Vol. 5 (4) : 257 - 263 (2003) (%

SUGARCANE

Biomass Analysis and Selection of Sugarcane Genotypes for Drought Tolerance M.E. Wagih 1, A. Ala 2 a n d Y. M u s a 1,2 1The Biotecbnology Centre, The University of Technology, Lae, Papua Niugini, North of Australia 2Faculty of Agriculture, Hasanuddin University, Makassar, Indonesia

In a completely randomized greenhouse pot trial, 26 sugarcane genotypes were evaluated under irrigated and water stress conditions during the formative growth phase (90 - 117 days after planting). The e v a l u a t i o n was based on visual assessment at 117 days after planting and measuring agronomical parameters of cane, leaf, root and hiomass over four time intervals, viz. 90, 101, 109 and 117 days after planting. An ANOVA showed that the genotypes possessed high degree of diversity, in the selection process for drought tolerance. The interaction, gcnotype x water treatment, was highly significant for cane height, cane girth, root length, root fresh weight, root bulk density, biomass fresh weight and biomass dry weight. At the formative stage, cane height and cane girth were the only practically viable parameters; best reflected by biomass dry weight, where correlation coefficient was (r = 0.517) and (r = 0.314) for cane height and girth, respectively. The 26 genotypes were classified into three categories in response to water stress: 5 tolerant, 11 moderate and 10 sensitive. Visual evaluation matched the evaluation based on biomass analysis in 16 cases, nearly matched in 9 cases and differed in 1 case. Visual evaluation is fast, inexpensive and relatively accurate and it may he a useful predictor for drought tolerance in s c r e e n i n g l a r g e number of genotypes. However, more objectively, the procedure highlights the importance of biomass analysis in the evaluation of reasonable number of genotypes in response to water stress. The study allowed for selecting drought tolerant sugarcane genotypes suitable for cultivation in Ramu Valley and Morobe Province of Papua New Guinea.

KEYWORDS : Evaluation, drought, sugarcane genotypes, visual observation, biomass analysis

The Papua New G u i n e a (PNG) sugar indus t ry has a shor t history, but is p rone to f requen t drought . In the ear ly 1980s, a c o m m e r c i a l sugarcane p l an t a t i on and Ramu Sugar L imi t ed (RSL) were es tab l i shed on 7 ,000 ha at the G u s a p - D a m p u site on the north bank of R a m u River. The Es ta te is loca ted at a m e a n a l t i t u d e of 400 m in the u p p e r R a m u V a l l e y ( 1 4 5 ~ 5 ~ To date, RSL remains the on ly sugar c o m p a n y in the count ry .

The G u s a p - D a m p u site was favoured over two other a l t e rna t ive sites in M o r o b e Province , Erap and K a i a p i t . . T h e chosen site d id not need i r r iga t ion or f l ood -p ro t ec t i on work and l and prepara t ion cost was low (Chartres , 1981). Also , the site was access ib le by road f rom Lae and M a d a n g ( H a r t e m i n k a nd Kunia ta , 1996). At the G u s a p - D a m p u , the average a n n u a l ra infa l l is 1950 m m with most p rec ip i t a t ion rece ived be tween N o v e m b e r and Apri l . The per iod f rom May to Oc tober is a dry per iod with an average

Author for Correspondence : M . E . Wagih e-mail : mwagih@ag.unitech.ac.pg; Fax : +'(675) 4734477

mon th ly ra infa l l of 30 - 175 mm, when mon th ly evapora t ion exceeded the ra infa l l with the def ic i t of 40 - 210 mm per mon t h (Kun ia t a and Sweet , 1994).

S ince the i nc e p t i on of RSL, severe and p ro longed drought per iod occurred in the years 1980, 1987, 1991, 1993 and 1997, p r o n o u n c i n g dramat ic crop loss and poor y i e ld ( K u n i a t a and Swee t , 1994; Vaux 1999) . M o r e o v e r , s t q d i e s have i n d i c a t e d tha t i r r iga t ion is no t feas ib le (Egan, 1986; Vaux, 1999). The inc idences of d rought and the i n feas ib i l i t y of i r r iga t ion for suga rcane in the Ramu Valley and the lack of d rough t to le ran t var ie t ies resu l t ed in p lac ing a g r e a t e r a t t e n t i o n to the a l t e r n a t i v e s i t e s for suga rcane g r o w i n g ~n the count ry . S ince r a in - f ed sugarcane requi res m i n i m u m ra infa l l of 1000 - 1200 m m per a n n u m ( W i l l i a ms et al., 1989), and that sugarcane is a wa te r - lov ing crop that suffers f rom water stress (Scott , 1972), it is unc l e a r why Gusap- Dampu site was favoured over the wet ter sites of Erap and Kiapi t .

As a mois t area, Morobe P rov ince is perhaps a

257

more su i t ab le s i te for c o m m e r c i a l s u g a r c a n e production. As monitored from Lae City, the Province has an average annual rainfall of 3807 mm, nearly evenly distr ibuted throughout the year. While Gusap- Dampu exper ienced frequent droughts over the last 20 years, Morobe Province exper ienced no severe drought, only mild and short drought occurred f r o m Augus t to N o v e m b e r in 1997 with an ave rage monthly rainfall o f 70 - 95 mm and average annual ra infal l o f 2243 m m (Univers i ty of Technology, Morobe Province, Weather Station). The less severe and shorter drought in Morobe Province, however, does not e l iminate the needs for drought tolerant varieties of sugarcane to safeguard the sugar industry against severe crop losses. In our earl ier studies, we screened 26 hybrid varieties of sugarcane for drought t o l e r a n c e b a s e d on v i sua l a s s e s s m e n t and measurements of agronomical parameters (Wagih et al., 2000). Visual assessments were conf i rmed with the measurements of the assessed parameters , and both were helpful in screening the variet ies under study, at early stage. However, identified tolerant var ie t i es n e e d e d fu r the r c o n f i r m a t i o n pr ior to recommendation. Research was needed to substantiate the results with m ax i m um avoidance of non-target sources of variation, such as competi t ion and location effects, that might have affected sugarcane at such sens i t ive ear ly g rowth per iod . T h e r e f o r e , more comprehens ive evaluation and selection of varieties for drought to lerance is necessary.

The object ive of this study was to evaluate the 26 sugarcane genotypes of the hybrid varieties under adequate water appl icat ion and in response to water stress under g reenhouse condi t ion, and to select drought tolerance varieties suitable for cultivation in the target areas of Papua New Guinea. The study, also, a ims at m o n i t o r i n g changes in pa rame te r s related to drought and sugar yield over the time of exposure to water stress.

M A T E R I A L S A N D M E T H O D S

Locat ion and exper imenta l details

This work was carried out at the Biotechnology Centre of the Universi ty of Technology, Lae, PNG (6 ~ 45' S, 147 ~ E) at about 60 m.a.s.1. In this study, 26 genotypes of hybrid varieties of sugarcane were evaluated for drought tolerance (Table 1).

A pot trial inc luding the 26 geno types , each replicated three t imes under two water treatments was conducted under greenhouse condit ions. One- eye sets were planted at 5 cm depth in plastic pots (20 x 25 cm) containing 4.5 kg top Eutric fluvisol soil. A total of 390 pots (26 genotypes x 15 reps) were prepared, comple te ly randomized and placed at a uniform site in a greenhouse. Two water treatments were applied, adequate water (T0-control) and water stress (T i - s t ress ) . Up to 90 days, all pots were

watered daily with 250 ml pot-l; maintaining soil mois ture at field capaci ty (approx imate ly 18 %). Genotypes under water stress (Tl) were exposed to aggressive water regime applied over 7 cycles, each of four days. On the 1 st day of each cycle, pots received water at 350 ml pot- ' followed by three days of water withholding.

At 90 days, 78 pots (26 genotypes x 3 reps) were b a g g e d out for m e a s u r i n g roo ts and b i o m a s s parameters . 156 pots (26 genotypes x 6 reps) out of the 312 remaining pots continued to receive water at 250 ml pot 1 day "l (To). The other 156 pots (26 genotypes x 6 reps) were exposed to the water stress t rea tment (T1). At 101 days, 78 control pots (26 genotypes x 3 reps) and 78 stress pots (26 genotypes x 3 reps) were again bagged out for measuring root and b i o m a s s p a r a m e t e r s , a f t e r cane and l ea f parameters were assessed. At 109 days, sampling was not necessary as no measurements were taken on root and biomass. At 117 days, the remaining 156 pots including were bagged out for root and b iomass p a r a m e t e r s , a f t e r m e a s u r i n g cane p a r a m e t e r s . Measurements for different parameters were started early in morning prior to watering.

Visual evaluat ion and assessment of parameters

Visual eva lua t ion was ca r r i ed out by th ree scientists using a set of photographs , each shows a control plant and a plant under stress for each of the 26 genotypes under study taken at 117 days after planting under uniform photographic conditions, i.e. distance, focus etc. Plants under adequate water and under water stress were given a score from 1 - 9 as compared to their respect ive control. Rating 1 - 3 was considered best per formance , 4 - 6 medium and 7 - 9 worst pe r fo rmance . When the eva lua tors differed in opinion, compromises were made to reach agreement among them.

Root, cane, leaves and biomass parameters were m e a s u r e d at four t ime in t e rva l s , d i rec t ly a f t e r watering. The first t ime interval was day 90 th, the first day of the first cycle and the three other t ime intervals were after 72 h of water withholding of every second cycle thereafter; cycle three (101 days), cycle five (109 days) and cycle seven (117 days). Root pa ramete r s including length, volume, fresh weight and dry weight and fresh and dry weight of above soil growth biomass were measured at three t ime intervals; 90, 101 and 117 days after planting. Root bulk density, was calculated by the ratio of root dry weight over root volume (g ml-1). Cane parameters including height and girth were measured at four t ime po in t s , w h e r e a s the n u m b e r of internodes, number of tillers, and leaf parameters including length, width and number of green leaves were measured at three t ime intervals : 90, 101 and 109.

Root parameters were measured essent ial ly as

258

Table - 1 : Biomass and cane parameters of 26 sugarcane genotypes at 117 days under adequate water applicat ion (control) and in response to water stress (reduction %)

Genotype Biomass fresh weight Biomass dry weight Cane height Cane girth Code

Control Reduction Control Reduction Control Reduction Control Reduction (g) (%) (g) (%) (cm) (%) (cm) (%).

1 347.07 82 64.96 77 59.33 39 1.47 34

2 274.76 76 51.18 68 48.33 26 1.40 19

3 252.08 74 47.29 65 39.33 16 1.33 33

4 268.58 77 50.73 70 54.67 28 1.30 13

5 259.13 76 45.53 65 46.17 20 1.33 28

6 286.25 68 54.13 62 54.17 22 1.40 9

7 292.77 77 53.81 69 57.67 23 1.30 23

8 239.35 78 42.93 70 49.17 26 1.17 37

9 268.02 70 49.28 53 51.50 15 1.37 20

10 293.88 75 54.95 70 48.00 16 1.47 23

11 317.49 79 58.61 73 48.00 16 1.30 20

12 330.51 75 61.84 68 54.50 35 1.43 26

13 301.01 78 54.71 73 49.17 15 1.43 30

14 337.81 75 62.81 70 51,50 26 1.47 27

15 323.79 82 56.99 77 51,67 25 1.37 29

16 322.38 74 59.60 68 56.17 22 1.47 27

17 305.58 79 55.59 73 42.50 21 1.53 28

18 311.88 79 58.02 75 58.00 26 1.30 33

19 317.22 80 58.34 76 49.83 29 1.27 18

20 263.00 70 45.01 62 39.50 24 1.30 13

21 271,42 75 50.78 70 47.67 17 1.33 23

22 334.69 73 61.76 67 62.17 29 1.40 21

23 277.08 74 49.10 65 54.50 21 1.53 30

24 317.79 74 58.30 67 62.67 37 1.27 24

25 326.46 73 59.81 67 54.67 18 1.47 16

26 298.99 72 55.08 65 42.17 21 1.53 30

Ave. 297.65 75.49 54.66 69.09 51.27 23.62 1.38 24.29

Min. 239.35 68.34 42.93 61.89 39.33 15.21 1.17 9.30

Max. 347.07 81.70 64.96 77.43 62.67 39.33 1.53 36.84

SDEV 29.5152 3.4450 5.8564 4.4002 6.3156 6,6205 0.0949 7.0962

SE 5.7884 0.6756 1.1485 0.8629 1.2386 1.2984 0.0186 1.3917

d e s c r i b e d by S h e u ( 1 9 9 6 ) a n d J a g t a p e t at . ( 1 9 9 2 ) .

R o o t s w e r e c o l l e c t e d , w a s h e d g e n t l y a n d t h e n

m e a s u r e m e n t o f r o o t l e n g t h , v o l u m e and f r e s h w e i g h t .

R o o t d r y w e i g h t w a s r e c o r d e d a f t e r d r y i n g at 800 C.

C a n e h e i g h t w a s m e a s u r e d f r o m the b a s e to the t op

m o s t v i s i b l e d e w l a p a n d g i r t h w e r e m e a s u r e d at t h e

m i d d l e p o r t i o n o f t h e s t a lk . I n t e r n o d e s , t i l l e r s a n d

n u m b e r o f g r e e n l e a v e s f r o m fu l ly e x p a n d e d l e a f w e r e

c o u n t e d . L e a f l e n g t h w a s m e a s u r e d f r o m t ip to b a s e

o f 3 ra l e a f c o u n t e d f r o m t h e top , a n d the w i d t h was

m e a s u r e d at t he c e n t r e o f t he s a m e l e a f ( S u n i l a n d

L a w r e n c e , 1996) .

259

Data analysis

Comple te ly randomized d e s i g n (CRD) was used involving the 26 varieties, two water treatments and three r ep l i c a t e s . One and two way ana lys i s of va r i ance (ANOVA), Leas t s ign i f i can t d i f fe rence (LSD) , s i m p l e mu l t i p l e l inear r e g r e s s i o n and correlat ion analysis were applied using Statistix 1.0 for W i n d o w s s o f t wa re ( A n a l y t i c a l Sof tware , Tal lahassee FL). S imple mul t ip le regress ion and correlat ion were run for biomass dry weight (DW) as dependent var iable and cane height, cane girth, leaf length and leaf width at 101 days, as independent variables expressed as, Y = a + X 1 + X 2 + X 3 + X4; where Y = Biomass dry weight, X 1 = cane girth, X 2 = cane height, X 3 = leaf length and X 4 leaf width. Regression analysis for biomass dry weight, cane height and cane girth was applied at 117 days.

RESULTS AND D I S C U S S I O N

Screening sugarcane at early age

In an a t t empt to carry out the screening and selection for drought tolerance at an early stage of sugarcane growth, parameters were assessed during the fo rma t ive s tage, f rom 90 to 117 days af ter p l an t ing , u n d e r g r e e n h o u s e cond i t i ons . It was reported that the formative growth phase in sugarcane (from 60 th to 150 th day) is the most critical water- d e m a n d i n g pe r i od , and t h e r e f o r e g r e e n h o u s e s c r e e n i n g . m e t h o d s were c o m m o n l y used for mon i to r ing r e s p o n s e to water s t ress (Singh and Reddy, 1980; Venkara tamana et al . , 1983; Naidu and Venka ta ramana , 1987). Lessons learned f rom a s i m i l a r trial (Wagih, et al . , 2000) were helpful in designing the current experiment, avoiding non-target sources of variat ion that affect sugarcane at such sensitive growth period. One one-eye set pot -1 and complete ly randomized design (CRD) were used in order to min imize plant compet i t ion and location effects, respect ively.

Diversity of genotypes

Table 2 presents a summary of one and two-way ANOVA showing the significance of differences in root , cane, l e a f and b iomass p a r a m e t e r s among genotypes under adequate water applicat ions and in response to water stress. Over the t ime intervals, the s ignif icance of the differences among genotypes in all parameters assessed was widening as indicated by the progress ive ly decreasing p-values. Maximum differences were reached at 109 and 117 days after planting. This indicated that the genotypes possesed a high deg ree of d ivers i ty , f u n d a m e n t a l in the selection process for drought tolerance. Differences among genotyp'es at 109 and 117 days after planting in most cane, root, leaf and biomass parameters were highly s ignif icant (p < 0.01). Dif ferences in leaf length and number o f green leaves of plant under stress were significant (p < 0.05). Differences were not s ignif icant (p > 0.05) in the number of internodes

and number of tillers of plants under adequate watel and under water stress and in leaf length and number of green leaves of plants under adequate water. The r e su l t s sugges t that , unde r these e x p e r i m e n t a l conditions, 109-117 days after planting would be the earliest age at which sugarcane genotypes would have the max imum differential response to water strcss.

Visual evaluation

While visual evaluation of control plants and those under water stress was carr ied out in the four time interval observation, differences among varieties were most obvious at 117 days after planting. Table 3 shows a compar ison between evaluation based on visual assessment and on biomass analysis of the different genotypes under study. Under adequate water, visual evaluation matched the evaluation by b iomass analysis in 16 genotypes (62 %). Under wa t e r s t ress same m a t c h i n g was found in 16 genotypes (62 %). The precision obtained in both cases reflects some degree on consistency in visual evaluation.

The r e m a i n i n g 10 g e n o t y p e s when v i sua l l y evaluated they fell in the next category from their ca tegory as assessed based on b iomass analys is . Genotypes of L 1, 8, 11, 14, and 19 moved from sensitive to medium; L 2 and 23 moved from medium to tolerant; L 9 moved f rom tolerant to medium and geno types L 4, and 25 moved f rom m e d i u m to sensitive. It was noted that the three evaluators had their marginal differences in visually evaluating these ten g e n o t y p e s . H o w e v e r , b e c a u s e it is fast , i n e x p e n s i v e and r e l a t i v e l y accu ra t e , the v i sua l evaluation may be the best predictor in screening large number of genotypes for drought tolerance; unless high accuracy is needed.

Cane parameters

Up to 109 days, number of internodes and number of t i l lers were amb iguous . Count ing n u m b e r of internodes was interrupted by leaf sheath freshness, i.e. the p r e sence o f g r een l ea f sheath c o v e r e d internodes and on the contrary more internodes were exposed when leaf sheath turned dry or fe l l -of f due to water stress. Therefore , despite the s ignif icant d i f ference found among geno types in number of internodes, the difference did not ref lect the actual n u m b e r of i n t e rnodes . Also , whi le t ak ing measurements on number of tillers, it was noted that tillers have also varied among genotypes in vigor and size, and, therefore, the number was considered irrelevant . Based on this observa t ion , number of tillers was not recorded at 117 days a f t e rp l an t ing .

Other than the number of internodes and number of tillers, cane height and cane girth were the most relevant parameters. Singh and Reddy (1980) and Muchow et al. (1996) found that cane height and cane girth are direct attributes to yield and therefore were considered of pr ime importance in the selection

260

Tahle - 2 : Summary of one and two-way ANOVA showing the significance of difference (p-value) among genotypes under adequate water (To) application and water stress (TI) at 90, 101, 109 and 117 days

Parameters Water Days after planting measured t r ea tmen t

One-way ANOVA (p)

90 101 109 117

Two-way ANOVA (p)

SV 117

CANE

Height T O .0000"* .0000"* .0000"* .0000"* G .0000"* T I x .0004** .0013"* .0002** W .0000"*

G x W .0000"*

Girth T O .0825ns .0335* .0048** ,0001"* G .0000"* T I x .0000"* .0000"* ,0000"* W .0000"*

G x W .0000"*

No. lnternodes T o .05474ns .0972ns .0904ns NA G NA T 1 x .9821ns .9472ns NA W NA

G x W NA

No. tiller T o 1.000ns .9992ns .9456ns NA G NA T I x .9999ns .9217ns NA W NA

G • NA LEAF

Length T o .1879ns .0001"* .1517ns NA G NA T l x .0000"* .0032** NA W NA

G x W NA

Width T O 0000"* 0000"* 0000"* NA G NA T l x .3570ns .0175"* NA W NA

G x W NA

No. green T o .0270* .2034ns .1192ns NA G NA T l x .8973ns .2160ns NA W NA

G x W NA

ROOT

Length T o .0315" .0002** x .0000"* G .0000"* T l x 1.000ns x .0000"* W ,0000"*

G x W .0000"*

Fresh weight T O .0001"* .0056** x .0000"* G .0000"* T 1 x .1669ns x .0000"* W .0000"*

G x W .0000"*

Bulk density T O .5688ns .6020ns x ,0000"* G .0000"* T 1 x .8764ns x .0017"* W .0000"*

G x W .0000"*

BIOMASS

Fresh weight T o .0000"* .0000"* x .0000"* G .0000"* T I x .0000"* x .0000"* W .0000"*

G x W .0000"*

Dry weight T O .0000"* .0000"* x .0000"* G .0000"* Tj x .0000"* x .0000"* W .0000"*

G x W .0000"*

(ns) = not significant; (*) = significant; (**) = highly significant; (G) = Genotypes; (W) = Water; (x) = data were not recorded; (NA) = Not assessed as the 3 rd leaf of all genotypesunder stress died before re._zhing 117 days

f o r d r o u g h t t o l e r a n c e . T a b l e 1 s h o w s t h a t a t 117

d a y s , u n d e r a d e q u a t e w a t e r , g e n o t y p e s 1,24, 22 , 1,

18, 7 a n d 16 w e r e t h e t a l l e s t ( 5 6 to 63 c m ) ; L3 , 20 ,

26 a n d 17 w e r e t h e s h o r t e s t ( 3 9 to 43 c m ) , a n d t h e

r e m a i n i n g 16 g e n o t y p e s w e r e o f m e d i u m c a n e h e i g h t

( 4 4 to 55 c m ) . A m o n g t h e t a l l e s t g e n o t y p o s , L1 , 16

a n d 2 2 h a d t h e g r e a t e s t c a n e g i r t h ( 1 . 4 3 to 1 .47 c m ) .

U n d e r w a t e r s t r e s s , c a n e h e i g h t w a s l e a s t a f f e c t e d

in g e n o t y p e s w e r e L 9, 13 , 3 , 10 a n d 11 w i t h

r e d u c t i o n s r a n g i n g f r o m 15 to 16 %, w h i l e t h e m o s t

s e n s i t i v e g e n o t y p e s w e r e L 1, 24 , 12, 2 2 a n d 19 w i t h

r e d u c t i o n s r a n g i n g f r o m 2 9 to 3 9 %. T h e a v e r a g e

r e d u c t i o n f o r c a n e h e i g h t w a s 2 4 %. F o r c a n e g i r t h ,

t h e l e a s t a f f e c t e d g e n o t y p e s w e r e L 6, 20 , 4 , 25 , 19,

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Table - 3 : E v a l u a t i o n of 26 s u g a r c a n e g e n o t y p e s (L1 - 26) based on v i sual a s s e s s m e n t and b i o m a s s ana lys i s

P e r f o r m a n c e S u g a r c a n e under S u g a r c a n e under c a t e g o r y a d e q u a t e water w a t e r s tress (rat ing)

V i s u a l B i o m a s s V i sua l B i o m a s s a s s e s s , ana ly s i s a s se s s , ana lys i s

Best (1 - 3) *L 12 *L 1 22 14 25 12 5 22 1 25 14 16 18 I1 6 19

24 18

Medium (4-6)

Worst (7-9)

*L 6 *L 6 26 20 2 9 20 26 3 3 23

2 15 1 4 4 17 5 10 7 26 7 7 8 10 8 12 9 13 9 16 10 6 10 25 11 7 11 2 15 2 12 22 16 14 24 17 16 5 24 19 23 26 22

24

19 8 15 14 3 20 4 21 20 5 13 8 23 3 18 17 21 23 25 13 13 9 17 11

4 21 18 21 19

1 15

*L : Genotypes in each column are ranked from the higher to lower performers

2 and 9 with reduct ions ranging from 9 to 20 %, while the most sensi t ive genotypes were LS, 1, 3 and 18 with reduct ions ranging from 33 to 37 %. The average , reduc t ion for cane gir th was 24 %. Singh and Reddy (1980) repor ted that at formative stage, the th icker the girth the more sensit ive the genotype to water stress. Their observat ion was made on nine genotypes , and could not be general ized.

L e a f p a r a m e t e r s

Due to the severe effects of water stress, leaf parameters were not measurable at 117 days and were assessed at 109 days after planting. Adher ing strictly to measur ing lea f length and leaf width on the third e x p a n d e d l ea f and s ince new th i rd leaves were consecut ively growing out, measurements were not necessar i ly taken on the same leaf in all t ime points. This is r e f l e c t e d on the f l u c t u a t e d d e g r e e of s ignif icance in the dif ferences among genotypes in leaf length and width. The few leaves on each plant of most genotypes under water stress were severely

affected, therefore, measur ing leaf length, leaf width and number of green leaves were not taken at 1 17 days for both plants under adequate water and those under water stress.

With adequate water appl ica t ion , the s ignif icant

d i f ference found in number of green leaves at 90 days was e s s e n t i a l l y due to the d i f f e r e n c e in

g e r m i n a t i o n e a r l i ne s s . As cane grew o lder , the d i f f e rence among g e n o t y p e s in number of green

leaves at 101 and 109 days became insignificant, with the number of leaves at 109 days ranging from 5 to

8 leaves. Under water stress, all genotypes di f fered in the severity of the reduct ion of leaf parameters . Reduct ion in leaf length ranged from 1 to 15 %, in leaf width ranged from 5 to 29 % and the reduct ion

in number of green leaves ranged from 36 to 65 %.

R o o t p a r a m e t e r s

Signif icance in the d i f ferences of root parameters increased with time. At 117 days, genotypes under

adequate water appl ica t ion and water stress var ied s i g n i f i c a n t l y (p < 0 .01) in all roo t p a r a m e t e r s

inc luding root length, fresh weight and bulk density. All genotypes under water stress showed an increase

in root length ranging from 3 to 66 % with an average of 22 %. However, this increment was not cor re la ted

with the response of plants to drought to lerance. Perhaps, the pot size may have l imited the potent ia l

of the different genotypes to search for water. In the absence of abundant water, the over growth of roots of some genotypes might have exaspera ted the stress

and aggravated the deter iorat ion of plants under water stress.

Root fresh weight was reduced by an average of 55 % with a range of 8 to 76 %. Root dry weight d iv ided by root volume gave root bulk density. High and posi t ive correla t ion was found between root dry

weight and root volume (r = 0.921). This ref lec ted an associat ion between high root dry weight and high volume, and between low dry weight and low volume. For this reason, the d i f ferences among genotypes in root bulk density fa i led to ref lect the per formance of genotypes in response to water stress.

B i o m a s s o f c a n e a n d l e a f p a r a m e t e r s

Signif icant di f ferences were found in all b iomass parameters at the three t ime points (Table 1). At 1 17 days after planting, under adequate water appl icat ion, genotypes L 1, 14, 22, 12 and 25 had the highest

b iomass fresh weight ranging from 326 to 347 g, while the lowest biomass fresh weight were L 8, 15,

5 and 4 ranging from 53 to 62 g. In terms of biomass dry weight the highest were L 1, 14, 12, and 22

ranging from 62 to 65 g, while the lowest were L 8, 15, 19 and 18 ranging from 13 to 15 g. The remaining

16 genotypes were of medium biomass dry weight, ranging from 15 to 62 g.

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U n d e r w a t e r s t ress , b i o m a s s f r e sh we igh t was r e d u c e d to an ave rage o f 75 % ( r anged 68 to 82 %). G e n o t y p e s wi th the l o w e s t r e d u c t i o n were L 6, 9, 20, 26 and 22 r a n g i n g f r o m 69 to 73 %, whi le the h i g h e s t r e d u c t i o n was f o u n d in g e n o t y p e s L 1, 15, 19, 18 and 17 r a n g i n g f r o m 79 to 82 %. S i mi l a r l y , the l o w e s t r e d u c t i o n in b i o m a s s dry we igh t was for g e n o t y p e s L 6, 20, 9, 26 and 3 wi th r e d u c t i o n s rangi f ig f rom 62 to 65 %, w h i l e the h ighes t r e d u c t i o n was for g e n o t y p e s L 15, 1, 19, 18 and 11, wi th r e d u c t i o n s r a n g i n g f rom 74 to 77 %. S imi l a r t r end o f r e d u c t i o n in b i o m a s s f r e sh we igh t and b i o m a s s d ry w e i g h t was e x p e c t e d as the two a t t r ibu tes were f o u n d to be h i g h l y and p o s i t i v e l y c o r r e l a t e d (r = 0 .979) . The re is a t e n d e n c y that g e n o t y p e s wi th m o r e v i g o r o u s g rowth have h i g h e r r e d u c t i o n in b i o m a s s , as can be seen in cases fo r L 1, 14, 18 and 15.

R e g r e s s i o n a n d c o r r e l a t i o n

A m u l t i p l e r e g r e s s i o n and c o r r e l a t i o n a n a l y s i s were run t a k i n g b i o m a s s d r y we igh t o f cane and l e a f as d e p e n d e n t v a r i a b l e and cane he igh t , cane g i r th , l e a f l eng th and l ea f wid th as i n d e p e n d e n t va r i a b l e s , w h e r e p o s s i b l e at 101 and !17 days af te r p l an t ing . At 101 days , the a n a l y s i s s h o w e d that a t t r ibu tes had no s i g n i f i c a n t c o r r e l a t i o n (p > 0 .05) with b i o m a s s d ry we igh t . Very low c o r r e l a t i o n coe f f i c i en t s were f o u n d for cane he igh t (r = 0 .082) , cane gi r th (r = - 0 .187) , l e a f l eng th (r = -0 .030 ) and l ea f wid th (r = -0 .050) . On the con t r a ry , at 117 days there were h i g h l y s i g n i f i c a n t (p = < 0 .01) pos i t i ve c o r r e l a t i o n s b e t w e e n cane he igh t (r = 0 .517) and cane g i r th ( r = 0 .314) wi th b i o m a s s d ry we igh t . This h igh l i gh t s the i m p o r t a n c e o f c a n e p a r a m e t e r s as a t t r i b u t e s to s u g a r c a n e y i e ld , a f i nd ing a l so r e p o r t e d by M u c h o w et a l . (1996) . A n a l y s i s o f va r i ance i nd i ca t ed that cane p a r a m e t e r s w e r e s i g n i f i c a n t l y a f f e c t e d by w a t e r s t ress , t he re fo re , r e d u c t i o n in b i o m a s s dry w e i g h t was v a l i d a t e d as an i n d i c a t o r o f va r i e t a l r e s p o n s e to

wa te r s t ress .

C O N C L U S I O N

E v a l u a t i o n o f 26 d ive r s e g e n o t y p e s of suga rc a ne , at e a r ly age, in r e s p o n s e to wa te r s t ress r e su l t ed in g r o u p i n g them in th ree c a t e g o r i e s , to le ran t , m e d i u m and sens i t ive . G e n o t y p e s tha t e x p r e s s e d t o l e r a n c e to d rough t were R570, Q77N1232 , B72177, C o l 148 and R a g n a r . T h e s e g e n o t y p e s m a y be s u i t a b l e fo r c u l t i v a t i o n as r a i n - f e d in the d ry a reas o f the t rop ic s , or w h e r e d ry s ea sons are f r e q u e n t l y e n c o u n t e r e d , such as in the Ramu Val ley and M o r o b e P r o v i n c e o f P a p u a New Guinea .

Visua l eva lua t i on was f o u n d fast , i n e x p e n s i v e and r e l a t i v e l y accu ra t e . It m a y be a use fu l m e t h o d for p r e d i c t i n g d r o u g h t t o l e r a n c e in s c r e e n i n g l a r g e n u m b e r o f g e n o t y p e s . H o w e v e r , for eva lua t i on o f a few g e n o t y p e s , this work h i g h l i g h t s the i m p o r t a n c e o f b i o m a s s a n a l y s i s for m o r e accu ra t e resu l t s . The

m e t h o d o l o g i e s d e v e l o p e d m a y be h e l p f u l to worke r s w i sh ing to sc reen and eva lua t e s u g a r c a n e for d rough t t o l e r ance

A C K N O W L E D G E M E N T

T h e a u t h o r s w i sh to t h a n k P r o f e s s o r S. W i r y o w i d a g d o a n d Dr. J.V. K a i u l o f o r t h e i r a s s i s t a n c e , Mr. R. M a y e r for h is a d v i s e on d a t a ana lys i s , Mr. A. H a r t e m i n k for c r i t i c a l r ev iew of the m a n u s c r i p t and Mr. D A r a p i and S. Taisa for a s s i s t ing in the v i sua l e va lua t i on c a r r i e d ou t in this s tudy, Ramu S u g a r Ltd. for the t e c h n i c a l suppor t , t he I n d o n e s i a n G o v e r n m e n t f o r p r o v i d i n g the n e c e s s a r y funds .

R E F E R E N C E S

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Hartemink, A.E. and Kuniata, L.S. (1996). Some factors influencing yield trends of sugarcane in Papua New Guinea. Outlook on Agriculture, 25(4) : 227-234.

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Muchow, R.C., Robertson, M.J. and Wood, A.W. (1996). Growth of sugarcane under high input conditions in tropical Aastralia. II. Sucrose accumulation and commercial yield. Filed Crops Research, 48 : 27-36.

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Sunil, H.K. and Lawrence, M.J. (1996). Quantitative genetics of sugarcane: A large-scale evaluation of Saccharum germplasm. Sugar Cane, 6 : 3-10.

Vaux, S. (1999). Ramu Sugar Ltd. Corporate Report, Paper presented at the Department of Agriculture, University of Technology, Lae, Papua New Guinea, 3 rd June 1999: 15pp.

Venkataramana, S., Rao, P.N.G. and Nadiu, K.M. (1983). Evaluation of cellular membrane thermostability for screening drought resistani stigarcane varieties Sugar Cane, 4 : 13-15.

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