Sex and ploidy of anther culture derived papaya (Carica papaya L.) plants

Summary To improve the efficiency of papaya anther culture, we investigated (1) hormonal medium conditions for inducing haploids or dihaploids; (2) identified the sex of established plantlets using a sex-specific DNA molecular marker and (3) estimated their ploidy by flow cytometry analysis of DNA content. Anthers with a mixture of uninucleate, mitotic, and binucleate microspores were collected from a male plant, and cultured on MS agar medium with different concentrations of CPPU and NAA. An embryo induction rate of 13.8% was attained on MS agar medium with 0.01 mg l⁻¹ CPPU and 0.1 mg l⁻¹ NAA. The induced embryos were subcultured on medium with 0.0025 mg l⁻¹ CPPU. Rooting of the developed shoots was promoted by treating their basal parts with 1500 mg l⁻¹ IBA in a 50% ethanol solution for about 10 seconds. All the embryo-derived plantlets (27 plants) were identified as female, implying that they were derived from microspores. In addition, 26 plants were determined to be triploids and one to be tetraploids. We also observed a wide range of morphological variation (e.g., in tree height and fruit size) among the established plants. Based on the results, we discussed a potential value of anther culture techniques for the breeding of papaya.     

Morphology of papaya plants derived via anther culture

This study was set up to investigate the morphological and fruiting characteristics of anther derived triploid papaya and evaluate their usefulness in commercial fruit production and breeding. A commercial diploid dwarf cultivar, ‘Wonder blight’ and 26 anther derived papaya strains were raised in the same green house. Data were collected on their morphological and fruiting characteristics like trunk height, fruiting height and the sizes of leaves, flowers and fruits. The anther derived papaya strains were variable in height and could be classified into dwarf, semi dwarf and tall. All the anther derived papaya strains bore only female flowers and produced fruits parthenocarpically. Parthenocarpic ability was variable among the strains. The dwarf and semi dwarf strains were fewer than the tall strains and they had good bearing and high yield of fruits. Two dwarf strains particularly produced parthenocarpic fruits that weighed an average of 670.0 and 871.3 g, compared to the diploid cultivar, ‘Wonder blight’, whose fruits weighed 696.4 g. The combination of short stature with a high yield of large fruits means that these strains have a lot of potential for exploitation in both breeding and commercial fruit production.