Physical Purity and Germination of Caryopses of Chloris Gayana Kunth and Panicum Coloratum L

ARTICLES RIA / Vol. 44 / N.º 1

Physical purity and germination of caryopses of Chloris gayana Kunth and Panicum coloratum L. harvested from plants grown in an alkaline-sodium soil

GARCÍA, M.D.1; PESQUEIRA, J.1; OTONDO, J.2

ABSTRACT The objective of the study was to evaluate physical purity, germination percentage (G) and germination velocity (GV) of caryopses of Chloris gayana cv. Finecut (Cg) and Panicum coloratum cv. Klein Verde (Pc) collected from plants grown in an alkaline-sodic soil (pH = 9.8, ECe = 0.69 dS m-1, EPS = 26.2%). To compare G of both species, 50 caryopses (n= 5) were incubated in deionized water. To evaluate G responses to salinity and alkalinity, an experiment with completely randomized design and factorial structure (n= 4) of two species x four concentrations of Na+-salts (25, 50, 100 and 150 mM) x two pHs (6 and 10) was per- formed. Treatments consisted in combinations 1:1 of NaCl + SO4Na (pH= 6) and Na2CO3 + NaHCO3 (pH= 10): 25mMpH6 (control); 25mM-pH10; 50mM-pH6; 50 mM-pH10; 100mM-pH6; 100mM-pH10; 150mM-pH6 and 150mM-pH10. Samples of the natural-dispersal material from panicles of Cg and Pc contained (mean ± SEM; % of total weight): caryopses covered by glumes (53 ± 2.6; 41.3 ± 4.6), isolated caryopses (1.4 ± 0.6; 10.3 ± 1.95), empty caryopses (32.9 ± 2.4; 22.7 ± 2.4) and inert materials (12.5 ± 2.2; 25.7 ± 2.1). Caryopses of Cg and Pc incubated in water showed similar values (mean ± SEM, in %) of G (96.5 ± 2.4 and 89.2 ± 3.6) and GV (54.7 ± 7 and 51.7 ± 5.5). In the presence of salt 25 mM, the increment of pH from 6 to 10 did not inhibit G of Cg (94.4 ± 2.55 and 90.7 ± 3.7) or Pc (93.9 ± 2.2 and 92.95 ± 1.9). Incubation in 50mM-pH=10 inhibited G of Pc (33.2 ± 4.7) but not G of Cg (93.5 ± 3.3). The solution 100mM-pH=10 inhibited more the germination of Pc (2.5 ± 1.5) than that of Cg (66.35 ± 5.5), and 150mM-pH10 strongly inhibited germination of both species, Cg (3.5 ± 1.5) and Pc (0 ± 0). In solutions with pH = 6, the G of Cg and Pc was not affected up to 100 mM of salt, but 150 mM induced decreases of 25 % and 20 % of G, respectively, in relation to that observed in 25mM-pH=6. The increment of pH also affected more GV of Pc than that of Cg. GV of both species responded in a similar way to increases of salinity in neutral (pH= 6) solutions. The GV of the caryopses incubated in 50mM-pH=6 did not differ from their respective controls. From 50 mM, each increase of salt concentration induced the decrease of GV of both species, relative to their respective controls.

Keywords: salinity, alkalinity, megathermic forage poaceae, germination velocity.

1Universidad Nacional de Lomas de Zamora, Facultad de Ciencias Agrarias, Ruta 4 km 2 (1836) Llavallol, Buenos Aires, Argentina. 2Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria (EEA) Cuenca del Salado, (7130) Chasco- mús, Buenos Aires, Argentina. Correo electrónico: [email protected]

Received September 19, 2016 // Accepted August 15, 2017 // Published online April 3, 2018

Pureza física y germinación de cariopses de Chloris gayana Kunth y Panicum coloratum L. cosechados de plantas cultivadas en un suelo alcalino-sódico April 2018, Argentina 5

INTRODUCTION 2015; Avaca et al., 2015) and have a moderate tolerance to frost (Jones, 1969, Pesqueira et al., 2016). For these, they According to estimates of FAO / UNESCO, the global are an interesting fit to plant in the Salado’s basin. area affected by salinity and alkalinity exceeds 900 million hectares (Wicke et al., 2011). For example, in the province P. coloratum cv. Klein verde and C. gayana cv. Finecut of Buenos Aires about 7 million ha (24% of the province’s were planted in 2012, in the Integrated Experimental Farm surface) are occupied by soils with hydrohalomorphism of Chascomús (Buenos Aires). Soil pH= 9.8; ECe= 0.69 dS problems (Miaczynski, 1995), the vast majority of which are m -1 and ESP= 26.2%. The emergence and biomass pro- located in the Cuenca del Salado [Salado’s Basin]. duction of P. coloratum and C. gayana were similar (Oton- do et al., 2014) the year of implantation. After three years, Among the soils that predominate in this basin are the P. coloratum cv. Klein produced 36% more biomass than Natracualfs and typical Natralcuols, that in the province co- the average of the natural grassland, Thinopyrum ponticum ver more than 4.7 million ha (@ 15.66% of the total area). (Podp.) Liu & Wang and C. gayana (Pesqueira et al., 2015). These soils have a low-permeability clay horizon, with a high content of sodium salts (Miaczynski, 1995). There con- The flowering of P. coloratum is very heterogeneous, with ditions generate a restrictive soil environment for germina- seeds that mature irregularly and are dormant at the time tion and growth of most plant species, especially when the of dispersion. The type of reproduction is mainly by seeds, mentioned factors are combined in the same soil (salinity, which completely lose dormancy 6 months after post-matu- alkalinity and flooding or drought). ration (Petruzzi and Stritzler, 2003). C. gayana propagates vegetatively via stolons, flowering is concentrated in the There are numerous studies on the effects of salinity on first half of autumn and produces large numbers of seeds the plant germination and growth, but there is little informa- with high germinative power, which favors reseeding and tion on the effects of alkalinity. In recent years,there has been rapid soil cover (Avila et al., 2012) . an increase in the number of studies on the effects of alkalinity on germination of seeds, growth and metabolism of plants. However, under the cultivation conditions of the plots in Chascomús, new seedlings of C. gayana and P. coloratum In these studies, the pH of the nutrient solution are not observed during the spring-summer coverage eva- has normally been alkalized and stabilized by adding luations, despite the fact that established plants produce Tris(hydroxymethyl)aminomethane buffer (which allows to abundant seeds every summer (data not shown). completely separate the pH from the salt concentration) (Singh et al., 2002; Avaca et al., 2015), or by combining The environment in which the parent plant grows can affect different proportions and concentrations of sodium bicarbo- different characteristics of the seeds, such as production, nate and sodium carbonate (which generates solutions with weight, viability, and dormancy level, to give some examples different levels of alkalinity and salinity) (Guo et al., 2010; (Fenner, 1991). Young and Evans (1981) observed that the Li et al., 2010). emergence and growth of Elymus cinereus (Scribn. & Merr.) A. Löve seedlings in a saline - alkaline soil was better from These investigations have shown that the alkaline sodium seeds obtained from plants that had grown in a non-alkaline salts (NaHCO3 and Na2CO3) produce a more damaging soil, when compared to plants grown in a saline-alkaline soil. effect on the plants than equimolar concentrations of neutral salts (NaCl and Na2SO4). For example, seed germination However, Koyro and Eisa (2008) observed that Cheno- was more inhibited in the presence of alkaline salts than podium quinoa Willd. plants grown in nutrient solutions neutral salts in Medicago sativa L. (Li et al., 2010), Leymus containing NaCl 100, 300 or 500 mM produced seeds with chinensis (Trin.) Tzvelev (Ma et al., 2015), Medicago rutheni- higher germination speed in saline media than seeds ob- ca (L.) Sojak, (Guan et al., 2009), Chloris virgata Sw. (Lin et tained from plants grown in nutrient solutions without the al., 2015), Triticum aestivum L. (Guo et al., 2010), Sorghum addition of NaCl. bicolor (L.) Moench (Zhao et al., 2014), Panicum virgatum L. To date, no data has been published on the quality attri- (Lui et al., 2014), Chloris gayana Kunth y Panicum coloratum butes (purity, germination potential, and germination rate) L. (García et al., 2015), Setaria viridis (L.) P. Beauv. (Guo et of the seeds produced by C. gayana and P. coloratum al., 2011), Helianthus annuus L. (Liu et al., 2010), and diffe- plants grown on alkaline-sodium soils. rent grass species (Zhang and Rue, 2014), to name some. The objectives of this study were to evaluate the physical Panicum coloratum L. and Chloris gayana Kunth are purity, final germination (G) and germination velocity (GV) subtropical perennial Poaceae characterized by a high bio- of Chloris gayana cv. Finecut (Cg) and Panicum coloratum mass production, with an adequate nutritional value to sa- cv. Klein Verde (Pc) cariopses harvested from plants grown tisfy the requirements of the cattle breeding herd (Avila et in an alkaline-sodium soil. al., 2012). The implantation of C. gayana and P. coloratum led to an increase in the productivity when compared to the natural community of halophytes, although their nutritional MATERIALS AND METHODS quality is lower (Otondo, 2011). Plant material They are also tolerant to drought (Ghannoum, 2009, Pon- sens et al., 2010), salinity (Ribotta et al., 2013), short pe- Dispersion units (caryopses covered by glumes and glu- riods of flooding (Imaz et al., 2015), alkalinity (García et al., mella) harvested from Chloris gayana cv. Finecut (Cg) and

GARCÍA, M.D.; PESQUEIRA, J.; OTONDO, J. ARTICLES RIA / Vol. 44 / N.º 1

Panicum coloratum cv. Klein Verde (Pc) plants growing in a The dishes were stored 26 days under an alternating typical Natracualf soil with pH= 9.8, electrical conductivity of regime of 12 h of light / 12 h of darkness at temperatu- the aqueous extract, ECe = 0.69 dS m-1 and exchangeable res (mean ± SEM, ºC) of 28.00 ± 0.14 and 23.04 ± 0.08, sodium percentage, ESP= 26.2%. respectively. The data were analyzed using analysis of variance, and when significant differences were detected, the means were separated by Fisher’s Least Significant Methods Difference (LSD), p≤0.005, using the program Infostat (Di The inflorescences were wrapped with translucent tulle Rienzo et al., 2013). from March 9 to April 10, 2015 to collect the calypses natu- The germination percentage was calculated using the fo- rally dispersed during that period. The physical purity was llowing formula: determined from 10 sub-samples of each species, from which the partial weights of the following fractions were G (%) = number of sprouted caryopses / total number of recorded: dispersion units, bare caryopses, empty caryop- caryopses x 100. ses and inert material. Due to the low germination (mean The GV was estimated using the modified GV index of ± SEM, in%) shown by the caryopses of Pc (26.4 ± 3.4), a Timson (Timson, 1965): pretreatment with H2SO4 was applied to break dormancy. GV (% day-1) = S G / t The pretreatment consisted in the immersion of dispersion units with cariopses of PC developed in concentrated Where G is the percentage of new germinated caryopses H2SO4 for 10 minutes (50 caryopses per ml), followed by in each count and t are the days elapsed until that count three consecutive rinses with: (Zhang and Rue, 2014). i) Ice water (cooled to 0 °C with ice), ii) 1 M solution of NaHCO3 to neutralize and iii) ice water (adapted from Voigt RESULTS and Tischler, 1997). The total weight of the samples collected from the disper- In order to evaluate the response of the germination to the sion of the panicles of Cg and Pc was composed of 54% salinity / alkalinity of the incubation solution, we conducted an and 52%, respectively, of developed caryopses (both cove- experiment with a completely randomized design and factorial red by glumes and bare), and the remaining percentage by structure of two species x four concentrations of Na+ salts x empty caryopses and inert materials (Table 2). two pH, with four repetitions. The treatments consisted of 1:1 combinations of neutral Na+ salts (NaCl + SO4Na, pH= 6) or The values (mean ± SEM) of G (%) and GV (% d-1) of the alkaline salts (Na2CO3 + NaHCO3, pH= 10) in the following caryopses incubated in water were similar for Cg (96.5 ± 2.4, concentrations (mM): 25, 50, 100 and 150 (Table 1). and 54.7 ± 7.9, respectively) and Pc (89.2 ± 3.6 and 51.7 ± 5.5, respectively). The latter were pretreated with H2SO4. In Forty days after collection, dispersion units containing addition, the values of G and GV of both species in N25 (Figu- developed caryopses (hereafter called caryopses) were se- res 1 a and b) did not differ from the values obtained in water, lected and placed in 9 mm Petri dishes on two filter paper for which the N25 treatment was considered as the control to disks (50 caryopses per dish) embedded in deionized water evaluate on germination the effects of salinity and pH. to determine the germination potential, or in the correspon- ding treatment solution (Table 1) to evaluate the response The three evaluated factors and their interaction affected to salinity/alkalinity. G (p <0.001). The caryopses of Cg and Pc incubated in A25

Concentration (mM) of salt -1 Treatment pH ECs (dS m ) NaCl SO4Na2 NaHCO3 Na2CO3 N25 (control) 6 4,24 12,5 12,5 0 0 N50 6 7,28 25 25 0 0 N100 6 12,35 50 50 0 0 N150 6 19,15 75 75 0 0 A25 10 3,31 0 0 12,5 12,5 A50 10 6,16 0 0 25 25 A100 10 11,32 0 0 50 50 A150 10 16,01 0 0 75 75

Table 1. Saline composition, pH and electrical conductivity (ECs) of the incubation solutions (treatments) of the caryopses.

Pureza física y germinación de cariopses de Chloris gayana Kunth y Panicum coloratum L. cosechados de plantas cultivadas en un suelo alcalino-sódico April 2018, Argentina 7

Fraction (% of total weight) Germination Species Dispersion units with Bare developed Dispersion units with Inert potential (%) developed caryopses caryopses empty caryopses material C. gayana 53,0 ± 2,6 1,4 ± 0,6 32,9 ± 2,4 12,5 ± 2,2 96,5 ± 2,4 P. coloratum 41,3 ± 4,6 10,3 ± 1,95 22,7 ± 2,4 25,7 ± 2,1 89,2 ± 3,6

Table 2. Physical purity and Germination Potential (%) of C. gayana cv. Finecut and P. coloratum cv. Klein Verde caryopsis collected from the natural dispersion of plants grown in an alkaline-sodium soil. Values: mean ± SEM.

presented percentages of G similar to those incubated in cial Pc seeds from different origins present a high variability N25 (Figure 1a). In contrast, the G of Pc was inhibited more in the purity (between 31% and 98%) (percentage of true than that of Cg in caryopses incubated in A50 and A100. seed over the total sample) (Lauric et al., 2014). The A150 solution strongly inhibited the germination of both Under high alkalinity and low salinity conditions, eg. pH= species (Figure 1a). 10 and ECs= 3.3 dS m-1, the caryopses of Cg and Pc pre- Caryopses incubated in solutions with pH= 6 presented sent germination percentages similar those of caryopses similar values of G with salt concentrations up to 100 mM. incubated in water. These levels of electrical conductivity In contrast, caryopses of Cg and Pc incubated in N150 ger- and pH are slightly higher than those observed in soils whe- minated 25% and 20% less, respectively, than those incu- re the parent plants grew (pH= 9.8 and ECs= 0.7 dS m-1). bated in N25 (Figure 1a). Even in alkaline solutions with a moderate level of salinity The interaction between the three evaluated factors (ECs= 6 dS m-1) the germination of Cg was not modified was significant for the GV (p= 0.006) (Figure 2b). With low and 31% of the Pc caryopses germinated. In the soil where and moderate salt concentrations caryopses of C. gaya- these plants are grown, these values of soil electrical con- na showed a better response to alkalinity than those of P. ductivity (SEC) are expected when the water content of the coloratum. soil drops and the salts concentrate (Hussain et al., 2002). Therefore, the production of viable seeds and the levels of The caryopses of P. coloratum incubated in N25, N50 electrical conductivity and soil pH indicate that the natural and N100 presented a higher GV than those of C. gayana. reseeding of both species could occur. The increase of the pH in these salt concentrations (A25, A50 and A100) induced the reduction in the GV of P. colora- However, there are other factors in the soil that can affect tum, but not that of C. gayana, when compared to the VG in the viability of the dispersed seeds that remain on the sur- N25, N50 and N100, respectively (Figure 1b ). In contrast, face during the winter and, thus, their subsequent germina- when using 50 mM of salt, the increase in pH increased the tion, such as variations in water availability, in temperature, GV of Cg by 31%. The increase in pH in the presence of increased compaction (Martín et al., 2012), etc. In the soil, 150 mM of salt induced a strong decline in the GV of both where the seeds of both species were harvested, planting species (Figure 1b). at a depth of 0.5 cm increased the density of Cg and Pc plants 5 and 6 times, respectively, when compared with sur- In neutral solutions (pH = 6) the GV also decreased from face planting (Otondo et al., 2014) . N50 when the saline concentration increased, when compared to the respective control (Figures 1b and 2). In addition, the coverage of the dominant species (Pes- queira et al., 2015), added to the presence of other species and dead plant material on the soil surface, could have ge- DISCUSSION nerated an environment with too low light intensity to allow the settling of the seedling. On the one hand, we observed in samples obtained from the natural dispersion of panicles of C. gayana and P. colora- The G of the caryopses obtained from plants grown in tum grown in an alkaline - sodium soil that 54% and 52% of an alkaline / sodium soil is similar to the G of caryopses the total weight corresponds to developed caryopses (cove- from commercial seeds. The responses of G to salinity are red by glumes + bare). This indicates a germination potential similar in both species, but C. gayana is more tolerant to of 96% and 89%, respectively. These germination percenta- alkalinity (Figures 1 and 2) (García et al., 2015). ges are similar to those observed in commercial samples of In several grass species it was also observed that germi- Cg (Avaca et al., 2015) and Pc (Lauric et al., 2014). nation is not inhibited when alkalinity is combined with low On the other hand, commercial seeds of Cg cv. Finecut salinity levels (Zhang and Rue, 2014). However, with in- shows a viability percentage of approximately 50% over the creasing concentrations of Na+ salts, the detrimental effect total sample (Avaca et al., 2015), and samples of commer- on G and GV is more marked in the presence of alkaline

GARCÍA, M.D.; PESQUEIRA, J.; OTONDO, J. ARTICLES RIA / Vol. 44 / N.º 1

a a 100 a a a ab a a ab bc bc 80 c

60 ) ( %

G 40

20 e e e 0 N25 A25 N50 A50 N100 A100 N150 A150

Incubation solution

60 a abc ab bc 50 bc ) 1 - cd cd

d 40 de de % ( 30 e

G ef V 20 f f

10 g g g 0 N25 A25 N50 A50 N100 A100 N150 A150

Solución de incubación

C. gayana P. coloratum

Figure 1. Final germination (a) and germination velocity (b) of C. gayana cv. Finecut and P. coloratum cv. Green Klein caryopses harvested from plants grown in an alkaline-sodium soil and incubated 26 days in solutions with different concentrations of Na+ salts (25, 50, 100 and 150 mM) neutral (pH= 6: N25, N50, N100 and N150) and alkaline (pH= 10: A25, A50, A100 and A150). Different letters indicate significant differences according to Fisher’s Least Significant Difference test, p ≤ 0.05.

salts than in neutral salts. Species with different tolerance CONCLUSIONS levels to salinity/alkalinity presented the same response, for The following observations were obtained from the analy- example Medicago sativa (Li et al., 2010), Triticum aestivum (Guo et al., 2010), Sorghum bicolor (Zhao et al., 2014), sis of material from the natural dispersion of Cg and Pc Medicago ruthenica (Guan et al., 2009), Panicum virgatum plants panicles grown in an alkaline - sodium soil: (Lui et al., 2014), Chloris gayana and Panicum coloratum • The fraction containing developed caryopses (disper- (García et al., 2015), to name some. sion units + bare caryopses) represents 51.6% and Under conditions with similar levels of salinity and high 54.4% of the total weight of the Pc and Cg samples, alkalinity, C. gayana presented a higher G and GV than respectively. Chloris virgata (Lin et al., 2015), a natural annual species that grows in alkaline soils in northeastern China, which is • Developed caryopses of Pc (after treatment with sul- very tolerant to salinity and alkalinity. However, Pc is more furic acid) and Cg incubated in water present similar sensitive than Cg to alkalinity but not to high salinity. values of G and VG (Figure 1).

Pureza física y germinación de cariopses de Chloris gayana Kunth y Panicum coloratum L. cosechados de plantas cultivadas en un suelo alcalino-sódico April 2018, Argentina 9

a b

100 100 90 90 80 80 70 70 60 60 ) )

( % 50

( % 50 40 40 30 30 20 20 10 10 Accumulated daily germination Accumulated daily germination 0 0 0 10 20 0 10 20 Imbibition time (d) Imbibition time (d)

Cg-N25 Cg-A25 Cg-N50 Cg-A50 Pc-N25 Pc-A25 Pc-N50 Pc-A50

c d

100 100 90 90 80 80 70 70 60 60 ) ) ( % ( % 50 50 40 40 30 30 20 20 10 10 Accumulated daily germination Accumulated daily germination 0 0 0 10 20 0 10 20 Imbibition time (d) Imbibition time (d)

Cg-N100 Cg-A100 Cg-N150 Cg-A150 Pc-N100 Pc-A100 Pc-N150 Pc-A150

Figure 2. Evolution of the germination of C. gayana cv Finecut (Cg) and P. coloratum CV Klein Verde (Pc) caryopses incubated in different concentrations of Na+ salts (mM): 25 (a), 50 (b), 100 (c) ) and 150 (d). Neutral salts (pH= 6): N25 and N50, N100, N150. Alkaline salts (pH= 10): A25 and A50, A100, A150. Caryopses were harvested from plants grown in an alkaline-sodium soil.

• High alkalinity (pH= 10) does not inhibit the germina- ACKNOWLEDGEMENTS tion of Cg in the presence of low to moderate salinity This study was financed by the Universidad Nacional de values (up to 50 mM). Lomas de Zamora [National University of Lomas de Zamo- • High alkalinity (pH= 10) does not inhibit the germination of ra] (Subsidy Lomascyt ii, period 2015-2107) and the Se- Pc in the presence of low salinity values (up to 25 mM). cretariat of University Policies of the Ministry of Education • In the neutral solutions (p= 6), the G percentages of Cg (Subsidy for Technology Transfer Projects “Capacidades and Pc are similar in the presence of 25, 50 and 100 Universitarias para el Desarrollo Productivo” [University mM and slightly decrease in the presence of 150 mM Capabilities for Productive Development] Amílcar Oscar of Na+ salts (Figure 1a). Herrera, period 2014-2016).

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Pureza física y germinación de cariopses de Chloris gayana Kunth y Panicum coloratum L. cosechados de plantas cultivadas en un suelo alcalino-sódico