Differences in size and architecture of the potato cultivars root system and their tolerance to drought stress

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1 Plnt Soil Environ. Vol. 63, 217, No. 4: doi: /4/217-PSE Differences in size nd rchitecture of the potto cultivrs root system nd their tolernce to drought stress Krystyn ZARZYŃSKA 1, *, Dominik BOGUSZEWSKA-MAŃKOWSKA 1, Artur NOSALEWICZ 2 1 Plnt Breeding nd Acclimtiztion Institute, Jdwisin, Polnd 2 Institute of Agrophysics, Polish Acdemy of Science, Lublin, Polnd *Corresponding uthor: k.zrzynsk@ihr.edu.pl ABSTRACT Zrzyńsk K., Boguszewsk-Mńkowsk D., Noslewicz A. (217): Differences in size nd rchitecture of the potto cultivrs root system nd their tolernce to drought stress. Plnt Soil Environ., 63: Drought cn cuse substntil yield losses, prticulrly for crops with shllow root systems, such s potto (Solnum tuberosum). This study tested whether root system rchitecture could ffect potto yield under drought conditions. The following prmeters of the roots were mesured: depth rnge, totl length, totl re, surfce re, verge dimeter, nd totl dry weight of the root system. These prmeters in soil lyers were lso mesured t different depths. Five potto cultivrs from group of mid-erly cultivrs were exmined in this study. The sme cultivrs were tested under two conditions: control with optiml irrigtion nd drought stress tretment without irrigtion for three weeks fter the end of tuberiztion to check the tuber yield. Significnt differences were observed mong cultivrs in the size of the root system nd its rchitecture. The biggest differences in the individul lyers of soil profile relted to the dimeter of the root, the root length, nd the surfce re. Also reltionship between the size of the root system nd yield of tubers ws found. The strongest correltions involved the root length nd the root surfce re with the decrese in tuber yield under the drought, then the dry root mss with the decrese in yield. These correltions were negtive: the higher the vlue of the prmeter, the smller the observed decrese in yield. This showed reltionship between root length nd mss with the decrese of yield; this reltionship ws stronger for roots in deeper lyers thn in the shllowest lyers. Therefore, this study indictes tht breeding potto cultivrs with deep root systems might improve tuber yields under drought conditions. Keywords: stress tolernce; tuber crops; wter; nutrient; rinfll The plnt root system tkes up wter nd dissolved nutrients from the soil; therefore the size nd extent of the root system hve importnt implictions for plnt development, yield, nd survivl under stress conditions. Potto plnts (Solnum tuberosum) hve reltively shllow root systems nd, consequently, potto growth nd yield depend on regulr rinfll nd re sensitive to wter shortges (Wisconsin University 22, Iwm 28, Joshi et l. 216). Cultivrs with lrger nd more expnsive root systems re more likely to be le to retrieve wter nd nutrients from the soil. Therefore, these cultivrs should be less susceptible to periodic droughts (Głusk 24, Wishrt et l. 213, Villrdon et l. 214) nd more suitle for growing in production systems tht use fewer inputs (wter nd fertilizer). Mesurement of the size nd extent of the root system of different cultivrs gives key informtion for breeding cultivrs dpted to regions with frequent shortges of rinfll. Such cultivrs my lso be better suited to orgnic production nd other low-input cropping systems. Informtion out the size of the root system cn lso provide importnt informtion for breeders. A reserch from the Iwm group (1998, 1999, 28) indictes tht breeding cn select for the size of the root system nd Jpnese breeding 159

2 Vol. 63, 217, No. 4: Plnt Soil Environ. doi: /4/217-PSE progrms hve used root system rchitecture s trit for selection (Iwm 1999, 28, Kshiwgi et l. 2). For exmple, the cv. Konyu ws bred using the size of the root mss in the rle lyer nd tuber yield s selection criteri. Indeed, cv. Konyu plnts show significntly less-severe responses to wter shortges in the soil, compred with commercil cultivrs (Iwm 28). Mesurements of root system prmeters require difficult nd time-consuming lour (Smith et l. 1994, Trcy et l. 211, Silberbush 213, Khn et l. 216). Therefore, most studies exmine only smll prt of the totl plnt mteril nd comprehensive studies wit improved methods for phenotyping. Severl centres hve crried out studies on the root system in wide rnge of potto cultivrs. The reserch presented here is continution of work conducted in Polnd. In the current study, the vriility of root system size nd rchitecture ws evluted in severl potto cultivrs nd looked for correltions between root system prmeters nd the tolernce of these cultivrs to soil drought. MATERIAL AND METHODS The study ws conducted in the yers in specilly constructed cylindricl pots with open bottoms. Pots were mde of sheets of glvnized steel with thickness of.8 mm nd were 1 m tll nd 4 cm wide, llowing for proper development of the ove-ground nd below-ground prts of the plnts. These pots cn be opened long the sem of the cylinder, llowing the extrction of the entire root system, without dmge (Głusk 1996). Pots were filled with light, lomy soil brought from the field where pottoes re grown nd mixed with snd in rtio of 1:1. Every 2 cm, metl net with mesh size of pprox..5 cm ws plced dividing the pot into 5 horizontl lyers 2 cm thick. Seed potto tubers were plced pproximtely 5 cm below the upper surfce of the soil. The roots of the growing plnts pss into the soil profile nd the mesh discs do not impede the growth of roots. During the growing seson the plnts were fed twice. The root systems were mesured when the plnts were in full vegettion (blooming), in the third week of June, s the previous study found tht potto plnts show the lrgest differences in the size of the root system (Iwm 28). After being removed from the pots, the roots were wshed nd cut long the mesh grids, thus producing five portions from ech plnt for mesurements. The following mesurements were mde: the depth rnge (cm), the totl length of roots (m), the length of the roots of the individul lyers (m), the totl re of roots (m 2 ), the surfce re of the roots in the individul lyers (m 2 ), the verge dimeter of roots (mm), the dimeter of the roots of the individul lyers (mm), the totl dry weight of the root system (g), nd the dry weight of the roots in the individul lyers (g). The length, dimeter, nd surfce re of the roots were mesured using the Epson Expression scnner (Seiko Epson Corp., Jpn) nd the 1XL WinRhizo softwre (Regent Instruments, Cnd). Five potto cultivrs from the group of miderly cultivrs (Bogtk, Cekin, Gwin, Stin, nd Tjfun), for which prior observtions of the response to wter scrcity re ville, were tested nd ech cultivr ws tested in 3 replictions. For the sme cultivrs, pot experiment ws conducted in the greenhouse. Two conditions were pplied: control with optiml irrigtion nd drought stress tretment with reduced irrigtion for three weeks fter the end of tuberiztion. After the end of the growing seson, tuber yield (kg) ws mesured. Sttisticl nlysis of results ws performed by n nlysis of vrince nd regression using the Sttistic softwre (SttSoft, Polnd). The significnce of the sources of vrition ws tested by the Fisher-Snedecor test. The significnce of differences ws ssessed by the Tukey s test. RESULTS The potto cultivrs showed differences in the root system size. The tested cultivrs showed significnt differences in ll tested prmeters, including the length, re, dimeter, nd dry weight of roots (Tle 1). The totl length of the roots per plnt rnged from 83.5 m in cv. Stin to 1399 m in cv. Gwin. Sttisticl nlysis divided the cultivrs into four groups with vrying totl lengths of roots (Figure 1). The totl re of the roots rnged from 79.5 m 2 in cv. Stin to 14.8 m 2 in cv. Gwin. The surfce of the root system increses with its length, but division of cultivrs into homogeneous groups 16

3 Plnt Soil Environ. Vol. 63, 217, No. 4: doi: /4/217-PSE Tle 1. Vrition in the whole root system Source of vrition Prmeter P Men totl length of roots (m) Cultivr totl re of roots (m 2 ) < verge dimeter of roots (mm) <.1.33 totl dry weight of the root system (g) < P <.5 ws considered sttisticlly significnt ws somewht different for root re, s sttisticl nlysis distinguished two groups of cultivrs with different root system res (Figure 1b). The verge dimeter of the roots rnged from.274 mm in cv. Bogtk to.319 mm in cv. Gwin. Sttisticl nlysis divided the cultivrs into four groups bsed on root dimeter (Figure 1c). The dry weight of the roots rnged from 5.6 g in cv. Cekin to 8.56 g in cv. Gwin nd the division into groups bsed on dry weight is shown in Figure 1d. Differentition of the rchitecture of the root system. The cultivrs differed significntly in terms of root rchitecture nd in the distribution of roots in individul lyers. The biggest differences relted to the dimeter of the root, the smllest length nd the root re (Tle 2). Rooting depth of ll tested cultivrs rnged up to 1 cm, but in the lst lyer (8 1 cm), the length nd mss of roots were very smll. On verge, the cultivrs hd the gretest length of roots in the second nd third lyer (t depth of 2 to 6 cm) (Figure 2). The root length in these lyers ws more thn hlf the size of the entire root system. The fourth nd the first lyers hd more roots thn the bottom lyer, but less thn the second nd third lyers. Cultivrs differed only in the first two lyers; the other lyers showed no significnt differences (Tle 2). () (m) c bc Gwin Tjfun Bogtk Cekin Stin (b) (m 2 ) b b Gwin Tjfun Bogtk Stin Cekin (c) (mm).33,33.32,32.31,31.3,3.29,29.28,28.27,27.26,26.25,25 b c Gwin Tjfun Bogtk Stin Cekin (g) c bc Gwin Tjfun Bogtk Stin Cekin Figure 1. () The length; (b) the surfce; (c) the dimeter, nd (d) the dry weight of the root system depending on the cultivr.,b,c Men vlues indicted by the sme letters re not sttisticlly significnt t the.5 level by Tukey s test (d) 161

4 Vol. 63, 217, No. 4: Plnt Soil Environ. doi: /4/217-PSE Tle 2. Vrition in the root systems of different cultivrs in the soil profile Tested prmeter Lyer I Lyer II Lyer III Lyer IV Lyer V P men P men P men P men P men Root length (m) < < Root re (m 2 ) < < Root dimeter (mm) Root mss (g) < P <.5 ws considered sttisticlly significnt The surfce re of roots in the individul lyers of the soil profile corresponded to the length of the roots. Chnges in the vlue of this prmeter lso coincided with the differences observed for the length of the root system. For most cultivrs, the lrgest root surfce re ws recorded in the second nd third soil lyer (Figure 2b). Differentition mong the cultivrs ws observed for the first three lyers, but not in the other lyers (Tle 2). The dimeter of the roots of ll cultivrs decresed with incresing depth in the soil profile (Figure 2c). In the first lyer (to depth of 2 cm), the men root dimeter ws 2% greter thn tht of the lst lyer (8 1 cm). The cultivrs showed significnt differences in ll lyers (Tle 2). Like the root dimeter, the dry weight of roots lso decresed in the soil profile (Figure 2d), however, this prmeter showed much lrger decrese. Root mss in the first lyer ws out 83% higher thn in the lst lyer. In the first two lyers, the dry weight of roots exceeded 5% of the totl root mss. There were significnt differences mong the cultivrs in ll five lyers. The reltionship between root system size nd rchitecture nd the yield of tubers. The yield of tubers decresed to vrying degrees when different cultivrs were subjected to drought stress. The smllest decrese ws observed in yield in cv. Gwin, nd the lrgest decrese in cv. Cekin (Tle 3). Using the dt on the size of the root system, the dependencies between root system prmeters () (m) 6 4 Bogtk Cekin Stin Tjfun Gwin (b) (m 2 ) (c) (mm),5.5,4.4,3.3,2.2, Depth (cm) Figure 2. Vrietl differences in () the length; (b) the re; (c) the dimeter; (d) dry weight of the root system in the soil profile 162 (d) (g) 33 2, , , Depth (cm)

5 Plnt Soil Environ. Vol. 63, 217, No. 4: doi: /4/217-PSE Tle 3. Tuber yield from 1 plnt (g) in control nd drought combintion nd decrese in yield (%) Cultivr Control Drought Decrese (%) Gwin Tjfun Bogtk Stin Cekin nd yield were clculted (without drought, with drought, nd the decrese in yield s result of the pplied drought). The strongest correltions involved the root length nd surfce re nd the decrese in yield; the next-strongest correltions involved the dry root mss nd the decrese in yield. Negtive correltions were observed; tht is, the higher the vlue of the tested prmeters, the smller the observed decrese in yield. Weker correltions involved the size of the root system nd the yield of tubers fter the drought tretment. There ws positive correltion for root system size nd higher yield, but it ws not sttisticlly significnt. The wekest correltions involved the size of the root system nd yield of tubers without drought. This pper further describes only the significnt reltionships. The clculted coefficients of correltion between the length nd dry weight of roots in the individul lyers nd the decrese of yield due to drought showed the gretest correltion between the prmeters in the fourth lyer; tht is, the greter the length nd weight of roots in the deeper lyer (6 8 cm), the smller the decrese in yield (Tle 4). Tle 4. Correltion coefficients between the length nd dry mss of roots in the individul lyers nd the decrese in tuber yield under drought Root length Correltion coefficient with yield decrese Dry mss of roots Correltion coefficient with yield decrese Lyer I.552 lyer I.37 Lyer II.47 lyer II.516 Lyer III.574 lyer III.478 Lyer IV.72 lyer IV.6 Lyer V.618 lyer V.532 DISCUSSION Under globl climte chnge, drought tolernce will likely become incresingly importnt for producing stle yields in ll crops (Hijmns 23, Coms et l. 213). Since current potto cultivrs hve low tolernce to drought, the enhncement of drought tolernce is n urgent tsk for potto reserchers in the 21 st century. Breeding of new cultivrs with excellent root chrcteristics to sorb wter from deeper regions of the soil nd under lower soil wter potentil will increse the usge of soil wter nd contribute to efficient utiliztion of wter from precipittion or irrigtion in potto production. Severl studies hve shown tht potto cultivrs differ in the size of the entire root mss nd distribution of the roots of the individul lyers of the soil (Open nd Porter 1999, Stlhm nd Allen 21, Bttilini et l. 28, Joshi et l. 216). Roots re concentrted mostly in the plowed lyer, up to 3 cm deep, nd even under the mother tubers. Other studies showed greter rnge in depth of roots. For exmple, Rykczewsk et l. (215) found the mximum depth of rooting ws 19 cm for mini-tubers nd Głusk (24) found tht the depth of rooting rnged from cm for regulr seed pottoes. In our study, the depth of rooting of ll cultivrs ws 1 cm (t the depth of the pots). The totl length of the roots per plnt showed lrger differences in different cultivrs. Wishrt et l. (213) showed tht root length of 28 genotypes rnged from m per plnt. In our study, this prmeter rnged from 8 14 m. The totl root length hs been shown to vry gretly in different cultivrs, with differences in the length of the root system of more thn 4%. The surfce re of the root system vried similrly nd cultivrs differed in the dimeter nd the dry weight of the roots. In our study, the dry weight of roots ws g. Lhlou nd Ledent (25) found tht root dry weight rnged from g. Głusk (24) nd Rykczewsk (215) obtined similr results. Our study lso confirmed the vried distribution of roots in different soil lyers nd confirmed the common presumption tht most of the root mss of potto occurs t depth of 5 6 cm. Indeed, for the five tested cultivrs, more thn 5% of the roots (by weight) were in the first nd the second lyer t depth of 2 4 cm, nd 23% of the roots were in the third lyer t 6 8 cm deep. The lrgest root length (over 5%) ws found in the second nd third 163

6 Vol. 63, 217, No. 4: Plnt Soil Environ. doi: /4/217-PSE lyers (4 8 cm) nd out 22% ws found in the fourth lyer (6 8 cm). The smllest root length ws found in the first nd fifth lyers. The root surfce re showed the sme distribution. Mny studies found positive reltionship between the size of the root system nd the mount of oveground biomss (Iwm 28, Rykczewsk 215). In our reserch dependence ws lso observed, but these correltions were not sttisticlly significnt. More interesting correltions involved the size of the root system nd the tuber yield. In our study no significnt correltion ws found between the size of the root system nd yield of tubers in the sence of drought tretment. Also stronger (but not lwys significnt) correltion ws observed with the yield of tubers from the drought-treted conditions. A good correltion ws found with the decrese in yield between the control nd drought tretments. This ws, of course, n inverse reltionship: the lrger the root system, the smller drop in yield. Attempts to find correltion between the size of the root system nd the size of the crop hve been undertken by mny reserchers (but not ll mnged to identify simple reltionships. In review of reserch on the root system of potto, Iwm (28) sttes tht the mss of roots generlly indictes positive correltion with the yield of tubers. Also Rykczewsk (215) found tht the drought-resistnt cv. Tetyd ws chrcterized by the gretest root system mss of the 17 tested cultivrs. In our work, this observtion ws extended trying to find whether the distribution of roots in the soil profile is correlted with the response of potto plnts to soil drought. Our nlysis showed greter correltion between the length nd weight of roots in the deeper lyers thn in the shllowest lyer. It cn be concluded tht the plnts tht hve more-developed root system t greter depths of the soil profile tend to hve milder rections to drought. REFERENCES Bttilni A., Pluborg F.L., Hnsen S., Doleżl F., Mzurczyk W., Bizik J. (28): Root development model for potto mngement. In: Proceedings of the V th IS on Irrigtion of Horticulture Crops Act Horticulture, 792: Coms L.H., Becker S.R., Cruz V.M., Byrne P.F., Dierig D.A. (213): Root trits contributing to plnt productivity under drought. Frontiers in Plnt Science, 5: 442. Głusk A. (1996): Construction of big cylindricl pot for mesurements of potto plnt root system. Act Agrobotnic, 54: (In Polish) Głusk A. (24): Root differentition of potto cultivrs Biul. Bulletin of Plnt Breeding nd Acclimtiztion Institute, 232: (In Polish) Hijmns R.J. (23): The effect of climte chnge on globl potto production. Americn Journl of Potto Reserch, 8: Joshi M., Fogelmn E., Belusov E., Ginzberq I. (216): Potto root system development nd fctors tht determine its rchitecture. Journl of Plnt Physiology, 25: Iwm K., Uemur T., Umemur Y. (1998): A simple method for selection of potto lines with higher root/totl rtio t n erly stge in the seedling genertion. 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