Effect of Salinity Stress on Growth Parameters of Potato Genotypes

Transcription

1 African Journal of Basic & Applied Sciences 8 (4): 85-9, 06 ISSN IDOSI Publications, 06 DOI: 0.589/idosi.ajbas Effect of Salinity Stress on Grow Parameters of Potato Genotypes Shitaye Homma Eiopian Institute of Agricultural Research, Debre Zeit Agricultural Research Center, Debre Zeit, Eiopia Abstract: This study aims at examining e effect of salinity stress on some grow parameters of diploid potato genotypes and determining e heritability of ese traits and eir association. Ninety four potato genotypes which were progeny from a cross between parents C and E were evaluated in hydrophonics wi a salinity level of 0 mm NaCl. The experiment was arranged in RCBD wi five replications; ree of em were salt treated and e remaining was control. Different grow parameters were measured and counted at different periods of salt stress. Variance and correlation analysis were conducted using GenStat statistical software. Heritability of measured traits was also calculated from ANOVA outputs. Potato genotypes showed reduction in grow parameters due to salinity stress. The result indicated at e highest reduction (75%) was observed on shoot fresh weight followed by leaf area (7%), shoot dry weight (69%), root dry weight (64%), root fresh weight and shoot leng (49%). The number of new leaves developed between six and irteen days after salt stress showed reduction by 5% under salt stress relative to e control. Heritability of grow parameters ranged from 46% to 8% under control and from 69% to 90 % under salt stress condition. The highest heritability was observed for root/shoot dry weight ratio (90%) and leaf area (86%) under salt stress. Leaf area showed strong positive correlation wi all measured grow parameters wi e exception of root/shoot dry weight ratio bo under treated and untreated condition. Salt stress affects development of new leaves in e potato genotypes later an six days of stress. The study suggests furer study on evaluation of e genotypes under various salinity levels and e presence of substances in osmotic adjustment. Furermore, studying e association + + between salt tolerance and analysis results of tissue Na and K may give information wheer e salt tolerance + is due to e tolerance to Na concentration or exclusion of is ion. Key words: Salinity Grow parameters Salinity tolerance Heritability INTRODUCTION can also cause e problem of salinity in some areas [4, 5]. Likewise, long-term accumulation of salts in arid and Salinity is one of e major abiotic stresses affecting semi-arid areas, weaering of parental rocks and agricultural production worldwide. Based on e FAO deposition of oceanic salts carried in wind and rain are database, more an 6% of e world s total land area, oer possible causes of salinity []. The day-to-day which is about 0% of cultivated land, was affected by natural processes and human activities play a paramount salt [, ]. Agricultural production in e dry land role in e grow of is worldwide problem. Hence, accounts for about half of e world s land. e increase in salinization togeer wi e current This production system largely depends on irrigation global climate change poses a reat to e food supply practices []. However, irrigation contributes to e for e rapidly growing population of e world [,, 5] by development of salinity by raising e water table, limiting e grow and productivity of food crops like which brings salts from deeper layers of e soil and potato concentrates in e root zone []. This leads to e Potato (Solanum tuberosum L.) is an herbaceous decrease in osmotic potential of e soil and interferes perennial plant grown for its swollen underground stem wi e water uptake of roots. Moreover, e use of poor called tuber. The crop is believed to be originated in e quality water due to e limited availability of fresh water Andes of Sou America [6]. In terms of productivity and Corresponding Auor: Shitaye Homma, Eiopian Institute of Agricultural Research, Debre Zeit Agricultural Research Center, Debre Zeit, Eiopia. 85

2 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 nutritional value potato is e four most important food using MS medium. Axillary shoots taken from each crop in e world [7, 8] next to rice, wheat and maize. genotype were sterilized and cultured in e media. Currently, potato is grown worldwide under different The cultures were kept under 6 h photoperiod, C climatic conditions. China is e first in production temperature and Photosynetic Photon Flux (PPF) of followed by Russian Federation, India and USA [8]..75 µmolm s supplied by fluorescent light. After two The production of potato like oer crops is affected weeks, e plantlets were transferred to hydroponics in by a number of biotic and abiotic stresses among which greenhouse. salinity is one of e major abiotic stresses. This abiotic The experiment was conducted in an 8 x 8 (64 m²) stress has a major impact on food production. Therefore greenhouse compartment located at Radix, Uniform, it is important to improve salinity tolerance of e crops Wageningen University, latitude 5 N. Potato plantlets at provide e largest food source globally. Potato is were transplanted on 7 June (Replications, and ) moderately sensitive to salinity stress [9, 0] and a salinity and 8 June (Replications 4 and 5), 009 in small level of.0-.0 ds/m is reported to cause a reduction in rockwool slabs. The plantlets in e rockwool slabs were grow and up to 50% of yield loss [0]. This indicates e planted in a tray wi a circular whole (4 hole per tray, remarkable effect of salinity in yield reduction and 8 plants per tray) and dipped in e hydroponics. economic loss on potato production. Therefore, The experiment was arranged in RCBD wi five development of tolerant genotypes to is abiotic stress replications out of which ree of em were salt treated is crucial to maintain yield of potato. (replication, and 5) and e rest (replication and 4) Saline soils are managed for agricultural production were control treatments. Per box, ere were 8 plants by applying different soil and water management practices (8 genotypes). The remaining 6 holes were filled wi []. Applying surface irrigation to leach e salts rockwool slabs to avoid evaporation rough e open accumulated in e root zone and soil amendments wi holes. Therefore, a total of 480 plants were planted gypsum to improve e soil texture and drainage are some including two of e parents. One of e genotypes of e options to manage saline soils. However, ese soil (genotype 447), died after some days in replication and reclamation approaches are expensive to deal wi e 4 and replaced wi parent E and C respectively. problem of salinity. Therefore, breeders should attempt to The growing condition in e greenhouse was 8/5.6 C develop crops which can tolerate salinity stress using day/night temperature, 6 h day leng and 60 /80% different crop improvement approaches. Marker assisted day/night RH. selection and biotechnology togeer wi conventional The hydroponics was prepared by filling a box wi breeding were reported as a good approaches to cope approximately liters of standard nutrient solution on wi e problem of salinity []. This in turn requires e e planting dates (7 and 8 June, 009). The nutrient availability of salt tolerant plants as well as variability in solution contains e cations K 7.9, Ca.9, Mg.6, salt tolerance between genotypes of e same species []. NH and Na 0.4 (mmol/l); e anions NO.0, SO4 _ - - Hence, e presence of tolerant plants or variability in salt.9, PO 4.94, HCO 0.4 and Cl 0. (mmol/l); e micro tolerance offers e possibility for breeders to identify nutrients Fe 4, Mn, B 9.8, Zn 4.4, Cu 0.7 and Mo 0. genes responsible for tolerance and transfer ese to (µmol/l) and Si 0.0 mmol/l. The nutrient solution had an commercial cultivars. This requires knowledge on e EC of. ms/cm and a ph of 5.7. mechanisms determining salinity tolerance and e A salinity level of 0 mm NaCl was selected to availability of tools to measure e response of e plants observe e response of genotypes. The treatment was to salinity. Therefore, e current study aims at examining started after irteen days of adaptation time e effect of salinity stress on e grow parameters of (transplanting); on 0 June 009 (for replication and ). diploid potato genotypes and determining e heritability On is date e control treatment (replication ) was of ese traits and eir association. refreshed wi e standard nutrient solution while 60 mm of NaCl was added to e standard nutrient solution and MATERIALS AND METHODS applied to replications and after removing e previous media (e standard nutrient solution filled on e planting Plant Material and Experimental Set up: Ninety four date). On e next date ( July 009) 0 mm NaCl was potato genotypes were used in is experiment. added to e standard nutrient solution and applied to e The genotypes were progeny from a cross between boxes of replications and after removing e previous parents C and E. Planting materials were prepared in vitro media wi e 60 mm NaCl. On July 009 e media of 86

3 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 replication 4 was refreshed and 60 mm NaCl was applied In bo cases (one-way and two-way ANOVA), 5% to replication 5. On e next day ( July 009) 0 mm probability level (P = 0.05) was used to test e significant NaCl was applied to e boxes of replication 5 after differences between genotypes, treatment effects and changing e previous media of 60 mm NaCl. The growing interactions. media (hydroponic solution) of all replications was refreshed for e second time on 8 July 009 wi e RESULTS respective treatments i.e. wi 0 mm NaCl for e salt treated boxes (replications, and 5) and wi Overall genotypes showed reduction in grow standard nutrient solutions for e control treatments parameters in response to salinity stress. Alough (replications and 4). grow parameters were reduced under salt stress condition, variability among genotypes was observed Measured Parameters: In is experiment different (result not shown). grow parameters (plant height, shoot leng, leaf area, shoot fresh weight, root leng, root fresh weight, Effect of Salinity on Plant Height: At e initial period of shoot dry weight and root dry weight) were measured and salt treatment (zero days after salt stress) genotype and numbers of leaves (living, yellow + wilted and dead treatment showed no significant (P = 0.898) interaction leaves) were counted for bo e control and salt effect and no significant (P = 0.77) treatment effect on treatments over time. The number leaves were counted on plant height; however genotypes showed significant 6 and 7 July 009 for replications, and. A label was (P < 0.00) differences (Table ) in plant height. placed on e tip of e shoot after counting. Then new Seven days after salt stress, genotype and treatment leaves above e label were counted on July 009 and showed significant (P < 0.00) interaction effect on plant summed up wi e living leaves counted on 6 and 7 July height (Table ). The variation in plant height ranged from 009 for analysis. Plant height was measured zero and (cm) under control and from (cm) under seven days after salt treatment. salt tress condition. Relative to e control, genotypes The genotypes were harvested on 6 (replication showed.4% reduction in plant height under salt stress and ), 7 and 8 (Replication, 5 and part of replication (Table ). 4) and 0 (e remaining boxes of replication 4) July 009. After carefully removing e plants out of e Effect of Salinity on Grow Parameters at Harvest: hydroponics, e root was gently cleaned to separate it After sixteen days of salt stress treatment, genotype and from e rockwool. Subsequently, e water left on e treatment showed significant (P < 0.00) interaction effect roots dried wi tissue and grow parameters were on shoot leng, shoot fresh weight, root fresh weight, measured. The parameters measured at harvest were: leaf area, shoot dry weight, root dry weight and shoot leng (cm), root leng (cm), leaf area (cm²), root/shoot dry weight ratio (Table ). Root leng was not shoot fresh weight (g), root fresh weight (g), shoot dry significantly affected by e interaction between weight and root dry weight (g). Leaf area was measured genotype and treatment (P = 0.998) and e main effect of using leaf area meter (LI-COR model 00). Dry weight treatment (P = 0.46); however, genotypes showed was measured after oven drying shoots and roots significant (P < 0.00) differences in root leng (Table ). separately at 70 C for 7 hours. Root/shoot dry weight Relative to e control, shoot fresh weight showed ratio were calculated from e dry weights of root and e highest reduction (74.6%) under salt stress followed shoot. by leaf area (7.9%), shoot dry weight (69.4%), root dry weight (6.6%), root fresh weight (49.5%) and shoot Statistical Analysis: Analysis of variance (ANOVA) and leng (49.%). Root leng showed e lowest relative correlation analysis were conducted using GenStat reduction under salt stress (.9%) whereas e value of statistical software. One-way ANOVA was carried out for root/shoot dry weight ratio increased (7.6%) under salt e salt treated and control treatments to observe e stress (Table ). presence of genotypic differences. Heritability of measured traits was calculated from one-way ANOVA Effect of Salinity on Number of Leaves: Six days after salt outputs to determine e percentage variation due to e treatment genotype and treatment showed no significant genetic factor. Two-way ANOVA was carried out to (P = 0.086) interaction effect on number of living leaves. examine e interaction between genotype and treatment. The effect of treatment was also not significant 87

4 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 Table : Effect of salinity on plant height (cm) measured zero and seven days after salt stress Control Salt treated Two-way ANOVA P- value Days after Relative salt treatment Mean Range Mean Range G 4 T 5 G * T reduction (%) C.V (%) <0.00 ns ns < < Mean values are averages of 94 genotypes over and replications for e control and salt treated conditions respectively. Non significant. 4 5 Genotype, Treatment, Genotype by treatment interaction. Table : Effect of salinity on grow parameters sixteen days after salt treatment (measured at harvest) Control Salt treated Two-way ANOVA P- value Relative Parameters Mean Range Mean Range G 4 T 5 G * T reduction (%) C.V (%) Shoot leng (cm) < < Root leng (cm) <0.00 ns ns.9.9 Shoot fresh weight (g) < < Root fresh weight (g) < < Leaf area (cm²) < < Shoot dry weight (g) < < Root dry weight (g) < < Root/shoot dry weight <0.00 ns < Mean values are averages of 94 genotypes over and replications for e control and salt treated conditions respectively. Non significant. 4 5 Genotype, Treatment, Genotype by treatment interaction. Table : Heritability of plant height measured zero and seven days after salt treatment under control and salt treated conditions. Values are calculated from one-way ANOVA outputs Parameters Days after treatment Treatment Vg Ve H (%) P-value Plant height 0 Control <0.00 Salt < Control <0.00 Salt <0.00 Genetic variance. Environmental variance. Heritability. 4 Non significant. (P = 0.074), however genotypes showed significant of dead leaves e interaction between genotype and (P <0.00) differences in number of living leaves treatment (P = 0.645) and e main effect of treatment (Data not shown). Genotype and treatment showed no (P = 0.8) were not significant; however, genotypes significant (P = 0.666) interaction effect on e number of showed significant (P < 0.00) differences. The interaction dead leaves after six days of salt treatment. Moreover, between genotype and treatment (P = 0.958), e main e main effects of genotype (P = 0.08) and treatment effects of genotype (P = 0.455) and treatment (P = 0.9) (P = 0.5) on e number of dead leaves were also on e number of yellow + wilted leaves were not not significant after similar period of salt stress. significant. Genotype and treatment showed significant The interaction between genotype and treatment (P < 0.00) interaction effect on e number of new leaves (P = 0.98) and e main effects of genotype (P = 0.65) developed between six and irteen days after salt stress and treatment (P = 0.495) on e number of yellow + wilted (Data not shown). leaves were also not significant. Alough e interaction effects were not always Thirteen days after salt stress, genotype and significant, e relative reduction in number of living treatment showed significant (P = 0.0) interaction effect (healy) leaves increased from 5.% after six days of salt on total number of living leaves (Table ). For e number treatment to.8% after irteen days of salt treatment 88

5 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 Table 4: Heritability of parameters measured at harvest (6 to 8 days after salt treatment). Values are calculated from one-way ANOVA outputs Parameters Treatment Vg Ve H (%) P-value Shoot leng (cm) Control <0.00 Salt <0.00 Root leng (cm) Control <0.00 Salt <0.00 Shoot fresh weight (g) Control <0.00 Salt <0.00 Root fresh weight (g) Control <0.00 Salt <0.00 Leaf area (cm²) Control <0.00 Salt <0.00 Shoot dry weight (g) Control <0.00 Salt <0.00 Root dry weight (g) Control <0.00 Salt <0.00 Root/shoot dry weight Control <0.00 Salt <0.00 Genetic variance. Environmental variance. Heritability. (Table ). The number of living leaves increased from 9.5 Correlation Between Parameters to 7. under control and from 4.6 to 8. under salt Control: Leaf area showed strong positive correlation treated condition when e stress period was extended wi shoot fresh weight (r = 0.9), shoot dry weight from six to irteen days. The number of new leaves (r = 0.9), root dry weight (r = 0.8), root fresh weight developed between six and irteen days after salt stress (r = 0.78), root leng (r = 0.6) and shoot leng (r = 0.57), showed 5.6% reduction under salt stress relative to e however it showed a moderate negative correlation control. (r = -0.8) wi root/shoot dry weight ratio (Table 0). Root dry weight showed strong positive correlation wi Heritability of Parameters root fresh weight (r = 0.94), shoot dry weight (r = 0.8), Plant Height: Genotypes showed significant (P < 0.00) shoot fresh weight (r = 0.79) and root leng (r = 0.59). differences in plant height after zero and seven days of It showed a moderate positive correlation (r = 0.44) wi salt treatment bo for e control and salt stress shoot leng (Table 0). Root fresh weight showed strong condition. Heritability of plant height (80.8%) increased positive correlation wi shoot dry weight (r = 0.79), after seven days of salt stress (Table ). shoot fresh weight (r = 0.75) and root leng (r = 0.6). It showed a moderate positive correlation (r = 0.9) wi Grow Parameters Measured at Harvest: Genotypes shoot leng (Table 5). Root leng showed strong showed significant (P < 0.00) differences in all grow positive correlation wi shoot dry weight (r = 0.69), parameters (shoot leng, root leng, shoot fresh weight, shoot fresh weight (r = 6) and moderate positive root fresh weight, leaf area, shoot dry weight, root dry correlation wi shoot leng (r = 0.44), but it showed weight and root/shoot dry weight ratio) measured at negative correlation (r = -0.5) wi root/shoot ratio harvest under control and salt stress condition (Table 4). (Table 5). Root/shoot dry weight ratio showed a moderate The heritability of all grow parameters measured at negative correlation wi shoot leng (r = -0.49), harvest increased under salt stress except root fresh shoot dry weight (r = -0.49) and shoot fresh weight weight. The heritability of grow parameters ranged from (r = -0.8). Shoot dry weight showed strong positive 45.5% to 8.9% under control and from 69.% to 89.5 % correlation wi shoot fresh weight (r = 0.9) and shoot under salt stress condition. The highest heritability was leng (r = 0.65). Shoot fresh weight showed strong observed for root/shoot dry weight ratio (89.5%) and leaf positive correlation (r = 0.69) wi shoot leng area (85.9%) under salt stress condition (Table 4). (Table 5). 89

6 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 Table 5: Correlation between parameters measured at harvest under control condition Leaf area Root DW Root FW Root Leng Root /Shoot Shoot DW Shoot FW Shoot leng Leaf area - Root DW Root FW Root Leng Root/Shoot Shoot DW Shoot FW Shoot leng Dry weight. Fresh weight. Table 6: Correlation between parameters measured at harvest under salt stress condition Leaf area Root DW Root FW Root Leng Root/Shoot Shoot FW Shoot DW Shoot leng Leaf area - Root DW Root FW Root Leng Root/Shoot Shoot FW Shoot DW Shoot leng Dry weight. Fresh weight Salt Treated: Leaf area showed strong positive DISCUSSION correlation wi shoot fresh weight (r = 0.94), shoot dry weight (r = 0.94), root dry weight (r = 0.78), root fresh The current study aimed at examining e effect of weight (r = 0.76), root leng (r = 0.67) and shoot leng salinity stress on e grow parameters of diploid potato (r = 0.56), but a moderate negative correlation (r = -0.5) genotypes and determining e heritability of ese traits wi root/shoot dry weight ratio (Table 6). Root dry and eir association. Accordingly ninety four diploid weight showed strong positive correlation wi root fresh potato genotypes, which are progenies from a cross weight (r = 0.97), shoot fresh weight (r = 0.85), shoot dry between C and E parents, were examined based on grow weight (r = 0.80) and root leng (r = 0.67). It showed a parameters under hydroponics condition. Hydroponics moderate positive correlation (r = 0.49) wi shoot leng was chosen to study e response of e genotypes to (Table 6). Root fresh weight showed strong positive salt stress because it provides a uniform salinity correlation wi shoot fresh weight (r = 0.8) and shoot environment and reduces e interaction wi oer dry weight (r = 0.78), root leng (r = 0.7) and shoot environmental factors. Furermore, e study under leng (r = 0.5); (Table 6). Root leng had positive hydroponics provides e opportunity to measure root correlation wi shoot fresh weight (r = 67), shoot dry parameters more easily an under field condition and it weight (r = 0.68) and shoot leng (r = 0.55), but it gives an insight to predict e response under field showed a moderate negative correlation (r = -0.4) condition. wi root/shoot dry weight ratio (Table 6). Root/shoot dry The results of e current study revealed significant weight ratio showed a moderate negative correlation interaction effect of genotype and treatment on grow wi shoot leng (r = -0.46), shoot dry weight (r = -0.40), parameters except root leng (Tables and ). Grow shoot fresh weight (r = -0.). Shoot fresh weight showed parameters like plant height, shoot fresh weight, leaf area, strong positive correlation wi shoot dry weight (r = 0.97) shoot dry weight, root dry weight, root fresh weight and and shoot leng (r = 0.6). Shoot dry weight shoot leng showed remarkable reduction due to salt showed positive correlation (r = 0.65) wi shoot leng stress. Similar results were reported by several auors (Table 6). [, 5, 9,, ]. In contrast, root leng was hardly affected 90

7 African J. Basic & Appl. Sci., 8 (4): 85-9, 06 by salt stress in our study (Table ). This might be e differences in e number of new (young) leaves because of e limited availability of space for e grow developed between six to irteen days after salt stress. of roots in order to see e clear treatment effect on root A reduction of.8% in number of living leaves was leng. It showed e lowest (.9%) relative reduction observed after irteen days of salt stress relative to e (Table ). Moreover, less sever reduction in root leng control. In agreement wi is result, a significant an shoot leng due to salt stress was also reported for reduction in number of leaves due to salt stress was also potato cultivars on e study by [0, 4] under in vitro reported by [] on sugar beet and cabbage. Furermore, condition. Shoot fresh weight and leaf area showed e e effect of salinity in reducing leaf area is greater an highest relative reduction due to salt stress wi values its effect on e total number living of leaves (Tables ). of 74.6% and 7.9% respectively (Table ). In line wi is Thus, maintaining high leaf area is more important an result, significant effect of salinity in shoot fresh weight number of leaves for salinity tolerance, since e was reported by [9] on potato and high reduction in leaf correlation between leaf area and grow parameters is area was reported by [5] on tomato and [] on faba bean strong, but weak correlations were observed between (Phaseolus vulgaris L.). Moreover, [] reported e total number of living leaves and grow parameters adverse effect of salinity on shoot fresh and dry weights (data not shown). and a reduction of 60-6% shoot fresh weight of soybean due to salt stress. The current result also showed high CONCLUSION relative reduction in shoot (69.4%) and root (6.6%) dry weights due to salt stress. However, e reduction in Genotypes showed high reduction in grow shoot dry weight was more an root dry weight (Table ). parameters in response to salt stress. The highest Similar results were reported by [] in eir studies of reduction was observed for shoot fresh weight and leaf salinity effect on sugar beet and cabbage. In e current area. Under hydroponics condition root leng was not study, root leng was not affected by salt stress whereas affected by salt stress. Alough high reduction in grow root dry weight was significantly affected. This indicates parameters was observed in response to salt stress, at e effect of salinity on root dry weight in our ere was high genetic variability in is potato experiment might be resulting more from its effect on root population. Moreover, high heritability was observed branching raer an root leng. Among all grow under salt stress an control condition. Until irteen parameters root/shoot dry weight ratio showed an days after salt stress, no effect was observed on e increase due to salt stress (Table ). Similar to is result, number of dead leaves. This indicates at e effect of [6] reviewed an increase in is parameter due to salt salt stress on leaf senescence of e potato genotypes stress in cotton and [] on bean (Phaseolus vulgaris L.). may be observed later an e specified period of stress. The increase in root/shoot dry weight ratio can be The effect of salt stress on number of living leaves was explained by e higher reduction in shoot dry weight not observed till six days after salt stress. This parameter an root dry weight under salt stress. was affected by salinity after a stress period of irteen In e current study e interaction between days. This suggests at salt stress affects development genotype and treatment and e treatment effects on e of new (young) leaves in e potato genotypes later an number of dead leaves were not significant after six and six days of salt stress. Finally, e study suggests furer irteen days of salt stress; however, genotypes showed study on evaluation of e genotypes under various significant differences after irteen days of salt stress. salinity level and e presence of substances involved in This may indicate at e effect of salt stress on e osmotic adjustment. Furermore, studying e senescence of potato leaves may not be observed until six association between salt tolerance and analysis results of to irteen days after salt stress. On e oer hand, + + tissue Na and K may give information wheer e salt e interaction between genotype and treatment and + tolerance is due to e tolerance to Na concentration or treatment effects on e number of living leaves after six exclusion of is ion. days of salt stress were not significant but, significant interaction effects were observed after irteen days of ACKNOWLEDGMENT salt stress. Strong positive correlations (r = 0.75 control, r = 0.68 salt treated) were also observed between total The auor would like to ank Wageningen number of living leaves and new leaves developed University for providing study admission and Nuffic for between six to irteen days after salt stress (data not fellowship opportunity. The auor is also grateful to shown). This result suggests at e differences in e Dr. Gerard Vander Linden and Marcel Van Culemborg for total number of living leaves between treatments is due to supervision. 9

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