Agriculture Reference
In-Depth Information
125
100
Fruit
length
75
Seed
length
50
Pericarp
thickness
25
0
0
50
100
Days from full bloom
150
200
Fig. 7.6.
Rate of total fruit and seed growth and the increase in pericarp thickness of
the West Indian cultivar 'Waldin' (redrawn from Valmayor, 1967).
a tetraploid (2n = 48). Karyotype in
Persea
is asymmetric, with chromosomes
ranging in size from 2.3 μm to 6.1 μm.
Garcia and Tsunewaki (1977), using peroxidase isozyme analysis, found
signifi cant variations between Mexican strains, within and between nine
states in Mexico. The three races showed signifi cant variation in their pattern
of activities. The frequency of signifi cant variations within strains of the three
races is high in the Guatemalan (62.5%), intermediate in the West Indian
(50.0%) and relatively low in the Mexican race (39.0%). Isozymes have also
been used as genetic markers to detect dif erent genotypes resulting from
natural outcrossing and controlled pollinations (Bergh and Ellstrand, 1986).
A number of molecular approaches have been used as genotypic markers and
assignment of racial composition. Ef orts to apply these techniques in avocado
breeding programmes are hampered by the long generation time and the
inability to perform controlled pollinations (Violi
et al.
, 2009).
Skin colour, fl owering group and anise scent in the leaves are probably
coded by several loci, having several alleles in each loci (Lavi
et al.
,
1993a). The
juvenile period also has a major genetic component. Quantitative traits, such
as tree size, fl owering intensity, fruit weight, fruit density and harvest duration,
show both additive and non-additive genetic variance (Lavi
et al.
,
1991).
