Botany and Improvement 21
embryo in most of the cases can be cultivated through embryo culture. Crosses between
species of Group B and C have not been successful. Species like C. candamarcensis,
C. guercifolia, C. monoica, C. cauliflora, C. goudotiana, C. petandra and C. micro-
carpa have significance in breeding for biotic and abiotic stresses (Chadha 1992).
Carica pubescens, C. stipulata, C. Heibornii and C. candicans have been reported to be
resistant to ‘Distortion RingSpot Virus’ (Horovitz and Jimenez 1967).
The progeny of crosses with V. caulifliora were the only hybrids showing some
virus resistance but they were unfruitful when attacked. There were no viable seeds
and 30% of the fruits were seedless. C. monoica proved well adapted to Palmira,
bore small, yellow fruits, but succumbed to virus. The introductions from Brazil
were by far the most promising. ‘Zapote’ with rich, red flesh is much grown on the
Atlantic coast of Colombia.
2.4 Sex Forms
Except three species of Carica, all members of Caricaceae are dioecious. The three
exceptions are C. monoica, C. pubescens and C. papaya. They have sexually ambivalent
forms which go through ‘sex reversals’ in response to climatic and/or photoperiodic
changes during the year. C. monoica is strictly monoecious but at certain times of the
year may lack pistillate flowers. Plants of C. pubescens exist in three basic sex forms:
pistillate, staminate and hermaphrodite. The pistillate and staminate plants are unrespon-
sive to seasonal climatic changes. The hermaphrodite plants are sexually ambivalent,
producing staminate, perfect and pistillate flowers in varying proportions at different
times of the year. C. papaya exists in the same three basic sex forms as C. pubescens. The
pistillate plant is stable. Staminate and hermaphrodite plants may be: (a) phenotypically
stable or (b) phenotypically ambivalent, going through seasonal sex-reversal, during
which they produce varying proportions of staminate, perfect and pistillate flowers.
2.4.1 Classification
Since papaya is a polygamous species, many forms of inflorescence have been
reported. Generally, there are three types of flowers namely, staminate, pistillate and
hermaphrodite but variation within each type has led to further classify them into
six categories (Figure 2.4):
i. Dioecious pistillate – large sessile pistillate flowers in the leaf axil. It is the
normal female, occurring in higher proportion than other forms.
ii. Dioecious staminate – long, narrow, tabular flowers on long peduncles
hanging from leaf axil. It is described as the normal male.
iii. Andromonoecious – male and hermaphrodite flowers on a long peduncle.
iv. Polygamous – (a) male, female and hermaphrodite flowers on the same tree
on long peduncles, (b) like (a) but hermaphrodite flowers being of two type
namely, with 10 stamens and with 5 stamens. Fruits are long in shape.
v. Staminate – (a) staminate flowers on short peduncles directly, (b) hermaph-
rodite flowers with few female flowers on long peduncles and (c) separate
staminate and cluster of staminate with hermaphrodite: (ci) hermaphrodite