RESEARCH WORK

Combined effect of scarification and temperature on the germination of herbaceous legume seeds

J. Reino¹, J. A. Sánchez², Bárbara Muñoz² , Yolanda Gónzalez¹ y Laura Montejo<sup>2

1</sup>Estación Experimental de Pastos y Forrajes "Indio Hatuey". Central España Republicana, CP 44280, Matanzas, Cuba
E-mail: jreino@indio.atenas.inf.cu
²Instituto de Ecología y Sistemática, La Habana, Cuba

ABSTRACT

Seeds from five herbaceous legumes with different collection times were used: Indigofera sp., Desmanthus virgatus, Clitoria ternatea, Crotalaria sp. and Centrosema pubescens, from the genebank of the Experimental Station of Pastures and Forages "Indio Hatuey", Matanzas, Cuba. A simple classification experiment with factorial arrangement and five replications (25 seeds per each) was designed, in order to evaluate the combination of four pregerminative treatments: intact seeds (control); water at 80ºC for 2' (Water 2'); 96% H2SO4 during 5' (Acid 5') and 96% H2SO4 for 10' (Acid 10'), with temperature alternance (25/30ºC, 25/35ºC and 25/40ºC). The highest germination percentages in all species were obtained at the alternate temperature 25/30ºC, and the scarification treatments were adequate to eliminate the exogenous dormancy present in each of the species. The best combination was concluded to be the alternate temperature 25/30ºC with the acid scarification in all species, except in Crotalaria sp., in which water at 80ºC for 2' combined with 25/30ºC turned out to be better.

Key words: Germination, legumes, scarification.

INTRODUCTION

The application of pregerminative treatments, such as thermal or acid scarification, is part of the traditional agricultural methodology to increase and accelerate the germination of fresh seeds from legumes which have exogenous dormancy due to impermeability of seed coats to water (Nikolaeva et al., 1985). With this purpose, some authors have studied the effect of the combination of scarification and temperature on legume seed germination, such as Albizia lebbeck, Gliricidia sepium and Bauhinia purpurea (Reino et al., 2008).

In this sense, treatments should be applied that in addition to stimulating germination, increase plant vigor during emergence and thus ensure later regeneration, which should be a permanent task in all genebanks.

Among the most used ones are hydration-dehydration treatments (Sánchez et al., 2001; Sánchez et al., 2007). In Cuba remarkable increases have been obtained in seed germination as well as seedling establishment of several forage species, such as Macroptilium atropurpureum Urb (Orta et al., 1983) and Crotalaria spectabilis (González et al., 2006) and of some trees such as A. lebbeck and G. sepium (González et al., 2009).

Due to the above-explained the objective of this work was the determination of the optimum combination of temperature and scarification treatments for the seeds from Indigofera sp., Desmanthus virgatus, Clitoria ternatea, Crotalaria sp. and Centrosema pubescens, as well as its effect on germination.

MATERIALS AND METHODS

Plant material. Seed from five species of herbaceous legumes with different collection times were used: Indigofera sp. (1998), D. virgatus (1998), C. ternatea (1999), Crotalaria sp. (1999) and C. pubescens (1997), from the Experimental Station of Pastures and Forages "Indio Hatuey", which were stored under controlled conditions (20 ± 2ºC) until they were used on January, 2002.

Design and treatments. A simple classification experiment with factorial arrangement and five replications (25 seeds each) was designed. Four pregerminative treatments were combined: intact seeds (control); water at 80ºC for 2' (Water 2'); 96% H2SO4 during 5' (Acid 5') and 96% H2SO4 for 10' (Acid 10'), and temperature alternance (25/30ºC, 25/35ºC and 25/40ºC), with eight hours for the highest temperature and 12 hours for 25ºC, and a four-hour transition.

Studied variables. The final germination percentage (G) was determined and the TZ test (ISTA, 1999) was practiced on the seeds that did not germinate, in order to establish the percentage of dead (M) and dormant (D) seeds. The moisture content was also determined through drying for 17 hours in an oven maintained at 103 ± 2ºC (ISTA, 1999).

The germination tests were conducted on Petri dishes (9 cm diameter), which were placed in growth chamber (Gallenkamp, London) with fluorescent 40-W lamps located 20 cm above the level of the dishes, with a photoperiod of 8 hours-light, which coincided with the highest-temperature thermoperiod.

Data analysis. The data expressed in percentage were transformed into arcsin ?% and were processed by simple classification ANOVA. A Duncan's test was applied (P<0,05) to detect differences among means.

RESULTS AND DISCUSSION

Seed moisture content. The seeds from the five studied species showed a moisture content that varied between 7,9 and 11,8% (table 1), for which they belong to the orthodox category initially proposed by Roberts (1973). The values of this indicator were close to the ones reported for fresh legume seeds, which varied between 7 and 11% and that is possibly due to the high impermeability of the seed coats in these species, important aspect for avoiding variations in the moisture content, because of the storage environment (Nikolaeva et al., 1985).

Germination test. Most of the intact seeds (control) did not germinate or showed very low final germination values, when they were put in the three essayed thermoperiods. However, the dormant seed percentage in most species with the different treatments had an inverse performance to the final germination percentage, except in C. pubescens, which was lower. On the other hand, in the control the dead seed percentage was very low for Indigofera sp. and relatively low in C. ternatea and D. virgatus. This last indicator increased in most cases when the seeds were subject to pregerminative treatments and as the substratum temperature increased (table 2).

In general, in all the studied species the factor pregerminative treatment was the most influential on germination (table 3). In three species there was a highly significant interaction (P<0,001) among germination, temperature and pregerminative treatment (Indigofera sp., C. ternatea and Crotalaria sp.) and in the other two (D. virgatus and C. pubescens) the interaction was significant (P<0,01) between germination and such treatment.

In Indigofera sp., D. virgatus and C. pubescens the best results for increasing germination were reached when their seeds were subject to scarification in sulfuric acid during 10 minutes and were placed at 25/30ºC; while for C. ternatea they were obtained at 25/40ºC for 5 minutes, without differing from 25/30ºC. In Crotalaria sp. the scarification in water at 80ºC during 2 minutes and planting at 25/30ºC was more effective for this purpose. These results proved the effectiveness of scarification treatments (acid or thermal) to eliminate the dormancy imposed by the seed coats of fresh seeds from the studied species, and in general are in correspondence with the ones obtained by other authors in Cuba and fresh legume seeds (Muñoz et al., 2009).

The best combination was concluded to be the alternate temperature 25/30ºC with acid scarification, in all species, except Crotalaria sp. for which water at 80ºC during 2' combined with 25/30ºC turned out to be the best.