Agriculture Reference
In-Depth Information
CULTIVAR DEVELOPMENT
Cytogenetics and genetics
There are suggestions that the litchi may have been derived from more than
one wild progenitor. Haploid chromosome numbers of 14, 15, 16 and, rarely,
17 have been reported, with diploid numbers of 28, 30 or 32. The diploid
number for longan is 2n
= 30. It is possible to generate intergeneric hybrids
using litchi as the female parent with longan. The hybrid plants are similar to
the maternal parent with smaller leaves.
Breeding and selection
Like most single-seeded fruit, the litchi and longan do not lend themselves to
breeding by a controlled pollination system between two selected parents
(Zee
et al.
, 1998). The highly heterozygous nature of the species means that
planting open-pollinated seeds derived from within a cultivar collection is
the usual procedure used in new cultivar development. For example, the
Hawaii litchi cultivar 'Kaimana' is a selected seedling of open-pollinated seeds
of 'Hei Ye'.
Litchi genetic diversity is indicated by the large number of cultivars in
China and India, and these provide the basis for the development of new
cultivars. Singh and Singh (1954) reported that the 33 or so cultivars grown
in India are all selected from seedling populations derived from introduced
Chinese cultivars.
It is dii cult to identify longan cultivars by skin colour alone. Useful
criteria for identifi cation include the retention of total soluble solids after
harvest, crispness and smoothness of the fl esh, and taste (Table 9.3).
Selection and evaluation
Galán Saúco (1989) has presented a detailed list of characteristics for a litchi
cultivar:
• Fruit: large, with small or shrivelled seed and a high proportion of edible
aril; bright red skin colour; long shelf-life and ability to retain skin colour
under storage conditions; fi rm fl esh with acceptable sugar/acid ratio; and
resistance to diseases.
• Tree: vigorous; precocious; regular and high yielding; resistant to water
stress, wind, soil salinity, diseases and insects; and adapted to regular
fl owering under warmer temperatures in the tropics.
