Production of F1 hybrid seeds from a 6x6 diallel of papaya (Carica papaya L.)

 Y. K. Chan and C. Mak

Abstract

Six papaya inbreds namely Sunrise Solo, Eksotika, L19, Paris, Subang 6 and Morib were crossed in a diallel to evaluate their compatibility and production of F1 seeds. Four rounds of crosses were carried out when trees were 9, 12, 15 and 18 months old. The seed production capacity of inbreds used as females or males was assessed by the number of seeds formed in the fruit, the percentage of non-viable seeds which included pre-germinated seeds and ‘floaters’ which had underdeveloped embryos.The results showed that all combinations between the six inbreds were compatible and seed production appeared to be related to the age of the trees. Fruit from older trees bore more seeds but there was also a higher percentage of pre-germination in these seeds.The ANOVA showed that inbreds differed in their production of seeds, both when used as female or male (pollen source). Eksotika and its sib line L19 produced abundant seeds (in excess of 1 000 seeds/fruit) while Paris was the least seedy (690 seeds). Differences also arose when inbred lines were used as pollen donors, particularly in influencing the occurrence of pre-germinated seeds in fruit. L19 was an undesirable male parent because 27% of the seeds developed as a result of fertilization by L19 pollen pre-germinated in the fruit.Overall, Eksotika, Sunrise Solo and L19 were highest in gross seed yield because of high fruit set and large number of seeds per fruit. The seed yield per 100 pollinations from these three inbreds ranged from 75 795 to 94 746 seeds.However, the percentage of viable seeds of L19 was lower because of high percentage of pre-germinated seeds. It was estimated that the cost of producing hybrid seeds using low seed-yielding inbreds like Paris and Morib may be 2.5–3 times that of Eksotika, whose hybrid seed is currently sold at    RM3 000/kg.

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