RESEARCH WORK

Phenological performance of 23 Leucaena spp. accessions

Hilda B. Wencomo¹ y R. Ortiz²

¹Estación Experimental de Pastos y Forrajes "Indio Hatuey" Central España Republicana, CP 44280, Matanzas, Cuba

E-mail: hilda.wencomo@indio.atenas.inf.cu

²Instituto Nacional de Ciencias Agrícolas, La Habana, Cuba

ABSTRACT

Twenty three Leucaena spp. accessions of a collection of 180 were evaluated, in order to characterize the performance of their phenological patterns in the establishment stage; the plants were sown at a distance of 6 x 3 m between rows and between plants. The number of pinnae per leaf and of pinnule per pinna was counted; in addition, the length and width of the pinnule were measured, and the quantity of legumes per capitulum, the length and width of the pods were determined. The form of the pinnae, the type and position of the glands and the color of he flowers were taken into consideration. The emergence of flowers and fruits was different among the species of this genus, and it occurred only annually in some of them. The accessions of each species had a similar performance, in the rainy, as well as the dry season, except L. diversifolia CIAT-17503, L. macrophylla CIAT-17233 and L. esculenta CIAT-17229 (which remained in vegetative stage). Likewise, the individual flowers of the Leucaena species and accessions were observed to be generally small. It is concluded that there are differences among the species and accessions evaluated in this stage; as well as in the performance of their flowering and fructification patterns.

Key words: Evaluation, phenology, Leucaena spp.

INTRODUCTION

A clear understanding of phenological events (flowering, fructification and leaf production) is necessary for the efficient planning of seed collections. Phenology is also important to understand the natural or spontaneous hybridization events, interactions with pollinators, seed dispersal and psyllid defoliator, as well as the evaluation and population dynamics of the species.

The main characteristics of every phenological pattern are: frequency, amplitude (response intensity), duration (short or large), date and synchrony in which it is expressed. According to Hughes (1998), the phenology data for the Leucaena species are limited to abstracts at species level, only based on data from observations obtained in expeditions of seed collection.

This author also states that there are few detailed studies per species; however, Bendeck and Foroughbakch (1988) for the case of L. greggii, showed data from herbarium species (natural populations) and observations made in different zones, such as Hawaii (Brewbaker, 1998) and Taiwan (Pan, 1988), where the collections from this genus were cultivated as exotic. This situation still persists. For such reason, this study was conducted in order to characterize the performance of the phenological patterns of the evaluated accessions in the establishment stage. (Wencomo and Ortiz, 2010)

MATERIALS AND METHODS

Location of the experimental area. The study was conducted in areas of the Experimental Station of Pastures and Forages «Indio Hatuey», which is located at 22º 48' and 7'' latitude north and 79º 32' and 2'' longitude west, at an altitude of 19,9 masl, in the Perico municipality, Matanzas province, Cuba (Academia de Ciencias de Cuba, 1989).

Climate characteristics. In the last 15 years the average annual temperature of the zone was 24,3ºC; July was the hottest month (28,6ºC) and January the coldest one (20,6ºC).

The maximum temperatures reached 33,4ºC in August and the minimum temperatures were down to 14,2ºC in January. The average sum of annual rainfall was 1 331,18 mm, with the highest value in June (235,8 mm) and the lowest one in February (27,4 mm). The rainfall during the rainy season (May-October) represented, as average, 79,8% of the total annual volume. The evaporation in the zone increased since January with maximum values in April (220 mm). Annual average relative humidity was 82,6%, with the highest value in July (89,0%) and the lowest one in April (75,5%).

Soil characteristics. The trial was conducted on a plain topography soil, with 0,5 to 1,0% in slope and classified by Hernández et al. (2003) as lixiviated Ferralitic Red, hydrated humic nodular ferruginous, of quick desiccation, clayey and deep on calcareous rocks. This type is equivalent to the Ferrosol group, in the classification system of FAO-UNESCO (Alonso, 2003). The average depth to the calcareous rock is 150 cm.

The soil of this area tends to be slightly acid, while the organic matter content is high, higher than the one reported by Hernández (2000), which is from 2 to 3%. The total nitrogen content is considered moderate; it shows low values of available phosphorus and the exchangeable bases (K, Ca, Mg) show moderate to high values. Regarding these characteristics, the soil can be considered to have moderate fertility.

It shows low apparent density, high total porosity and moderate granular structure, conditions that favor good root development, aeration and water movement. Water retention is low, which can stress the problems derived from seasonal drought (Hernández et al., 2003).

Plant material used. From the 180 accessions existing in the Leucaena spp. collection which is preserved in the germplasm bank of the institution, 23 were used (table 1), representative of the populations (four plants from each).

Experimental procedure. This trial began when the seedlings reached approximately between 30 and 45 cm (three months of age), with healthy appearance; four seedlings from each accession were transplanted to the field, in rows spaced at 6 m and a separation of 3 m between plants. The experimental period had a total duration of 30 months and it was divided into: initial establishment (lasting approximately 16 months) and final establishment (14 months), which included the plant flowering and fructification stage and the morphological characterization of the accessions.

Flowering and fructification stage. The performance of the flowering and fructification phenological patterns was observed in all the accessions, with a weekly frequency, and 50% or more of flowers and fruits was considered in the information. For this, the symbols established for that purpose were used (Machado et al., 1999).

In addition, the number of pinnae per leaf and of pinnules per pinna were counted; the length (mm) and width of the pinnules (mm) was measured, the quantity of pods per head, the length (cm) and width (mm) of the pods were also determined. The form of the pinnae, the type and position of the gland and the color of the flowers were taken into consideration. These measurements and observations were made on 15 leaves per plant and equal number for the case of flowers and fruits, during two years (Cronquist, 1981).

Statistical processing. The cluster analysis was used for the grouping and selection of the accessions, using as similarity index the Euclidian distance, from the data obtained in the PCA (Torres et al., 2006), and the stadigraphs mean and standard deviation were determined for the variables analyzed in these stages. Thus, groups of species were obtained that allowed making a simpler and more objective analysis of their performance. These results were subject to an ANOVA according to simple classification lineal model, and the means were compared by means of Duncan's test for 5% significance, after verifying that they fulfilled the normal distribution adjustment and the variance homogeneity, through the statistical program SPSS® version 11.5 for Microsoft Windows® (Visuata, 1998).

RESULTS AND DISCUSSION

Phenology is an interesting element which must be taken into consideration in this stage, as in the others of plant development, even during exploitation, because it can be used as a rule in plantation management. The emergence of flowers and fruits in the species of this genus, according to Hughes (1998), occurs differently and it can be annual in some of them (fig. 1).

It is important to state that, according to the field observations, the accessions of each species had a similar performance, in the rainy as well as the dry season, except L. diversifolia CIAT-17503, L. macrophylla CIAT-17233 and L. esculenta CIAT-17229 (which remained in vegetative stage), and for such reason figure 1 only shows the results per species and not per accessions, because it constitutes a specific character and not a character of the population variants of the species, according to Wencomo (2009). The observations made on such accessions coincide with the studies conducted by Sacandé and Venter Van De (2000), who express that in certain environments it is possible that some species do not produce fruits, as occurred with L. esculenta when it was established in low hills of Hawaii.

In the accessions of L. diversifolia the flowering period occurred from May to June and the fructification period from August to February; the L. esculenta accessions flowered from October to November and produced fruits from February to March. On the other hand, the L. lanceolata accessions flowered in the period from September to October and fructified from November to March, and according to the observations made in the field, they lost most of their leaves (like the leaves of L. esculenta) during the period from December to April (dry season); this could be related to the physiological stress to which they are exposed in this season, which affects some species more than the other ones, according to their capacity of response to biotic or abiotic factors. In this sense, Brewbaker and Sun (1996) found similar results when evaluating these species out of their origin zones.

The L. leucocephala accessions produced flowers and fruits practically throughout the year, because as it is stated by González et al. (2005) this is a heterogeneous flowering species, which seeds do not mature at the same time, although it is important to state that two well marked massive flowering peaks occurred: one from February to March (with harvest between May and July) and another between August and September (with harvest between October and December) , according to the accession; while the L. macrophylla accessions flowered in the period from September to December and fructified from March to May.

The L. lanceolata accessions enlarged their fructification cycle from November to April, and those of L. macrophylla from December to February, which can be due to the fact that phenological patterns are manifested very differently when trees grow out of their native zones (Wencomo, 2009). On the other hand, the edaphoclimatic conditions could have influenced, which in certain places are not suitable for the plants to show their capacity of reproduction and adaptation to the environment in which they are, or as according to Hidalgo (2003) to the genetic expressions of plants in certain environments or to physiological stresses.

For example, Anon (2002) observed in Taiwan that the flowering of all these species occurred from June to August, except for L. esculenta which flowered from November to January. Similar performance was observed in Cuba by Machado (2006) in Ciénaga de Zapata, where soil and climate conditions prevail different from the ones in this study.

Table 2 shows the phenotypical or morphological differences among the accessions. All the species of the Leucaena genus have bipinnate leaves; in addition, the leaves and pinnules are opposed. The accessions of the species L. lanceolata and L. macrophylla show oval or elliptical pinnae, with weakly asymmetric base; while the accessions of L. esculenta, L. diversifolia and L. leucocephala have lineal or lineal-oblong pinnae, with strongly asymmetric base. The number of pinnae pairs per leaf varies from 4 to 18 and the number of pinnula pairs per pinna from 10 to 50; although in other species they can reach higher values.

Likewise, the L. leucocephala accessions are observed to show elliptical and concave glands; while those of L. lanceolata are round elliptical, dome-shaped, except for the accession CIAT-17253, in which their presence was not observed in spite of being one of the species characteristics as such.

In the case of the L. diversifolia accessions discoid glands were found, little deep, cup-shaped and elliptical or round triangular; while in the L. macrophylla accessions they were elliptical, convex, round or conic, except for the accession CIAT-17231, which did not show any gland. In the L. esculenta accessions they are flat, elliptical, large, little deep, concave and cup-shaped.

According to Hughes (1997), glands constitute an identification indicator of the species of this genus, because their number and disposition is very variable. They are also known as extrafloral nectaries (Hughes, 1998), because they appear in the leaves and secrete nectar; they often appear dry and inactive in the oldest leaves.

All the accessions have oval seeds and they are light to dark brown; just like the pods; they show white flowers, except L. diversifolia CIAT-17270, which has pink, reddish or light purple flowers. According to Anon (2002), the flowers, fruits and seeds are indicators that serve to identify the species of this genus.

During the observations the individual flowers of the Leucaena species and accessions were observed to be generally small (5-15mm long) and arranged in capitulums; according to Anon (2002), the anthers, the stamen filaments and the style determine the color of the flower, and not the corolla and the calyx, which are closer to the base.

It is convenient to emphasize that the individual flowers within the head are sustained by small bracts; they are almost always peltate (they are attached to the basal surface instead of being at the margin of the bracts, as in an umbrella). The bracts are only observed when the flowers are in the bud, moment in which they cover the head, they hide when the flowers open and in most species they are round. It is also valid to state that the flowers of the species and accessions of this genus are arranged in groups of two to five, sometimes even seven in the nodes and the axils of the young developing leaves or bracts.

In the accessions of the species L. leucocephala and L. diversifolia, the flowering stems keep growing and form leaves after flowering, with the pods formed under the stem apex. According to Anon (2003) these stems have indeterminate growth and are called auxotelic. In this case the pods mature inside and not in the periphery of the tree crown.

In the accessions of the species L. lanceolata, L. macrophylla and L. esculenta the pods appear in groups of one to four per capitulum, but in some species there can be from six to 15 and up to 45; the stem stops growing after flowering, the pods are formed on the stem tips in the periphery of the tree crown; this type of stem which has definite growth is known as anauxotelic. They die after the pods mature.

This characteristic of producing flowers, pods and seeds during the establishment stage is very important, because it shows the struggle of species with the environment, for survival. The importance of this lies on the fact that the seed is the starting point for any livestock production system that is to be promoted and agroforestry (silvopastoral) systems are no exception. For such reason the knowledge about the flowering and fructification of trees, the characteristics of their seeds, as well as their processing after harvest, and the indicators and conditions for their storage, is necessary and essential, in order to achieve high quality seed lots that allow the development of silvopastoral systems, which guarantee a posteriori the necessary edible biomass to increase animal production.

The phenotypical differences found in each of the Leucaena species and accessions, were reported in studies made by Hughes (1998) and Wencomo (2009). The knowledge of these differences is very important when using them in the development of a certain system, silvopastoral or not, because it has a remarkable influence regarding their management or the productive purpose for which they are destined. For example, the differences in the performance of the flowering and fructification phenological patterns of each would provide the possibility of using them indistinctly in the same area unit: some for seed production and harvest and others for biomass production, for future breeding studies or to define when pruning should be conducted.

According to the results, it is concluded that there are differences among the evaluated species and accessions regarding the performance in the establishment stage; Leucaena spp. showed its flowering and fructification capacity, with differences among individuals.

Taking into account the results of this study and the little available information about this topic, which is important, it is recommended to continue doing further studies with the accessions of this genus and other forage shrubs.