Twenty-two-year papaya breeding program: from breeding strategy establishment to cultivar development

The papaya crop occupies 32 thousand hectares of planted area in Brazil, with a total annual production of 1.6 million tons (12.5% of the world supply). The country stands out in this scenario as the second biggest producer of the fruit worldwide, only after India. The narrow genetic base of the crop once limited its variability, but the use of classical and molecular plant breeding techniques has enabled the development of a number of higher-yielding cultivars with different levels of resistance to fungal diseases. However, many studies still ought to be undertaken to investigate the papaya crop, given the constant search for higher-yielding cultivars with quality and flavor attributes and the wide range of pathogens affecting the crop, which has not yet shown fully resistant genotypes. Advances in the genomics of papaya provide tools that may improve cultivar production and development systems. This article describes studies conducted by the genetics and breeding group at UENF, in a partnership with Caliman Agricola S.A., using conventional breeding, diallel cross, and topcross, among other techniques, for the development of 21 hybrids, which were registered at MAPA, in addition to studies with DNA-based markers for sex determination and for the generation of resistant and productive cultivars. This review focuses on the 22 years of conventional breeding for the most recent molecular progress in papaya growing. The information reported here is extremely useful for breeders to develop resistant, productive, and high-quality varieties through assisted selection.