RESEARCH WORK
Performance of forage tree species under nursery conditions
Odalys C. Toral
Estación Experimental de Pastos y Forrajes ¨Indio Hatuey¨. Central España Republicana CP 44280, Matanzas, Cuba.
e-mail: odalys.toral@indio.atenas.inf.cu
ABSTRACT
The performance of 60 accessions was studied under nursery conditions, with the objective of characterizing forage trees and shrubs and further evaluating the possible variations among species. According to the main component analysis there was a high variability (36%) in the first component and the indicators initial height, stem diameter, height 90 days after planting and pest incidence contributed to it. In addition, a good part of this percentage was also explained by the contribution of diseases (plane CP1-CP3). From the six groups formed, IV and VI (L. longistylus, Schizolobium sp., M. nigra and T. gigantea) showed 63% positive contribution of the variables; while the accessions in group I were the less outstanding. Germination, survival and stem diameter were concluded to have high influence on the development of seedlings in the nursery stage, for which, together with the indicator plant height, they should be taken into consideration to determine the optimum moment of transplantation. L. longistylus, Schizolobium sp., M. nigra and T. gigantea were the most outstanding species regarding the studied characters.
Key words: Trees, germination, survival
INTRODUCTION
Nowadays, the use of trees and shrubs in livestock production is a common practice in several regions of the world, which means a challenge for modern tropical livestock production that debates in the alternative of rapidly increasing milk and production to supply the growing demand of population, in addition to guaranteeing the conservation of natural resources and the environment.
The implementation of silvopastoral systems in Cuba has favored the development of positive experiences in the management of pasturelands of grasses and legumes, which have been established including tree species in the same exploitation system (Simón et al., 2005).
Nevertheless, there is little information on the performance of tree species in their first development stages, for which the objective of this work was to characterize forage trees and shrubs under nursery conditions and further evaluate the possible variations among species.
MATERIALS AND MERHODS
Treatments. They were constituted by 60 tree accessions. A simple classification design with factorial arrangement and ten replications per accession was used.
Experimental procedure. For the nursery stage of the seedlings, 28 x 13 cm pierced bags were used, in which a substratum composed by 70% soil and 30% organic matter was placed.
Before planting the weeds and surface crust were eliminated, weeding the surface or pressing the top part of the bag until loosening the soil. The seeds (three per bag) were placed at the center of the container and sown after harvesting, without performing any treatment on them.
For each accession 40 bags were planted, with the objective of evaluating only the 20 bags in the center; while the 20 others were used to avoid the edge effect of the neighboring species.
All the material sown in the nursery (40 bags per accession) received daily irrigation (8:30-10:00 a.m. and 3:00-4:30 p.m.), for maintaining the humidity necessary for germination and development of the seedlings.
With the objective of leaving only one seedling per bag (the most vigorous), a negative selection was made when the seedlings reached an average height of 7 cm.
As nursery period the time that passed since planting until the transfer of the seedlings to field conditions or evaluation stage was considered, which ended when they reached a height between 30 and 40 cm.
Measured or estimated variables
Germination. It was determined by counting the emerged seedlings, every three days since planting until they were 30 days old.
Survival. Since 30 days after planting and every seven days, survival counts were carried out in the germinated seedlings.
Height. After concluding the germination test and every seven days, height was measured.
Number of leaves. From 30 days after planting and every seven days, the number of leaves was counted.
Stem diameter. This measurement was carried out when the seedling reached 20 cm high, every seven days.
Plant health observations. Since 30 days after planting and every seven days, the pest and disease incidence rate was determined according to the value scale from 1 to 5, where:
I- very high incidence degree (100% affected leaf area)
II-high incidence degree (50% affected leaf area)
III-moderate incidence degree (25% affected leaf area)
IV-slight incidence degree (10% affected leaf area)
V- incipient incidence degree (1% affected leaf area)
Mathematical analysis. For comparing the accessions the mean value of all the observations was taken and a comparison matrix was formed.
The variability and relationship among indicators was obtained by means of a main component analysis (MCA); while in the grouping of treatments with similar characteristics, regarding the measured and/or estimated variables, the cluster analysis was used. Before this analysis such values were typified, so that all had the same bearing on class or group formation. The statistical pack SPSS version 10.0 (Visauta, 1998) was used.
In order to obtain the contribution of the variables to group formation, the following procedure was followed: after the groups were formed (through the automatic classification analysis) the mean was determined for each indicator, from the data matrix obtained in each group and, afterwards, the population mean of all the groups was calculated for each indicator. In the case of variable contribution (positive as well as negative), it was taken as base that the total of indicators represented 100%; thus, all those indicators that exceeded the population mean in each group were identified as positive and all the ones that were below, as negative. After pre-fixing the number of indicators (positive and negative) the percentage value with regards to the total was determined, by proportions.
In the case of the indicators pests and diseases the inverse value was taken, because the means higher than the population mean represented higher incidence.
RESULTS
Table 1 shows the results of the MCA. Regarding the measured and estimated indicators for the treatment, it was proven that the accumulated variability of the first three components was high and that the first component (CP1) extracted 35,73%. The indicators that better explained the variation percentage in this axis, which were positively related, were initial height, stem diameter, height 90 days after planting and pest incidence, although this latter indicator showed acceptable representativeness in CP2, for which it is explained in the plane CP1-CP2; a good part of the accumulated variation percentage was explained by the contribution of diseases in the plane CP1-CP3.
The second component (CP2) extracted 21,12% of the variance and the most related variables with this axis were survival and germination, which were inverse to pests, indicator that was also related to the axis even when its highest contribution was obtained in CP1.
The third component (CP3) only extracted 17,30% of the variance and in its formation mainly the number of leaves that interacted contrary to diseases, explained in the plane CP3-CP1.
When performing the cluster analysis, based on the measured and estimated indicators during this stage, six groups were formed. Table 2 shows the accessions belonging to each group. In group I, where 44 accessions are included, Leucaena and Albizia stood out for the number of accessions that represent them; while in group II Bauhinia stood out. The other groups were represented by different species, which in turn constituted the accessions.
When the measured values of each group were compared to the population mean, the accessions that formed groups IV and VI showed 63% positive contribution (table 3); while Pithcellobium dulce (group V) contributed 25%. Within group IV, formed by the accessions Schizolobium sp. and Lonchocarpus longistylus, good indexes of germination (87%), survival (77%), initial height (16 cm) and little incidence of pests and diseases were reflected; while the accessions of group VI (Morus nigra and Trichanthera gigantea) showed the best height values 90 days after planting (50 cm) and stem diameter (1,0 cm); the other indicators had similar performance to group IV.
Group II had good initial height (20 cm), height 90 days after planting (86 cm), stem diameter (0,59 cm) and number of leaves (29). However, germination and survival were below the population mean. In this group, the accessions Bauhinia variegata, Bauhinia sp. and Gliricidia sepium stood out for their good values in the above-mentioned indicators.
The accession of group III showed better survival rates (71%) and stem diameter (0,45 cm); while the accession of group V (P. dulce) only stood out in number of leaves (18) and had a similar performance to the average in the rate of pest incidence (3); the other indicators were below the population mean.
The accessions of group I had the worst performance in all the indicators studied and never exceeded the population mean.
With regards to attacks by pests, the incidence of Colapsis brunnea Fabricius was observed in most species, with an incidence rate from incipient to moderate, according to the pre-fixed scale, with the exception of the Erythrina accessions, which were affected by Terastia meticulosellus Gueneé (stem borer) in similar magnitude.
In addition, chlorosis symptoms were observed, which could have been caused by fungus or bacteria, because moist and dry lesions were observed.
DISCUSSION
According to the results of the MCA, it is possible to state that there was high contrast among the accessions, proven by the high accumulated variability, regarding the measured or estimated indicators.
In this sense, a high differentiation was present among the studied variables, particularly for initial height, height 90 days after planting, stem diameter, germination and pest incidence; aspects that certainly contributed in the grouping of the accessions and their later selection.
This indicates that these variables characterized the development of the seedling in this growth stage, which reasserts the existence of high phenotypical variability in the population and, especially, in the indicators of plant development and the incident stress degree during that period.
Similar results were reported by Hernández and Seguí (1998), who when evaluating a wide collection of Leucaena spp. obtained a very effective variability (60,4%) in the first component, when analyzing such variables as stem diameter, plant height and number of branches, in the nursery stage.
Also Wencomo et al. (2003) worked with this collection, formed by 145 accessions of Leucaena spp. and found an accumulated variance of 76,8% in the first two components, when similar indicators to the ones in this work were used, during the nursery stage, which were positively related and contributed strongly to the later grouping of the accessions.
All the above-expressed indicates that, independently from the existing edaphoclimatic conditions during this stage, the populations and particularly these accessions, can express remarkable variation among individuals for some indicators and thus be grouped regarding those variables, which represents a positive element in the evaluation work.
In addition, variability was observed to be well distributed, because the proper value in all cases was higher than one, acceptable value for the variability corresponding to each indicator to be related more effectively to each axis, in correspondence with this type of analysis (Philippeau, 1986). For such reason, all the indicators taken into consideration were included in the grouping of these accessions through the cluster analysis, which results will be discussed later.
Although the variance in CP2 only reached 21,12%, it can be considered acceptable, especially if its proper value is considered. This indicates that germination and survival, as well as the effect caused by the presence of pests, can constitute indicators of contrast between the studied trees and shrubs, and that such indicators, were not related to the previously analyzed ones. This is completely logical if the nature and transcendence of such indicators is analyzed, which can have incidence in a very independent way.
However, the effective relationship established for CP2 between germination and survival, as well as the contrast with the presence of pests and diseases, is a consequence of the development of seedlings, because survival can only be expected from the material that germinates and is not considerably affected later by the stress produced due to the incidence of pests and diseases on small seedlings. These variables were inversely expressed to the two former ones, that is, affecting, germination or survival.
In the third axis (CP3), with low percentage of total variance (17,30%), the disease incidence and number of leaves, which were contrary oriented, contributed decisively. According to the variance value this component extracted, it can be deduced that the bearing of number of leaves with regards to total variance, was remarkably lower than that of the variables which were referred before.
The contrast between the number of leaves and the degree of disease incidence is logical, because an increase of the incidence rate of disease can be in correspondence with a relative decrease of the number of leaves, as these indicators act contrary.
When comparing the accessions among themselves, it was possible to verify the existence of encouraging results, because some had a very positive performance when using the cluster analysis; this was closely related to the contrasting responses that were manifested among treatments, effect that caused a considerable individual differentiation and the subsequent formation of well defined groups (tables 2 and 3).
In spite of the little representativeness in the number of evaluated species and taking into consideration the results reached in this stage, it can be stated that the differences among the six groups formed showed contrasts among and within the species and accessions, for which these indicators should not be established statically for all of them in general, but at least one criterion should be considered for each accession separately.
It could also be observed that all the evaluated accessions in this stage showed a better performance than the commercial varieties Leucaena leucocephala cvs. Cunningham and CNIA-250, which coincides with the research works carried out by Hernández and Seguí (1998), where CNIA-250 also showed problems during the nursery stage, as well as the results obtained by Machado and Núñez (1994) and Wencomo et al. (2003).
Although the available literature does not offer much information about the study of leguminous trees, authors like Jones and Jones (1982), Shelton et al. (1991) and Clavero (1998) stated that the leucaena plants, under favorable nursery conditions, have a fast growth and are ready to be transplanted when they reach about 30-50 cm of height, which prevents the roots from perforating the bags and get fixed to the soil and the stems from becoming too large. This corroborates the results of this research with the 13 Leucaena accessions, which 90 days after being planted in nursery reached an average height of 39 cm.
Conclusions
Germination, survival and stem diameter had great influence on the development of seedlings in the nursery stage, for which, together with the indicator plant height, they must be taken into consideration to determine the optimum transplantation time.
From the species under study, L. longistylus, Schizolobium sp., M. nigra and T. gigantea were the most outstanding ones.
