Agriculture Reference
In-Depth Information
Fig. 11.8.
Changes in fruit starch and total sugar of developing 'Solo' papaya fruit.
Note the dramatic increase in sugars during the last phase of fruit development
(Chan
et al.
, 1979; Chittiraichelvan and Shanmugavelu, 1979).
known polyploid cultivars. Seeds of self-pollinated 'Solo' and 'Eksotika' and
the cross-pollinated varieties 'Sekaki' and 'Khaek Dum' can be reproduced
readily with good genetic purity, if care is taken in seed production. For the F
1
hybrids, such as 'Rainbow' and 'Eksotika II', seed is dii cult to produce as two
inbred parents have to be crossed for production of the hybrid seeds.
Some
Vasconcella
species have resistance to diseases to which
C. papaya
L. is susceptible, e.g.
Vasconcella
caulifl ora
's resistance to distortion ringspot
virus. This resistance has lead to attempts to cross these species. Successful
interspecifi c hybrids have been reported between other
Vasconcella
species but
not with
C. papaya
L. However, hybrids of
C.
papaya
L. with
V. caulifl ora
and
with
V. pubescens
,
V.
quercifolia
and
Vasconcella stipulata
were obtained using
embryo rescue techniques to overcome post-zygotic barriers to hybridization.
In vitro
propagation coupled to rapid disease resistance screening, anther
culture to generate haploid papaya lines and
Agrobacterium
-mediated gene
transfer has been used to develop disease-resistant papaya lines.
Sex of papaya is determined by monogenic inheritance involving three
alleles (Hofmeyr, 1938). The alleles are M for male, M
H
for hermaphrodite and
m for female. All homozygous dominants, i.e. MM, MM
H
and M
H
M
H
, are lethal
to the zygotes. Therefore male genotypes (Mm) and hermaphrodite (M
H
m) are
