Philippine Journal of Crop Science 2004, 29(1) 29-39 Copyright 2005, Crop Science Society of the Philippines Released 15 March 2005

SCREENING CASSAVA GENOTYPES FOR RESISTANCE To WATER DEFICIT DURING CROP ESTABLISHMENT alREYNALDO V BERGANTIN', ANTRA YAMAUCHI2, JOSE R PARDALES JR' & DIOSCORO M BOLATETE 'Plant Environmental Response Laboratory, PhilRootcrops, Leyte State University, Baybay, Leyte 6521-A, Philippines, and 2Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan

Although known to be drought-resistant, cassava is usually constrained in its development and productivity by lack of soil moisture especially during the earlier stages of growth, hence the need for screening for resistance. The performance of 28 cassava genotypes under deficit soil moisture content (smc) of 10% was studied during their establishment period. The plants were grown in plastic pots (24.5 cm wide, 26.5 cm deep) that were filled with sandy loam soil and kept under a rain shelter covered with transparent acetate 0.08 mm thick. This study was undertaken to determine the vegetative and physiological traits in juvenile cassava plants that may confer drought resistance to the crop. The results showed that with reference to the well- watered plants (25% SMC), the plant height, number of leaves, and total shoot dry weight were significantly (P<0.01) reduced by lack of water supply. In terms of variety, these traits varied significantly (P<0.01) in their degree from one variety to another. In droughted plants, the stomatal resistance was significantly higher (P<0.01) and the rate of transcription significantly lower (P<0.05) than in the well-watered controls. The effect of water regime on leaf water potential OW and water use efficiency (WUE) was not at all significant, however. The values of these physiological traits generally varied among the varieties, although significant effects (P<0.01) were noted only for 1111, but not for transpiration rate. Overall, the results made it possible for some genotypes to be identified as resistant to limited soil water supply. With the well-watered plants as basis, genotypes that performed well under limited soil water conditions were observed to manifest any of the following traits: lesser inhibition in shoot vegetative development, higher stomatal resistance, lower rate of transpiration, higher dry biomass, and higher WUE. cassava, drought, leaf water potential, limited water supply, stomata]. resistance, transpiration rate, water use efficiency

INTRODUCTION (www.iwmui.org). Withthe growing world population and increasing water scarcity, major Increasingly, water scarcityis becoming a efforts and strategies in agriculture have to be universal problem at the present time. Report geared towards sustaining crop production and shows that water insufficiency threatens the food increasingproductivityunderlimitedwater supply of nearly 3 billion people, as well as the resources. Among the crops in cultivation today, productivity of many ecosystems around the world root crops deserve particular attention not only (www.worldwaterforum.org). Currently, some 450 because many of the world's poorest and most food- million people in 29 countries face water shortage insecure households are highly dependent on these problems. By 2025, about 2.7 billion people in 29 crops as a contributing, if not the principal, source of countries will live in regions facing severe water food,nutrition, and cash income (Alexandratos scarcity. Asia and Sub-Saharan Africa, containing 1995), but also that the crops' individual ability to the most heavily populated and poorest regions in grow even in areas with limited water supply can be theworld,willbemostseverelyaffected exploited to help ensure food security, especially that about 2 billion people in the tropics and drought resistance on the crop can also be improved subtropicsdepend onthesecropsfortheir by breeding & selection in order to come up with sustenance and livelihood (Scott et al 2002). varieties that will perform well under limited soil Cassava (Manihot esculenta) is one of the most moisture supply. widely grown rootcrops in the world. Millions of However, varietal response of cassava to soil farmers,processorsandtradersearntheir water deficiency is not yet well understood. It is livelihood from this crop. As food, it is the basic postulated that different varieties show different staple of about 500 million people in the tropical and reactions to drought and that the mechanism of sub-tropical parts of the world (www.fao.org), being drought tolerance varies from one variety to another a very reliable and cheap source of body energy. It among the resistant ones. A basic understanding of follows that cassava can then be an important the drought response of different cassava varieties engine for growth in many countries if production, is therefore important so that the traits that give diversification, and the commercial uses of the crop the crop the ability to withstand drought stress and are improved or developed. thus help stabilize the productivity of the crop, can Cassava is commonly known to be resistant to be identified. This information will be beneficial to drought and withstands prolonged periods of water plant breeders for them to have a good idea of the shortage (Cock 1985, El-Sharkawy & Cock 1987) traits that can be directly worked on in designing especially after it has fully established itself in the new drought-resistant varieties of the crop. field. This can be the reason why the crop is commonly planted in marginal areas including MATERIALS & METHODS those that are frequented by water shortage or drought. Generally, however, the economic yield of The study was conducted in an open-air non- the crop depends on the growing conditions to which shaded space at the Philippine Rootcrops Research it is exposed, and water appears to be the most and Training Center (PhilRootcrops) located in the limiting growth factor (Pardales et al 2001). The campus of Leyte State University, Baybay, Leyte studies of Pardales & Esquibel (1996) and Agili & (10°44' N: 124°47' E: 12 m ask). A rigid rain shelter Pardales(1997) have shown that cassavais (9.5 meters wide, 16 meters long, 2.5 meters high) sensitivetosoilwaterdeficiencyduring the with a transparent acetate (0.08 mm thick) roof was establishment period,ie, the first 3 months ofconstructed to protect the experimental pots (of growth from planting. Drought stress during this polyethylene, 24.5 cm wide, 26.5 cm deep) against periodsignificantlyreducesthegrowthand the rain, thereby allowing the regulation of the development of both the roots and shoots, which in moisture content of the soil in the pots. turn affects the succeeding development of the plant including tuber development, even if the drought Test Varieties And Plant Establishment stress is alleviated later. This generally results in Twenty-eight cassava genotypes obtained from either low tuber yield at the normal maturity time the cassava germplasm collection of PhilRootcrops of the crop, or calls for a delay in the timing of the were used inthisstudy.These included10 harvest to allow an increase in storage root yield to traditional varieties (Golden Yellow, Indang 2, a desirable level. Kadabao, Kaplutan, Namaya, Nito-nito, Pintuyan 3, In places where the soil moisture supply is Siasi,Tandang 2,and Zapote),15Philippine highly dependent on rainfall, the production of Seedboard- (PSB) released varieties (Datu 1, Lakan cassava is often unstable particularly when the rain 1, Sultan 1, Vassourinha, Sultan 2, VC-1, VC-2, VC- pattern is fluctuating or when the genotype planted 4, PSB Cv-11, PSB Cv-12, PSB Cv-13, PSB Cv-14, PSB is sensitive to water stress. The potential for genetic Cv-15, PSB Cv-16, and PSB Cv-19), and 3 introduced improvementincassavahasbeenclearly varieties from Thailand (KU-5, Rayong 5, and demonstrated in increasing the yield and improving Rayong 60). Six stem cuttings (20 cm long) of each the traits of the crop that has something to do with variety were planted upright at one cutting to a pot the yield like harvest index and root dry matter filled with 9 kg of air dried sandy loam soil mixed content (Mariscal & Bergantin 1998, Kawano et al with 1.6 grams of powdered complete fertilizer (14- 1998). It is also assumed that traits conferring 14-14 NPK). Two days prior to planting, the soil in each pot was saturated with 1,125 mL tap water to Experimental Design & Statistical Analysis bring the soil to field capacity (ie, 25% SMC). This The treatments were laid out insplit-plot amount of water in the soil was maintained in all arranged in a randomized complete block design the pots from planting to 30 days after planting (RCBD) with three replications. Water regimes (well- (DAP) by regularly determining the SMC with a watered and droughted) served as the main plots, digital readout volumetric water content measuring the varieties as the subplots. device (Hydro Sense: Decagon, USA). The amount of The analysis of variance was applied on the water lost through evaporation and transpiration data obtained following the General Linear Model from each pot every other day was re-supplied (SAS 1989). When necessary, differences among accordingly. A total of 180 pots were prepared. variety means were separated using Duncan's Multiple Range Test (DMRT) at (P<0.05) level. Least Imposition Of Drought Significant Difference (LSD) was used to determine Beginning at 30 DAP (referred to as Day 0 of the level of significance of the difference in water stress), half of the total number of pots for between the well-watered and the droughted plants each genotype were not applied with water until in every variety. their SMC leveled off at around 10%, to simulate a severedroughtcondition.Thisamount was RESULTS & DISCUSSION maintained throughout the whole duration of the drought stress (ie, until 85 DAP). The SMC of the Plant Development remaining half of the pots was kept at its original The stem elongation (expressed as plant height) level (25%) to serve as well-watered controls. and leaf formation (expressed as number of leaves) During the course of the drought imposition, the in cassava were significantly (P<0.01) affected by L (MPa),stomata].resistance(scm-1)and both water regime and genotype (Table 1). Drought transpiration rate (tig cm-2 s-1) were measured in generally rendered the cassava plants stunted in situ from the middle lobe of the third open leaf of their height and leaf production when compared each of the droughted and well-watered plants with withtheirwell-wateredcounterparts.When the use respectively of dewpoint microvoltmeter considered across varieties, the average percent (HR-33T,WESCOR,USA)and asteadystate reductions in plant height and number of leaves in porometer (Li-Cor 1600, LI-COR, USA). On day 55 of droughtedplantswere62.05%and54.98%, water stress (85 DAP), the droughted plants were respectively (Table 2). This result confirms the sampled for determination of the total dry weight of findings of Pardales & Esquibel (1996) and Agili & their aboveground parts, excluding the original Pardales (1997), who showed earlier that shoot planting materials. The dry biomass weight of the development in cassava is highly suppressed when plants was to be used in the calculation of the WUE juvenile plants are exposed to prolonged limited soil of the various genotypes studied. In this particular water condition. study, WUE means the weight of the shoot dry The magnitudes of suppression of plant height biomass produced per unit of water transpired by and leaf production by drought were dissimilar theplants.Thelossof waterthroughsoil among the different varieties. In plant height alone, evaporation was determined from unplanted pots the fact that there was a significant (P<0.01) whose SMC followed that of the well-watered and the interaction between water regime and variety droughted ones. (Table 1) indicates differentiating reactions of the During the time drought was enforced, the varieties to the prevailing soil moisture condition. ranges of environmental conditions deduced from What is worth noting, however, is that the taller daily data recording under the rain shelter were as varieties appeared to have the greater plant height follows: maximum solar radiation - 50.90 to 936.33 reduction when exposed to drought, whereas the Wm2, photosynthetic active radiation (PAR) - 35.38 shorter ones had lesser. Whether plant height has to 1817.40 timol s-1 m-2, minimum air temperature - some bearing on the ability of cassava to resist 24.23 to 26.82°C, maximum air temperature - 27.62 drought or not is not known, but the finding of the to 39.88°C, and relative humidity - 36.65 to 87.62%. present study is something that can be further investigated. PSB v-19, which is traditionally of moderate plant height, and known to perform well defoliations had their leaves drooping most of the in the field even during periods of long dry soil time during the whole drought duration. The conditions,exhibitedtheleastplantheight lowermost leaves manifested the severest wilting. reduction (34.65%) amidst thesevere drought In general, the results affirm that cassava is imposed (Table 2). sensitive to diminished water supply in the soil and The reduction in the total number of fully thatthissensitivity,especiallyduringcrop developed leaves present in droughted plants at any establishment, is associated with the inhibition in given time was also variable depending on the the development of the shoot. variety. The absence of any interactioneffect between water regime and variety suggests that Leaf Water Potential leaf number reduction in droughted plants was At predawn, the WL of the plants at Day 21 of basically the result of lack of moisture supply to the water stress (51 DAP), regardless of variety, was plants. Reduction in the number of leaves was generally higher in the well-watered (-0.78 MPa) primarily due to leaf abscission, which took place than in the droughted (-0.99 MPa). These values did towards the later half of the droughted period. The not differ significantly, however (Table 3).It is varieties that showed a very high percentage of leaf highly possible that the droughted plants were able

Table 1.Analyses of variance on plant height, number of fully developed leaves, plant biomass, and water use efficiency of cassava as affected by water regimes and variety

Source Of df Mean Squares Variation Plant Number of fully Plant biomass Water use height developed leaves efficiency Block 2 164.87 12.78 3.58 0.17

Water Regime (W) 1 68294.69** 13505.55** 7510.51** 0.10 ns Error a 2 252.51 0.72 3.33 0.20 Variety (V) 27 286.19** 107.27** 19.03** 0.99** W x V 27 295.32** 51.62ns 15.15** 0.67* Error b 162 55.76 41.93 4.72 0.41 ns = Not Significant, * Significant, ** Highly Significant reduction,like VC-1 (77.49%) and PSB Cv-11 to extract moisture from the soil during the night (75.01%), did not have any mature functional leaves when evaporative demand was low, thus, allowing left except the terminal leaf, which was either not the plants to adjust osmotically. The range of fully opened or was inhibited in size. Severe wilting predawn values irrespective of the variety was precededleafabscission,whichtookplace from -0.27 to -1.15 MPa but decreased to -0.51 to - acropetally (ie, commencing from the lowest leaves). 1.84 MPa when the plants were exposed to drought. lke & Thurtell (1981) observed leaf fall in severely For a number of varieties, the difference in predawn water-stressed cassava.Shedding of the most Lbetween the well-watered and the droughted was mature leaves in cassava is widely believed to be an either significant or highly significant (Table 4). adaptive mechanism of the cropto withstand In terms of the midday TL, the effect of water excessive lack of moisture. The leaves are abscised regime followed that of the predawn, but the in order to conserve water. averages of the well-watered (-1.06 MPa) and the The varieties that did not exhibit acute leaf droughted (-1.12 MPa) tended to be closer this time.

32 Screening Cassava Genotypes For Water Deficit Table 2.Percent reduction on plant height, number of fully developer leaves, transpiration rate, and plant biomass of cassava as affected by soil water deficit

Variety Percent Reduction Relative To The Well-Watered Control Plant Number of fully Transpiration Shoot biomass height developed leaves rate Golden Yellow 51.43 56.41 89.81 89.77 Indang 2 66.08 60.77 68.71 89.83 Kadabao 58.69 48.81 42.60 92.40 Kaplutan 52.42 58.48 58.25 91.81 Namaya 53.57 63.06 94.65 91.55 Nito-nito 70.48 40.35 36.05 92.05 Pintuyan 3 70.76 42.31 82.37 93.88 Siasi 72.58 46.96 93.09 94.12 Tandang 2 63.23 54.00 74.80 93.10 Zapote 74.36 62.84 73.02 94.56 Datu 1 61.45 51.03 84.49 92.50 Lakan 1 68.93 64.14 61.13 92.06 Sultan 1 62.31 40.87 86.21 89.03 Vassourinha 63.50 65.10 50.37 93.91 Sultan 2 61.11 59.06 45.64 92.26 VC-1 48.15 77.4 79.01 92.45 VC-2 61.29 46.65 64.88 93.35 VC-4 81.06 58.21 23.78 94.96 PSB Cv-11 65.76 75.01 87.22 94.51 PSB Cv-12 62.08 58.16 92.56 94.02 PSB Cv-13 52.60 43.43 70.04 90.37 PSB Cv-14 73.91 46.67 85.14 92.97 PSB Cv-15 75.20 44.32 84.29 93.28 PSB Cv-16 74.86 44.1 72.89 91.89 PSB Cv-19 34.65 52.95 92.73 84.97 KU-50 58.44 66.67 83.28 92.48 Rayong 5 51.67 54.09 89.67 87.81 Rayong 60 43.12 57.62 88.96 89.19 Mean 62.05 54.98 73.42 92.00

RV Bergantin et al 33 It is very likely that because of high atmospheric If this view is true, then it follows that variation in demand especially during the clear days (high transpiration among varietiesiseither due to radiation, air temperature etc), the leaves of the differentialstomata]. response to limited water well-watered plants lost enough water due to rapid supply or difference in water absorptive capacity of transpiration, thus causing due decrease in the the plants. Regardless of the variety, droughted amount of water in the leaf tissues. The air plants routinely manifested reduced transpiration temperature alone under the rain shelter was rates (5.18 tig cm-2 s-1) as against the well-watered usually higher by 2-3°C during ordinary clear days ones (20.51 tig cm-2 s-1). The average reduction in than it was outside the shelter, hence the greater transpiration rates across varieties when plants cooling requirement by the leaves. The range of were droughted was 73.42%, the range in values midday TL, as it was at predawn, varied with being 36.05-94.65% (Table 2). Transpiration was variety, but it is not understood why 7 of the 28 inversely related (r = 0.48, P<0.01) with stomatal varieties showed distinctly higher midday lin, under resistance, so that it follows that the suppressed drought than when they were well-watered (Table transpiration in droughted cassava plants was the 4). Of the 7 varieties, 5 (Siasi, Zapote, PSB CV-12, function of increased stomata]. resistance. PSB Cv-16 and KU-50) actually exhibited the same trend at predawn, in that the water-stressed plants Water Use Efficiency had higherlin,than thecontrols.Generally, Water regime, variety and their interaction had however, the variation among varieties in lin, can be a significant influence (P<0.01) on the shoot biomass duetodifferentialstomata].behaviorand (Table 1). The poor shoot dry matter production differential ability of the root system to extract (1,018 grams vs 14.82 grams in the control) of the water from the soil. drought-exposed plants, not considering the variety, could be attributed largely to suppressed stem Stomatal Resistance & Transpiration Rate elongation and leaf production. When based on the The midday stomata]. resistance measured on well-watered plants, the average reduction in the Day 31 of stress(ie, 61 DAP) was significantly shootbiomassofthedroughtedplants was (P<0.01) affected by water regime but not by variety exceedingly high at 92.00%, ie, ranging from 84.97% (Table 3). Irrespective of the variety, the stomatal in PSB Cv-19 to 94.96% in Cv-4 (Table 2). In other resistance in droughted plants (10.27 s cm-1) was crops, shoot dry matter is linearly related to the generally higher than that of the well-watered (0.63 amount of water applied (Pandey et al 1984). s cm-1). Taken relative to the control, the percent As for the WUE, its trend relative to the controls increase in stomata]. resistance of the different depended on the variety, in that some exhibited varieties is reflected in Table 5. The result tends to positive values (greater than that of the well- indicate that cassava is quite sensitive to acute drop watered) while others exhibited negative values in moisture supply from the soil. El-Sharkawy & (lesser than that of the well-watered) (Table 5). This Cock(1984)mentionedthatdirectstomatal shows that cassava varieties differ in their ability to response of cassava exposed to water stress is an utilize the critically reduced amount of water immediate leaf adaptive mechanism to minimize available to the plant during the incidence of water loss. Generally, the stomata]. resistance of the drought.If biomass production of the different different varieties was very variable. Mastrorilli et varieties and the trend of WUE are taken into al(1999) likewise obtained high variations in account, it follows that when water available to the stomata]. conductance in sweet sorghum but they plantisnot limitingso that transpirationis interpreted this as a consequence of the effect of air unimpeded by stomata]. activity, WUE is not of such saturation deficit on stomata]. behavior. importance. What matters most is that when the In terms of the midday transpiration rate on amount of water in the soil is limited and that the Day 31, significant (P<0.01) effect was observed only stomata close amidst high evaporative demand, in water regime and not in varieties (Table 3). This then WUE is favored. The important consideration of suggests that transpiration rate is dependent more the stomata]. closure therefore in cassava during on theinfluenceof environmental factor(ie, periods of inadequate water lies on its contribution moisture supply) than the influence of the genotype. to efficient use of available water. In the present study the WUE of the varieties associated with any of the other measured traits of differed. Nevertheless, an average increase of about the plants, but experience in the field indicated that 4% WUE in droughted plants was realized (Table 5). varieties with high positive values are the ones that The differentiating WUE could not be directly perform better under a pronounced dry spell.

LITERATURE CITED

Agili SM & JR Pardales Jr. 1997. Influence of moisture and allelopathic regimes in the soil on the development of cassava and mycorrhizal infection of its roots during establishment period. Philippine Journal of Crop Science 22: 99-105 Alexandratos N. 1995. World Agriculture: Towards 2010, An FAO Study. New York: FAO and John Wiley & Sons Cock JH. 1985. Cassava: New Potential For A Neglected Crop. Westview Press, London El-Sharkawy MA & JH Cock. 1984. Water use efficiency of cassava I. Effect of air humidity and water stress on stomata]. conductance and gas exchange. Crop Science 24: 497-502 El-Sharkawy MA & JH Cock. 1987. Response of cassava to water stress. Plant & Soils 100: 345-360 Food and Agriculture Organisation. 2001. Press Release. http://www.fao.org Food and Agriculture Organisation. 2002. Cassava can play a key role in reducing hunger and poverty. http://www.fao.org Ike IF & GW Thurtell. 1981. Response of indoor-grown cassava to water deficits and recovery of leaf water potential and stomata]. activity after water stress. Journal of Experimental Botany 32: 1029-1034 International Water Management Institute. 2001. Press Release. http://www.iwmi.orgrams Kawano K, K Narintaroporn, P Narintaroporn, S Sukarharm, A Limsila, J Limsila, D Suparhan, V Sawarat & W Watanonta. 1998. Yield improvement in a multistage breeding program for cassava. Crop Science 38: 325-332 Mariscal AM & RV Bergantin. 1998. Recent progress in cassava varietal improvement in the Philippines. In: Cassava Breeding, Agronomy and Farmer Participatory Research in Asia. Proceedings of the 5th Regional Workshop (RH Howeler, ed) Danzhou, Hainan, China, pp 131-148 Mastrorilli M, N Katerji & G Rana. 1999. Productivity and water use efficiency of sweet sorghum as affected by soil water deficit occurring at different vegetative growth stages. European Journal of Agronomy 11: 207-215 Pandey RK, WAT Herrera, AN Villegas & JW Pendleton. 1984. Drought response of grain legumes under irrigation gradient. III. Plant growth. Agronomy Journal 76: 557-560 Pardales JR Jr & CB Esquibel. 1996. Effect of drought during the establishment period on the root system development of cassava. Japanese Journal of Crop Science 65(1): 93-97 Pardales JR Jr, A Yamauchi, DV Belmonte Jr & CB Esquibel. 2001. Dynamics of root development in rootcrops in relation to the prevailing moisture stress in the soil. In Proceedings Of The 6th Symposium Of The International Society Of Root Research, Nagoya, Japan, November. pp 72-73 SAS. 1989. SAS /STAT User's Guide, Version 6, 4th ed. Volume 2 SAS Institute, Cary. 846 p Scott GJ, M Rosegrant & C Ringler. 2002. Roots And Tubers For The 21st Century: Trends, Projections, And Policy Options. International Food Policy Research Institute and International Potato Center Third World Water Forum. 2001. Press release. http://www.worldwaterforum.org Table 3.Analyses of variance on predawn and midday leaf water potentials of cassava as affected by water regime and variety

Source Of df Mean Squares Variation Leaf water potentials df Stomatal Transpiration at day 21 of stress resistance rate

Predawn Midday at day 31 of stress Block 2 0.27 0.03 2 41.96 1085.28

Water regime (W) 1 1.78ns 0.14 ns 1 3344.31** 9436.00* Error a 2 0.14 0.03 2 19.06 337.13 Variety (V) 27 0.12** 0.16** 27 57.86 ns 50.05 W x V 27 0.18** 0.23** 27 55.25 ns 27.90 Error b 101 0.02 0.02 99 65.66 33.12 ns = Not Significant, * Significant, ** highly significant

36 Screening Cassava Genotypes For Water Deficit Table 4.Effect of soil water deficit on the predawn and midday leaf water potentials of different cassava varieties

Variety Leaf Water Potentials (MPa) Predawn Difference Midday Difference Control Stress Control Midday Golden Yellow -1.00 -1.07 0.70 -1.08 -1.15 0.08 Indang 2 -0.71 -0.90 0.19 -1.30 -1.15 0.15 Kadabao -1.15 -1.17 0.17 -1.45 -0.87 0.58** Kaplutan -1.09 -0.93 0.15 -1.26 -1.21 0.53 Namaya -0.63 -0.70 0.07 -1.24 -1.23 0.01 Nito-nito -0.41 -0.94 0.53* -0.59 -1.12 .053** Pintuyan 3 -0.78 -1.03 0.25 -1.37 -1.11 0.25* Siasi -1.07 -0.51 0.56* -1.20 -0.54 0.66** Tandang 2 -0.96 -1.02 0.90 -1.13 -1.14 0.17 Zapote -0.85 -0.79 0.06 -1.31 -1.06 0.25* Datu 1 -0.66 -1.84 0.18 -1.13 -1.33 0.21 Lakan 1 -0.89 -0.95 0.17 -1.16 -1.13 0.03 Sultan 1 -0.40 -1.01 0.61* -0.49 -1.06 0.57** Vassourinha -0.75 -0.84 0.07 -0.97 -1.24 0.27* Sultan 2 -0.46 -1.04 0.58* -0.60 -1.37 0.77** VC-1 -1.03 -1.07 0.04 -1.17 -1.19 0.02 VC-2 -1.04 -1.04 0.00 -1.39 -1.19 0.2 VC-4 -0.54 -1.18 0.65* -0.65 -1.21 0.57** PSB Cv-11 -1.01 -1.23 0.22 -1.38 -1.25 0.13 PSB Cv-12 -1.42 -0.98 0.42* -1.64 -1.22 0.42** PSB Cv-13 -0.61 -1.20 0.59* -0.94 -1.25 0.31* PSB Cv-14 -0.77 -1.19 0.42* -1.03 -1.27 0.24 PSB Cv-15 -0.65 -1.05 0.40* -0.87 -1.18 0.31* PSB Cv-16 -0.95 -0.54 0.41* -1.32 -0.64 0.68** PSB Cv-19 -0.27 -1.15 0.88** -0.5 -0.99 0.49** KU-50 -1.00 -0.99 0.00 -1.37 -1.08 0.28* Rayong 5 -0.38 -1.16 0.78** -0.54 -1.23 0.69 Rayong 60 -0.57 -1.14 0.57* -0.92 -1.14 0.22 Mean -0.78 -0.99 0.21 -1.06 -1.12 0.06 Predawn: LSD (0.05) = 0.25, LSD (0.01) = 0.60, Midday: LSD (0.05) = 0.24 LSD (0.01) = 0.37

RV Bergantin et al 37 Table 5. Percent increase in water use efficiency and stomata' resistance of cassava as affected by soil water deficit

Variety Percent Increase Relative To Well-Watered Control Water use efficiency Stomatal resistance

Golden Yellow 43.48 1048.11 Indang 2 -1.93 3096.67 Kadabao -4.76 1693.43 Kaplutan 18.23 2842.86 Namaya 16.19 8891.18 Nito-nito 4.69 244.44 Pintuyan 3 -22.33 704.67 Siasi .26.11 2776.74 Tandang 2 14.62 612.90 Zapote -13.75 1994.12 Datu 1 -18.45 3055.10 Lakan 1 -10.95 465.38 Sultan 1 60.87 741.82 Vassourinha -1.36 1232.35 Sultan 2 8.97 1014.58 VC-1 28.50 804.55 VC-2 11.00 1231.82 VC-4 -33.46 24.03 PSB Cv-11 -29.49 2200.00 PSB Cv-12 -13.17 3057.50 PSB Cv-13 -39.09 907.41 PSB Cv-14 -14.23 2227.91 PSB Cv-15 7.41 1537.50 PSB Cv-16 -34.22 1766.67 PSB Cv-19 75.22 1466.67 KU-50 -1794 1200.00 Rayong 5 39.52 2840.38 Rayong 60 41.18 1200.00 Mean 3.98 1817.10

38 Screening Cassava Genotypes For Water Deficit Table 6.Midday stomata' resistance and transpiration rate of 28 cassava varieties (means of well-watered and droughted plants)

Variety Stomatal Resistance Transpiration Rate (s cm-1) (Fig cm' s-1) Golden Yellow 6.62 8.43 Indang 2 4.94 17.65 Kadabao 1.97 12.66 Kaplutan 5.33 17.13 Namaya 15.45 11.13 Nito-nito 0.89 15.67 Pintuyan 3 9.52 7.14 Siasi 6.4 12.85 Tandang 2 3.78 11.21 Zapote 3.73 15.89 Datu 1 7.98 11.62 Lakan 1 1.49 12.09 Sultan 1 5.18 12.26 Vassourinha 2.44 18.20 Sultan 2 2.91 15.51 VC-1 5.13 8.20 VC-2 3.69 12.64 VC-4 1.45 13.6 PSB Cv-11 4.92 12.66 PSB Cv-12 7.74 9.50 PSB Cv-13 1.25 20.71 PSB Cv-14 5.22 12.17 PSB Cv-15 3.54 12.49 PSB Cv-16 3.84 14.25 PSB Cv-19 7.25 9.88 KU-50 4.97 13.68 Rayong 5 7.91 11.64 Rayong 60 4.52 10.21 Mean 5.30 12.90

RV Bergantin et al 39