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Identification of salt tolerance traits in sugarcane lines
ELSEVIER
Field Crops Research
Field Crops Research 54 (1997) 9-17
Identification of salt tolerance traits in sugarcane lines Abdul Wahid, Altaf-ur-Rehman Rao, Ejaz Rasul
*
Department of Botany, Universityof Agriculture, Faisalabad-38040, Pakistan Received 30 September 1996; revised 5 March 1997; accepted 5 March 1997
Abstract
Sugarcane, being a typical glycophyte, grows poorly on saline lands. Identification and utilization of salt-tolerant traits can make an important contribution to greater productivity in these areas. Nine cane lines were selected out of a vast gene pool, based upon contrasting morphological characters and screened in pots and plots at germination, formative, grand growth and maturity stages of growth under 0 ( = 2.5 dSm-1), 7, 14 and 21 dSm -1 levels of sodium chloride. Significant differences were seen amongst the lines and growth stages. Salt tolerance limit (ECs0 value) of the lines varied considerably, being lowest (8.63 dSm -1) in CP-71-3002 and the highest (15.51 dSm - t ) in CP-4333. Characters like pink and waxy-coated stem, large number and area of green leaves, greater root and shoot yield, high-tillering and ratooning potential revealed positive correlation with ECs0 values, while the dark green color of leaves, prolonged time taken to leaf rolling in saline solution and increased leaf senescence under salinity were negatively correlated. Lines showing xeric characters were better able to tolerate high salinity. To conclude, tolerant lines and salt tolerance-linked traits identified here can be exploited to enhance the production of this crop in saline areas. © 1997 Elsevier Science B.V.
Keywords: Growth stages; Salt tolerance; Selection criteria; Sugarcane; Xeric traits I. Introduction
Sugarcane (Saccharum officinarum L.) is a glycophyte confined to tropical and sub-tropical irrigated regions, where salinity is an ever-increasing problem. According to a conservative estimate, Pakistan's cane production suffers a loss of over two billion rupees per annum on this account alone (Anonymous, 1994). Despite this loss, systematic work has scarcely been reported locally or globally. Susceptible plants display signs of salt damage and arrested growth of various parts (Maas and Niemann, 1978), while resistant plants cope with adverse saline environments by possessing inherent genetic abilities. Salt resistance is often measured by * Corresponding author.
the yield response equation of Maas and Hoffman (1977), but other indicators are also used viz. percentage of dead leaves (Ponnamperuma, 1977), visible growth and vigor (Srivastava and Jana, 1984), large area of seedling leaves (Rawson et al., 1988), pattern of biomass partitioning (Igartua et al., 1995), leaf number and ionic content (Cruz et al., 1990), chlorophyll fluorescence (Belkhodja et al., 1994), seed and oil yield (Francois, 1996) etc. All these parameters vary with growth stage of the plant (Maas et al., 1986; Heenan et al., 1988; Ashraf, 1994). The present study was undertaken to identify genetic variability for NaC1 salinity tolerance in the locally available gene pool. Nine advanced lines were selected, out of vast gene pool based upon contrasting features, for trials under increasing levels of NaC1 salinity during the years 1991-92 and
0378-4290/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. Pll S0378-4290(97)00038-5
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A. Wahid et al. / Field Crops Research 54 (1997) 9-17
1992-93. Behavior of plants to salinity was assessed on the basis of germination rate, number and area of green leaves, tillering and ratooning capacity, number of senesced basal leaves, stripped cane and dry matter yields.
2. Material and methods 2.1. Selection o f material
Nine lines were selected, based upon highly contrasting morphological features, from the advanced gene pool of Ayub Agricultural Research Institute (AARI) Faisalabad, Pakistan (Table 1). Leaf area was measured of intact plants. Color, hairiness, and waxiness were rated by visual scoring. Leaf rolling time was calculated by placing the cut end (5 cm) of excised leaf in 5% NaC1 solution. Leaf sheath index was calculated as leaf blade dry weight (g)/leaf sheath dry weight (g) x 100. 2.2. Experimental details and growth conditions
Pot and plot experiments, in a completely randomized factorial design, were run together. The pot experiment was carried out in 50 X 30 cm earthen pots having a double-layered lining of polyethylene filled with 15 kg loamy soil. The physico-chemical characteristics of the soil were; organic matter 1.90%, cation exchange capacity 16.40 meqL -1, pH 7.8, ECe 2.50 dSm -1, sodium adsorption ratio 0.09 meqL -1, Na + 2.45 meqL -1, C1- 8.52 meqL -1, SO 2- 1.98 meqL -1, and C a + M g 14.3 meqL -1 Two one-budded sets (stem cuttings) were planted in each pot with the bud upwards. For the plot study, 60-cm deep trenches (5 X 2 m) were dug and lined with double-layered polyethylene before refilling with 1300 kg of soil. Twenty sets of cane lines were planted in each plot. Finally, one plant per pot and 15 per plot were maintained. Data were recorded at germination, formative, grand growth and maturity stages at 60, 150, 245 and 340 days after sowing, respectively. The average temperatures during the experimental years were between 16°C + 8 (winter; Oct. to Feb.) and 40°C _+ 8 (summer; Mar. to Sep.). Relative humidity ranged between 75% _+ 10 (winter) and 42% _+ 9 (summed and rainfall ranged from 280 to 325 ram.
2.3. Salt application
Besides the control (2.5 dSm -1), three levels of sodium chloride (E. Merck) salinity viz. 7, 14 and 21 dSm -1, were developed gradually over six days based upon full saturation percentage of soil. For formative, grand growth and maturity stages, NaC1 was added 60, 150 and 245 days after sowing respectively, while for germination, the salt was mixed prior to sowing. The pots and plots were frequently irrigated with canal water (EC =0.5 dSm -1) and occasionally with tap water (EC = 0.8 dSm-l). To avoid nutrient depletion, 150 ml per pot and 1500 ml per plot of half strength nutrient solution (Hoagland and Arnon, 1950) was applied fortnightly. 2.4. Harvesting
The plants were harvested 60, 90, 95 and 85 days after salt application at four respective stages of growth. Leaf area was calculated as maximum length × maximum width X 0.68. Shoots were cut at ground level. To remove the roots, the pots or plots were flooded a day before the operation. The roots were cleaned by keeping them overnight in running water. Dry weights were taken after drying them at 70°C for three days. Harvested plants were separated into leaves, stem, root, trash and tillers. Tolerance was assessed from germination percentage, yield of shoot, roots, number and area of green leaves, tillering and ratooning potential, number of senesced basal leaves and stripped cane yield per plant. ECs0 values (salt level at which growth or yield is reduced 50%) of lines were computed at each growth stage using the yield response equation of Maas and Hoffman (1977). To record ratooning capacity, plants grown separately in pots or plots were harvested as described above. Ratoon production was studied for 60 days in plants from which roots were not recovered after harvest. 2.5. Statistical analyses
The data collected from the experiments were analyzed in the Minitab Programme. Because of death of plants due to salinity at different stages, the analyses were performed of uniform values for the lines at each level of salinity and growth stage
68.2 3 to 4 pinkish
light pink
Leaf sheath index Leaf rolling time (minutes) Young shoot color
medium on base and adges 66.3 3 to 4
Leaf wax Leaf hairiness
light green pinkish 1138 medium to heavy light on edges
light green pinkish 1249 heavy
Leaf color Stem color Leaf area (cm 2) Stem wax
S-86-S-699
CP-4333
Characteristics
dark pinkish
61.8 6 to 8
light hairy
mdeium green pinkish green 1430 medium
CO-1148
green
63.3 5 to 8
medium green yellowish green 1812 light to medium none few
L-118
light green
60.5 15 to 16
light none
light green yellowish 1868 light
BF-162
Table 1 Preliminary selection criteria of sugarcane lines based upon some morphological characters
pink green
56.1 10 to 12
none hairy
medium green pinkish green 1680 medium
BL-4
green
46.4 10 to 12
dark green yellowish green 2210 medium to heavy light on edges
Triton
pink green
dark green yellowish green 2026 medium to heavy light leaf surface and edges 56.0 8 to 10
COL-54
green
57.5 16 to 20
none few on edges
dark green yellowish 2281 light
CP-71-3002
.q
I
t..n 4~
t~
12
A. Wahid et al. / Field Crops Research 54 (1997) 9 - 1 7
Table 2 G e r m i n a t i o n p e r c e n t a g e s o f nine s u g a r c a n e lines at f o u r levels o f NaC1 salinity Lines
CP-4333 S-86-US-699 C O - 1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
NaC1 levels ( d S m - 1) 0
7
14
21
88.7 83.0 81.7 89.7 86.7 82.7 88.0 86.0 90.3
80.0 64.3 75.7 71.0 85.3 75.3 63.7 75.7 78.3
71.0 59.7 64.0 60.0 67.7 56.7 61.7 69.3 55.0
44.0 38.3 37.7 26.3 42.3 40.3 -
Standard error ( 0 - 1 4 d S m - 1 ) for lines = 1.5 * *; treatments = 0.9 * * a n d lines × treatments = 2.6 * *. S t a n d a r d error (21 d S m -1 ) for lines = 2.1 * * - indicate no germination.
(Table 2). In the absence of any radical differences between pot and field experiments the data were averaged for final analyses.
3. Results
3.1. Germination, growth and yield characteristics Lines indicated significant reduction in germination percentage with interactions between lines and
treatments (Table 2). CP-71-3002 germinated well under control but poorly under salinity. BF-162 had the highest germination at 7 dSm-1 while CP-4333 germinated better at 14 and 21 dSm -1. Most of the lines showed poor germination or stunted growth of young shoots at 21 dSm -1, while L-118, BL-4 and CP-71-3002 did not germinate at all. Dry weight of green leaves decreased significantly in the lines at all salt levels and growth stages but there was no interaction between these factors (Table 3). At the formative stage, COL-54 had the greatest shoot yield under control, but L-118 and CP-4333 proved the best under salinity (Fig. 1). CP-71-3002 had the greatest shoot dry weight under control, while CO-1148 at 7 and 21 dSm -1 and CP-4333 at 14 dSm-1 were greater in shoot yield at grand growth stage. At maturity CP-71-3002 and CO-1148 under 0 and 7 dSm - l yielded more. CO1148 and Triton at 14 dSm -1 and CP-4333 at 21 d S m - 1 gave better yield; however, L-118, COL-54 and CP-71-3002 died at this level. Root dry weight was significantly reduced (Fig. 1) showing significant interactions among the lines, stages and salinity (Table 3). At the formative stage, under control, L-118 and CP-71-3002 grew most roots. S-86-US699 and L-118 were equal at 7 dSm -1, followed by CP-4333, which had prolific roots at 21 dSm -1 (Fig. 1). CO-1148 at 0 to 14 dSm -1 and CP-4333 at 21
Table 3 A n a l y s i s o f variance (standard errors) o f g r o w t h a n d yield p a r a m e t e r s o f s u g a r c a n e lines u n d e r 0, 7, 14 a n d 21 d S m - 1 levels o f salinity at three g r o w t h stages S o u r c e o f variation d.f. S h o o t dry w e i g h t (g) R o o t d r y w e i g h t (g) No. o f green leaves L e a f area per plant ( c m 2) No. o f tillers per plant A Lines (V) Treatments (T) Stages (S) V × T V × S T × S V × T × S B Lines C Lines D Lines E Lines F Lines
8 1 2 8 16 2 16 2 2 2 2 2
2.78 b 7.46 b 13.89 b 2.57 b 3.73 b 1.74 b 2.24ns 1.50ns 5.96 b 4.13 b 3.56 a 4.93 b
0.57 b 2.34 b 3.63 b 2.57 b 0.51 b 1.06 b 0.65 a 0.21ns 1.03 b 1.35 b 0.46ns 0.48 b
3.98 b 6.06 b 4.66 b 5.49 b 2.47 b 0.89ns 2.05ns 6.81 b 10.11 b 8.99 b 10.12 b 8.22 b
67.20 b 3.80 b 480.45 b 112.84 b 76.95 b 109.41 b 125.29 b 77.25ns 184.74 b 273.26 b 150.74 b 145.01 a
0.59 b 0.44 b 0.48 b 0.69 ~ 0.41 b 0.16ns 0.43ns 1.53 b 0.78 b 1.33 b 0.78 b 1.51 b
a P < 0.05 b p<0.01
ns, non-significant. Statistical analysis o f data, 0 to 7 d S m - 1 at all g r o w t h stages (A), 14 d S m - I at formative stage (B), 14 d S m - 1 at g r a n d g r o w t h stage (C), 14 d S m -1 at maturity (D), 21 d S m -1 at g r a n d g r o w t h stage (E) and 21 d S m -1 at maturity (F).
A. Wahid et al. // Field Crops Research 54 (1997) 9 - 1 7
13
[ PI0 r7 r ~'114 l1211 Grand growth
Forma~ve
~
Maturity
75.
~o-
~4s~= 30i
15o ';5129-
~
0
.
.
.
.
.
.
c~/
.,~" ~'+ -" "" 4" "+ ,,'°°
Fig. 1. Shoot and root dry weight of sugarcane lines at three stages of growth under 0, 7, 14 and 21 dSm -~ levels of salinity. Missing bars in this and subsequent figures indicate the motality of lines under given levels of salinity.
[3o I77 ~t4 I1~ ] Formative
Maturity
Grand growth
I1
°l tt
q) 1~
2,40O-
E 1,800-
1,200'
0
.
.
.
.
.
.
.
.
.
Fig. 2. Number and area of green leaves of sugarcane lines at three stages of growth under 0, 7, 14 and 21 d S m - 1 levels of salinity.
14
A. Wahid et al. / Field Crops Research 54 (1997) 9 - 1 7
Maturi~/
Grand growth
Formative
3
Q.
6, O
6
Z
°o"+"'¢+o°"+'+',r"~'~
+~" +"°°o~+ ,"°~
d "~" ~
oO'
~ ¢:"
~ 4~" ~o~d ~
Fig. 3. Tillering and ratooning potential of sugarcane lines at three stages of growth under 0, 7, 14 and 21 dSm- 1 levels of salinity.
d S m - ~ g r e w m o s t roots at the grand g r o w t h stage. A t maturity, B L - 4 had the greatest root mass at 0 and 7 d S m -1, w h i l e for CP-4333, roots g r e w m o s t at 14 and 21 d S m -1. T h e n u m b e r o f green leaves per plant fell m a r k e d l y (Fig. 2) with significant differences a m o n g the lines, treatments and stages (Table 3). A t the f o r m a t i v e stage, under control, C O - 1 1 4 8 had the m o s t leaves, but C P - 4 3 3 3 p r o d u c e d m o s t at 7 and 14 d S m -~. A t the grand g r o w t h stage CP-4333, p r o d u c e d the m a x i m u m foliage under all the salt levels and C P - 7 1 - 3 0 0 2 the m i n i m u m ; h o w e v e r , B F - 1 6 2 , Triton and C P - 7 1 3002 did not survive at 21 d S m -1. A t maturity, CP-4333 r e s p o n d e d best to salinity p r o d u c i n g the largest n u m b e r o f leaves. Salinity drastically r e d u c e d l e a f area too (Fig. 2), indicating significant differences a m o n g the lines, treatments, g r o w t h stages and their interactions (Table 3). A t the f o r m a t i v e stage C O - 1 1 4 8 p r o d u c e d the greatest l e a f area u n d e r control, and C O L - 5 4 the least. C O - 1 1 4 8 at 7 d S m -1 and C P - 4 3 3 3 at 14 d S m - ~ r e v e a l e d the largest but L - 1 1 8 the smallest l e a f area at grand g r o w t h stage. CP-4333 at 7 and 14 d S m -~ and S - 8 6 - U S - 6 9 9 at 21 d S m -1
had the largest, w h i l e Triton, C P - 7 1 - 3 0 0 2 and C O L 54 under these levels had the smallest l e a f area. Greatest l e a f area under maturity was a c h i e v e d by C P - 7 1 - 3 0 0 2 under control, B L - 4 at 7 d S m -1 and S - 8 6 - U S - 6 9 9 at 14 and 21 d S m -1.
Table 4 Stripped cane yield (g) per plant of sugarcane lines under increasing salt levels Lines CP-4333 S-86-US-699 CO-1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
NaCI levels (dSm- 1) 0
7
14
21
1147 1000 1375 982 988 1003 1278 1247 1225
1138 920 902 592 486 732 981 678 546
950 816 604 243 419 503 387 166 156
858 750 355 159 150 260 -
Standard error at 0-14 dSm -l for lines = 412 * *; treatments = 1416 * * and lines×treatments=253 * *. Standard error (21 dSm- 1) for lines = 89 * *. - indicate death of plants.
A. Wahid et al. / FieM Crops Research 54 (1997) 9-17
15
Table 5 Salt tolerance limits (ECs0 values) of cane lines at four growth stages and four salinity levels Lines Germination stage Formativestage Grand growth stage Maturitystage
Mean
Rank
CP-4333 S-86-US-699 CO-1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
15.5 15.2 12.9 11.0 10.4 11.1 10.9 10.3 8.6
ht ht t t s t t s hs
15.3 14.8 14.4 13.3 14.8 13.7 15.1 14.7 11.4
12.4 12.2 7.5 8.2 6.9 7.3 7.1 6.4 6.3
17.1 17.1 15.6 13.2 10.5 12.2 10.3 10.2 8.5
17.2 16.7 14.1 9.2 9.5 10.9 11.1 9.9 8.3
a
a ht, highly tolerant; t, tolerant; s, sensitive; hs, highly sensitive.
3.2. Tillering and ratooning potential
3.4. Salt tolerance limits (ECso values)
Fig. 3a indicates significant differences among lines, treatments and growth stages, but no interaction among them for tillering capacity (Table 3). Salinity reduced tillering in all lines except CP-4333 and S-86-US-699. CO-1148, at grand growth stage, tillered most at 7 dSm-~ but less at higher levels. The remaining lines had reduced tillering under salinity, except CP-71-3002, which if survived did not tiller. CP-4333, up to 14 d S m - 1 and S-86-US-699 at 21 dSm -1 had the greatest and CP-71-3002 the lowest tillering. Statistical analyses of ratooning data could not be made due to numerous missing values (Fig. 3b). Increase in salinity halted or reduced ratooning in most lines at all stages. In CP-4333, CO-1148 and S-86-US-699 the ratooning was proportionately increased or least affected. L-118, BF162, BL-4, COL-54 and CP-71-3002 ratooned poorly at all stages under highest salinity.
Salt tolerance limits (ECs0) of all the lines were assessed on percent germination, dry matter yield of shoot and root, number and area of green leaves, tillering and ratooning capacity, number of senesced basal leaves and stripped-cane yield. These data have been presented separately as well as the average of all stages (Table 5). The tolerance of each line was rated as highly tolerant, tolerant, sensitive or highly sensitive. The lines had different tolerance levels, but the highest ECs0 was shown by CP-4333 at all the stages followed by S-86-US-699. CP-71-3002 proved the least tolerant. All lines showed relatively greater tolerance at germination compared with other stages.
3.3. Stripped-cane yield Stripped-cane yield was significantly decreased under increased salinity (Table 4). Lines yielding well under control could not maintain yield under salinity. CP-4333, however, yielded little under control, but yielded most at all salt levels, followed by Triton at 7 dSm -1, and S-86-US-699 at 14 and 21 dSm -~. L-118, COL-54 and CP-71-3002 did not survive at 21 dSm -1.
4. Discussion Wide differences in the salt tolerance of germplasm of a number of crops have been reported (Ashraf, 1994; Meinzer et al., 1994; Shannon and Noble, 1995), but comparative information is limited for sugarcane. Cane lines studied here, showed a wide range of salt tolerance. It was greatest at germination but less and variable at subsequent growth stages. Marcer (1987) and Maas et al. (1986) reported similar patterns in other crops. Thus, tolerance capability measured at germination remains meaningless unless verified at subsequent stages. Symptoms of adverse effect of NaC1 salinity on
16
A. Wahid et al. / Field Crops Research 54 (1997) 9-17
cane were chlorosis, tip burning, arrested growth, thinning of stem and reduced foliage. There were large differences in symptoms among the tolerant and non-tolerant lines. We established a positive correlation of ECs0 with deep pinkish color of emerging shoot (r = 0.84), stem (r = 0.88), and its waxiness (r = 0.70), and negative correlation for time taken for leaf rolling in saline solution (r = - 0 . 8 6 ) and dark green color of leaves (r = - 0.70). Characters like leaf sheath index and leaf hairiness were not correlated. It is suggested that pink pigmentation is a stress tolerance trait, but further studies are needed to establish its specific role in salt tolerance. Stemwaxiness restricts moisture loss. Rapid leaf rolling may be a good determinant of salt tolerance, because it reduces surface area and conserves the moisture to sustain osmotic activity (Hsiao et al., 1984). It is worth noting that the characters related with salt tolerance are also related to drought tolerance, providing a firm basis for selection of cane genotypes. The tolerant lines showed genetic potential for continued filleting (Fig. 3a), which was positively correlated (r = 0.94) with ECs0. Abundant tillering in tolerant lines appears to share the salt load with the primary tillers (dilution effect). Prolific roots (Fig. lb) were positively correlated with salt tolerance (r = 0.82). A similar trend was reported by Dudeck et al. (1983) for cynodon turf grasses and Shalhevet et al. (1995) for maize and soybean. Increased ratooning by tolerant lines supports this finding (r=0.90). McElgunn and Lawrence (1973) reached similar conclusions for forage grasses. Increased production of green leaves is another important feature of the resistant germplasm studied here (Fig. 3a). Salinity has been reported to suppress the production and expansion of leaves (Rawson et al., 1988; Kumar et al., 1994), so reducing growth and yield. A similar trend was observed in this study, but to a lesser extent in tolerant lines. Increased photosynthetic area and plant dry weight were positively related (r = 0.83), suggesting substantial adaptability of tolerant lines to salt. Moreover, a positive correlation was found between ECs0 and increased number (r = 0.81) and area of leaves (r = 0.93), and a negative correlation between increased leaf senescence (r = -0.95), thus indicating a great salt tolerance potential. Up to three leaves in tolerant, and six in sensitive lines, were senesced (data
not shown). It is possible that tolerant lines either diluted ion toxicity, through quicker growth or compartmentalized excess ions into physiologically less active older leaves (Chavan and Karadge, 1986; Schachtman and Munns, 1992; Wahid, 1994), thus halting or slowing the reduction in photosynthetic area (Fig. 3). Increased production of green leaves was positively correlated (r = 0.77) with cane yield under salinity. This appeared to enhance the sucrose biosynthesis in leaves and its storage in stalk of the tolerant lines (Table 4), thus giving high cane yield.
5. Conclusion Sugarcane genotypes possessed substantially exploitable genetic potential for salt tolerance with growth stages and salt levels. Salt tolerant lines, studied here, possessed characters related with drought tolerance which proved of great significance in their selection. Useful traits, associated with salinity tolerance are pink and waxy stem and shoot, fast and profuse emergence of tillers, dense and ramified roots, maintenance of green leaf number and area, and rapid leaf-rolling tendency. Introduction of these traits may prove rewarding for improvement of salt tolerance of this crop.
Acknowledgements We thank Mr. Katim Bukhsh Malik for supplying sugarcane material.
References Anonymous, 1994. Punjab Development Statistics, Bureau of Statistic, Government of Punjab, Lahore, Pakistan. Ashraf, M., 1994. Breeding for salinity tolerance in plants. Critical. Rev. Plant Sci. 13, 17-42. Belkhodja, R., Morales, F., Abadia, A., Gomez-Aparisi, J., Abadia, J., 1994. Chlorophyll fluorescence as a possible tool for salinity tolerance screening in barley (Hordeum vulgare L.). Plant Physiol. 104, 667-673. Chavan, P.D., Karadge, B.A., 1986. Growth, mineral nutrition, organic constituents and rate of photosynthesis in Sesbania grandiflora grown under saline conditions. Plant Soil 93, 395 -404. Cruz, V., Cuartero, J., Bolariu, M.C., Romero, M., 1990. Evalua-
A. Wahid et aL / Field Crops Research 54 (1997) 9-17 tion of characters for ascertaining salt stress responses in Lycopersicon species. J. Amer. Soc. Hort. Sci. 115, 10001003. Dudeck, A.E., Singh, S., Giordano, C.E., Nell, T.A., McConnell, D.B., 1983. Effect of sodium chloride on cynodon turf grasses. Agron. J. 75, 927-930. Francois, L.E., 1996. Salinity effects on four sunflower hybrids. Agron. J. 88, 215-219. Heenan, D.P., Lewin, L.G., McCaffey, D.W., 1988. Salinity tolerance in rice varieties at different growth stages. Hort. Sci. 28, 343-349. Hoagland, D.R., Amon, D.I., 1950. The water culture method of growing plants without soil. Calif. Agric. Exp. Stu. Univ. Calif., Berkeley Coll. Agric. Circular No. 347. Hsiao, T.C., O'Toole, J.C., Yambao, E.B., Turner, N.C., 1984. Influence of osmotic adjustment on leaf rolling and tissue death in rice (Oryza sativa L.). Plant Physiol. 75, 338-341. Igartua, E., Gracia, M.P., Lasa, J.M., 1995. Field responses of grain sorghum to a salinity gradient. Field Crops Res. 42, 15-25. Kumar, S., Naidu, K.M., Sehtia, H.L., 1994. Causes of growth reduction in elongating and expanding leaf tissue of sugarcane under saline conditions. Aust J. Plant Physiol. 21, 79-83. Maas, E.V., Hoffman, G.J., 1977. Crop salt tolerance-current assessment. J. Irrg. Drain. Div. Amer. Soc. Civil Eng. 103, 115-134. Maas, E.V., Niemann, R.H., 1978. Physiology of plant tolerance to salinity. In: eds. G.A. Jung, Crop Tolerance to Sub-Optimal Land Conditions, American Society of Agronomy Publications, pp. 277-298. Maas, E.V., Poss, J.A., Hoffman, J.G., 1986. Salinity sensitivity of sorghum at three growth stages. Irrig. Sci. 7, 1-11.
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Marcer, N.E., 1987. Salt tolerance in genus Lolium (Ryegrass) during germination and growth. Aust. J. Agric. Res. 38, 297-307. McElgunn, J.D., Lawrence, T.L., 1973. Salinity tolerance of altai wild ryegrass and other forage grasses. Can. J. Plant Sci. 53, 303-307. Meinzer, F.L., Plaut, Z., Saliendra, N.Z., 1994. Carbon isotope discrimination, gas exchange and growth of sugarcane cultivats under salinity. Plant Physiol. 104, 521-526. Ponnamperuma, F.N., 1977. Screening rice for tolerance to mineral stresses. IRRI Research Paper Series 6. Rawson, H.M., Richards, R.A., Munns, R., 1988. An examination of selection criteria for salt tolerance in wheat barley and triticale genotypes. Aust. J. Agric. Res. 39, 759-772. Schachtman, D.P., Munns, R., 1992. Sodium accumulation in leaves of Triticum species that differ in salt tolerance. Aust. J. Plant Physiol. 19, 331-340. Shalhevet, J., Huch, M.G., Schroeder, B.P., 1995. Root and shoot growth responses to salinity in maize and sorghum. Agron. J. 87, 512-516. Shannon, M.C., Noble, C.L., 1995. Variation in salt tolerance and ion accumulation among subterranean clover cultivars. Crop Sci. 35, 798-804. Srivastava, J.P., Jana, S., 1984. Screening wheat and barley germplasm for salt tolerance. In: eds. R.C. Staples and G.H. Toeniessen, Salinity Tolerance in Plants-Strategies for Crop Improvement. pp. 223-284. John Wiley, New York. Wahid, A., 1994. Some studies on physiology of sugarcane under NaC1 salinity. P h . D . thesis submitted to the Department of Botany, University of Agriculture Faisalabad, Pakistan.
Field Crops Research
Field Crops Research 54 (1997) 9-17
Identification of salt tolerance traits in sugarcane lines Abdul Wahid, Altaf-ur-Rehman Rao, Ejaz Rasul
*
Department of Botany, Universityof Agriculture, Faisalabad-38040, Pakistan Received 30 September 1996; revised 5 March 1997; accepted 5 March 1997
Abstract
Sugarcane, being a typical glycophyte, grows poorly on saline lands. Identification and utilization of salt-tolerant traits can make an important contribution to greater productivity in these areas. Nine cane lines were selected out of a vast gene pool, based upon contrasting morphological characters and screened in pots and plots at germination, formative, grand growth and maturity stages of growth under 0 ( = 2.5 dSm-1), 7, 14 and 21 dSm -1 levels of sodium chloride. Significant differences were seen amongst the lines and growth stages. Salt tolerance limit (ECs0 value) of the lines varied considerably, being lowest (8.63 dSm -1) in CP-71-3002 and the highest (15.51 dSm - t ) in CP-4333. Characters like pink and waxy-coated stem, large number and area of green leaves, greater root and shoot yield, high-tillering and ratooning potential revealed positive correlation with ECs0 values, while the dark green color of leaves, prolonged time taken to leaf rolling in saline solution and increased leaf senescence under salinity were negatively correlated. Lines showing xeric characters were better able to tolerate high salinity. To conclude, tolerant lines and salt tolerance-linked traits identified here can be exploited to enhance the production of this crop in saline areas. © 1997 Elsevier Science B.V.
Keywords: Growth stages; Salt tolerance; Selection criteria; Sugarcane; Xeric traits I. Introduction
Sugarcane (Saccharum officinarum L.) is a glycophyte confined to tropical and sub-tropical irrigated regions, where salinity is an ever-increasing problem. According to a conservative estimate, Pakistan's cane production suffers a loss of over two billion rupees per annum on this account alone (Anonymous, 1994). Despite this loss, systematic work has scarcely been reported locally or globally. Susceptible plants display signs of salt damage and arrested growth of various parts (Maas and Niemann, 1978), while resistant plants cope with adverse saline environments by possessing inherent genetic abilities. Salt resistance is often measured by * Corresponding author.
the yield response equation of Maas and Hoffman (1977), but other indicators are also used viz. percentage of dead leaves (Ponnamperuma, 1977), visible growth and vigor (Srivastava and Jana, 1984), large area of seedling leaves (Rawson et al., 1988), pattern of biomass partitioning (Igartua et al., 1995), leaf number and ionic content (Cruz et al., 1990), chlorophyll fluorescence (Belkhodja et al., 1994), seed and oil yield (Francois, 1996) etc. All these parameters vary with growth stage of the plant (Maas et al., 1986; Heenan et al., 1988; Ashraf, 1994). The present study was undertaken to identify genetic variability for NaC1 salinity tolerance in the locally available gene pool. Nine advanced lines were selected, out of vast gene pool based upon contrasting features, for trials under increasing levels of NaC1 salinity during the years 1991-92 and
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A. Wahid et al. / Field Crops Research 54 (1997) 9-17
1992-93. Behavior of plants to salinity was assessed on the basis of germination rate, number and area of green leaves, tillering and ratooning capacity, number of senesced basal leaves, stripped cane and dry matter yields.
2. Material and methods 2.1. Selection o f material
Nine lines were selected, based upon highly contrasting morphological features, from the advanced gene pool of Ayub Agricultural Research Institute (AARI) Faisalabad, Pakistan (Table 1). Leaf area was measured of intact plants. Color, hairiness, and waxiness were rated by visual scoring. Leaf rolling time was calculated by placing the cut end (5 cm) of excised leaf in 5% NaC1 solution. Leaf sheath index was calculated as leaf blade dry weight (g)/leaf sheath dry weight (g) x 100. 2.2. Experimental details and growth conditions
Pot and plot experiments, in a completely randomized factorial design, were run together. The pot experiment was carried out in 50 X 30 cm earthen pots having a double-layered lining of polyethylene filled with 15 kg loamy soil. The physico-chemical characteristics of the soil were; organic matter 1.90%, cation exchange capacity 16.40 meqL -1, pH 7.8, ECe 2.50 dSm -1, sodium adsorption ratio 0.09 meqL -1, Na + 2.45 meqL -1, C1- 8.52 meqL -1, SO 2- 1.98 meqL -1, and C a + M g 14.3 meqL -1 Two one-budded sets (stem cuttings) were planted in each pot with the bud upwards. For the plot study, 60-cm deep trenches (5 X 2 m) were dug and lined with double-layered polyethylene before refilling with 1300 kg of soil. Twenty sets of cane lines were planted in each plot. Finally, one plant per pot and 15 per plot were maintained. Data were recorded at germination, formative, grand growth and maturity stages at 60, 150, 245 and 340 days after sowing, respectively. The average temperatures during the experimental years were between 16°C + 8 (winter; Oct. to Feb.) and 40°C _+ 8 (summer; Mar. to Sep.). Relative humidity ranged between 75% _+ 10 (winter) and 42% _+ 9 (summed and rainfall ranged from 280 to 325 ram.
2.3. Salt application
Besides the control (2.5 dSm -1), three levels of sodium chloride (E. Merck) salinity viz. 7, 14 and 21 dSm -1, were developed gradually over six days based upon full saturation percentage of soil. For formative, grand growth and maturity stages, NaC1 was added 60, 150 and 245 days after sowing respectively, while for germination, the salt was mixed prior to sowing. The pots and plots were frequently irrigated with canal water (EC =0.5 dSm -1) and occasionally with tap water (EC = 0.8 dSm-l). To avoid nutrient depletion, 150 ml per pot and 1500 ml per plot of half strength nutrient solution (Hoagland and Arnon, 1950) was applied fortnightly. 2.4. Harvesting
The plants were harvested 60, 90, 95 and 85 days after salt application at four respective stages of growth. Leaf area was calculated as maximum length × maximum width X 0.68. Shoots were cut at ground level. To remove the roots, the pots or plots were flooded a day before the operation. The roots were cleaned by keeping them overnight in running water. Dry weights were taken after drying them at 70°C for three days. Harvested plants were separated into leaves, stem, root, trash and tillers. Tolerance was assessed from germination percentage, yield of shoot, roots, number and area of green leaves, tillering and ratooning potential, number of senesced basal leaves and stripped cane yield per plant. ECs0 values (salt level at which growth or yield is reduced 50%) of lines were computed at each growth stage using the yield response equation of Maas and Hoffman (1977). To record ratooning capacity, plants grown separately in pots or plots were harvested as described above. Ratoon production was studied for 60 days in plants from which roots were not recovered after harvest. 2.5. Statistical analyses
The data collected from the experiments were analyzed in the Minitab Programme. Because of death of plants due to salinity at different stages, the analyses were performed of uniform values for the lines at each level of salinity and growth stage
68.2 3 to 4 pinkish
light pink
Leaf sheath index Leaf rolling time (minutes) Young shoot color
medium on base and adges 66.3 3 to 4
Leaf wax Leaf hairiness
light green pinkish 1138 medium to heavy light on edges
light green pinkish 1249 heavy
Leaf color Stem color Leaf area (cm 2) Stem wax
S-86-S-699
CP-4333
Characteristics
dark pinkish
61.8 6 to 8
light hairy
mdeium green pinkish green 1430 medium
CO-1148
green
63.3 5 to 8
medium green yellowish green 1812 light to medium none few
L-118
light green
60.5 15 to 16
light none
light green yellowish 1868 light
BF-162
Table 1 Preliminary selection criteria of sugarcane lines based upon some morphological characters
pink green
56.1 10 to 12
none hairy
medium green pinkish green 1680 medium
BL-4
green
46.4 10 to 12
dark green yellowish green 2210 medium to heavy light on edges
Triton
pink green
dark green yellowish green 2026 medium to heavy light leaf surface and edges 56.0 8 to 10
COL-54
green
57.5 16 to 20
none few on edges
dark green yellowish 2281 light
CP-71-3002
.q
I
t..n 4~
t~
12
A. Wahid et al. / Field Crops Research 54 (1997) 9 - 1 7
Table 2 G e r m i n a t i o n p e r c e n t a g e s o f nine s u g a r c a n e lines at f o u r levels o f NaC1 salinity Lines
CP-4333 S-86-US-699 C O - 1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
NaC1 levels ( d S m - 1) 0
7
14
21
88.7 83.0 81.7 89.7 86.7 82.7 88.0 86.0 90.3
80.0 64.3 75.7 71.0 85.3 75.3 63.7 75.7 78.3
71.0 59.7 64.0 60.0 67.7 56.7 61.7 69.3 55.0
44.0 38.3 37.7 26.3 42.3 40.3 -
Standard error ( 0 - 1 4 d S m - 1 ) for lines = 1.5 * *; treatments = 0.9 * * a n d lines × treatments = 2.6 * *. S t a n d a r d error (21 d S m -1 ) for lines = 2.1 * * - indicate no germination.
(Table 2). In the absence of any radical differences between pot and field experiments the data were averaged for final analyses.
3. Results
3.1. Germination, growth and yield characteristics Lines indicated significant reduction in germination percentage with interactions between lines and
treatments (Table 2). CP-71-3002 germinated well under control but poorly under salinity. BF-162 had the highest germination at 7 dSm-1 while CP-4333 germinated better at 14 and 21 dSm -1. Most of the lines showed poor germination or stunted growth of young shoots at 21 dSm -1, while L-118, BL-4 and CP-71-3002 did not germinate at all. Dry weight of green leaves decreased significantly in the lines at all salt levels and growth stages but there was no interaction between these factors (Table 3). At the formative stage, COL-54 had the greatest shoot yield under control, but L-118 and CP-4333 proved the best under salinity (Fig. 1). CP-71-3002 had the greatest shoot dry weight under control, while CO-1148 at 7 and 21 dSm -1 and CP-4333 at 14 dSm-1 were greater in shoot yield at grand growth stage. At maturity CP-71-3002 and CO-1148 under 0 and 7 dSm - l yielded more. CO1148 and Triton at 14 dSm -1 and CP-4333 at 21 d S m - 1 gave better yield; however, L-118, COL-54 and CP-71-3002 died at this level. Root dry weight was significantly reduced (Fig. 1) showing significant interactions among the lines, stages and salinity (Table 3). At the formative stage, under control, L-118 and CP-71-3002 grew most roots. S-86-US699 and L-118 were equal at 7 dSm -1, followed by CP-4333, which had prolific roots at 21 dSm -1 (Fig. 1). CO-1148 at 0 to 14 dSm -1 and CP-4333 at 21
Table 3 A n a l y s i s o f variance (standard errors) o f g r o w t h a n d yield p a r a m e t e r s o f s u g a r c a n e lines u n d e r 0, 7, 14 a n d 21 d S m - 1 levels o f salinity at three g r o w t h stages S o u r c e o f variation d.f. S h o o t dry w e i g h t (g) R o o t d r y w e i g h t (g) No. o f green leaves L e a f area per plant ( c m 2) No. o f tillers per plant A Lines (V) Treatments (T) Stages (S) V × T V × S T × S V × T × S B Lines C Lines D Lines E Lines F Lines
8 1 2 8 16 2 16 2 2 2 2 2
2.78 b 7.46 b 13.89 b 2.57 b 3.73 b 1.74 b 2.24ns 1.50ns 5.96 b 4.13 b 3.56 a 4.93 b
0.57 b 2.34 b 3.63 b 2.57 b 0.51 b 1.06 b 0.65 a 0.21ns 1.03 b 1.35 b 0.46ns 0.48 b
3.98 b 6.06 b 4.66 b 5.49 b 2.47 b 0.89ns 2.05ns 6.81 b 10.11 b 8.99 b 10.12 b 8.22 b
67.20 b 3.80 b 480.45 b 112.84 b 76.95 b 109.41 b 125.29 b 77.25ns 184.74 b 273.26 b 150.74 b 145.01 a
0.59 b 0.44 b 0.48 b 0.69 ~ 0.41 b 0.16ns 0.43ns 1.53 b 0.78 b 1.33 b 0.78 b 1.51 b
a P < 0.05 b p<0.01
ns, non-significant. Statistical analysis o f data, 0 to 7 d S m - 1 at all g r o w t h stages (A), 14 d S m - I at formative stage (B), 14 d S m - 1 at g r a n d g r o w t h stage (C), 14 d S m -1 at maturity (D), 21 d S m -1 at g r a n d g r o w t h stage (E) and 21 d S m -1 at maturity (F).
A. Wahid et al. // Field Crops Research 54 (1997) 9 - 1 7
13
[ PI0 r7 r ~'114 l1211 Grand growth
Forma~ve
~
Maturity
75.
~o-
~4s~= 30i
15o ';5129-
~
0
.
.
.
.
.
.
c~/
.,~" ~'+ -" "" 4" "+ ,,'°°
Fig. 1. Shoot and root dry weight of sugarcane lines at three stages of growth under 0, 7, 14 and 21 dSm -~ levels of salinity. Missing bars in this and subsequent figures indicate the motality of lines under given levels of salinity.
[3o I77 ~t4 I1~ ] Formative
Maturity
Grand growth
I1
°l tt
q) 1~
2,40O-
E 1,800-
1,200'
0
.
.
.
.
.
.
.
.
.
Fig. 2. Number and area of green leaves of sugarcane lines at three stages of growth under 0, 7, 14 and 21 d S m - 1 levels of salinity.
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A. Wahid et al. / Field Crops Research 54 (1997) 9 - 1 7
Maturi~/
Grand growth
Formative
3
Q.
6, O
6
Z
°o"+"'¢+o°"+'+',r"~'~
+~" +"°°o~+ ,"°~
d "~" ~
oO'
~ ¢:"
~ 4~" ~o~d ~
Fig. 3. Tillering and ratooning potential of sugarcane lines at three stages of growth under 0, 7, 14 and 21 dSm- 1 levels of salinity.
d S m - ~ g r e w m o s t roots at the grand g r o w t h stage. A t maturity, B L - 4 had the greatest root mass at 0 and 7 d S m -1, w h i l e for CP-4333, roots g r e w m o s t at 14 and 21 d S m -1. T h e n u m b e r o f green leaves per plant fell m a r k e d l y (Fig. 2) with significant differences a m o n g the lines, treatments and stages (Table 3). A t the f o r m a t i v e stage, under control, C O - 1 1 4 8 had the m o s t leaves, but C P - 4 3 3 3 p r o d u c e d m o s t at 7 and 14 d S m -~. A t the grand g r o w t h stage CP-4333, p r o d u c e d the m a x i m u m foliage under all the salt levels and C P - 7 1 - 3 0 0 2 the m i n i m u m ; h o w e v e r , B F - 1 6 2 , Triton and C P - 7 1 3002 did not survive at 21 d S m -1. A t maturity, CP-4333 r e s p o n d e d best to salinity p r o d u c i n g the largest n u m b e r o f leaves. Salinity drastically r e d u c e d l e a f area too (Fig. 2), indicating significant differences a m o n g the lines, treatments, g r o w t h stages and their interactions (Table 3). A t the f o r m a t i v e stage C O - 1 1 4 8 p r o d u c e d the greatest l e a f area u n d e r control, and C O L - 5 4 the least. C O - 1 1 4 8 at 7 d S m -1 and C P - 4 3 3 3 at 14 d S m - ~ r e v e a l e d the largest but L - 1 1 8 the smallest l e a f area at grand g r o w t h stage. CP-4333 at 7 and 14 d S m -~ and S - 8 6 - U S - 6 9 9 at 21 d S m -1
had the largest, w h i l e Triton, C P - 7 1 - 3 0 0 2 and C O L 54 under these levels had the smallest l e a f area. Greatest l e a f area under maturity was a c h i e v e d by C P - 7 1 - 3 0 0 2 under control, B L - 4 at 7 d S m -1 and S - 8 6 - U S - 6 9 9 at 14 and 21 d S m -1.
Table 4 Stripped cane yield (g) per plant of sugarcane lines under increasing salt levels Lines CP-4333 S-86-US-699 CO-1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
NaCI levels (dSm- 1) 0
7
14
21
1147 1000 1375 982 988 1003 1278 1247 1225
1138 920 902 592 486 732 981 678 546
950 816 604 243 419 503 387 166 156
858 750 355 159 150 260 -
Standard error at 0-14 dSm -l for lines = 412 * *; treatments = 1416 * * and lines×treatments=253 * *. Standard error (21 dSm- 1) for lines = 89 * *. - indicate death of plants.
A. Wahid et al. / FieM Crops Research 54 (1997) 9-17
15
Table 5 Salt tolerance limits (ECs0 values) of cane lines at four growth stages and four salinity levels Lines Germination stage Formativestage Grand growth stage Maturitystage
Mean
Rank
CP-4333 S-86-US-699 CO-1148 L-118 BF-162 BL-4 Triton COL-54 CP-71-3002
15.5 15.2 12.9 11.0 10.4 11.1 10.9 10.3 8.6
ht ht t t s t t s hs
15.3 14.8 14.4 13.3 14.8 13.7 15.1 14.7 11.4
12.4 12.2 7.5 8.2 6.9 7.3 7.1 6.4 6.3
17.1 17.1 15.6 13.2 10.5 12.2 10.3 10.2 8.5
17.2 16.7 14.1 9.2 9.5 10.9 11.1 9.9 8.3
a
a ht, highly tolerant; t, tolerant; s, sensitive; hs, highly sensitive.
3.2. Tillering and ratooning potential
3.4. Salt tolerance limits (ECso values)
Fig. 3a indicates significant differences among lines, treatments and growth stages, but no interaction among them for tillering capacity (Table 3). Salinity reduced tillering in all lines except CP-4333 and S-86-US-699. CO-1148, at grand growth stage, tillered most at 7 dSm-~ but less at higher levels. The remaining lines had reduced tillering under salinity, except CP-71-3002, which if survived did not tiller. CP-4333, up to 14 d S m - 1 and S-86-US-699 at 21 dSm -1 had the greatest and CP-71-3002 the lowest tillering. Statistical analyses of ratooning data could not be made due to numerous missing values (Fig. 3b). Increase in salinity halted or reduced ratooning in most lines at all stages. In CP-4333, CO-1148 and S-86-US-699 the ratooning was proportionately increased or least affected. L-118, BF162, BL-4, COL-54 and CP-71-3002 ratooned poorly at all stages under highest salinity.
Salt tolerance limits (ECs0) of all the lines were assessed on percent germination, dry matter yield of shoot and root, number and area of green leaves, tillering and ratooning capacity, number of senesced basal leaves and stripped-cane yield. These data have been presented separately as well as the average of all stages (Table 5). The tolerance of each line was rated as highly tolerant, tolerant, sensitive or highly sensitive. The lines had different tolerance levels, but the highest ECs0 was shown by CP-4333 at all the stages followed by S-86-US-699. CP-71-3002 proved the least tolerant. All lines showed relatively greater tolerance at germination compared with other stages.
3.3. Stripped-cane yield Stripped-cane yield was significantly decreased under increased salinity (Table 4). Lines yielding well under control could not maintain yield under salinity. CP-4333, however, yielded little under control, but yielded most at all salt levels, followed by Triton at 7 dSm -1, and S-86-US-699 at 14 and 21 dSm -~. L-118, COL-54 and CP-71-3002 did not survive at 21 dSm -1.
4. Discussion Wide differences in the salt tolerance of germplasm of a number of crops have been reported (Ashraf, 1994; Meinzer et al., 1994; Shannon and Noble, 1995), but comparative information is limited for sugarcane. Cane lines studied here, showed a wide range of salt tolerance. It was greatest at germination but less and variable at subsequent growth stages. Marcer (1987) and Maas et al. (1986) reported similar patterns in other crops. Thus, tolerance capability measured at germination remains meaningless unless verified at subsequent stages. Symptoms of adverse effect of NaC1 salinity on
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A. Wahid et al. / Field Crops Research 54 (1997) 9-17
cane were chlorosis, tip burning, arrested growth, thinning of stem and reduced foliage. There were large differences in symptoms among the tolerant and non-tolerant lines. We established a positive correlation of ECs0 with deep pinkish color of emerging shoot (r = 0.84), stem (r = 0.88), and its waxiness (r = 0.70), and negative correlation for time taken for leaf rolling in saline solution (r = - 0 . 8 6 ) and dark green color of leaves (r = - 0.70). Characters like leaf sheath index and leaf hairiness were not correlated. It is suggested that pink pigmentation is a stress tolerance trait, but further studies are needed to establish its specific role in salt tolerance. Stemwaxiness restricts moisture loss. Rapid leaf rolling may be a good determinant of salt tolerance, because it reduces surface area and conserves the moisture to sustain osmotic activity (Hsiao et al., 1984). It is worth noting that the characters related with salt tolerance are also related to drought tolerance, providing a firm basis for selection of cane genotypes. The tolerant lines showed genetic potential for continued filleting (Fig. 3a), which was positively correlated (r = 0.94) with ECs0. Abundant tillering in tolerant lines appears to share the salt load with the primary tillers (dilution effect). Prolific roots (Fig. lb) were positively correlated with salt tolerance (r = 0.82). A similar trend was reported by Dudeck et al. (1983) for cynodon turf grasses and Shalhevet et al. (1995) for maize and soybean. Increased ratooning by tolerant lines supports this finding (r=0.90). McElgunn and Lawrence (1973) reached similar conclusions for forage grasses. Increased production of green leaves is another important feature of the resistant germplasm studied here (Fig. 3a). Salinity has been reported to suppress the production and expansion of leaves (Rawson et al., 1988; Kumar et al., 1994), so reducing growth and yield. A similar trend was observed in this study, but to a lesser extent in tolerant lines. Increased photosynthetic area and plant dry weight were positively related (r = 0.83), suggesting substantial adaptability of tolerant lines to salt. Moreover, a positive correlation was found between ECs0 and increased number (r = 0.81) and area of leaves (r = 0.93), and a negative correlation between increased leaf senescence (r = -0.95), thus indicating a great salt tolerance potential. Up to three leaves in tolerant, and six in sensitive lines, were senesced (data
not shown). It is possible that tolerant lines either diluted ion toxicity, through quicker growth or compartmentalized excess ions into physiologically less active older leaves (Chavan and Karadge, 1986; Schachtman and Munns, 1992; Wahid, 1994), thus halting or slowing the reduction in photosynthetic area (Fig. 3). Increased production of green leaves was positively correlated (r = 0.77) with cane yield under salinity. This appeared to enhance the sucrose biosynthesis in leaves and its storage in stalk of the tolerant lines (Table 4), thus giving high cane yield.
5. Conclusion Sugarcane genotypes possessed substantially exploitable genetic potential for salt tolerance with growth stages and salt levels. Salt tolerant lines, studied here, possessed characters related with drought tolerance which proved of great significance in their selection. Useful traits, associated with salinity tolerance are pink and waxy stem and shoot, fast and profuse emergence of tillers, dense and ramified roots, maintenance of green leaf number and area, and rapid leaf-rolling tendency. Introduction of these traits may prove rewarding for improvement of salt tolerance of this crop.
Acknowledgements We thank Mr. Katim Bukhsh Malik for supplying sugarcane material.
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