Effect of long-term storage on viability of buffel grass (Cenchrus ciliaris L.) seeds

Jamille Cardeal da Silva Jailton de Jesus Silva Simonica Sousa da Silva Raquel Araujo Gomes Bárbara França Dantas About the authors

Abstract:

Prolonged storage of seeds may lead to decreases in seed quality, negatively affecting germination and vigor and preventing the obtaining of a promising stand. Seed quality is a critical factor, and the performance of the lot can be altered by vigor, dormancy and, mainly, by the time and conditions in which the seeds were stored. In the experiment, the physiological quality of seeds 14 genotypes of buffel grass (Cenchrus ciliaris L.) genotypes stored for a period of thirteen years in cold conditions was evaluated. The seeds were subjected to germination induction treatment with potassium nitrate (KNO3) and evaluated to identify seeds with presence and absence of embryos. The seed storage period affected their germination capacity and the use of KNO3 did not increase seed germination. A low number of full seeds was found for genotype 613 (12%). The relative germination percentages did not underestimate the buffel grass seed germination potential, as it is usually calculated, providing an improved distinction between the evaluated genotypes. The use of KNO3 increased the seedling root and shoot weights of some genotypes, as well as the dry matter weight of seedlings, an important characteristic for forage production. The prolonged storage affects the physiological quality of buffel grass seeds. The production of seeds without embryo is a problem found for this species, which affects the final quality of the seed lots produced.

Index terms:
forage grass species; genotypes; physiological quality; seed production; storage

Resumo:

O armazenamento prolongado pode levar a perda da qualidade das sementes, influenciando negativamente na germinação e vigor e impedindo a obtenção de um estande promissor. A qualidade das sementes é um fator crucial, e o desempenho do lote pode ser alterado pelo vigor, dormência e principalmente, pelo tempo e condições em que as sementes ficaram armazenadas. No experimento foi avaliada a qualidade fisiológica de sementes de 14 genótipos de capim-bufel (Cenchrus ciliaris L.) armazenados por treze anos em câmara fria. As sementes foram submetidas a tratamento para indução da germinação com nitrato de potássio (KNO3), e posteriores avaliações para identificação da presença e ausência de embrião. O período em que as sementes ficaram armazenadas afetou sua capacidade de germinação e o KNO3 utilizado não induziu aumento na germinação das sementes. Baixo número de sementes cheias foi verificado para o genótipo 613 (12%). As porcentagens de germinação relativa não subestimaram o potencial de germinação das sementes de C. ciliaris, como usualmente é calculada, fornecendo distinção melhorada entre os genótipos avaliados. O KNO3 incrementou positivamente nas partes das plântulas de alguns genótipos, bem como na biomassa seca destas, sendo uma característica importante para a forragicultura em geral. O armazenamento prolongado afetou a qualidade fisiológica das sementes de C. ciliaris. A produção de sementes sem embrião é um problema encontrado nessa espécie, interferindo na qualidade final dos lotes produzidos.

Termos para indexação:
gramínea forrageira; genótipos; qualidade fisiológica; produção de sementes; armazenamento

INTRODUCTION

Buffel grass (Cenchrus ciliaris L.) is among the most cultivated forages in tropical and subtropical arid grasslands in the world due to its easy adaptation to climatic conditions, high drought tolerance and ability to withstand heavy grazing (Marshall et al., 2012MARSHALL, V.M.; LEWIS, M.M.; OSTENDORF, B. Buffel grass (Cenchrus ciliaris) as an invader and threat to biodiversity in arid environments: A review. Journal of Arid Environments, v.78, p.1-12, 2012. https://doi.org/10.1016/j.jaridenv.2011.11.005
https://doi.org/10.1016/j.jaridenv.2011....
). This grass is a perennial species, with variable growth and a well-developed root system, capable of withstanding prolonged periods of drought, and has a high nutritional value for ruminants (Marshall et al., 2012MARSHALL, V.M.; LEWIS, M.M.; OSTENDORF, B. Buffel grass (Cenchrus ciliaris) as an invader and threat to biodiversity in arid environments: A review. Journal of Arid Environments, v.78, p.1-12, 2012. https://doi.org/10.1016/j.jaridenv.2011.11.005
https://doi.org/10.1016/j.jaridenv.2011....
; Burson et al., 2015BURSON, B.L.K.; RENGANAYAKI, C.D.; DOWLING, L.L.; HINZE, R.W. Genetic diversity among pentaploid buffel grass accessions. Crop Science, v.55, n.4, p.1637-1645, 2015. https://doi.org/10.2135/cropsci2014.09.0655
https://doi.org/10.2135/cropsci2014.09.0...
). Buffel grass is recommended for growing in degraded areas or in intercropped pastures, as it has long flowering, rapid growth and maturation, and high seed production (Martin et al., 2015MARTIN, T.G.; MURPHY, H.; LIEDLOFF, A.; THOMAS, C.; CHADÈS, I.; COOK, G.; FENSHAM, R.; MCIVOR, J.; VAN KLINKEN, R.D. Buffel grass and climate change: a framework for projecting invasive species distributions when data are scarce. Biological Invasions, v.17, n.11, p.3197-3210, 2015. https://doi.org/10.1007/s10530-015-0945-9
https://doi.org/10.1007/s10530-015-0945-...
).

The creation of tropical forages is important for the Brazilian livestock sector. In the 1970s, an Active Germplasm Bank of forage species was implemented in the Caatinga experimental unit of the Empresa Brasileira de Pesquisa Agropecuária (Embrapa Semiárido), including several buffelgrass genotypes, which was the most outstanding among the evaluated species, due to its greater potential for forage production (Oliveira et al., 1999OLIVEIRA, M.C.; SILVA, C.M.M.; SOUSA, F.B. Capim-buffel (Cenchrus ciliaris L.) preservação ex-situ e avaliação aprofundada. In: QUEIROZ, M. A. DE.; GOEDERT, C. O.; RAMOS, S. R. R. Recursos genéticos e melhoramento de plantas para o Nordeste Brasileiro. Petrolina, PE: Embrapa Semiárido: Recursos Genéticos e Biotecnologia, 1999. https://www.alice.cnptia.embrapa.br/bitstream/doc/133707/1/Celia.pdf
https://www.alice.cnptia.embrapa.br/bits...
). Based on this, an Active Germplasm Bank was implemented for Cenchrus species and, in 2009, it integrated the National Platform of Genetic Resources, in the Vegetal Genetic Resources Network - Vegetal Network (Embrapa Cenargen, 2009EMBRAPA CENARGEN. Rede Nacional de Recursos Genéticos Vegetais, 2009. http://plataformarg.cenargen.embrapa.br/rede-vegetal
http://plataformarg.cenargen.embrapa.br/...
; Jank et al., 2021JANK, L.; SANTOS, M. F.; VALLE, C. B.; BARRIOS, S. C.; SIMEÃO, R. M. Forage Genetic Resources in Brazil. In: XXIV International Grassland Congress / XI International Rangeland Congress (Sustainable Use of Gr Use of Grassland and Rangeland Resources Land and Rangeland Resources for Impr ces for Improved Livelihoods), 2020. Sustainable use of grassland and rangeland resources for improved livelihoods. Proceedings... Kenya: Kenya Agricultural and Livestock Research Organization, 2021. https://www.alice.cnptia.embrapa.br/handle/doc/1137138
https://www.alice.cnptia.embrapa.br/hand...
). The improvement of these plants is essential to obtain information and develop cultivars that present desirable characteristics considering local needs.

The seeds of this species have an orthodox character, with the presence of physiological dormancy in their seeds, leading to germination asynchrony, mainly demonstrated when the seeds are freshly harvested, but the seeds may have their dormancy suppressed during storage. The quality of the seeds will depend on the period in which the seeds will be stored, which can interfere with their germination, and this will depend on several factors such as temperature conditions, relative humidity of the environment in which these seeds are stored and the time they will remain in a storage environment (Saeed et al., 2020SAEED, M.F.; JAMAL, A.; AHMAD, I.; ALI, S.; SHAH, G.M.; HUSNAIN, S.K.; FAROOQ, A.; WANG, J. Storage Conditions Deteriorate Cotton and Wheat Seeds Quality: An Assessment of Farmers’ Awareness in Pakistan. Agronomy, v.10, n.9, p.1246, 2020. https://doi.org/10.3390/agronomy10091246
https://doi.org/10.3390/agronomy10091246...
). Adequate storage is one of the determining factors for the production of high quality seeds; even if the storage period does not improve its quality, it prolongs the maintenance time of the seeds.

Seeds that have spent many years in storage, it is necessary to make evaluations to know what situation they are in, and with increasing storage time there is also an increase in deterioration and consequently a significant reduction in the percentage of germination and vigor. Evaluations of seed germination and vigor are important to monitor the physiological potential of seeds and occurrence of dormancy, and to establish vigorous and homogeneous populations in the field (Marcos-Filho, 2015aMARCOS-FILHO, J. Seed vigor testing: an overview of the past, present and future perspective. Scientia Agricola, v.72, p.363-374, 2015a. https://doi.org/10.1590/0103-9016-2015-0007
https://doi.org/10.1590/0103-9016-2015-0...
).

Another way of evaluating seed quality is relative germination, which is little studied by seed technologists, who consider that the final germination (G%) is enough to evaluate the quality of seed lots. This evaluation is more used to evaluate botanical families that present problems with non-embryonic (without embryo) and non-viable seed production, such as Asteraceae, Cyperaceae, Melastomataceae, and Poaceae (Dayrell et al., 2016DAYRELL, R.L.C.; GARCIA, Q.S.; NEGREIROS, D.; BASKIN, C.C.; BASKIN, J.M.; SILVEIRA, F.A.O. Phylogeny strongly drives seed dormancy and quality in a climatically buffered hotspot for plant endemism. Annals of Botany, v.119, n.2, p.267-277, 2016. https://doi.org/10.1093/aob/mcw163
https://doi.org/10.1093/aob/mcw163...
). Santana et al. (2018SANTANA, D.G.; CARVALHO, F.J.; TOOROP, P. How to analyze germination of species with empty seeds using contemporary statistical methods? Acta Botanica Brasilica, v.32, p.271-278, 2018. https://doi.org/10.1590/0102-33062017abb0322
https://doi.org/10.1590/0102-33062017abb...
) reported this problem in Lychnophora ericoides seeds and explained that this adversity during the seed development is important to understand the reproduction potential of a species, and should be considered in statistical analyses as well as germination evaluations for species that produce large quantities of seeds without embryo.

Thus, aim of this work was to evaluate the effect of prolonged storage on the physiological quality of buffelgrass seeds stored for 13 years in a germplasm bank and to examine the occurrence of seeds without embryo in the studied lots.

MATERIAL AND METHODS

Seeds of 14 genotypes (123, 129, 144, 147, 148, 149, 151, 199, 476, 570, 591, 613, Pusa Giant and Biloela) of C. ciliaris, harvested in 2006 and stored for 13 years in a cold chamber at a temperature of 10 ± 2 °C and 40% UR.

Preliminary evaluations

The seeds were first evaluated for 1000-seed weight, using 8 replications of 100 seeds; and water content, determined by the oven method (105 ± 3 °C for 24 hours) (Brasil, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento. Regras para análise de sementes. Ministério da Agricultura, Pecuária e Abastecimento. Secretaria de Defesa Agropecuária. Brasília: MAPA/ ACS, p.395, 2009. http://www.agricultura.gov.br/assuntos/insumos-agropecuarios/arquivos-publicacoes-insumos/2946_regras_analise__sementes.pdf
http://www.agricultura.gov.br/assuntos/i...
). The seed water content was obtained based on the mean weight of samples and expressed in percentages.

Germination (G%)

Germination was evaluated in a completely randomized experimental design, with a 14×2 factorial arrangement, consisting of the 14 genotypes described above and 2 imbibition solutions, with four replications. Fifty (50) seeds were sown in 11x11x3.5 acrylic boxes containing two sheets of blotting paper moistened with distilled water (H2O) or a 0.2% potassium nitrate (KNO3) aqueous solution at the proportion of 2.5-fold the substrate paper dry weight. The seeds were maintained in a germination chamber at a 30 °C with a photoperiod of 12 h (Brasil, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento. Regras para análise de sementes. Ministério da Agricultura, Pecuária e Abastecimento. Secretaria de Defesa Agropecuária. Brasília: MAPA/ ACS, p.395, 2009. http://www.agricultura.gov.br/assuntos/insumos-agropecuarios/arquivos-publicacoes-insumos/2946_regras_analise__sementes.pdf
http://www.agricultura.gov.br/assuntos/i...
). The evaluations were carried out at every 7 days for 21 days. These data were used to calculate the final germination percentage (G%).

Relative germination (GR%)

After the germination test, the percentage of empty seeds in each lot was evaluated; non-germinated seeds were cut in half with the aid of a scalpel to determine the number of seeds with and without embryo. The number of germinated seeds divided by the number of seeds with embryo was used to calculate the relative germination percentage. Dead seeds were counted at the end of the experiment and added to the number of seeds with embryo. These data were used to calculate the relative germination percentage, considering GR% = germinated seeds at the end of the experiment × 100 / number of full seeds (Santana et al., 2018SANTANA, D.G.; CARVALHO, F.J.; TOOROP, P. How to analyze germination of species with empty seeds using contemporary statistical methods? Acta Botanica Brasilica, v.32, p.271-278, 2018. https://doi.org/10.1590/0102-33062017abb0322
https://doi.org/10.1590/0102-33062017abb...
).

Normal and abnormal seedlings (NS% and AS%)

Normal and abnormal seedlings were evaluated 21 days after sowing by individually analysing seedlings and its essential structures present for normal growth (Brasil, 2009BRASIL. Ministério da Agricultura, Pecuária e Abastecimento. Regras para análise de sementes. Ministério da Agricultura, Pecuária e Abastecimento. Secretaria de Defesa Agropecuária. Brasília: MAPA/ ACS, p.395, 2009. http://www.agricultura.gov.br/assuntos/insumos-agropecuarios/arquivos-publicacoes-insumos/2946_regras_analise__sementes.pdf
http://www.agricultura.gov.br/assuntos/i...
).

Seedling root and shoot lengths (SRL / SSL)

The roots and shoots of ten normal randomly chosen seedlings of each replication were measured after the final counting of the germination test with the aid of a ruler, and the results were expressed in centimeters per seedling.

Seedling root and shoot dry matter weights (SRDW / SSDW)

The same seedlings evaluated for length were placed in paper bags and taken to a forced air-circulation oven at 65 °C until constant weight (72 hours); then, their weights were determined in analytical balance with precision of 0.001 g, and the results were expressed in grams per seedling. These tests were carried out together with the germination test, following the Brazilian procedures for seed analysis (Nakagawa, 2020NAKAGAWA, J. Testes de vigor baseados na avaliação das plântulas. In: KRZYZANOSWKI, F. C.; VIERIA, R. D.; FRANÇA-NETO, J. B.; MARCOS-FILHO, J. (Eds.). Vigor de sementes: conceitos e testes. Londrina: ABRATES, p.601, 2020.).

Statistical analyses

The data were firstly analyzed to verify the assumptions of analysis of variance. The Shapiro-Wilk test was used to evaluate the normality of residues for the response variables (Shaíro and Wilk, 1965SHAPIRO, S.S.; WILK, M.B. An Analysis of variance test for normality. Biometrika , v.52, n.3, p.591-611, 1965. https://www.jstor.org/stable/2333709?seq=1#metadata_info_tab_contents
https://www.jstor.org/stable/2333709?seq...
); the Levene test was used for the homogeneity of variances (Levene, 1960LEVENE, H. Contributions to probability and statistics. Essays in honor of Harold Hotelling. In: OLKIN, I.; CHURYES, S. G.; HOEFFDING, W.; MADOW, W. G.; MANN, H. B. (Eds.) Stanford studies in mathematics and statistics. California: Stanford University Press, p.278-292, 1960.); and the d statistic of Durbin-Watson was used for the independence of residues (Durbin and Watson, 1950DURBIN, J.; WATSON, G.S. Testing for serial correlation in least squares regression, I. Biometrika, v.37, n.3/4, p.409-428, 1950. https://www.jstor.org/stable/2332391?seq=1#metadata_info_tab_contents
https://www.jstor.org/stable/2332391?seq...
); all tests were carried out at 0.05 probability level.

The distribution and link function were chosen for each response variable according to the variable results and it’s better fit to these parameters. The germination (G%), relative germination (GR%), normal seedling (NS%), and abnormal seedling (AS%) data were analyzed using the quasibinomial distribution with the logit link function (Agresti, 2007AGRESTI, A. An Introduction to Categorical Data Analysis, 2nd Edition, Wiley, New York, USA, 2007. https://mregresion.files.wordpress.com/2012/08/agresti-introduction-to-categorical-data.pdf
https://mregresion.files.wordpress.com/2...
). The seedling root (SRL) and shoot (SSL) length data were analyzed using gamma distribution (Thom, 1958THOM, H.C.S. A note on the gama distribution. Monthly Weather Review, v.86, n.4, p.117-122, 1958. https://water.usgs.gov/osw/bulletin17b/MWR_Thom_1958.pdf
https://water.usgs.gov/osw/bulletin17b/M...
) with the log link function. Gamma distribution was used for the seedling root (SRDW) and shoot (SSDW) dry matter weight data, with the identity and inverse link functions, respectively. An adjustment procedure using generalized linear models (GLM) was used due to the violation of the assumptions of ANOVA and the option of not using angular transformation for the response variable.

The deviances were calculated for each factor alone, for the interaction, and for the null models. The inferences of analysis of deviance (ANODEV) were based on the qui-square (x2) statistic for the quasibinomial distribution, and based on the F statistic for the gamma distribution.

After the GLM analysis, significant differences within each genotype, treatment, and variables studied were evaluated by comparisons of pairs of means by the post-hoc Tukey’s test at 5% significance. The means followed by confidence intervals were fitted by the Šidák method (Šidák, 1967ŠIDÀK, Z. Rectangular confidence region for the means of multivariate normal distributions. Journal of the American Statistical Association, v.62, n.318, p.626-633, 1967. https://www.jstor.org/stable/2283989?seq=1#metadata_info_tab_contents
https://www.jstor.org/stable/2283989?seq...
). The analyses were carried out using the R program (R Core Team, 2020R CORE TEAM. R. A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, 2020. https://www.R-project.org/
https://www.R-project.org/...
).

RESULTS AND DISCUSSION

According to the assumptions of the analysis of variance, the Shapiro-Wilk tests indicated residues with normal distribution only for relative germination (0.4565) and shoot length (0.1094). The analysis of independence of residues by the Durbin-Watson test to assess the experiment randomization showed that all studied variables met the assumption; contrastingly, the homogeneity of variances found by the Levene test showed that none of the variables met the assumption.

The percentage of germination was statistically significant (p < 0.05) only among the access factor (Table 1), where seeds from accession 144 had a higher percentage of germination (68%) when germinated in distilled water (Table 2). Accession 147 did not differ statistically from 144, regardless of whether germination occurred in distilled water (60%) or KNO3 solution (55%). The accessions that showed the lowest germination in distilled water were 613 (14%), followed by 570 (27%) and Pusa Giant (28%). As with distilled water, the seeds of accessions 613, Pusa Giant and 570 showed the lowest percentages of germination when the seeds were hydrated with KNO3.

Table 1
Analysis of deviance (ANODEV) for buffelgrass (Cenchrus ciliaris L.) seeds stored for 13 years, treated with potassium nitrate (KNO3) and distilled water (H2O).

The relative germination percentages did not underestimate the germination potential of C. ciliaris seeds, as it is usually calculated, providing a better separation between the evaluated accessions. Seeds germinated in distilled water showed the highest percentage of relative germination when compared to those that were hydrated in KNO3 solution (Tables 1 and 2). The lowest percentages of relative germination in distilled water were for accession 613 (18.1%), followed by accessions 570 (36.2%), Pusa Giant (37.5%) and 129 (45.5%). Using KNO3 hydration, the lowest percentages of relative germination were for accessions 613 (12.1%), Pusa Giant (26.8%), 476 (33.6%) and 570 (33.6%). The only accessions that showed significant interaction were Pusa Giant, 199 and 476 (Table 2).

Table 2
Germination (G), relative germination (GR), normal (NS) and abnormal (AS) seedlings formed from C. ciliaris seeds stored for 13 years and treated in potassium nitrate (KNO3) and distilled water.

Some accessions presented low germination (G%) and relative germination (GR%), as was the case of accession 613 (Table 2), which presented a low number of full seeds, resulting in a lower percentage of germination.

The accessions that obtained the highest percentages of normal seedling formation were 144 and 147, both in distilled water and in KNO3 (Tables 1 and 2). Accession 613 showed the lowest percentage of normal seedlings in distilled water and in KNO3 solution, 10% and 9%, respectively. There was a significant difference between the hydration treatments only for accession 129, where KNO3 provided greater formation of normal seedlings (NS = 37%), (Table 2).

Seeds germinated in distilled water had a higher percentage of abnormal seedling formation compared to seeds hydrated in KNO3 solution (Tables 1 and 2). The accessions that showed the highest formation of abnormal seedlings when the seeds were hydrated in distilled water were 129 (19%), 149 (15%) and Biloela (14%). The KNO3 provided a lower formation of abnormal seedlings for the accessions evaluated, mainly 149 (12%) and 151 (10%). There was a significant difference between hydration in distilled water and KNO3 for accessions Biloela, 570, 476, 151 and 129, and of these genotypes only 151 showed higher formation of abnormal seedlings when the seeds were hydrated in KNO3 solution (Table 2).

For some accessions, germination in distilled water favored the growth of the main root (SRL) of the seedlings, as can be observed for accessions 199 (4.38 cm), 144 (4.36 cm), 147 (3.58 cm) and 151 (2.91 cm) (Tables 1 and 3). In this same context, hydration with KNO3 also favored root growth in some accessions, such as 149 (4.60 cm), 147 (2.82 cm) and 199 (2.27 cm). There was a difference between the hydrations only for accessions 144, 149, 151 and 199, where only accession 149 with the seeds hydrated in KNO3, presented a root length greater than that of distilled water (Table 3).

Table 3
Length of taproot (SRL) and shoot (SSL), dry biomass of root (SRDW) and shoot (SSDW) of C. ciliaris seedlings formed from seeds stored for 13 years and treated in nitrate of potassium (KNO3) and distilled water.

For shoot length (SSL) the accessions that developed the best were 144 (4.53 cm), 147 (4.14 cm), Biloela (4.01 cm), 613 (3.88 cm) and 476 (3.85 cm) in distilled water (Table 3). For seeds germinated in KNO3, the highest values were for accessions 149 (6.8 cm), 129 (6.35cm), 147 (5.76 cm), 148 (3.79 cm) and 199 (3.61 cm). Accessions 149, 129, 147, 148 and 199 showed a statistical difference between the hydrations, where the seeds germinated in the KNO3 solution provided seedlings with greater shoot length compared to those that germinated only in distilled water (Table 3).

The accessions with the highest incorporation of biomass in the root when the seeds were hydrated with distilled water were 123 (0.0095 g) and 476 (0.0089 g). These same accessions also showed superior results when their seeds were hydrated with KNO3 (Tables 1 and 3). The accessions that showed a statistical difference between the hydrations were 570, 199, 151 and 129, however the only one that showed better incorporation of biomass in the root when the seeds were hydrated with H2O was 151 (0.0028 g).

For the dry biomass weight of the aerial part, the accessions that presented better results when the seeds were hydrated in distilled water were Biloela (0.0107 g), 476 (0.0116 g), 149 (0.0094 g) and 123 (0.0163 g), (Table 3). When the seeds were hydrated with the KNO3 solution the only accession that presented greater incorporation of biomass and that was statistically different from the others was accession 149. Hydration with KNO3 provided greater incorporation of biomass to the aerial part of C. ciliaris seedlings (Table 3) for accessions 476, 199, 148 and 129, as it showed significant differences and superior results in relation to seedlings originating from seeds hydrated with distilled water (Table 3).

There was no significant difference between the treatments used to induce germination and the germinated seeds, there was a significant difference only between the genotypes (Table 2), which may be linked to the wide variation in the physiological potential of the seeds. Considering factors such as humidity 40%, temperature 10 °C and storage time of 13 years for all accessions evaluated in this study, it can be inferred that the genetic characteristics and quality of the lots may have been decisive in the performance variations observed between the hits. According to Marcos-Filho (2015b)MARCOS-FILHO, J. Seed Physiology of Cultivated Plants. 2nd Edition, ABRATES, Londrina, p.660, 2015b. https://www.bdpa.cnptia.embrapa.br/consulta/busca?b=ad&id=1026580&biblioteca=vazio&busca=autoria:%22MARCOS%20FILHO,%20J.%22&qFacets=autoria:%22MARCOS%20FILHO,%20J.%22&sort=&paginacao=t&paginaAtual=1
https://www.bdpa.cnptia.embrapa.br/consu...
, the physiological quality of seeds has its basis established in the genotype and that of some cultivars are less prone to deterioration, but the proportion of more vigorous seeds gradually decreases as storage time is increased. Thus, the intensity of seed deterioration will depend on the characteristics of the species, their chemical composition and genetic differences, seed quality and environmental conditions in which they are stored (Marcos-Filho, 2015bMARCOS-FILHO, J. Seed Physiology of Cultivated Plants. 2nd Edition, ABRATES, Londrina, p.660, 2015b. https://www.bdpa.cnptia.embrapa.br/consulta/busca?b=ad&id=1026580&biblioteca=vazio&busca=autoria:%22MARCOS%20FILHO,%20J.%22&qFacets=autoria:%22MARCOS%20FILHO,%20J.%22&sort=&paginacao=t&paginaAtual=1
https://www.bdpa.cnptia.embrapa.br/consu...
).

The KNO3 at different soaking times did not induce an increase in germination in Bouteloua dactyloides seeds. A fact also observed in annatto seeds (Bixa orellana) stored for more than 10 years. However, in both cases, improvement was observed in the other germination variables when using this salt (Kreuser et al., 2016KREUSER, K.; KREUSER, W.C.; SARATH, G.; AMUNDSEN, K. L. Potassium nitrate alters buffalograss bur permeability. HortScience, v.51, n.12, p.1566-1572, 2016. https://doi.org/10.21273/HORTSCI11126-16
https://doi.org/10.21273/HORTSCI11126-16...
; Fernandes et al., 2021FERNANDES, A.C.; FARIA, J.C.T.; FARIA, J.M.R.; PIRES, R.M.D.O.; CARVALHO, E.R.; SANTOS, H.O.D. Use of different conditioning agents and quality evaluation of two lots of annatto (Bixa orellana) seeds. Ciência Florestal, v.31, p.808-829, 2021. https://doi.org/10.5902/1980509844156
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). The use of KNO3 is generally indicated for promoting germination and overcoming dormancy in different types of seeds, including forage (Bareke, 2018BAREKE, T. Biology of seed development and germination physiology. Advances in Plants & Agriculture Research, v.8, n.4, p.336-46, 2018. https://www.researchgate.net/profile/TuraBareke/publication/326913832_Biology_of_seed_development_and_germination_physiology/links/5b72c549a6fdcc87df798bf8/Biology-of-seed-development-and-germination-physiology.pdf
https://www.researchgate.net/profile/Tur...
; Golmohammadzadeh et al., 2020GOLMOHAMMADZADEH, S.; ZAEFARIAN, F.; REZVANI, M. Priming techniques, germination and seedling emergence in two Papaver species (P. rhoeas L. and P. dubium L., Papaveraceae). Brazilian Journal of Botany, v.43, n.3, p.503-512, 2020. https://link.springer.com/article/10.1007/s40415-020-00629-0
https://link.springer.com/article/10.100...
; Ali et al., 2021ALI, L.G.; NULIT, R.; IBRAHIM, M.H.; YIEN, C.Y.S. Efficacy of KNO3, SiO2 and SA priming for improving emergence, seedling growth and antioxidant enzymes of rice (Oryza sativa), under drought. Scientific Reports, v.11, n.1, p.1-11, 2021. https://doi.org/10.1038/s41598-021-83434-3
https://doi.org/10.1038/s41598-021-83434...
; Pereira et al., 2021PEREIRA, T.S.; JEROMINI, T.S.; NEVES, B.R.; BARROS, R.T.; MARTINS, C.C. Potassium nitrate to overcome dormancy of Urochloa humidicola common seeds. Semina: Ciências Agrárias, v.42, n.3, p.963-978, 2021. http://www.uel.br/revistas/uel/index.php/semagrarias/article/view/40397
http://www.uel.br/revistas/uel/index.php...
).

Seeds of the Poaceae family usually produce large quantities of empty seeds (Dayrell et al., 2016DAYRELL, R.L.C.; GARCIA, Q.S.; NEGREIROS, D.; BASKIN, C.C.; BASKIN, J.M.; SILVEIRA, F.A.O. Phylogeny strongly drives seed dormancy and quality in a climatically buffered hotspot for plant endemism. Annals of Botany, v.119, n.2, p.267-277, 2016. https://doi.org/10.1093/aob/mcw163
https://doi.org/10.1093/aob/mcw163...
), as well as dormant seeds, which is noticed mainly when recently harvested. The evaluation of the relative germination showed that the seed lots presented a large number of empty seeds (Table 2), decreasing even more the obtaining of quality seeds.

A trade-off can occur when there is a limitation in pollen and the effect of genetic load, i.e., an exchange between sexual and asexual reproduction (Oliveira et al., 2015OLIVEIRA, R.S; GALVÃO, H.C.; CAMPOS, M.C.R.; ELLER, C.B.; PEARSE, S.J.; LAMBERS, H. Mineral nutrition of campos rupestres plant species on contrasting nutrient-impoverished soil types. New Phytologist, v.205, n.3, p.1183-1194, 2015. https://doi.org/10.1111/nph.13175
https://doi.org/10.1111/nph.13175...
; Hewitt, 2020HEWITT, A. Genetic and environmental factors in the trade-off between sexual and asexual reproduction of a rare clonal angiosperm. Austral Ecology, v.45, n.2, p.187-194, 2020. https://doi.org/10.1111/aec.12846
https://doi.org/10.1111/aec.12846...
). These factors may affect seed development, increasing the number of empty seeds. Seeds without embryos are resulted from phylogenetic lines and can occur in different families (Dayrell et al., 2016DAYRELL, R.L.C.; GARCIA, Q.S.; NEGREIROS, D.; BASKIN, C.C.; BASKIN, J.M.; SILVEIRA, F.A.O. Phylogeny strongly drives seed dormancy and quality in a climatically buffered hotspot for plant endemism. Annals of Botany, v.119, n.2, p.267-277, 2016. https://doi.org/10.1093/aob/mcw163
https://doi.org/10.1093/aob/mcw163...
). Therefore, the low seed germination found may be due to other factors and not by this reason.

Although the KNO3 solution had no significant effect on the germination of the buffel grass seeds, it significantly increased normal seedlings, root and shoot lengths, and roots and shoot dry matter weights (Tables 2 and 3), respectively. Potassium is absorbed mainly at the vegetative growth stage; several physiological processes are affected by potassium nitrate, such as: meristematic growth, water distribution, photosynthesis, and long-distance transport (Grimme et al., 1974GRIMME, H.; BRAUNSCHWEIG, L.C.; NEMETH, K. Potassium, calcium and magnesium interactions as related to cátion uptake and yield. Landw. Forsch, v.30, n.2, p.93-110, 1974. http://agris.fao.org/agris-search/search.do?recordID=US201302778824
http://agris.fao.org/agris-search/search...
). A different result was found when the seeds were treated with water, as there was an increase in the percentage of abnormal seedlings (Table 2). This high percentage may be justified, since the seed initial reserves were probably used during the germination period for the initial establishment of the seedlings. In addition, the seed’s physiological integrity is important for their satisfactory performance (Marcos-Filho, 2015bMARCOS-FILHO, J. Seed Physiology of Cultivated Plants. 2nd Edition, ABRATES, Londrina, p.660, 2015b. https://www.bdpa.cnptia.embrapa.br/consulta/busca?b=ad&id=1026580&biblioteca=vazio&busca=autoria:%22MARCOS%20FILHO,%20J.%22&qFacets=autoria:%22MARCOS%20FILHO,%20J.%22&sort=&paginacao=t&paginaAtual=1
https://www.bdpa.cnptia.embrapa.br/consu...
).

Differences in seed vigor can lead to the formation of seedlings with greater unevenness, due to the reduced capacity to use the reserves present in the embryo’s structures, in fact affecting the growth rate and dry mass production, due to the inequality in the issue of growth of the plant between the different vigor levels (Meneguzzo et al., 2021MENEGUZZO, M.R.R.; MENEGHELLO, G.E.; NADAL, A.P.; XAVIER, F.D.M.; DELLAGOSTIN, S.M.; CARVALHO, I.R.; GONÇALVES, V.P.; LAUTENCHLEGER, F.; LÂNGARO, N.C. Seedling length and soybean seed vigor. Ciência Rural, v.51, 2021. https://doi.org/10.1590/0103-8478cr20190495
https://doi.org/10.1590/0103-8478cr20190...
). Only one of the 14 seed lots presented a significant response in the percentage of normal seedlings to KNO3 (Table 2); these seeds probably had low vigor due to the storage time. Seed deterioration is an irreversible process during the storage period (Moncaleano-Escandon et al., 2013MONCALEANO-ESCANDON, J.; SILVA, B.C.; SILVA, S.R.; GRANJA, J.A.; ALVES, M.C.J.; POMPELLI, M.F. Germination responses of Jatropha curcas L. seeds to storage and aging. Industrial Crops and Products, v.44, p.684-690, 2013. https://doi.org/10.1016/j.indcrop.2012.08.035
https://doi.org/10.1016/j.indcrop.2012.0...
).

The treatments used were favorable and the parts of the normal seedlings evaluated showed rapid and uniform growth, with little different lengths, even those from seed lots that showed low germination, in addition to presenting significant and satisfactory responses for root and root lengths shoots and dry matter weights of some genotypes (Table 3). KNO3 application is highly recommended for physiological quality evaluations of grass seeds, due to its easy absorption by plant tissues.

A significant effect in seedling length was found when using KNO3 in Johnson grass (Sorghum halepense L.) seeds, with increases in seedling root length of up to 31.8% (Baličević et al., 2016BALIČEVIĆ, R.; RAVLIĆ, M.; BALIĆ, A. Dormancy and germination of Johnson grass seed (Sorghum halepense (L.) Pers.). Journal of Central European Agriculture, v.17, n.3, p. 725-733, 2016. https://jcea.agr.hr/en/issues/article/1769
https://jcea.agr.hr/en/issues/article/17...
). Similarly, positive effects were found in root and shoot lengths and seedling weight for redroot pigweed (Amaranthus retroflexus L.) treated with KNO3 (Ravlić et al., 2015RAVLIĆ, M.; BALIČEVIĆ, R.; LUCIĆ, P.; MAZUR, P.; LAZIĆ, A. Dormancy and germination of velvetleaf (Abutilon theophrasti Medik.) and redroot pigweed (Amaranthus retroflexus L.) seeds. Herbologia, v.15, n.2, 2015. http://bib.irb.hr/datoteka/806459.03-ravlicbaliceviclucicmazurlazic.pdf
http://bib.irb.hr/datoteka/806459.03-rav...
). The seedling root and shoot length test is carried out considering that more vigorous seeds originate from more developed seedlings, with fast and homogeneous establishment in the field and more effective water and nutrient absorption from higher soil depths.

The storage condition in a relatively dry and cold environment in which the seeds were kept made it possible to maintain their viability even after so long. It was observed that genotype 144 presented a better conservation status with a higher germination rate compared to the other evaluated genotypes. Our results demonstrate that storing them under suitable conditions can reduce the speed and intensity of seed deterioration and maintain their physiological integrity longer.

CONCLUSIONS

The treatment adopted with KNO3 for the stored buffel grass (C. ciliaris) seeds did not increase the germination percentage in this experiment due to deterioration and storage time. The time in which the seeds were stored affected the quality of the lots, reducing the germination capacity of the evaluated genotypes. A high number of seeds without embryos (empty) was observed with the relative germination evaluation, reinforcing the importance of including evaluations like this in the germination test.

ACKNOWLEDGMENTS

The authors thank Rafaela Priscila Antonio for providing seeds and information on the genotypes; Embrapa for supporting the research and providing the infrastructure for experiments; Program in Plant Genetic Resources of Universidade Estadual de Feira de Santana (UEFS) for the support. The authors appreciate the research grants from Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE) and Coordenação Brasileira de Aperfeiçoamento de Pessoal de Nível Superior (CAPES; Finance Code 001).

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Publication Dates

  • Publication in this collection
    15 Apr 2022
  • Date of issue
    2022

History

  • Received
    01 Nov 2021
  • Accepted
    09 Mar 2022
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