Sarhad J. Agric. Vol.25, No.3, 2009

EFFECT OF WATER POTENTIAL ON SEEDLING GROWTH OF SORGHUM CULTIVARS

ABDUL KABIR KHAN ACHAKZAI

Department of Botany, University of Balochistan, Quetta, Pakistan ABSTRACT

A Laboratory experiment was conducted to evaluate the effect of five levels of water potential (ψw) viz., 0.00; -0.41; -0.82; -1.23 and -1.64 MPa on the seedling growth of six cultivars of sorghum (Sorghum bicolor L.). Mannitol was used as osmoticum alongwith half strength Hoagland culture solution. Results enumerated that in response to various levels of water potential all mentioned attributes of seedling growth (except shoot dry weight) as well as different cultivars responded significantly (P<0.05). Results also enumerated that as water potential level increases most of the growth attributes are inversely decreases. Generally a maximum reduction in root length (5.54 cm seedling-1), shoot length (9.63 cm seedling-1), root fresh weight (19.00 mg seedling-1) and shoot fresh weights (33.33 mg seedling-1) are recorded in higher water potential levels (-1.23 and -1.64 MPa). Results further stated that based on cumulative drought tolerance index (%), sorghum cv. ICSH=479 could be ranked as drought tolerant and cv. S.E.T P=14-2 as drought sensitive. While, remaining four cultivars viz., Giza-3; ICSV=107; 1747 and Pak S.S.II could be ranked as drought intermediate in response, respectively. Key Words: Sorghum, Water potential, Root-shoot length, Root-shoot weight Citation: Achakzai, A.K.K. 2009. Effect of water potential on seedling growth of sorghum cultivars. Sarhad J. Agric. 25(3): 385-390. INTRODUCTION

Sorghum [Sorghum bicolor (L.) Moench] is an important alternative for human and animal food, especially in regions of low water availability, in which seed is rich in protein, vitamins, carbohydrates and minerals. Also, the plants have a high green mass and are tolerant to drought (water stress) and high temperatures (Carvalho et al. 2000). Sorghum is one of the kharif food/fodder grain crops of Pakistan. Many cultivars of this crop are grown both on irrigated as well as rain-fed areas (Anonymous, 2006).

Sorghum is an important kharif food/fodder grain crop of the country. Many cultivars of this crop are grown both on irrigated as well as rain fed areas. In Pakistan, the crop is grown over an average of 3,49,900 hectares year-1 with an average annual production of 2,13,400 tones or 600 kg ha-1. In Balochistan province, it is grown on 20,700 ha with total production of 18,400 tones i.e., 833 kg ha-1 (MINFAL, 2006). Production of the country as well as of the province is very low as compared with potential production of the crop. The different factors responsible for low yield ha-1, are inadequate water supply (stress) at early, development stage and response of different sorghum cultivars to water stress. Water potential (ψw) is the chemical potential of water and water stress refers to a situation when plant cells/tissues are less than fully turgid (Levitt, 1980). It may conceivably arise either from an insufficient or an excessive water activity in plants environment. Water stress can be measured in terms of water potential (Kramer, 1969). Research revealed that water stress not only modifies the morphology of plant but also severely affects plants metabolism (Ober et al., 1991; Khan et al., 1993; 1994; Saeed et al., 1997).

To find out drought tolerance of a species preliminary study in relation to effect of water stress on germination, growth and endogenous level of some metabolites are prerequisite. In Pakistan very little work has been done on this aspect. Ashraf and Mehmood (1990) studied the response of four brassica species to drought stress and determined their drought tolerance. Some postgraduate students of this University also studied the effect of water stress on germination of four varieties of maize (Jabbar, 1985), mungbean (Akhter, 1985), eight species of agropyron (Batool, 1988), six exotic species (Ali, 1988), and some M. Phil students on six cultivars of maize and sorghum (Achakzai, 2007; Achakzai and Bazai, 2007). The present study was aimed to evaluate the different variety of sorghum for drought tolerance.

Abdul Kabir Khan Achakzai. Effect of water potential on seedling growth of sorghum… 386

MATERIALS AND METHODS

The work presented here deals with the effect of five different level of water potential (ψw) i.e., 0.00; -0.41; -0.82; -1.23 and -1.64 MPa on the seedling growth of six cultivars of sorghum (Sorghum bicolor L.) viz., Pak.S.S.II; S.E.T P=14-2; 1747; Giza-3; ICSV=107; and ICSV=479. The water potential treatments (ψw) were prepared by dissolving calculated amount of Mannitol (C6H14O6) in deionized water, following the formula as described by Ting (1982). Half strength of Hoagland culture nutrients was also dissolved separately in each treatment. ψw (MPa) = -2.18 x M x T 273

The certified seeds of each sorghum cultivar are obtained from Agricultural Research Institute (ARI), Quetta. Seedling growth in response to various level of ψw for each cultivar of sorghum was studied in petri dishes of 9.0 cm in diameter. Each treatment was replicated thrice. Sorghum seed were initially treated with 1.0% mercuric chloride solution for few seconds. A double layer of blotting paper was laid down in each petri dish, and thereafter 10 healthy treated seeds of uniform size were placed at an equal distance on filter paper (Whatman 42). These petri dishes were then placed in an Incubator at 30oC. Each of the petri dish was irrigated with their respective ψw solutions. Filter papers were also changed after every 48 hours. After 10 days of germination, a set of plant from each petri dish was taken out and the following growth measurements were made:

(1) Root and shoot length, cm. (2) Root and shoot fresh weight, g. (3) Root and shoot oven dry weight (g) at 80oC. This data was then used for the determination of drought tolerance index (DTI, %) by using the following formulae (Achakzai, 2007b): (1) DTI for seedling growth (%) = Total growth of individual parameter in Ψ5 x 100

Total growth of individual parameter in Ψ1 (2) Cumulative DTI (%) = Average of all growth parameters in Ψ5 x 100

Average of all growth parameters in Ψ1

Data obtained for seedling growth were also statistically analyzed, following the procedure as described by Steel and Torrie (1980). MSTAT-C computer software package was used. RESULTS AND DISCUSSION

ANOVA results exhibited that in response to various levels of water potential (ψw) and their interaction with sorghum cultivars for seedling growth (except of shoot dry weight) responded significantly (Table I). Different cultivars response was also found significant (P<0.05). Nearly similar results were obtained for maize and sorghum seedlings grown in mannitol medium as well as in mannitol plus culture solution (Achakzai 2007 ab; Achakzai and Bazai, 2007). Table I. Analysis of variance (ANOVA) for seedling growth of sorghum cultivars (Sorghum bicolor L.) in

response to different water potential (ψw) treatments F-value of variables at an error of 60 Growth Variables

Cultivars ψw Cultivars x ψw

CV (%)

1) Root length, cm seedling-1

2) Shoot length, cm seedling-1

3) Root fresh weight, mg seedling-1

4) Shoot fresh weight, mg seedling-1

5) Root oven dry weight, mg seedling-1

6) Shoot oven dry weight, mg seedling-1

70.2916 * 135.9767 * 118.5469 * 135.9535 * 8.7676 * 31.8880 *

19.9120 * 162.0538 * 108.6901 * 94.2340 * 8.9348 * 0.8500 ns

6.8102 * 7.7497 * 170.4420 * 3.9310 * 1.8845 * 0.4480 ns

12.74 9.64 14.63 12.39 15.56 16.36

* Significant at 5% level of probability and ns = non-significant. CV = coefficient of variation. Data presented in Table II and III depicted that various levels of water potential had significantly a linear

decreased both for root and shoot length. The reduction was much prominent in shoot as compared to the roots. Statistically maximum reduction in root length (5.54 cm seedling-1) and shoot length (9.63 cm seedling-1) are obtained in highest ψw treatments i.e. 1.23 and 1.64 MPa, respectively. However, comparatively shoot was much influenced by lowest water potential levels than root. Research revealed that lower water potential affects critically

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every aspect of plant growth and life, by changing the anatomy, agronomy, physiology and biochemistry (Kramer, 1969; Khan et al. 1992; Saeed et al. 1997; Medeiros Filho et al. 2000). The present reduction in seedling growth was expected because the growth rate of plant cells and the efficiency of their physiological processes are highest when the cells are at maximum turgor. The reduction in growth is a primary effect of stress, which may be due to different metabolic disturbances. Similar results have been reported in maize cultivars (Del Rosario et al. 1991; Ali et al. 1999; Achakzai, 2009; Achakzai and Bazai, 2007), sorghum cultivars (Achakzai, 2007) and wheat genotypes (Ashraf and Naqvi, 1995; Ashraf et al. 1995 and 1996). This decrease depends upon the sensitivity of crops and even lines/cultivars to water potential. Therefore, based on cultivars response in respect of both of their root and shoot length in relation to ψw levels, sorghum cv. ICSH = 479 and Giza-3 could be rated as drought tolerant and cv. S.E.T P = 14-2 as drought sensitive (Achakzai, 2007b). Whereas, remaining cultivars could be ranked as drought intermediate in response (Fig. 1).

Drought tolerant cultivars might maintain their turgor by reducing osmotic potential at lower seedling water

potential and they exhibited higher osmotic adjustment. Similar trend of variable response are also explained by Achakzai (2007-2009) and Achakzai and Bazai (2007) in maize and sorghum cultivars, respectively. While contrasting results are recorded by Mahmood et al. (2004) in field grown crops. It was also noted that the drought tolerance management of cultivars are not exactly same as those described by Achakzai (2007). Results further exhibited that by comparing the present study with those of Achakzai (2007) there was a sharp increase in shoot length (>200%) of sorghum cultivars grown in culture media over those of non-culture media (mannitol only). This might be due to sufficient amount of available macro and micronutrients by sorghum seedlings.

0

20

40

60

80

100

120

140

160

180

200

RL SL RFW SFW ROWD SOWD

Dro

ught

tole

ranc

e in

dex

(%)

Giza-3 ICSH=479 ICSV=107 Pak. SSII SET, P=14-2 1747

Fig. 1. Drought tolerance index (%) for various growth parameters (viz., RL = root length; SL = shoot length; RFW = root

fresh weight; SFW = shoot fresh weight; RODW = root oven dry weight and SODW = shoot oven dry weight) of six cultivates of sorghum (Sorghum bicolor L.) as influenced by highest water potential level

Table II. Effect of ψw on root length (cm seedling-1) of sorghum (Sorghum bicolor L.)

Sorghum Cultivars ψw (MPa) Pak. S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean

0.00 -0.41 -0.82 -1.23 -1.64

12.60 a 9.10 bc

8.33 bcd 7.38 def 9.19 b

6.69 efgh 5.47 hij

5.64 ghij 5.15 ij

7.13 def

7.85 cde 7.63 def 7.39 def 7.72 def 6.97 efg

5.38 hij 5.63 hij 3.66 kl 3.71 kl 3.54 l

7.79 cde 6.42 fghi 5.54 hij 4.37 jkl 2.07 m

5.06 j 7.44 def 7.00 def 4.91 jk 5.14 ij

7.562 a 6.949 b 6.260 c 5.540 d 5.673 d

*Mean 9.320 a 6.017 c 7.512 b 4.384 e 5.238 d 5.911 c 6.397 CD1 for cultivars = 0.5952; CD1 for ψw = 0.5433; CD1 for cultivars x ψw = 1.331 Values followed by the same letter within columns (cultivars) and rows (ψw), and similarly mean values (*) followed by the same letter within a column and row are not significantly differ with each other at 5% level of probability using LSD test.

Abdul Kabir Khan Achakzai. Effect of water potential on seedling growth of sorghum… 388

Table III. Effect of ψw on shoot length (cm seedling-1) of sorghum (Sorghum bicolor L.) Sorghum Cultivars ψw

(MPa) Pak.S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean 0.00 -0.41 -0.82 -1.23 -1.64

22.94 ab 24.05 a 18.99 de 20.22 cd 16.30 fgh

18.83 de 15.63 gh 5.64 pq 5.15 qr

10.24 lm

18.74 de 18.05 def 18.13 def 13.32 ij 12.00 jkl

17.09 efg 14.35 hi

10.58 klm 7.72 nop 6.65 opq

15.68 gh 12.49 ijk 8.91 mn 8.03 no 3.34 r

21.27 bc 17.66 efg 14.54 hi 11.45 jkl 9.26 mn

19.09 a 17.04 b 12.80 c 10.98 d 9.63 e

*Mean 20.50 a 11.10 d 16.05 b 11.28 d 9.69 e 14.84 c 13.908 CD1 for cultivars = 0.9794; CD1 for ψw = 0.8941; CD1 for cultivars x ψw = 2.190

Values followed by the same letter within columns (cultivars) and rows (ψw), and similarly mean values (*) followed by the same letter within a column and row are not significantly differ with each other at 5% level of probability using LSD test.

Results tabulated in Table IV and V revealed that water potential levels significantly decreased the root and

shoot (except in 0.41 MPa) fresh weights. A maximum decrease (i.e., 19.00 and 30.33 mg seedling-1) in both parameters is recorded in water potentials of -1.23 and -1.64 MPa, respectively. Similar significant response is also found in case of various cultivars. These findings are in agreement with the results described by Achakzai (2007&2009). Based on cultivars response in respect of their root and shoot fresh weights, sorghum cv. Giza-3 could be ranked as drought tolerant and cv. Pak S.S.II and cv. ICSV=107 as drought sensitive. While remaining cultivars are found to be intermediate in response (Fig. 1). The arrangement of cultivars in term of drought tolerance is also in line with those explained by Achakzai (2007). Results further enumerated that by comparing the present study with those of Achakzai (2007), a prominent decline (31.48-37.33%) in seedling fresh weights occurred. Therefore, these findings are not in accordance with the results of Achakzai and Bazai (2007) obtained for maize cultivars. Table IV. Effect of ψw root fresh weight (mg seedling-1) of sorghum (Sorghum bicolor L.)

Sorghum Cultivars ψw (MPa) Pak.S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean

0.00 -0.41 -0.82 -1.23 -1.64

21.00 efghi 26.00 cde 28.00 cd

23.00 defg 29.00 c

15.00 jk 42.00 b

24.00 cdefg 27.00 cd

25.67 cdef

17.00 ijk 18.00 hijk 21.00 efghi

17.00 ijk 20.00 fghij

160.00 a 17.00 ijk 16.00 ijk 14.00 k 15.00 jk

17.00 ijk 19.00 ghijk 24.00 cdefg 18.00 hijk

14.00 k

15.00 jk 20.00 fghij 19.00 ghijk

15.00 jk 15.00 jk

40.83 a 23.67 b 22.00 bc 19.00 d 19.78 cd

*Mean 25.40 b 26.73 b 18.60 c 44.40 a 18.40 c 16.60 c 25.056 CD1 for cultivars = 2.678; CD1 for ψw = 2.445; CD1 for cultivars x ψw = 5.988

Table V. Effect of ψw on shoot fresh weight (mg seedling-1) of sorghum (Sorghum bicolor L.)

Sorghum Cultivars ψw (MPa) Pak.S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean

0.00 -0.41 -0.82 -1.23 -1.64

91.00 ab 99.00 a

82.00 bc 73.00 cd 56.00 fgh

51.00 fghi 66.00 de 32.00 kl 26.00 lm 28.00 lm

56.00 fgh 57.00 efgh 50.00 ghi 31.00 klm 25.00 lm

39.00 jk 33.00 kl 28.00 lm 24.00 lm 22.00 m

50.00 ghi 54.00 fgh 59.00 efg 31.00 klm 24.00 lm

49.00 hi 60.00 ef 43.00 ij

30.00 klm 27.00 lm

56.00 b 61.50 a 49.00 c 35.83 d 30.33 e

*Mean 80.20 a 40.60 b 43.80 b 29.20 c 43.60 b 41.80 b 46.533 CD1 for cultivars = 4.213; CD1 for ψw = 3.846; CD1 for cultivars x ψw = 9.420

Values followed by the same letter within columns (cultivars) and rows (ψw), and similarly mean values (*) followed by the same letter within a column and row are not significantly differ with each other at 5% level of probability using LSD test.

Results pertaining to root and shoot oven-dry weight (Table VI and VII) showed that in relation to different levels of ψw, shoot dry weight responded non-significantly, while root dry weight exhibited significant but inconsistent increase. Statistically and numerically a maximum value for root dry weight (16.17 & 15.83 mg seedling-1) is recorded in ψw treatments of 0.82 and 1.64 MPa, respectively. These findings are therefore, not in accordance with the results of many researchers (Ashraf et al. 1996; Achakzai, 2007; Achakzai and Bazai, 2007). However, by comparing the varietal mean values, both attributes were found to be significant.

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Therefore, based on drought tolerance index (Fig. 1), sorghum cv. ICSH=479 and Giza-3 could be ranked as drought tolerant and cv. S.E.T P=14-2 as drought sensitive, while remaining cultivars are ranked as drought intermediate in response. Results further indicated that by comparing the present study with those of Achakzai (2007b), a prominent decline (40.21-46.61%) in dry weight of both shoot and root occurred. Therefore, these findings are not in accordance with the results discussed by Achakzai and Bazai (2007) for maize cultivars. Table VI. Effect of ψw on root oven dry weight (mg seedling-1) of sorghum (Sorghum bicolor L.)

Sorghum Cultivars ψw (MPa) Pak.S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean

0.00 -0.41 -0.82 -1.23 -1.64

15.00 bc 15.00 bc 20.00 a

15.00 bc 20.00 a

12.00 c 12.00 c

18.00 ab 13.00 c 20.00 a

13.00 c 13.00 c

18.00 ab 13.00 c

18.00 ab

13.00 c 13.00 c 14.00 c 12.67 c 13.00 c

14.00 c 13.00 c 14.00 c 13.00 c 12.00 c

12.00 c 13.00 c 13.00 c 12.00 c 12.00 c

13.17 b 13.17 b 16.17 a 13.11 b 15.83 a

*Mean 17.00 a 15.00 b 15.00 b 13.13 c 13.20 c 12.40 c 14.289 CD1 for cultivars = 1.624; CD1 for ψw = 1.483; CD1 for cultivars x ψw = 3.632

Table VII Effect of five ψw on shoot oven dry weight (mg seedling-1) of sorghum (Sorghum bicolor L.)

Sorghum Cultivars ψw (MPa) Pak.S.S.II S.E.T.P=14-2 1747 Giza-3 ICSV=107 ICSV=479

*Mean

0.00 -0.41 -0.82 -1.23 -1.64

28.00 a 29.00 a 28.00 a 27.00 a 29.00 a

20.00 bc 19.00 bcd 18.00 bcd 19.00 bcd 17.00 bcd

19.00 bcd 19.00 bcd 20.00 bc 19.00 bcd 19.00 bcd

16.00 bcd 15.00 cd 15.00 cd 15.00 cd

16.00 bcd

20.00 bc 19.00 bcd 21.00 b

18.00 bcd 15.00 cd

16.00 bcd 18.00 bcd 17.00 bcd 14.00 d 15.00 cd

19.83 a 19.83 a 19.83 a 18.67 a 18.50 a

*Mean 28.20 a 18.60 b 19.20 b 15.40 c 18.60 b 16.00 c 19.333 CD1 for cultivars = 2.310; CD1 for ψw = 2.108; CD1 (for cultivars x ψw = 5.165

Values followed by the same letter within columns (cultivars) and rows (ψw), and similarly mean values (*) followed by the same letter within a column and row are not significantly differ with each other at 5% level of probability using LSD test.

Results based on cumulative drought tolerance index (%) for seedling growth exhibited that sorghum cv. ICSH=479 could be ranked as drought tolerant and cv. S.E.T P=14-2 as drought sensitive. While, remaining four cultivars viz., Giza-3; ICSV=107; 1747 and Pak S.S.II could be ranked as drought intermediate in response, respectively (Fig. 2). These findings are not in agreement with those explained by Achakzai (2007) for the same experiment by using only mannitol as an osmoticum.

Giza-320%

ICSH=47921%

ICSV=10719%

Pak. SSII12%

SET, P=14-211%

174717%

Fig. 2. Cumulative drought tolerance (%) for seedling growth of

different sorghum (Sorghum bicolor L) varieties.

Abdul Kabir Khan Achakzai. Effect of water potential on seedling growth of sorghum… 390

CONCLUSION

It can be concluded that as the negativity of ψw level increases, most of the seedling growth attributes are inversely decreases. Generally a maximum significant reduction is recorded in highest ψw treatment (-1.64 MPa). A significant variation among different cultivars is also recorded. Therefore, on the basis of total or cumulative drought tolerance index (%) of cultivars for aforementioned attributes, sorghum cv. ICSH=479 could be ranked as drought tolerant, and cv. S.E.T P=14-2 as drought sensitive. Whereas, remaining four cultivars viz; Giza-3; ICSV=107; 1747 and Pak S.S.II could be rated as drought intermediate in response respectively.

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