38 Papaya
But such seeds involve the risk of higher segregating population and sometimes may
not be at par with F 1 in performance for yield and quality. Nevertheless, one can
expect substantial yield gain with hybrid over the conventional variety. Cariflora
derived by crossing two dioecious lines, K 2 and K 3 (K 2 × K 3 ). It bears round fruits
(13.5–14.5 cm diameter) with sweet yellowish flesh, good aroma and good quality.
The ratio of male: female flowers or plant is 1:1. It is dioecious and highly toler-
ant to PRSV. Two hybrids, IIHR-39 (Sunrise Solo × Pink Flesh Sweet) and IIHR-
54 (Waimanalo × Pink Flesh Sweet) developed at Indian Institute of Horticultural
Research, Bangalore have been found highly promising on account of superior fruit
quality. They bear medium-sized fruits, sweet in taste with good shelf life. Both
are gynodioecious. IIHR-39 has now been released as Surya (Dinesh and Yadav
1998). Another promising hybrid, HPSC-3 (Tripura Local × Honeydew) has been
developed at ICAR Research Complex, Tripura. It possesses high yield potential and
resistance to mosaic virus (Singh and Sharma 1996).
2.7.4 Inter-Specific Hybridisation
The brief account of crossing relationships and inherent resistance of C. monoica to
virus disease, namely bunchy top, has involved an intensive search of some of the
other species to seek breeding stock which might carry immunity and higher resis-
tance and to attempt the incorporation of such immunity into the ordinary papaya
which is highly susceptible. A wide range of inter-specific and reciprocal combina-
tions has been made by utilising some of the lesser known species. Carica cauliflora
has been found to be resistant to mosaic virus (Capoor and Verma 1961). Horovitz
and Jimenez (1967) have reported that C. cauliflora, C. pubescence, C. stipulate
and C. candicans are resistant to distortion ringspot virus. Zerpa (1959) made sev-
eral inter-specific crosses, namely C. cauliflorax C. microcarpa, C. monoica × C.
cauliflora, C. monoica × C. candamarcensis, F 1 (C. monoica × C. cauliflora) × C.
candamarcensis and C. cauliflora × C. candamarcensis. Cytological investigations
of these crosses revealed that only the cross, C. cauliflora × C. candamarcensis
produces multivalents at metaphase I, while others could produce bivalents indicat-
ing high inter-specific genetic affinity. Mekako and Nakasone (1975) while mak-
ing inter-specific hybrids using six Carica species obtained viable seeds from C.
monoica × C. goudotina, C. parviflora × C. goudotiana, C. goudotiana × C. mono-
ica and C. cauliflora × C. penata. They also observed heterosis for vegetative and
fruit yield characters in the crosses, C. parviflora × C. goudotiana and C. cauliflora
× C. monoica. Subramanyam and Iyer (1981) and Iyer and Subramanyam (1984)
attempted inter-specific hybridisation and found crossability barrier operating in
many species. Their study showed that F 1 hybrid of C. cauliflora × C. monoica when
crossed with C. papaya resulted in fertile hybrids. Although C. cauliflora and C.
monoica are incompatible with C. papaya, hybrids of C. cauliflora × C. monoica are
compatible. Iyer et al. (1987) later reported that inter-specific hybridisation between
C. papaya and C. cauliflora easily produced F 1 plants. After backcrossing with C.
papaya, they evolved a line, 21–19 showing resistance to mosaic virus with normal
fruit quality. Magdalita et al. (1997) found C. papaya × Carica cauliflora hybrids
resistant to Australian papaya ringspot potyvirus type P (PRSV-P) isolates.