VIGOR E EMERGÊNCIA EM CAMPO DE SEMENTES DE GIRASSOL COM ALTO
TEOR DE ÁCIDO OLEICO, NO SUDESTE DA PROVINCIA DE BUENOS AIRES
11Aceito para publicação em 30.12.2001; parte da Tese de Mestrado em
Agronomia, Área de Tecnologia de Sementes na FCA-UNCórdoba.
2Ing. Agr., Prof. Adjunta, Facultad de Ciencias Agrarias, UNMdP, C.C.
276 (7620) Balcarce, Argentina; e-mail: catebiol@balcarce.inta.gov.ar
3Lic. Prof. Titular, Facultad de Ciencias Agrarias, UNMdP; e-mail:
catebiol@balcarce.inta.gov.ar
4Estadística, Prof. Asociada, Facultad de Ciencias Agrarias, UNMdP;
e-mail: ssanmarti@balcarce.inta.gov.ar
5Ing. Agr., MSc., Jefa de Trabajos Prácticos, Facultad de Ciencias
Agropecuarias, UNC, Av. das. Valparaíso y R. Martinez, Ciudad
MÓNICA MURCIA2, ANNA PERETTI3, SILVINA SAN MARTINO4, ALEJANDRA PÉREZ5, OLGA DEL LONGO6,
JUAN ARGÜELLO7 E VICTOR PEREYRA8
RESUMO - A produção de girassol, até a pouco tempo baseava-se no uso de cultivares com alto teor de ácido linoleico, mas, nos últimos anos, a procura por óleo com conteúdo mais alto de ácido oleico tem aumentado. A produção de girassol se estabeleceu com a semeadura de cultivares de alto teor de ácido oleico, em regiões mais quentes, mas tem se tornado conveniente o cultivo em áreas temperadas, como o Sudeste de Província de Buenos Aires. Nesta região são recomendadas semeaduras antecipadas, para que o enchimento dos grãos coincida com épocas de disponibilidade hídrica e luminosidade suficientes para a obtenção de maiores rendimentos. Porém, a antecipação da semeadura pode ser prejudicada pela baixa temperatura do solo, retardando a emergência das plântulas e resultando em um estande heterogêneo. A finalidade deste trabalho foi avaliar o desempenho de sementes de quatro cultivars com alto teor de ácido oleico na área ao sul da Província de Buenos Aires, através de testes de vigor e ensaios de campo. Foram conduzidos testes de germinação, frio, tetrazólio a duas temperaturas, envelhecimento acelerado e três ensaios de campo, em condições climáticas distintas. Os dados foram analisados através de Anova usando modelos lineares generalizados e foram comparados os testes entre si e os cultivars entre si por medio de contrastes. A emergência das plântulas a temperatura ótima e sub-ótima para cultivars de alto teor de ácido oleico e de alto linoleico foi semelhante. O sucesso do estabelecimento do estande não aparenta estar relacionado à composição de ácidos graxos.
Termos para indexação: vigor, girassol, “alto oleico”, semeaduras precoces, emergência das plântulas.
VIGOR AND FIELD EMERGENCE IN “HIGH OLEIC” SUNFLOWER SEEDS, IN SOUTHEAST OF BUENOS AIRES PROVINCE
ABSTRACT - Sunflower crop was based, as yet, on high linoleic cultivars, but in the last years request for oil with higher content of oleic acid has increased, due to their dietary characteristics. At the beginning, high oleic cultivars were used to be sown in warm regions, but then the concern about growing it in temperate areas, as the south-east of Buenos Aires Province, was posed. In this region, early sowings are recommended, so that grain filling matches with a period of appropriate hydric and light conditions, as to result in greater yields. However, early sowings are limited by low soil temperature, that delays seedling emergence, resulting in heterogeneous stand establishment. The aim of this work was to evaluate seed performance of four high oleic cultivars in the southern area of Buenos Aires Province, by means of vigor tests and field trials. Germination,
Universitaria, (5000) Córdoba, Argentina; e-mail: maperez@agro.uncor.edu
6Dra., Facultad de Ciencias Agropecuarias, UNC; e-mail:
odellong@agro.uncor.edu
7Dr., Prof. Titular, Facultad de Ciencias Agropecuarias, UNC; e-mail:
nlarguello@hotmail.com
8Ing. Agr., Investigador, Director Programa de Oleaginosos, INTA, Estación
cold, tetrazolium viability, tetrazolium viability with cold, accelerated ageing tests and three field sowings at different soil temperatures were performed. Data were analyzed by Anova using generalised linear models, and tests and cultivars were contrasted among themselves. Similar seedling emergence under optimal and suboptimal temperatures for high oleic and high linoleic cultivars was recorded. The success of seedling establishment does not appear to be related to the acidic composition of seeds.
Index terms: vigor, sunflower, “high oleic”, early sowing, seedling emergence.
INTRODUCTION
Argentina is the second country in the surface sown with sunflower, (3.500.000 hectares in the cycle 1999/2000), with a production for the same period of 6.000.000 tons (Márgenes Agropecuarios, 2000). Of all the area sown in Buenos Aires Province with this crop, 30% corresponds to the south-east of this Province. Although sunflower crop was based on high linoleic cultivars, in the last years request for oil with higher content of oleic acid has increased, for its dietary and cooking characteristics (Pereyra et al., 1998 and Rivas & Matarazzo, 1998). At the beginning, high oleic (HO) cultivars were used to be sown in warm regions, where high temperatures, specially at night, caused a remarkable reduction of linoleic acid percentage, increasing oleic acid percentage (Gupta et al., 1985). However, advances in genetic breeding allowed acidic composition of sunflower seeds to be less dependent on the climatic conditions prevailing during grain filling. This fact would allow the use of high oleic cultivars in temperate regions, as the south-east of Buenos Aires Province. In this region, early sowings are recommended so that grain maturation would match a period of appropriate hydric and light conditions to assure increasing yield. However, early sowings are limited by low soil temperatures (lower than 15ºC), that delay seedling emergence, which are exposed to insect attack during a longer time, resulting in heterogeneous stand establishment (Aguirrezábal et al., 1996).
When focusing on seed production of high oleic acid content, it is necessary to have reliable vigor tests to estimate the potential of field emergence, in the especific climatic conditions of southern Buenos Aires Province. Seed technologists have recommended the use of tests that evaluate seed performance in particular and expected agroclimatic conditions for each region, by simulating in laboratory the main stress agents that operate in the field (Parvathamma et al., 1991 and Hampton, 1993)
Maeda et al. (1985) stated that accelerated ageing was effective to estimate physiological quality of seeds. Zelener et al. (1990) and Anfinrud (1997) registered that accelerating
ageing test correlated to the standard germination and field emergence.
Parvathamma et al. (1991) observed that the tetrazolium viability test identified vigorous seed lots of sunflower, classifying viable seeds according to stained area of embryos. Cold test was suitable to estimate seedling emergence, in south-eastern Buenos Aires Province, either with the classical methodology of Vienna (with compost) for early sowings, or between papers (rolled towels) for normal sowings (Murcia et al., 1998).
There are few reports about the performance of “high oleic” (HO) cultivars. Hernandez et al. (1998) tested two HO cultivars and identified significant differences in plant performance at temperatures lower than 18ºC in only one of them. Hernandez & Paoloni (1998), analyzing four hybrids, concluded that the major relation linoleic/oleic acid is directly related to better seed performance at suboptimal temperatures. It should be emphasized that all cultivars tested by those authors showed an oleic acid content lower than 35%. Germinability of cultivars with high levels (> 80%) of oleic acid at sub-optimal temperature at sowing is still unknown.
A research has been undertaken to study the behaviour of “high oleic” (HO) and “high linoleic “ (HL) cultivars at low temperatures, analyzing some quality parameters (in seeds and seedlings). As a part of this project, the aim of this work was to evaluate the seed performance of four high oleic cultivars, in south-east of Buenos Aires Province.
MATERIALS AND METHODS
Trials were carried out at the Unidad Integrada Balcarce, Buenos Aires, in 1999-2000. Samples of four cultivars classified as “ high oleic” (HO)(T 578, T870, T600, Aromo 10) and one “high linoleic” (HL) cultivar (Paraiso 20) were processed. All cultivars were produced in the same area (north of Buenos Aires Province), during the same growing cycle, as well as under similar agroclimatic conditions.
to Grosso (1992). Methylic esters of fatty acids were obtained and analyzed by gaseous chromatography, in three replicates. Relationship oleic/linoleic acids was calculated considering the quotient among the percentages of both fatty acids.
Experimental unity in laboratory tests was of 200 seeds (four replications of 50 seeds each). The tests were: germination (G) - seeds were sown on trays between paper, placed in a germination chamber at 25ºC during seven days, with light-darkness (8-16 hours), according to ISTA (1999); viability test (V) - pre-moistening of the seeds during 16 hours, in refrigerator (10ºC). Later, embryos were excised, stained in aqueous solution of 0.5%, 2,3,5-tryphenil tetrazolium chloride, at 30ºC in darkness, two hours. Classification of viable embryos was performed according to the staining pattern described by ISTA Tetrazolium Workshop (1997); viability test at low temperature - (V / Cold) - this essay was carried out in similar way to the previous test, except for embryo staining that was performed at 10ºC, during 24 hours; cold test (Cold)- seeds were sown in rolled towels, placed in containers in refrigerator at 10ºC, in darkness, for seven days. After cold treatment, seeds were transferred to a germination chamber at 25ºC, for six days in darkness. Seedlings were evaluated using the same criteria as those used for the germination test (ISTA, 1995). Cold test in towels, without other substratum, was selected to include only the variable cold in the assays; accelerated ageing(AA) - was conducted by placing seeds on a screen tray inserted into an inner chamber (plastic box), placed into an accelerating ageing (outer) chamber. Seeds were disposed in one layer on each tray, at 42ºC for 96 hours (Zelener et al., 1990). Later, seeds were sown on trays with sterilised sand, in a germination chamber at 25ºC during seven days. Seedling classification was done according to the same criteria adopted for the germination test (ISTA, 1999); field trials - seeds were sown in a typical Argiudol soil, on three dates: early, intermediate, normal, corresponding to soil temperatures of 10.4ºC, 14.5ºC and 22.3ºC respectively (average temperatures for each
sowing-emergence period). For each sowing a randomised block design of four replicates of 100 seeds was applied. Number of emerged seedlings was registered daily from seven to twenty days. Time to field emergence was recorded as the time from sowing to the time when the first pair of leaves started to spread out.
Data were analyzed by variance analysis (Anova) employing generalised linear models, because of the categorical nature of the data (McCullag & Nelder, 1989); the means of tests were contrasted among themselves (p≤ 0,05), and the means of cultivars too. The data were processed with the SAS system (SAS, 1998; Littel et al., 1991).
RESULTS AND DISCUSSION
The composition of total saturated fatty acids (palmitic and estearic) and insaturated (oleic and linoleic) are presented in Table 1. Relation oleic/linoleic of materials tested in the present work agree with breeder information. The relation oleic/linoleic of HO cultivars was clearly higher than that of cultivars processed in the previous work by Hernandez & Paoloni (1998), ranking between 0.28 and 0.7 values.
Results of laboratory tests and field trials are presented in Table 2. Significant interaction was registered among the variables, showing that cultivars behaved differently according to tests. Because of this interaction, tests were analysed separately among themselves, to determine their sensitivity to evaluate field emergence. The behaviour of each cultivar was also compared to the performance of high linoleic culti-var on each test.
Germination (G) differed from early and intermediate sowings in all the cases and confirmed that G did not estimate seed performance at field suboptimal conditions. G did not differ significantly from sowing at normal planting date, where the agroclimatic conditions were favourable. Viability, viability on cold and cold test did not differ significantly from G.
TABLE 1. Comparison of fatty acids percentage and oleic/linoleic relation of “high oleic” and “high linoleic” cultivars.
Cultivar Palmitic acid (16:0)
Estearic acid (18:0)
Oleic acid (18:1)
Linoleic acid (18:2)
Oleic/ linoleic relation
T 568 5.5 3.7 87.1 3.7 23.54
T 870 2.7 3.4 85.9 7.9 10.87
T 600 2.8 1.9 84.7 10.6 7.99
Aromo 10 2.8 2.8 82.2 12.1 6.79
Cold viability test was applied to assess differences in tolerance to low temperature between HO and HL cultivars, and unstained embryo areas were observed. The treatment did not cause a serious cell damage that would appear as unstained areas (dead cells), but it produced a lower cell respiratory activity manifested in the lighter pink color of living embryo cells than the red colour shown in a normal viability test. This test showed the same behaviour of seeds with different fatty acid composition. However, a higher cold tolerance in the HL cultivar should be expected, which presents higher unsaturated linoleic acid proportion, than HO cultivars. Accelerated ageing test (AA) showed significant difference with G in T568, T600 and Paraíso 20, with lower values. Paraíso 20 (HL) registered the lowest value, probably associated, as previously discussed, to its acidic composition. AA differed significantly from early sowing in all the cultivars. Those results are expected, since high temperature of AA test conditions is the contrary of the cold temperature in field. Effectively, stress applied to seeds in AA is similar to stress produced to crop where soil temperature exceeds 40ºC (Anfinrud, 1997). Likewise, AA did not differ from intermediate sowing in three HO cultivars, and in the normal sowing in two HO cultivars, so this was the only test that evaluated, although partially (on three out of five cases), field performance at temperature somewhat lower than optimal. Considering that AA imposed very strong stress conditions, high germination of seeds in this test expressed their high vigour that was also reflected in a good performance in the field. Therefore, AA test was not reliable to differentiate cul-tivar behaviour on the field at low temperature.
Cold test recorded similar values to results of G, viability and viability on cold. In stand establishment, cold test did not
differ from emergence in the normal sowing date, but it differed significantly from early and intermediate sowings. These results agree partially with previous results registered in the zone for HL cultivars (Murcia et al., 1998), and may confirm that these cold test conditions were not stressful enough to show field behaviour of cultivars at sub-optimal temperatures. According to these results, it would appear that temperature of 10ºC for seven days,as the only stress factor, did not affect germinability. It would be convenient to adjust cold test conditions in future trials, applying lower temperature (5-7ºC) or more days in cold conditions and sand-soil compost. On the other hand, the strong and uniform reduction of emergence in early sowing could be explained, because of the increased exposition time of seedlings to unfavourable biotic agents (insects, fungi) or abiotic (climatic), that affected stand establishment, in spite of the care taken (row protection with nets and application of phytosanitary products). It was proved that real field conditions were more complex than the simple effect of temperature.
Regarding HO cultivars quality, significant difference did not manifest in laboratory tests with high linoleic cultivar (control), except in accelerated ageing test, that affected this last cultivar. In field trials, emergence of HO cultivars did not differ from HL cultivar at any sowing date. At lowest temperature, Paraíso 20 showed higher emergence, probably related with its HL cultivar condition, but this value was not significantly different from HO emergence. It was verified that seedling establishment of HO cultivars in south-east of Buenos Aires Province did not appear closely associated with their acidic composition. Variability observed on emergence of these cultivars at low temperatures can be related to other characteristics, as pericarp morphology and anatomy, that TABLE 2. Results of the viability tests (% of viable seeds) and of germination, vigor and field tests (% normal
seedlings).
Test Cultivar G
(%)
AA (%)
Cold (%)
V (%)
V/ cold (%)
ES (%)
IS (%)
NS (%)
T 568 94 74 • 95 94 90 38 •♦ 64 •... 92 ♦
T 870 90 66 • 88 97 92 39 •♦ 57 • 84 ♦
T 600 95 92 93 100 98 36 •♦ 72 • 93
Aromo 10 91 80 85 91 87 36 •♦ 57 •♦ 81
Paraiso 20 (HL) 90 58 • 87 96 92 46 •♦ 66 •♦ 85 ♦
The symbols indicate significant differences (SD) between the compared tests (p≤0.05):
•SD between G and AA, ES, IS;
♦ ♦♦
♦SD between AA and ES, IS, NS;
SD between Cold and ES, IS.
affect in different ways the stress promoted by cold and oxygen transfer during germination (Hernandez et al., 1998). Culti-var T600 (84.7% of oleic acid) manifested the highest vigor for its good performance, except at very unfavourable field condition, as early sowing.
CONCLUSION
The germinative behaviour of “high oleic” and “high linoleic” cultivars, at optimal and suboptimal sowing temperatures, in south-east of Buenos Aires Province, was similar.
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