Biology of the papaya plant

Abstract

The papaya plant (Carica papaya L.) has been described with a large variety of adjectives, which acknowledge the structural and functional complexity and the high phenotypic plasticity of this giant tropical herb (León 1987). C. papaya, with a somatic chromosome number of 18, is the sole species of this genus of the Caricaceae, a family well represented in the Neotropics, that includes six genera with at least 35 species (Fisher 1980; Ming et al. 2008; Carvalho and Renner 2013 ). Most likely, papaya originated along the Caribbean coast of Mesoamerica (Fitch 2005 ) and spread to many tropical and subtropical regions around the world (Kim et al. 2002), where its distribution is limited by chilling sensitivity (Allan 2002; Dhekney et al. 2007). Domestication eventually led to substantial changes in vegetative growth and sexual forms that distinguish wild populations from cultivated genotypes (Paz and Vázquez-Yanes 1998; Niklas and Marler 2007). Because of its high yield, nutritional value, functional properties, and year-round fruit production, the importance of this crop around the world is undeniable. The papaya plant is a semi-woody, latex-producing, usually single-stemmed, short-lived perennial herb. The relatively small genome of this species shows peculiarities in major gene groups involved in cell size and lignification, carbohydrate economy, photoperiodic responses, and secondary metabolites, which place the papaya in an intermediate position between herbs and trees (Ming et al. 2008 ). Reproductive precocity, high photosynthetic rates of short-lived leaves, fast growth, high reproductive output, production of many seeds, and low construction cost of hollow stems (Fig. 2.1a–d), petioles, and fruits characterize this successful tropical pioneer. High phenotypic plasticity allows this plant to establish in recently disturbed sites, thriving during early stages of tropical succession and as members of diverse agroecosystems as well (Hart 1980; Ewel 1986), that constitute important genetic reservoirs (Brown et al. 2012 ). At any given time, adult papaya plants can sustain vegetative growth, fl owering, and dozens of fruits at different stages of development, simultaneously.