Vegetal material

The study was carried out on the ‘Roja púrpura’ selection chosen for its outstanding fruit characteristics, which are: red flesh, average weight of 150 g, moderately resistant to post-harvest handling. The age of the plants is 4 years, and they are established at 3 x 4 m between plants and rows, respectively. The period from flower bud to maturity of consumption is approximately 140 days.

Treatment design and experimental design

Two factors were evaluated: 1) Thidiazuron biostimulant at three levels (0, 400 and 800 ppm) and 2) plastic cover with irrigation at four levels (without cover and without irrigation, without cover and with irrigation, with irrigation and without cover, with irrigation and with cover), so there was a 3 x 4 factorial arrangement, generating 12 treatments, with three repetitions, the experimental unit was a group of four cladodes that received the same treatment, the experimental design was divided plots, where the large plot was the partial canopy cover with the emergency irrigation and the small plot was the TDZ dose.

Establishment and management of the experiment

In January 2018 12 plants of prickly pear cactus were selected with a minimum of 12 cladodes a year of growth to form three groups of four cladodes per plant receiving the same treatment. The selection criteria were based primarily on cladodes positioned vertically and with the lateral faces facing north-south, due to the fact that they received more solar radiation.

Thidiazuron application

One day before applying the treatments, a solution was prepared with 20% garlic oil from the San Lucas brand. 15% commercial product was mixed with 7.5 ml of Bayer^MR Inex-A surfactant. On February 14, 2018, two mixtures were prepared, using the mixture of garlic oil with Inex-A as the base components of these, 400 ppm of the 50% Bayer^MR TDZ biostimulant was added to the first, and the second 800 ppm of it. product, both were finally graduated at 1 L, with 500 mL of prickly pear mucilage diluted in tap water.

Installation of plastic covers and irrigation application

The partial canopy cover was made with 700 gauge plastic and 20% shade. The irrigation was done manually, depositing the water in bowls of 1m long, 1m wide and 15cm high. After the first irrigation (March, 2018), the 15cm deep bowl was covered with barley straw, this in order to retain moisture, the irrigations were applied once a month until July 2018, providing 30 L plant^-1 month^-1 to each cajete.

Temperature record outdoors and under plastic cover

Three daily readings of average temperature, outdoors and under plastic cover were recorded, using Steren model Ter-150a portable digital thermometers model 150-150 m high. The readings were at 8:00, 14:00 and 19:00.

Percentage of vegetative and flower sprouts

Fifteen days after the application of the treatments, the first sprouts emerged, weekly counts were made for 44 days of the total meristems sprouted from each cladode and they were converted to a percentage considering the total areolas per cladode (Figure 1).

Figure 1 Budding of flower and vegetative sprouts 30 days after TDZ application at a dose of 400 ppm. 

The floral and vegetative meristems were also differentiated. According to ^{Pimienta et al. (1993)} when a prickly pear cactus sprout emerged, it is differentiated by the shape of the upper part of the bud: floral (round) or vegetative (rectangular).

Statistical analysis

An analysis of variance and comparison of means was carried out with the Tukey test, with a reliability level of p≤ 0.05 for the response variable, the Statistical Analysis Software program, version 9.4 was used. (^{SAS Institute, 2013}).

Percentage of flower and vegetative sprouts

The analysis of variance indicates that there were differences (p≤ 0.5) between treatments due to the effect of TDZ and the growth conditions of the plant: canopy cover, irrigation or combination of both in the percentage of vegetative and flower sprouts. 15 days after the application of TDZ, the start of sprouting was observed in the cladodes with the application of TDZ under the different growth conditions. With irrigation and 800 ppm of TDZ, the highest percentage of vegetative sprouts was obtained, being 12.7% (Figure 3a).

Figure 3 Percentage of vegetative sprouts (a); and flowers (b) 15 days after TDZ application under four management conditions. Equal letters are not statistically significant Tukey (p≤ 0.05). 

The percentage of flower sprouts (Figure 3b) was higher with the use of cover and irrigation with the dose of 400 ppm of TDZ, since it stimulated 99.4% of budding, followed by treatment with cover and 800 ppm of TDZ with 90.8%. Twenty-two days after the application of TDZ, the prickly pear cactus plants under irrigation conditions and the application of 800 ppm of TDZ showed a higher percentage of vegetative sprouting with 21.3% (Figure 4a), while the percentage of flower sprouts decreased.

Figure 4 Percentage of vegetative sprouts (a); and flowers (b) 22 days after the application of the dose of TDZ and plastic cover with irrigation in prickly pear cactus ‘Roja purpura’. The lines represent the means and the equal letters are not statistically significant Tukey (p≤ 0.05). 

Using cover and irrigation with 400 ppm of TDZ the percentage was 99.4 (Figure 3b) against 93.7% counted 7 days before (Figure 4b), as well as with cover and 800 ppm of TDZ whose percentages were 90.8 (Figure 3b) and 80.9 (Figure 4b). The last appearance of new sprouts and changes from floral to vegetative meristems was at 44 days after the application of the doses of TDZ in the prickly pear cactus plants, in the case of vegetative sprouting, the cover with irrigation with 400 ppm of TDZ it ended with the highest percentage of sprouting with 99.4%, along with cover with 800 ppm of TDZ with 90.8% of sprouting (Figure 5a).

Figure 5 Percentage of vegetative sprouts (a); and flowers (b) 44 days after the application of the dose of TDZ and plastic cover with irrigation in prickly pear cactus ‘Roja purpura’. The lines represent the means and the equal letters are not statistically significant Tukey (p≤ 0.05). 

In the end, the highest percentage of flower sprouts occurred in the treatment of 800 ppm of TDZ with 53.9% and covered with irrigation with 400 ppm of TDZ with a sprouting of 46.8% (Figure 5b), surpassing the results obtained by ^{Aguilar (2005)} with 5% vegetative and 42.3% floral, making rings in ‘Tlaconopal’ prickly pear cactus.

From 22 to 37 days after applying the TDZ, the cover treatments began to decrease the percentage of flower sprouts and increase the vegetative ones, it is suggested that this was caused by the effect of the temperature of the plastic cover (Figure 6), According to ^{Avitia and Castillo (2007)} reported, there is a floral reversal when exposing the plants in the bud development stage to high temperatures, in vine plants. The data found suggests continuing to study the initial effect of heat on the environment and its relationship with Thiadizuron in the stimulation of the nopal flower sprouting.

Figure 6 Growth and development of cladodes of plants with cover, irrigation and TDZ. 

Yield

Fruits of 6 treatments were obtained, since the plants that were managed with canopy cover or irrigation and their respective dose of TDZ (400 and 800 ppm) did not have prickly pears, due to the fall of mother cladodes due to the excessive weight of new cladodes sprouted (Figure 7) and also due to floral reversal. Due to the lack of fruits in all the treatments, the yield values were estimated and a descriptive analysis was performed.

Figure 7 Fall of the mother cladode, due to overweight caused by the excess of new cladodes. 

The highest yields were obtained in the cover treatment with irrigation and 400 ppm of TDZ with a weight of 2193.6 g cladode^-1, this value contrasts with the control that had a yield of 339.7 g cladode^-1 (Table 1) , this response could be due to the effect of the application of TDZ, in conditions of canopy cover and irrigation, which exceeds the data reported by ^{Valdez et al. (2013)} with 1 186 g cladode^-1.

^{Martinez et al. (2001)} presented varied yields according to cladode markers, when removing 25% of the stalk obtained 16 kg plant^-1, pruning 50% 46 kg plant^-1 and with the elimination of 75% 76 kg plant^-1. Also ^{Zegbe and Mena (2006)} obtained yields in a first flowering of 48.3 kg plant^-1 later they induced a second flowering eliminating all the vegetative and floral sprouts of the same year, of this second flow, they reported 16.7 kg plant^-1. ^{Pinedo et al. (2010)} obtained a prickly pear productivity for refrigeration-refrigeration of 30 t ha^-1.

Fruit weight

The fruits with the highest weight were harvested from the 800 ppm TDZ treatment, with 140.2 g, surpassing the control with fruits of 67.9 g, it is suggested that this was the cause of rainfall in June and July, since the fruits obtained from treatments with cover presented approximate weights to the control (Table 1) (^{Gugliuzza et al., 2002}); however, ^{Corrales and Hernández (2005)} reported higher weight in ‘Cristalina’ prickly pear with 220 g seed and 180 g seedless treated with 150 mg L^-1 of gibberellic acid (^{Zegbe and Mena, 2008}).

They obtained fruits of prickly pear ‘Cristalina’ of 188.5g in the first flowering of April-May, while in the second flowering of September-October, induced by the elimination of cladodes and floral meristems, they harvested fruits of 202.5g ^{Aquino et al. (2012)} characterized fruits of varieties Opuntia spp. ‘Rojo púrpura’ reporting weight of 160.37 g, ^{Ochoa and Guerrero (2013)} obtained fruits of the‘ Blanca’ prickly pear weighing 99.17 g. And ^{Varela et al. (2018)} inducing parthenocarpy, they harvested ‘Cristalina’ prickly pear of 137.8 g and ‘Burrona’ 140.8 g.