level of significance according to DMRT.
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M.Y. ASHRAF ET AL.
values 3?71, 3?39 and 3?33 g were recorded for accessions 281/3, 274/6 and 239/2, respectively, while accession 268/8 exhibited a minimum of 2?02 g. In T2 and T3, same accession (281/3) showed maximum values 3?18 and 2?82 g, respectively. The least-tolerant accession in T2 and T3 was 279/2 exhibiting values 1?81 and 1?22 g, respectively. Treatment means revealed that at high salinity level 37?75% reduction occurred in this character. From the above results, it can be said that increase in salinity level progressively decreased yield per plant. Accession 281/3 proved to be the most tolerant with a mere reduction of 23?98% over control. Accession 291/3 appeared to be the most sensitive having a reduction of 62?83% over control.
Discussion Plant height is an important character in determining the competitive ability of a plant for capturing the sunlight. It depends upon both genetic and environmental factors. The least reduction (20?40% and 22?49%) in plant height under 15 dS m 1 was recorded in accessions 281/3 and 239/2, respectively, indicating best tolerance among accessions under study. Osmotic stress results from lowering of soil water potential as salt content of soil rises. This leads to a water deficit or a state of dehydration in plants. Specific ion toxicity results due to penetration of injurious concentrations of Na+ and Cl in the protoplast, which may lead to an inactivation of enzymes, inhibition of protein synthesis, change in membrane permeability, and damage to cell organelles. Ionic imbalance or nutritional imbalance results in salt-stressed plants due to the competition of salt ions with nutrients (Ashraf & Khan, 1994, 1999a; Dubey, 1997; Khan & Ashraf, 1988). All these changes affect extension growth of plant which is turgor dependent (Khan et al., 1992;; Ashraf & Khan, 1994; Shalhevet et al., 1995) leading to decreased plant height. The salt-tolerant accessions may develop an osmotic adjustment mechanism which allows cell enlargement and plant growth at low water availability caused by the presence of ions, especially Na+ and Cl ions (Khan et al., 1995). The accessions sensitive to salt stress fail to operate the dehydration-avoidance mechanisms (Ludlow & Muchow, 1990), thus cannot withstand high salt stress. Our results are in accord with the findings of Ashraf & Khan (1993), Ashraf & Bhatti (2000) noted a decrease in shoot length under high salinity stress. Visual observations indicated that root length decreased under stress conditions. Roots are directly in contact with salinity and are potentially the first line of defence, i.e. salinity inhibits the long-term root growth and disturbs the mineral nutrition of plants (Khan et al., 1990; Cramer, 1994). Under saline conditions, depletion of O2 deprives the plants of its primary energy source, and root growth declines. Accumulation of high levels of internal ethylene under stressed conditions can inhibit root elongation (Koning & Jackson, 1979). Decreased root length may lead to yield losses in legumes (Noble & Rogers, 1994). The accessions of salt-tolerant guar germplasm (281/3 and 239/2) might have developed osmo-regulatory mechanisms, hormonal balance and ion exchange to minimize the adverse effects of salinity on root length. Our data for guar are consistent with those Kumar et al. (1988), who observed a decrease in root length of guar with progressive increase in salt stress. Our data disagree with the results of Datta & Dayal (1988) who reported an increase in root length of guar under saline conditions. NaCl stress significantly reduced total dry matter yield for all cultivars but ecotype 281/3 was the least affected at all salinity levels. The degree of reduction in dry matter yield increased with increasing salt stress level. Other investigators have reported similar findings, with various bean cultivars and a number of other crops (Pessarakli & Huber, 1991; Al-Rawahy et al., 1992). The negative response of dry weight of
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increasing salinity stress may be attributed to decreased leaf area expansion, smaller amounts of radiation intercepted, and hence decreased photosynthesis. These results are in accord with those of Ashraf & Khan (1993), Ashraf et al. (1991), Sharma (1991), Ullah et al. (1993) and Cachorro et al. (1994). Seed yield of all the cultivars was significantly reduced at salinity levels above 8 dS m 1. As salinity levels increased the associated seed reduction of all cultivars was attributed primarily to a reduction in number of pods per plant and the number of seeds per pod. Some reduction in 100-seed weight occurred but its contribution to reduced seed yield was relatively small. These results are identical to those of Kumar et al. (1988), Sharma (1991), and Ullah et al. (1993). In the germplasm under study, exposure to salinity resulted in low pod set, reducing greatly the number of pods per plant and consequently the grain yield. Seed yield showed a highly variable pattern under salt stress with regard to different characters. At 15 dS m 1 accessions 281/3 and 239/2 (both from Balochistan province of Pakistan) were the heaviest yielders under Faisalabad environment. The success of these accessions may be due to their inherent genetic potential which conferred salt resistance through osmotic adjustment and hormonal control thus minimizing the adverse effect of salinity.
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