Botany and Improvement 33
that is, pistillate or female. Length and ramification of the inflorescences are second-
ary sex characters. The alleles that give them expression are on the sex chromosomes
but linkage with the sex-determining factors is not absolute. In effect, all staminate
and andromonoecious forms are identical. Therefore, the classification of plants as
one form or other depends largely upon the nature of the inflorescence. Elucidating
the structure of sex chromosomes, Ram et al. (1985a, b) have postulated that multiple
allelic genes are at play in determining sex of papaya plants. They suggested separate
symbols for pure male (M 1 rrm) and sex reversing males (M 1 Rrm) recognising dominant
gene for homozygous sex reversing maleness as M 1 RR; for heterozygous sex reversing
maleness as M 1 Rr and for pure maleness as M 1 rr. Chromosomal structures proposed by
Ram et al. (1985a, b) for different sexes are as follows:
mp
Female HermaphroditeSex reversing malemVsuF Xmp mv suF Xmp mVsuF Xmp M 2 v suF Ymp mVsuF XMp M 1 Rr v suF YmpPure Male
mVsuF XMp M 1 rr v suF
YIn this hypothesis, Mp or mp is the main distinguishing factor between male and
hermaphrodite plants (MP stands for male plant and mp for hermaphrodite plant). It
has been assumed that X chromosome carries a vitality gene (V) which is recessive
(v) in Y chromosome. The homozygous recessive (vv) state is lethal; thus, homozy-
gous recessive individuals are never seen in segregating populations; only the hetero-
zygote (Vv) and homozygous dominants (VV) can grow. The presence of the lethal
gene in recessive state in both males and hermaphrodites adds heterozygosity to the
sex forms. A dominant gene for suppressing femaleness (SuF) is present only in a
pure male. As a result, this plant never produces any fruit. The suppressor gene (SuF)
is absent in sex reversing males. Thus, all such plants are capable to bear fruits. This
explanation is a partial modification to the Hofmeyr’s (Hofmeyr 1967) hypothesis.
However, there still exists an urgent need to investigate the order of the genes in the
sex determining segment of a chromosome. Only detailed investigations will reveal
whether the above hypotheses are relevant or speculative.
Detailed studies on genetic and breeding aspects of the crop (Hofmeyr 1938, 1942,
1967; Nakasone and Storey 1955; Storey 1953; Yadav and Prasad 1990) have revealed
that yellow flower colour is dominant to white, purple stem colour is dominant to red,
yellow flesh colour is dominant to red, dwarfness in height is recessive to normal tall
stature, diminutive plant (short slender trunk, small leaves) is recessive to large plant,
crimpled leaf is recessive to normal leaf, rugose leaf recessive to normal smooth leaf,
waxy leaf is recessive to normal flat-bladed leaf and grey seed-coat colour is domi-
nant to black seed-coat colour. Morshidi (1998) studying the inheritance of isozymes
in papaya, has observed Mendelian inheritance pattern for eight out of nine polymor-
phic loci. The highest number of fruits per plant and the highest number of seeds per
fruit with the lowest fruit length are the most important selection indices to identify a
plant type producing maximum fruit yield in papaya (Dwivedi et al. 1998).