Origin

Stevia rebaudiana for research purposes was introduced in Mexico in 2010, the work mainly focused on determining the adaptation of the crop when realizing the productive potential of S. rebaudiana under irrigation conditions and validating some technological components such as: population densities, weed and disease control, in addition to determining the concentration of glycosides in leaves (^{Ramírez-Jaramillo et al., 2011a}).

The selection work began on the variety in 2012, the year in which we worked with genetic materials of ‘stevia’, in the project to promote innovation we worked on the production of ‘stevia’ seedlings in 2015 and 2016 the material continued to be evaluated in the project for the genetic improvement of the S. rebaudiana crop to obtain Mexican clonal varieties and in 2017, in the project for characterization of genetic materials of S. rebaudiana, the last agronomic tests of the variety were carried out.

The first varieties tested at an experimental level in Mexico were Morita II due to its high content of Rebaudioside-A and its tolerance to Septoria and the creole material from Paraguay, due to its variability and greater availability of Stevioside. The studies carried out indicated that the content of Rebaudioside-A in Morita II presented concentrations that were from 7 to 13% of Rebaudioside-A and of Stevioside from 1.2 to 5%, in the case of creole materials in addition to presenting a great variability, the content of Stevioside was higher than that of Rebaudioside A, therefore, with a less sweet taste (^{Ramírez et al., 2011b}).

Due to these results, selection works were carried out among the creole materials and currently the CIRSE has a group of outstanding clonal materials of S. rebaudiana. Of a total of 20 materials, two of them have phenological advantages suitable for the region such as: better plant height, leaves larger than Morita II, multi-stem, possibility of harvesting up to 6 times against the three or four of Morita II, being the best of the clonal varieties, the Ch’ujuk.

Plant height

Ch’ujuk is a clonal variety with an intermediate cycle (80 to 100 days), whose plant is semi-decumbent; that is, from 10 to 70% of the stems are in contact with the ground, with respect to the height present an average of 60 cm and the Morita II of 45 cm (Figure 1). Regarding its resistance to lodging, it shows resistance above all because it is multi stem and with abundant roots in relation to Morita II, which is one stem and with scarce root development, which makes it more susceptible to lodging and to the damage of fungi present in the soil.

Figure 1 The Ch’ujuk variety (left side), was up to 20 cm taller than Morita II (right side of the photo). 

Stem type and its characteristics

It presented up to eight primary stems while Morita II only presented three, with regard to secondary stems, the Ch’ujuk clone is highly branched compared to Morita II, which presented little branched stems (Figure 2). The stem diameter was 15.9 mm compared to 8.39 in Morita II, in the case of the length of the internodes it is greater in Morita II with 8 cm against 7 cm of the clone.

Figure 2 Ch’ujuk variety has 6 cm long leaves, is multi-stemmed and with abundant roots. 

Leaf type and its characteristics

An important factor in the performance of the ‘stevia’ crop is the leaves. The length of the leaf of the clonal variety Ch’ujuk is 6 cm, standing out in relation to Morita II with 4.5 cm. Regarding the width of the leaf, Ch’ujuk is 3 cm and Morita II is 1.5 cm, with petioles in both cases considered sessile, the margins of the leaves in the clonal variety Ch’ujuk are crenate, while in the case of Morita II it is serrated and the number of teeth in the margin of the blade is 12 and 18 respectively. The position of the leaves on the main stem is opposite in all three cases.

Color of the inflorescence of the clonal variety Ch’ujuk.

The color of the inflorescence is white (Figure 3).

Figure 3 cyclof . The color of the inflorescence in the clonal variety Ch’ujuk was white. 

Crop the clonal variety Ch’ujuk

In the case of the cultivation cycle, the clonal variety has a short cycle (80 to 100 days), while Morita II has an intermediate cycle (100 to 130 days). The above allows up to six cuts per year to the clonal variety.

Sanitary behavior

In the case of the Ch’ujuk clone, it shows a moderate resistance to Rhizoctonia solani, Fusarium sp. and Sclerotium rolfsii, but not in the case of Morita II, which is moderately susceptible, as regards Alternaria sp., Septoria sp. and Cercospora sp.

Industrial aspects

The concentration of the main glycosides is 6.78 g 100 g^-1 of Stevioside leaf dry, 7.46 g per 100 g of Rebaudioside-A leaf dry and Rebaudioside-C 2.14 g 100 g^-1 of dry leaf, contrary to Morita II content, which has 3.97 g 100 g^-1 of Stevioside leaf dry, 14.5 g 100 g^-1 of Rebaudioside-A leaf dry and 2.24 g per 100 g of Rebaudioside-C leaf dry.

Yield

The potential yield evaluated was 9.67 t ha^-1 year^-1 of dry leaf, which represents a content of Rebaudioside-A of 0.73 t, of Stevioside 0.65 t and Rebaudioside-C 0.2 t (Figure 4).

Figure 4 Yield in t ha^-1 year^-1 of dry leaf and of three of the main steviol glycosides in Morita II and the clonal variety Ch’ujuk. 

Conclusions

The clonal variety Ch’ujuk is a material that has a higher yield potential than Morita II, due to its more appropriate agronomic characteristics such as: plant height, number of stems, types of leaves and tolerance to diseases. The yield obtained was 9.67 t ha^-1 year^-1, which was more than twice the recorded yield of Morita II (3.5 t ha^-1 year^-1).

Regarding glycoside content, Morita II presented a high concentration of Rebaudioside A, which was expected; however, the clonal variety Ch’ujuk presented an adequate balance between the contents of Stevioside and Rebaudioside-A, making it attractive for the sweetener industry and for direct consumption for health purposes.

The new Ch’ujuk variety is recommended for the states of the Yucatán Península: Campeche, Quintana Roo and Yucatan, and potentially in other states of the Mexican tropics such as: Nayarit, Michoacán, Jalisco, Guerrero, Oaxaca, Chiapas, Veracruz, Tabasco, Campeche, Quintana Roo, Yucatan. The disposition of cuttings for commercial plantings of the clonal variety Ch’ujuk, can be acquired at the National Institute of Forestry, Agricultural and Livestock Research (INIFAP)-Campo Experimental Mococha.