PINEAPPLE - Tropical Fruits - page 342

CULTIVAR DEVELOPMENT
Cytogenetics and genetics
Information on cytogenetics and genetics comes from early studies conducted
at the former Pineapple Research Institute of Hawaii. Chromosome counts of
'Cayenne', 'Queen', 'Spiny Samoa', 'Ruby', 'Pernambuco', 'Spiny Guatemala',
an F 1 hybrid between 'Cayenne' and an unknown wild-type from Brazil and
B. pinquin L. showed the pineapple cultivars to possess n = 25 chromosomes
and B. pinquin has n = 48, with no irregularities in meiosis (Collins, 1960).
Several triploid plants with 75 chromosomes are found among the F 1 hybrids.
The triploids appear to be products of the conjugation between an unreduced
'Cayenne' egg cell with 50 chromosomes and normal haploid pollen of a
Brazilian wild type. The commercial cultivar 'Cabezona' is a natural triploid
with 75 chromosomes (Collins, 1933).
Collins and Kerns (1938) described about 30 heritable mutant forms in
'Smooth Cayenne' fi elds, most being undesirable. One desirable processing
mutant form is for elongated fruit. Collar-of-slips, a condition in which
excessive numbers of slips are either attached directly to fruitlets at the base of
the fruit or massed around its base, occurs in successive vegetative generations
(Fig. 12.5). These plants are continuously rogued out. This character is
dominant and occurs in a heterozygous state in 'Smooth Cayenne'. Spiny
leaf is due to a homozygous recessive gene, and the smooth leaf condition
of 'Smooth Cayenne' is carried as a heterozygous dominant. However, it is
unstable and mutates frequently to the spiny leaf type; other spiny conditions
also occur. Self-incompatibility in pineapple is an advantage in commercial
production of seedless fruit and in cross-pollination. Pollen shows good
viability for several cultivars, except that of the triploid 'Cabezona'. A single S
locus with multiple alleles and gametophytic control of pollen phenotype are
involved in self-incompatibility (Brewbaker and Gorrez, 1967), in which the
pollen tube growth beyond the upper third of the stylar canal is inhibited.
Breeding and cultivars
Breeding
Pineapple breeding and selection objectives vary with the locality, but almost
always emphasize disease and insect resistance (Coppens d'Eechkenbrugge et
al. , 1997; Chan et al. , 2003). More recently, development of cultivars for fresh
fruit consumption has been a major focus. Populations have been produced
from crosses to allow selection of improved types. This selection involves
constant roguing of undesirable mutations and selection of superior types.
Mutation continues to occur within selected clones, so the ef ects of selection
are not permanent, and without continued rouging and selection, commercial