Proc. of Second World Avocado Congress 1992 pp. 527-530

Selection of Dwarf Avocado Trees Within a Population of Seedlings of cv. Colin V-33

 

Salvador Sánchez-Colín, Martín Rubí Arriaga and Eulogio de la Cruz Torres

Centro de Investigaciones Cientfffcas y Tecnologicas del Aguacate en el Estado de Mexico, Palacio Municipal, Coatepec Harinas, C.P. 51700, Mexico

 

Abstract. An open-pollinated population of 347 nine-year-old seedlings from the dwarf avocado cultivar Colín V-33 was evaluated at Coatepec Harinas, Mexico, to choose those seedlings with promising characteristics, either as dwarf varieties or as dwarfing rootstocks.

Quantitative and qualitative parameters for each tree were evaluated, e.g. height of the tree, canopy and trunk diameter, ratio of canopy diameter to height, vigor, tree shape, and branch distribution, etc. Correlation among the different variables evaluated were analyzed for the purpose of establishing selection criteria.

 

One priority in avocado research is to find dwarf cultivars that are highly productive with good fruit quality and pest and disease resistance in order to establish high density plantations and to reduce production costs. This was performed in an attempt to address these needs.

Materials and Methods

To determine the main vegetative characteristics of each seedling, the description formulated by Barbabosa (1933) was used. Tree height, growth habit of the tree, canopy and trunk diameter, and the ratio of canopy diameter to height were used to rank the trees and to select those trees which exhibited dwarf habits.

Results and Discussion

In studying 347 seedlings of 'Colín V-33^', we found a great diversity of types according to morphological characters (Rubí, 1989). Since the main objective at CICTAMEX is to obtain dwarf cultivars, these characters are presented in relation to tree height.

Vigor types in relation to height. The frequency of three classes of vigor in relation to five classes of height intervals is presented in Table 1. The intermediate height category of 3.50 to 4.59 m predominated, comprising 44% of the total seedlings. However, of greater interest is that 27% were in the dwarf or very dwarf categories. In terms of tree strength, 31% had the low vigor that is an indicator of potential for use as dwarfing rootstocks (Barrientos and López, 1987)

Considering both factors (height and vigor), 41 seedlings (12%) were of maximum interest in that they combined low vigor with dwarf or very dwarf tree height.

Tree shape. The shape is very important because it determines the management practices used in the orchard, so that the spherical, semi-spherical and semi-elliptical forms are advantageous, permitting planting in high density without excessive shading. Distribution frequencies of tree shapes in terms of height is given in Table 2. Note that 111 seedlings exhibited the irregular form, typical of the 'Colín V-33' (Sanchez Colín, 1980).

Canopy diameter. There was a positive correlation between canopy diameter and tree height (r = 0.56). Seventy seedlings had a small or very small canopy diameter and were dwarf or very dwarf (Table 3), thus fulfilling the requirements for high density plantings.

Ratio of canopy diameter to height. Growth habit can be defined by the ratio of canopy diameter to tree height. A ratio greater than one indicates more horizontal growth, less than one more vertical growth. Only eleven seedlings had a ratio below one and were also very dwarf (Table 4).

Trunk diameter and height. A positive correlation between trunk diameter and height was found (r = 0.50). Barrientos and Lopez (1987) found a negative correlation (r = -0.91) between trunk circumference and bark ratio; and also a negative correlation between bark ratio and height of the tree. So we conclude that the 15 seedlings (Table 5) that are both very dwarf and small in trunk diameter can be considered true dwarf trees.

Conclusions

Table 6 lists the qualities that we consider desirable in a search for dwarf cultivars.

Table 7 lists eight outstanding seedling selections. They need to be studied intensively in terms of productivity and fruit quality and also to determine their usefulness as dwarfing rootstocks.

Literature Cited

Barbabosa, C.A. 1933. Abacateiro e do abacate. Brasil, Typ Siqueira, 343 p.

Barrientos Priego and A. López J. 1987. Selección de portainjertos enanizantesde aguacate (Persea americana Mill). Memoria de actividades CICTAMEX, Méx. pp. 37-74.

Rubí, A.M. 1989. Descripcion de una población de segregantes de aguacate de la variedad de porte bajo Colín V-33. Memoria CIC FRUTICOLA CICTAMEX. Coatpec Harinas, México pp. 21-30.

Sanchez, Colín S. 1980. 'Colín V-33' una neva variedad de aguacate en México. SAIMEX No. 52. 23p.