FACTORS AFFECTING GERMINATION AND PREGERMINATIVE TREATMENTS OF Lupinus montanus SEEDS

Jeanette Acosta-Percástegui and Dante Arturo Rodríguez-Trejo

Jeanette Acosta-Percástegui. Forest Engineer and Graduate Student, Universidad Autónoma Chapingo (UACh), Mexico.

Dante Arturo Rodríguez-Trejo. Forest Engineer, UACh, México. M.Sc. in Silviculture and Forest Management, Colegio de Postgraduados, Mexico. Ph.D. in Forest Restoration Ecosystems, University of Florida, EEUU. Profesor, UACh, México. Address: División de Ciencias Forestales, UACh, Chapingo, Edo. de México, C.P. 56230, Mexico. e-mail: dantearturo@yahoo.com

Resumen

Se estudió la germinación de la semilla de Lupinus montanus, tomando en cuenta los siguientes factores: régimen de temperaturas día/noche, luz y tratamiento pregerminativo. Para la germinación, resultó significativa la interacción entre los factores temperatura, luz y tratamiento pregerminativo. Los mayores valores de germinación se hallaron en el régimen de temperatura 20/15ºC, con escarificación química (ácido sulfúrico) durante 15 minutos, tanto con luz (100% de germinación) como sin luz (98% de germinación). La interacción entre temperatura y luz también fue significativa. En este último caso, la mayor germinación se alcanzó en el régimen de temperatura 20/15ºC, tanto con luz como sin luz (72,5 y 73,8%, respectivamente). A mayores temperaturas sin luz, la germinación fue mayor (41,2% a 25/20ºC, y 33,4% a 30/25ºC), que con luz (17,4% a 25/20ºC y 12,8% a 30/25ºC); lo cual indica que los micrositios con sombra pudieran beneficiar la germinación de la semilla de la especie a temperaturas altas.

Summary

The germinative characteristics of Lupinus montanus seeds were studied, taking into account the following factors: day/night temperature regime, light, and pregerminative treatment. The interaction between temperature, light and pregerminative treatment was significant for germination. The best germinations were found in the 20/15ºC temperature regime, with chemical scarification (sulfuric acid) during 15min, both under light (100% germination) and in darkness (98%). The interaction between temperature and light was also significant, with the best germination results in the 20/15ºC temperature regime, both with and without light (72.5 and 73.8%, respectively). At higher temperatures, the germination in absence of light was greater (41.2 and 33.4% at 25/20ºC and 30/25ºC, respectively) than under light (17.4 and 12.8% at 25/20ºC and 30/25ºC, respectively). This indicates that shady microsites can benefit germination of the species at higher temperatures.

Resumo

Estudou-se a germinação da semente de Lupinus montanus, tomando em conta os seguintes fatores: regime de temperaturas dia/noite, luz e tratamento pré-germinativo. Para a germinação, resultou significativa a interação entre os fatores temperatura, luz e tratamento pré-germinativo. Os maiores valores de germinação se acharam no regime de temperatura 20/15ºC, com escarificação química (ácido sulfúrico) durante 15 minutos, tanto com luz (100% de germinação) como sem luz (98% de germinação). A interação entre temperatura e luz também foi significativa. Neste último caso, a maior germinação se alcançou no regime de temperatura 20/15ºC, tanto com luz como sem luz (72,5% e 73,8%, respectivamente). A maiores temperaturas sem luz, a germinação foi maior (41,2% a 25/20ºC, e 33,4% a 30/25ºC), que com luz (17,4% a 25/20ºC e 12,8% a 30/25ºC); o qual indica que os microsítios com sombra podem beneficiar a germinação da semente da espécie a temperaturas altas.

Keywords / Chemical Scarification / Light / Seed Ecology / Temperature /

Received: 06/10/2005. Modified: 07/20/2005. Accepted: 07/21/2005.

Introduction

Lupinus montanus Kunth is a perennial plant, woody only at the base, with a height of up to 1m and compound, palm shaped leaves, blue and white colored flowers arranged in racemes, and legumes from 4 to 5cm in length (Dunn, 2001). The species is found in forests of pine (Pinus hartwegii Lindl, for example), oak (Quercus spp.), true fir (Abies religiosa (H.B.K) Cham. et Sch.) and alpine prairie, between 2500 and 4100masl (Benitez, 1986). It is present in burned sites, like in the State of Mexico (Rzedowski, 1978), which makes the species a candidate for restoration of burned forest areas.

There are over 400 species in the genus Lupinus that are distributed throughout North and South America (Gross, 1982). However, despite the existence of various of such species in Mexico and their potential use in restoration plantations and agroforestry systems, few studies have been made of this genus.

In Guatemala, L. montanus is used to increase soil fertility before resowing, given its capacity for nitrogen fixation (CIIFAD, 2001). In New Zealand and South America, Lupinus spp. have also been used as nitrogen fixation agents in the fertilization of forest plantations, where they also act as nurse species, as well as honey production (Gross, 1982; Shepherd, 1986). In addition, due to its adaptative capacity and because its content of protein and oil is higher than in other species cultivated at altitudes higher than 2000masl, Lupinus mutabilis can be used as a food source (Concha, 1992). In Mexico, some species are used as forage, although the genus includes some toxic species (Aguilar and Zolla, 1982).

There is physical dormancy in the seed of L. montanus, as in many legumes, given that its germination improves after the application of pregerminative treatments to soften the seed coat (Rodríguez and Rojo, 1997). The potential uses of the species and the conditions under which it can be grown, justify the search for a better understanding of its seed germination, to enable the efficient propagation of the species or to carry out direct sowing in the field. Therefore, the purpose of the present study was to investigate the effect of temperature, light and sulfuric acid scarification on the potential germination of the species, as well as their possible interactions.

Materials and Methods

Seed collection

Seeds were obtained in the Parque Nacional Cumbres del Ajusco, Delegación Tlalpan, Distrito Federal, Mexico. It is located at 19º12'-19º12'50"N and 99º14'35"-99º16'20"W, in a Pinus hartwegii forest, on a slope of the NW side of the Ajusco volcano, at 3200masl. Mature seed collection from brown pods was carried out between September and October 2002, from 12 plants of one population, over an area of 0.25ha.

Germination

Germination was recorded daily until no further germination was observed during 30 days. The seeds were considered to germinate when the radicle had reached the length of the seed. The seeds which produced radicles or cotyledons with malformations were not considered. During the tests, the seeds were watered with distilled water and 3% Captan solution.

Experimental design

The laboratory work was performed in the Forest Seeds Laboratory of the División de Ciencias Forestales, Universidad Autónoma Chapingo, Mexico, between October and December 2002, taking into consideration the following factors and levels: day/night temperature regime (four levels): 30/25ºC; 25/20ºC; 20/15ºC and 15/10ºC; light, with a 12h photoperiod (two levels): with and without light; and pregerminative treatment (five levels): immersion in sulfuric acid (H2SO4) at 98% for 0 (control), 5, 15, 25 and 35min. Seeds were washed afterwards.

Twenty seeds were used for each experimental unit (Petri jars with agrolite as a substrate), with 5 repetitions for each combination of levels of the factors, using a total of 4000 seeds. The experiment was carried out in Conviron controlled environment chambers. Incandescent and fluorescent lights were used simultaneously. For the option without light, Petri jars were covered with aluminum foil.

The experimental design was a randomized complete block design, with the blocks nested within the temperature factor. The other factors were light and scarification treatment.

Statistical model and statistical analysis

The following statistical model was used:

yijklm = µ+ai+ai(bj)+gk+dl+(ag)ik+(ad)il+(gd)kl+ai(bj)gk+ ai(bj)dl+(agd)ikl+ai(bj)gkdl+eijklm

where µ: overall mean, ai: effect of the i-th level of the temperature factor, ai(bj): effect of the j-th level of the block nested within the i-th level of the temperature factor, gk: effect of the k-th level of the light factor, dl: effect of the l-th level of the pregerminative treatment factor, and eijklm: experimental error. The combinations of factors represent interactions.

Temperature, light and pregerminative treatment were considered to have fixed effects, as well as the interactions in which the blocks were not present. The blocks and their interactions were considered to have random effects.

The analysis of variance was performed with Proc Mixed of SAS, and the Tukey test was performed to determine differences among treatments.

Results and Discussion

Germination

All of the applied treatments and their interactions were statistically significant. Figure 1 illustrates the accumulated germination for the best treatment. In the temperature, light and scarification treatment interaction the best conditions (p=0.0004) were found to be the 20/15ºC temperature regime, with chemical scarification during 35 minutes, both with (100% germination) and without light (98% germination). For all the combinations of light and scarification treatment (p=0.0001), the best germination was obtained in the day/night 20/15ºC regime (Figure 2a and b). The worst condition for germination (1%) was observed in the day/night 25/20ºC temperature regime, in the presence of light and without chemical treatment (Figure 2a).

In general terms, at each temperature level, with or without light, it was observed that the longer the time of scarification, the greater the resulting germination. In the treatments of 15/10ºC, 25/20ºC and 30/25ºC with light, the germination after chemical treatments for 5 and 15min was similar.

Under absence of light, the best temperature regime was also found to be 20/15ºC. As with the condition under light, the greater the time of scarification, the higher the values of germination. In all of the temperature regimes, the germination after scarification during 15 and 25min was similar. Without chemical treatment, germination was minimal (6%).

The tendencies observed indicate the 20/15ºC regime as optimal for germination, and the reduction of the latter at higher or lower temperatures indicates the approach to the maximum and minimum cardinal temperatures, respectively.

Tendencies similar to those described have been found in Lupinus arboreus in the USA, for which MacKay et al. (2001) found that the optimal temperature for germination is 18-24ºC, with scarification by means of concentrated sulfuric acid, while the longer the time of scarification (up to 60min), the greater the germination. Kaye and Kuykendall (2001) found that for Lupinus sulphureus ssp. kincaidii, it is necessary to apply mechanical scarification and cold stratification (4ºC for 4 to 8 weeks). The maximum germination was 95% with seed from one population and 55% from another.

In its natural environment, in the north of California, USA, the seed of Lupinus arboreus is consumed by a mouse known as deer mouse (Peromyscus maniculatus) (Wozniak, 2000). This rodent is also present (Ceballos and Galindo, 1984) in the natural environment from which L. montanus seeds were obtained for the present study, in which a scarification treatment was applied. Thus, the seeds consumed by this animal become scarified as they pass through its digestive tract. P. maniculatus could provide a natural chemical scarification, at least to a limited degree, given that according to Aguilar and Zolla (1982) the seed contains toxic agents such as lupanine.

A greater germination has been documented in legumes with physical dormancy which are consumed and excreted by animals, for example, Acacia tortilis (Forsk.) Hayne (Lamprey, 1967) and A. nilotica (Linn.) (Miller, 1995). However, the effect may be a result not only of the gastric juices, but also of partial mastication and of the higher temperatures and moisture to which the seeds are subjected when they come in contact with the feces (Baskin and Baskin, 1998).

Furthermore, P. maniculatus may contribute to the dispersal of the seed, and upon burying it, or placing it in shady microsites, provide it with conditions of little light which favor germination at high temperatures, such as the 30/25ºC and 25/20ºC day/night regimes with scarification for 35min (Figures 2a, b).

The fire may act as a scarification agent for several species of Lupinus. Martínez (in press), studying Lupinus bilineatus, refers a germination equal to 38.8% for fire-scarified seeds, and 17.5% for the control seeds, both in a 20/15ºC day/night temperature regime.

With respect to the greater germination observed under conditions of darkness and elevated temperatures, Pons (1992) considered that the variation among species in the seed germination response to light could be due to the variation in quantity and type of phytochrome. The Frl (induced by exposure to red light) is considered the biologically active form which induces the synthesis of enzymes essential for germination. The exposure to red light converts the phytochrome to its physically active form (Frl), and germination takes place. The exposure to infrared irradiation reconverts the phytochrome to its inactive form (Fr) and germination is blocked (Copeland and McDonald, 1995).

The germination of the majority of seeds can be inhibited by long exposure to light. This response is the so called response to high radiation. The interconversion among phytochrome types is involved in this, but how it takes place is unknown. The negative photoblastic seeds, in which germination is inhibited by light, have this response highly developed. However, brief exposure to light and to low irradiation are not inhibitory, and may even stimulate the germination of this type of seed, although they are considered as not germinating in the presence of light. (Lambers et al., 1998).

Finally, germination is heavily influenced by the intensity, duration and quality of the light (Copeland and McDonald, 1995), as well as other factors such as water, aeration and temperature, and their interactions.

Conclusions

Germination was affected by the interaction of temperature, light and scarification treatment. The scarification treatment by means of immersion in sulfuric acid for 35min led to the best germination of Lupinus montanus. The seeds of this species germinate better under the 20/15ºC temperature regime, both with and without light (100 and 98%, respectively). The interaction of the temperature and light suggests a partial inhibitory effect of the infrared radiation in the germination. The results of the present study suggest that the shady microsites in the field could reach higher values of germination of the species, given the lower temperatures and solar radiation. The results of the present study and others suggest that Peromyscus maniculatus could be a natural scarification agent and aid in the dispersal of the seed, placing the seeds in shady areas or burying them, providing low light conditions which can promote germination.

Acknowledgements

The authors thank the following Mexican organizations for their support: CONACYT-CONAFOR (Project 2002-C01-6181), CONACYT (Installation Project I35626-B), the Communities of San Miguel and Santo Tomás Ajusco, and the Forest Sciences Division, University of Chapingo, Mexico.

References

1.Aguilar CA, Zolla C (1982) Plantas tóxicas de México. IMSS. México. 271 pp.        [ Links ]

2.Baskin CC, Baskin JM (1998) Seeds. Ecology, biogeography, and evolution of dormancy and germination. Academic Press. San Diego, CA, USA. 666 pp.        [ Links ]

3.Benitez BG (1986) Árboles y flores del Ajusco. MAB-IE-MHNCM. México. 183 pp.        [ Links ]

4.Ceballos GG, Galindo LC (1984) Mamíferos silvestres de la Cuenca de México. Limusa. México. 299 pp.        [ Links ]

5.CIIFAD (2001) Annual report on agroforestry, 1999-2000. Cornell International Institute for Food, Agriculture and Development. Cornell University. Ithaca, NY, USA. 9 pp.        [ Links ]

6.Concha LS (1992) Introducción y selección del tarwi (Lupinus mutabilis Sweet) en el Valle de México. Tesis. Colegio de Postgraduados. Montecillo, México. 90 pp.        [ Links ]

7.Copeland L, McDonald MB (1995) Seed Science and Technology. Chapman and Hall. New York, USA. 409 pp.        [ Links ]

8.Dunn DC (2001) Lupinus L. In Rzedowski J, Rzedowski G (Eds.) Flora Fanerogámica del Valle de México. CECSA. México. pp. 298-299.        [ Links ]

9.Gross R (1982) El cultivo y la utilización del tarwi: Lupinus mutabilis Sweet. Producción y protección vegetal 36. FAO. Rome, Italy. 236 pp.        [ Links ]

10.Kaye TN, Kuykendall K (2001) Effects of scarification, cold stratification on germination of Lupinus sulphureus ssp. kincaidii. Seed Sci. Technol. 29: 663-668.        [ Links ]

11.Lambers HF, Chapin III S, Pons TL (1998) Plant Physiological Ecology. Springer. New York, USA. 540 pp.        [ Links ]

12.Lamprey HF (1967) Notes on the dispersal and germination of some tree seeds through the agency of mammals and birds. East African Wildlife J. 5: 179-180.        [ Links ]

13.MacKay WA, Davis TD, Sankhla D (2001) Influence of scarification and temperature on seed germination of Lupinus arboreus. Seed Sci. Technol. 29: 543–548.        [ Links ]

14.Martínez-José M. Ecología de la semilla de Lupinus bilineatus. Tesis. Universidad Autónoma Chapingo. Chapingo, México. (In Press).        [ Links ]

15.Miller MF (1995) Acacia seed survival, seed germination and seedling growth following pod consumption by large herbivores and seed chewing rodents. African J. Ecol. 33: 194-210.        [ Links ]

16.Pons TL (1992) Seed responses to light. In Fenner M (Ed.) Seed: The ecology of regeneration in plant communities. CABI. Wallingford, UK. pp. 259-283.        [ Links ]

17.Rodríguez DA, Rojo C (1997) Estudio de la semilla del arbusto Lupinus montanus H.B.K. (Leguminosae) Revista Chapingo, Serie: Ciencias Forestales III: 39-45.        [ Links ]

18.Rzedowski J (1978) Vegetación de México. Limusa. México. 432 pp.        [ Links ]

19.Shepherd KR (1986) Plantation silviculture. Nijhoff. The Hague, The Netherlands. 322 pp.        [ Links ]

20.Wozniak J (2000) Reversing invasion of Lupinus arboreus, (yellow bush lupine) an invasive species of northern California sand dune communities. www. hort.agri.umn.edu/h5015/00papers/wozniak.htm        [ Links ]