Introduction

Cotton belongs to the Malvaceae family (^{Matarrita, 1989}). The genus Gossypium, with approximately 20 species, is distributed in tropical and subtropical regions of both hemispheres. In Peru, the presence of Gossypium barbadense L. is reported and is commonly known as "brown cotton," also finding two ecotypes of G. raimondii Ulbrich. The first is known as "green cotton," and the second, as "wild cotton" that thrives in natural environments; it is probably the ancestor of the native and commercial varieties of cotton in Peru (^{Brako & Zarucchi, 1993}). According to Mostacero, Mejía and Gamarra (²⁰⁰⁹), wild cotton is endemic in the departments of Cajamarca and La Libertad, where today, cotton relics survive in surrounding areas where no human beings have established.

Morphologically, the cotton plant is relatively simple, and its phenology varies according to the species and the influence of the environment (^{López & Gil, 2017}; ^{Matarrita, 1989}). The ecotype known as wild cotton is the species G. raimondii, characterized as being a perennial, erect or prostrate and tree-like plant, which can reach a height of up to 4 m (^{Fernández & Rodríguez, 2007}). It is found in rocky, stony terrain, riverbeds, and irrigation ditches, at an altitude of 1,600 m a.s.l. (^{Mostacero et al., 2009}).

The ancient Peruvians on the north coast of Peru domesticated and cultivated native cotton with brown, green, and lilac fiber to elaborate their fabrics (^{Fernández, Rodríguez, & Westengen, 2003}). Archaeological studies by Stephens and Moseley (1975) have demonstrated the domestication process of wild to native cotton, with the report of seeds that represent an intermediate form between wild and native cotton in Huaca Prieta. It is assumed that the center of origin and diversity of native colored cotton is the northern part of Peru, where brown cotton (G. barbadense) and green cotton (G. raimondii) are closely related geographically, ecologically and genetically to the wild cotton ecotype (G. raimondii) (^{Fernández & Rodríguez, 2007}).

The cotton fruit is a capsule whose shape can be elongated, ovoid or spherical. The capsule takes approximately 50 days to mature, grows rapidly and reaches its normal size three weeks after fertilization. Its size varies according to the species, variety, and environmental conditions (^{Fernández & Rodríguez, 2007}). The fruits are characterized by the union of their carpels to a central axis, which originates a series of locules, which contain the seeds (^{Robles, 2012}); premature fruit fall is normal in the cotton plant and is increased by factors such as soil moisture, nutrient deficiency and temperature conditions (^{Matarrita, 1989}).

The seeds are usually ovoid, slightly angular, and with a fissure in the margin (^{Fernández, Rodríguez, & Westengen, 2003}). The seed consists of a testa, two large cotyledons, and a small embryo, containing between 15 % to 20 % protein, and up to 21 % oil (^{Fernández & Rodríguez, 2007}).

The fibers or hairs are formed from the constant lengthening of the epidermal cells of the seed, and the thickening results from the continuous deposition of cellulose in the primary fiber wall (^{Fernández & Rodríguez, 2007}; ^{Fernández et al., 2003}). Epidermal cells give rise to the formation of two different types of fiber: the first, long and thin, of 1.5 to 6.0 cm in length, with a thickness between 20 and 30 microns, can be woven or spun; the second, shorter and attached to the seed, constitutes the linter (^{Matarrita, 1989}).

For many years, the cultivation of colored fiber cotton was abandoned for improved varieties of white fiber, due to their precocity, production and lower incidence of pest insects (^{Gil & López, 2017}; ^{Kwiatkowska & López, 2000}); however, on the other hand, these fiber colored varieties have higher adaptability and drought resistance (^{Fernández et al., 2003}).

Nonetheless, this resulted in the loss of germplasm of many diverse and natural pigmented cotton varieties, which were used by thousand-year-old cultures in ancient Peru (^{Kwiatkowska & López, 2000}). However, the situation has changed since 2008, with Regulation No. 29224, which states color fiber cotton as a genetic, ethnic, and cultu- ral heritage (^{Pisani, Masiero, & Scrocco, 2015}). Currently, research has shown that color fiber is a genetically inherited trait, which results from the presence of pigments intermingled with cellulose, being controlled by partial dominance genes (^{Bhuyan & Saikia, 2005}; ^{De Carvalho, Correia, De Andrade, & Da Silva, 2014}; ^{Wang et al., 2014}).

At present, there is an interest in rescuing these varieties in response to the demand of the modern textile industry that seeks cleaner technologies, avoiding the use of carcinogenic dyes derived from petroleum. Thus, in the near future, these varieties of colored fiber may replace those of white cotton (^{Kwiatkowska & López, 2000}), due to their natural color and the valuation of their fibers in international markets (^{Pisani et al., 2015}). Although little is known about these varieties, there are communities in the departments of Lambayeque, Piura and San Martín that retain ancestral knowledge about the cultivation and processing of these varieties, from which they obtain thick yarns suitable for making bags, ornaments, clothing and other accessories (^{Cortijo & Cancio, 2012}).

Studies of fruit, seed and fiber characterization in cotton are of great importance, because they provide information on the genotype of a given species, to obtain recombinants with better characteristics (^{Méndez & Alcorcés, 2007}), as well as information that corroborates the denomination of wild cotton and the ecotype under study. Given the need for greater knowledge, the aim of this study was to characterize the fruits, seeds, and fibers of the G. raimondii ecotype called wild cotton.

Materials and methods

Measurement variables

Fruit and seed characteristics

The length and width of the fruits (cm) and seeds (mm) were measured using a precision gauge (vernier, Truper, U.S.), with a measuring scale between 0 and 150 mm. The number of seeds and locules per fruit was counted.

Fiber characteristics

The fiber length (mm) was measured with an Olympus SZX16 stereoscope. The equipment had a resolution of 900 pairs of lines/mm and a measuring scale of 3.5x to 230x. An Olympus BX41 microscope equipped with a DP72 camera was used to measure the fiber width (µm). The equipment had a resolution of 3.36-0.27 µm and a measurement scale between 40x and 1,000x.

Elaborated by the authors

Figure 1 Location of the departments of La Libertad and Cajamarca, Peru 

Data analysis

A descriptive statistical analysis was considered, consisting of a sample of 180 ripe fruits, of which 60 fruits were randomly selected, comprising the number of repetitions per component evalua- ted. For this, the average, the deviation, and the standard error were estimated using the statistical program R.

Results and discussion

Fruit and seed characteristics

Comparing the wild cotton ecotype (G. raimondii) and the brown cotton (G. barbadense), the first shows small fruits of 2.14 ± 0.18 cm long and 1.46 ± 0.11 cm wide (table 1), as well as very small seeds that measure 5.74 ± 0.45 mm long and 3.25 ± 0.33 mm wide; on the other hand, the fruits of the second, have an average length of 4.264 cm and a width of 4.107 cm. moreover, the seeds have an average of 0.784 cm long and 0.488 cm wide (^{López, López, Gil, Caicedo, & Mendoza, 2018}).

Nonetheless, wild cotton has a higher number of locules and seeds (23.6 ± 2.61) in comparison to the brown cotton, in which an average of 4 lobes and between 20 and 21 seeds per fruit are reported (^{Gil & López, 2015}). It is important to consider that Matarrita (¹⁹⁸⁹) reported that native and wild cotton could have between 4 and 5 lobes versus the commercial cotton that has up to 3 lobes per fruit. It is also essential to highlight the presence of green linters in the seed of the common ecotype (G. raimondii), which is not evident in the brown cotton (G. barbadense) (^{Gil & López, 2015}).

Another study considers that wild plants or with incipient domestication are those that show defense structures such as hairs in the seeds (linters) and small fruit and seed sizes, which are evidenced in wild cotton (G. raimondii) (^{Medina, 2010}). On the other hand, brown cotton (G. barbadense) shows characteristics associated with domesticated crops (^{Gil & López, 2015}), given that domestication syndrome is associated with dramatic alterations in plant morphology, with evidence of an increase in the weight and size of fruits and seeds (^{Medina, 2010}).

Table 1 Summary of the characteristics of the fruit, seed, and fiber of the wild cotton ecotype (G. raimondii) 

Elaborated by the authors

Figure 2 Length and width measurement of the fiber of the wild cotton ecotype (G. raimondii). 

Conclusions

The characterization of the fruit, seed, and fiber of the wild cotton ecotype (G. raimondii) allows diffe- rentiating it from the brown cotton (G. barbadense) and the common green cotton ecotype (G. raimondii). We recommend continuing with molecular studies that allow elucidating the degree of relatedness of these species and ecotypes.