Botany and Improvement 37
for GCA, five papaya inbreds namely, Pusa Delicious, Pusa Majesty, Washington,
Sunrise Solo and Waimanalo were crossed with three tester(s), namely Homestead,
Halflong and Ramnagar Local. The best GCA was found in Pusa Delicious and
Ramnagar Local was the best tester (Ram 1982). This study indicated that higher
performance needs to be correlated with high GCA effects.
Specific combining ability (SCA) is important in the identification of valuable
inbred lines for use in hybrid production. It is the expression of performance between
any two inbred lines and is attributed to dominant, epistatic and additive gene
action. Ram (1982) made several crosses and observed that Washington × Ramnagar
Local had the highest SCA for the fruit yield per plant, followed by Pusa
Delicious × Homestead, Waimanalo × Halflong and Pusa Delicious × Halflong. It
was observed that the best general combining line and tester did not necessarily
posses/show the maximum SCA values. It was the combination of average combin-
ers from both the inbred lines on one hand and testers on the other which showed
the maximum SCA (Ram 1993). Dinesh et al. (1991) observed that variety, Thailand
was a good combiner for fruit length, breadth and volume, while Sunrise Solo and
Waimanalo were good combiners for quality characters.
The selection of resistant genotypes is a sustainable alternative to disease control
in papaya cultivation. However, total resistance has not been observed in commercial
papaya genotypes with some degree of selection. There is, however, the possibil-
ity that crosses generate hybrids with higher resistance levels to fungal diseases.
Thus, crop breeding can contribute to the selection of resistant genotypes and/or
indicated the best hybrid combinations, based on the hybrid vigour also known as
heterosis. The hybrid vigour is directly related to the degree of genetic divergence of
parents involved. However, a high genetic divergence does not necessarily increase
the expression of heterosis. It is, therefore, important to use methods that identify
the best combinations (Duarte et al. 2003). Vivas et al. (2011) evaluated testers to
estimate combining ability and select hybrids resistant to black spot, phoma spot and
chocolate spot. The severity of phoma spot and black spot on leaves, and the lesion
area of black spot and chocolate spot on fruits were evaluated in two seasons. The
combining ability of crosses is negative for all traits: tester ‘JS 12’ with ‘Sunrise
Solo’ and ‘Kaphoro SoloPV’; tester ‘Americano’ with ‘Caliman M 5 ’, ‘Sunrise Solo’,
‘Baixinho de Santa Amalia’ and ‘Waimanalo’; and tester ‘Maradol’ with ‘Caliman
G’, ‘Caliman a.m.’ and ‘Sunrise Solo PT’. These results may be useful in breeding
for disease resistance by hybridisation.
2.7.3.3 Hybrids
Although some hybrids have been developed following inter-varietal or inter-generic
crosses, there still exists great scope for development of superior hybrids for better
yield and quality. This is more relevant particularly for the production of F 1 hybrid
seeds. At present, no private agency is producing F 1 papaya seeds in India. Very lim-
ited quantity is available at research stations and that too for experimental needs only.
Thus, there is an urgent need to produce large quantity of F 1 papaya seeds. Besides
this, two very vigorous F 1 s from specific inbred combinations can also be crossed
together to produce the hybrid seeds to meet the large demand. Because of heterosis
associated with each F 1 , the quantity of hybrid seed production can, thus, be raised.