Papaya Biology, Cultivation, Production and Uses

Botany and Improvement 31

2.6 Inheritance Pattern

Sex in papaya is controlled by five pairs of genes which occur in three sex determin-
ing complexes in sixth chromosome. Because of tight linkage between the genes, the
sex-determining complexes produce phenotypic results analogous to that produced by
three alleles of a single gene with pleiotropic effects. For practical convenience, the
complexes are generally designated as: M 1 dominant for maleness, M 2 dominant for
hermophroditism and m recessive for femaleness. The combination M 1 M 1 , M 2 M 1 and
M 2 M 2 are lethal and, thus, fail to produce viable seeds. M 1 m gives male trees, M 2 m
hermaphrodite trees and mm female trees. The crossing of two plants differing in sex-
form produces either two (male or female) or three (male, female and hermaphrodite
plants) in set ratios (Table 2.1). Yadav and Prasad (1990) observed some variation in
the ratio with hybrids from dioecious × gynodioecious crosses. Such a cross produced
the ratio of 1 male: 2 female: 1 hermaphrodite, with the exception of the two crosses
where female and hermaphrodite progenies were produced in the ratio of 1:1 and 3:1.
These observations confirm that the inheritance of sex is under polygenic control.
The size and shape of the fruits are determined by the parentage, particularly
the type of flowers used in pollination. By selfing hermaphrodite of known geneti-
cal constitution, for example ‘Solo’, uniform pyriform fruits are produced on the
hermaphrodite progeny and uniform larger round fruits on the female progeny. By
crossing mmxM 2 m, half the progeny will be female with round fruits and half will
be hermaphrodite with cylindrical fruits. Thus, all the progeny will be with fruit.
However, one of the difficulties of the breeder is that there are no reliable characters
to distinguish male, hermaphrodite and female trees until they flower. In dioecious
varieties, both male and female trees should be progeny of the same parents which
have the desired characters. Maintaining characters in hermaphrodite form is easier.
Also, genetic manipulation of hermaphrodite plants is easier by conventional breed-
ing methods as compared to other sex forms.

TABLE 2.1

Crossing among the Basic Sex Forms in Papaya and Ratio

of Segregating Progenies

Progenies

Cross

Female

(mm)

Hermaphrodite

(M 2 m)

Male

(M 1 m)

Non-Viable

(Lethal)

F* × S (mm × M 1 m) 1 – 1 –

F × H (mm × M 2 m) 1 1 – –

H × H (M 2 m × M 2 m) 1 2 – 1 (M 2 M 2 )

S × S (M 1 m × M 1 m) 1 – 2 1 (M 1 M 1 )

H × S (M 2 m × M 1 m) 1 1 1 1 (M 2 M 1 )

S × H (M 1 m × M 2 m) 1 1 1 1 (M 1 M 2 )

Source: Adapted from Hofmeyr, J. D. J, 1967, Agronomy Tropical, 17:345–51.

F* = Female; H = Hermaphrodite; S = Staminate.