Effect of hot water on the germination of seeds from Leucaena leucocephala cv. Peru
Yolanda González y F. Mendoza
Estación Experimental de Pastos y Forrajes "Indio Hatuey". Central España Republicana, CP 44280, Matanzas, Cuba
In a simple classification design the effect of the pregerminative treatment with water at 80ºC for two minutes, on the germination of seeds from Leucaena leucocephala cv. Peru stored under cold-storage room and ambient conditions, for seven years, was studied. The presence of moderate dormancy was proven, with a germination percentage of 67,3% in the newly harvested seed, which was lower than the germination potential shown through their high viability (98,2%). Under controlled and ambient conditions germination showed highly significant differences for the storage months (P<0,001) and the highest values without applying pregerminative treatment were achieved at 12, 42 and 48 months (77,6; 71,8 and 75,7%) and at 18 months (81,8%), respectively. The application of water at 80ºC for two minutes produced significant increases (P<0,001) in germination with regards to the untreated seed and under controlled conditions it was higher at 12, 24 and 48 months (98,6; 99,6 and 98,5%) and under ambient conditions at 6, 12 and 18 months (96,2; 97,7 and 97,7%). It is concluded that the newly harvested seeds from L. leucocephala cv. Peru show around 30% dormancy and can increase their germination by applying water to them at 80ºC for two minutes.
Key words: Storage, germination, Leucaena leucocephala, treatment of seeds
Leucaena leucocephala, a species that has been successfully adapted in Cuba, is used nowadays as animal feed, which is due to its excellent nutritional quality and its high palatability and digestibility (Shelton, 2000). Among the commercial varieties is the cv. Peru, which has been used in protein banks to supplement sheep (Espinosa, Araque, León, Quintana and Perdomo, 2001), as protein supplement to feed goats (Banda and Ayoade, 2004) and in semi-estabulated systems for sheep fattening (Mazorra, Borroto, Pérez, Fontes and Borges, 2004).
This cultivar in Cuba produces a high quantity of seeds, higher than 600 kg/ha (Pérez, Matías, González and Alonso, 2006), and the cheapest and most practical form for its propagation is considered to be the botanical seed (Torres, Alvarado, Chacón, Zerpa and Romero, 2002); although they show physical dormancy due to the impermeability of their seed coats, according to the description made by Willan (2000) and Kozlowski and Pallardy (2002) for the trees of the dry tropic, and the reports in Albizia lebbeck (Navarro, 2003). Thus, González, Hernández and Mendoza (1998) refer, for L. leucocephala cv. Cunningham, up to 80% dormancy.
Some researchers have recommended different methods for softening the seeds, among which is the treatment with hot water for five minutes (Teles, Alves, Oliveira and Bezerra, 2000) and two minutes (González et al., 1998). The latter reported satisfactory results with this treatment in seeds of the cultivar Cunningham stored for more than 10 years, which also coincides with the reports made by Toral and González (1999) in seeds from several trees.
In this work the germination performance of seeds from L. leucocephala cv. Peru was studied under two storage conditions, with the application of water at 80ºC for two minutes during seven years.
MATERIALS AND METHODS
Treatments and design. A simple classification design and four replications were used, to study the following treatments: untreated seed (control) and seed treated with water at 80ºC for two minutes applied before the beginning of the germination test, at 0, 6, 12, 18, 24, 30, 36, 42, 48, 58, 73, 81 and 85 months (approximately seven years).
Procedure. The seeds were from production areas. Their collection was carried out in November, 1984 and they were dried under roof; a part was stored in a cold-storage room (controlled conditions) and the other under ambient conditions. The germination was carried out according to the rules of ISTA (1985).
Measurements. The germination percentage was measured. The comparisons between the means were made through the multiple range test (Duncan, 1955). All the percent values were transformed according to sen-1 Ö%.
RESULTS AND DISCUSSION
The performance of germination during the storage under controlled and ambient conditions is shown in tables 1 and 2, respectively.
Highly significant differences were obtained (P<0,001) in germination in the months studied, in the control as well as with the application of water at 80ºC/2' in both storages. L. leucocephala cv. Peru showed an increase of germination when no treatment was applied, especially in the storage under ambient conditions, motivated by the increase of permeability of the seed coats, which was favored by the environmental conditions (higher temperature and humidity). The results in Teramnus labialis, and the works carried out with other tropical legumes, such as Stylosanthes guianensis, showed an increase of the permeability of seed coats during storage (Pérez et al., 2006).
In the case of the control under controlled conditions the highest values were found at 12, 42, 48 and 58 months, and afterwards this indicator decreased until reaching 14,6% at 85 months. When water was applied at 80ºC the germination was 89,7% in the newly harvested seed, higher than the control (67,3%). The highest values were observed at 12, 24 and 48 months, although they decreased afterwards, with the lowest value at 85 months (25,1%). There were increases in germination higher than 20% between 0 and 48 months with the pregerminative treatment applied (table 1).
Under ambient conditions there was also an increase until 18 months, moment in which the highest value was obtained (81,8%), with a later decrease and the lowest value was reached at 85 months (4,5%). The application of water at 80ºC for two minutes favored the highest germination percentages at 6, 12 and 18 months (96,2; 97,7 and 97,7%). The germination increases were higher than 20% from 0 to 12 months and between 12,8 and 16,9% from 18 to 48 months (table 2); they were lower than those obtained in a similar period when this treatment was applied to the seeds stored under controlled conditions. Some authors, such as Duguma, Kang and Okali (1988), state that the storage at high temperatures favors the elimination of the impermeability of seed coats and originates higher germinations than low temperatures (35 vs 25%). Cobbina, Kolawole and Atta-Krah (1990) reported a similar performance when comparing -4ºC to 30-45ºC.
In this work the deterioration of the seeds during storage was shown, due to the low germination values at 85 months, under both conditions. The increases of germination with the application of hot water were because of a sudden decrease of hardness, which has been reported by other authors. Thus, González et al. (1998) obtained up to 95% germination in the cv. Cunningham. Toral and González (1999) and González and Navarro (2001) reached positive results in other seeds from trees; while Sánchez, Reino, Muñoz, González, Montejo and Machado (2005) recommended a combination of treatments with water at 80ºC/2' plus hydration-dehydration (28-72 hours).
The newly harvested seeds of L. leucocephala cv. Peru showed about 30% dormancy, due to their hard coat, and even at 85 months they showed between 14 and 25% hardness under ambient and control conditions, respectively. To apply in both storages, the treatment with hot water at 80ºC to the seeds for two minutes before being sown is suggested, which ensures increases of germination under similar conditions, until 85 months.