Pasture Science and other Crops

Evaluation of Cenchrus purpureus varieties tolerant to drought in the western region of Cuba

R.S. Herrera^{*  1} 
http://orcid.org/0000-0003-1424-6311

¹Instituto de Ciencia Animal, Carretera Central km 47 ½, Apartado Postal 24, San José de las Lajas, Mayabeque, Cuba

ABSTRACT

A three-year experiment was carried out to evaluate the agronomic performance of new varieties of Cenchrus purpureus (CT-600, CT-601, CT-602, CT-603, CT-605, CT-607, CT-608 and CT -609), tolerant to drought, obtained by in vitro tissue culture, and compared with its parent (CT-115) through a completely random design with five replications. There were significant differences between the height of the varieties and in both seasonal periods CT-605 stood out with values higher (P<0.05) at 90 cm. The leaves content (%) was only significantly different between the varieties in the dry season during the experimental stage, while the percentage of stems showed a similar response pattern. There were varieties that exceeded the DM yield of the control and especially the CT-605 with values of 21.82, 16.37 and 9.05 t DM/ha/year for the first, second and third year, respectively. With the exception of the first year, the varieties did not express their potential for biomass production under water stress conditions and future researches are suggested where rainfalls is less than 800 mm, as well as studying the effect of strategic fertilization on regimes of greater rainfall.

Key words: water stress; tolerance; yields; population

Africa is the center of origin of Cenchrus genus, previously called Pennisetum, and its varieties (Cenchrus purpureus) are widely used for the production of animal food, mainly as forage (Pereira et al. 2017) or through direct grazing (Gomide et al. 2011). This is determined by its high capacity to use light energy, carrier of the C₄ photosynthetic cycle, high DM yields, acceptable quality (Coombs et al. 1973) and it adapts, grows and develops in a wide variety of soils and climatic conditions (^{Febles and Herrera 2015}). In addition, it can be used for other purposes, such as: production of energy (Chakraborty et al. 2012) and bioethanol (Santos et al. 2018), paper industry (Madakadze et al. 2010) and natural herbicide (Norhafizah et al. 2013).

Different varieties have been used in Cuba since the beginning of the 20th century, such as the Napier, which spread throughout the country very quickly due, among other factors, to its high yields and acceptable chemical composition. Subsequently, other varieties were introduced, one of which was the King grass, which in the mid-1980s occupied 85% of the country's forage areas and displaced those traditionally used, which was determined for its high capacity to convert light energy into biomass, its ecological plasticity, high biomass yields and adequate quality (^{Herrera 2009}).

On the other hand, due to the importance achieved by this genus, genetic improvement programs are developed (Sinche et al. 2021) with the objective of obtaining varieties that surpass those traditionally used. Also, at the Instituto de Ciencia Animal, a breeding program for C. purpureus was developed with the aim of improving the productive indicators of the most used variety (King grass), in commercial production and adapting to current climatic and soil conditions, including varieties tolerant to drought and salinity (^{Herrera 2020}).

Due to the above, the objective of this article is to report the results achieved in the evaluation of Cenchrus purpureus varieties obtained by in vitro tissue culture tolerant to drought.

Materials and Methods

Location. the experiment was carried out at the Miguel Sistachs Naya pasture station belonging to Instituto de Ciencia Animal. The soil was Typical Red Ferralitic (^{Hernández et al. 2015}) whose chemical composition appears in table 1 and some climate indicators are shown in the table 2.

Table 1 Chemical composition of the soil in the experimental area 

pH		mg/100 g		OM, %	Total salts, %
KCl	H2O	P2O5	K2O
4.7	6.3	2.2	7.3	2.1	0.44

Table 2 Some climate indicators during the experimental stage 

Indicator	Years			Historical
	1	2	3
Rain, mm	954.1	1520.4	1291.4	1381.0
Minimum temperature, °C	19.6	18.7	18.9	18.4
Maximum temperature, °C	30.0	28.9	29.0	29.2
Average temperature, °C	25.7	23.5	24.6	24.0

Treatment and design. A total of eight new Cenchrus purpureus varieties (CT-600, CT-601, CT-602, CT-603, CT-605, CT-607, CT-608 and CT-609) obtained at Instituto de Ciencia Anima were evaluated by in vitro tissues culture with tolerance to drought (^{Herrera et al. 2003}), from Cuba CT-115 variety, which was used as a control. A random block design with four replications in 5 x 4 m plots was used.

Procedure. During the dry season, conventional soil preparation was carried out and a distance of 1m between rows was used. In the planting, a similar number of buds per row were ensured. Irrigation was applied at the time of planting and three times later to ensure adequate humidity and establishment. One hundred and twenty days after sowing, the establishment cut was made to start the evaluation process without the application of irrigation or fertilization. The experiment lasted three years.

Measurements. Sampling was carried out every 60 and 90 days in the rainy and dry seasons, respectively, where five tillers were taken per row in each replication to determine: plant height considered from the base to the apical cone, percentage of leaves and stems, DM yield and population as described by ^{Herrera (2006)}.

Statistical analysis. The database was created and analysis of variance was performed (^{Di Rienzo et al. 2012}) according to the experimental design and the mean values were compared according to ^{Duncan (1955)}. The theoretical assumptions of the analysis of variance were verified for all the variables, based on the ^{Shapiro and Wilk (1965)} tests for the normality of errors and ^{Levene (1960)} for the variance homogeneity and there was only the need to transform the population variable using √x.

Results and Discussion

Throughout the experimental stage, there were significant differences between the varieties in each climatic season for height (table 3). This is an indicator that expresses the plant growth in response to environmental conditions (climate and soil) and the management to which they are subjected. This could be determined by the biochemical and physiological particularities of each variety (Sinche et al. 2021) and, therefore, they will show better growth under conditions of humidity or rainfalls stress, an aspect that does not happen in the rainy season, where the climatic factors such as rainfalls, temperatures, intensity and duration of light, among other aspects, do not limit the growth and development of grasses.

Table 3 Performance of height (cm) during the evaluation 

Varieties	Years
	1	3
Rainy season
CT-115	75.34^a	79.58^ab
CT-600	84.92^ab	83.58^abc
CT-601	81.84^ab	86.58^bc
CT-602	79.92^ab	77.23^a
CT-603	88.42^ab	88.33^c
CT-605	78.25^ab	75.75^a
CT-607	73.00^a	76.73^a
CT-608	92.92^b	89.88^c
CT-609	86.25^ab	89.78^c
SE ±	3.53**	1.89***
Dry season
CT-115	66.25^a	65.63^a
CT-600	85.25^b	86.88^de
CT-601	69.63^a	72.13^ab
CT-602	89.63^b	99.00^f
CT-603	65.25^a	78.65^bcd
CT-605	92.00^b	90.00^ef
CT-607	67.13^a	76.00^abc
CT-608	84.63^b	84.63^cde
CT-609	86.50^b	90.75^ef
SE ±	1.75***	2.54***

^abcdValues with uncommon letters differ at P<0.05 (^Duncan1955)

** P<0.01 *** P<0.001

On the other hand, Guimaraes de Favare et al. (2019) when evaluating 13 varieties of Cenchrus purpureus for bioenergy production found that the height did not differ between them in the dry period and there were differences in the rainy period in both experimental years, but in the second year the height was lower. A similar pattern of performance was previously reported by ^{Herrera and Ramos (2015)}. However, it was encouraging in this research that, after three years of study, there was no decrease in height, which could be a reflection of its adaptation to the environment despite not using irrigation and nitrogen fertilization.

During the rainy season there was no variation in leaves content between the varieties in the three years studied. However, in the dry season of the first year, only CT-603 exceeded (P<0.001) the control (CT-115), while in the same period of the third year none exceeded CT-115 (table 4). This drew attention, since the response pattern varied over the years. However, the values recorded in the rainy period were encouraging despite the values recorded for rainfalls while, in the third year of study, with the exception of CT-603, all varieties showed higher leaves content compared to the first year. This performance should be studied in future experiments due to the role that leaves play in the Physiology and Biochemistry of plants. On the other hand, leaves content is a fundamental element for ruminants feeding, since it is the part most intake by animals, so it is an important element when selecting new varieties.

Table 4 Leaves content (%) during the evaluation period 

Varieties	Years
	1	3
Rainy season
CT-115	48.00	32.02
CT-600	45.98	30.84
CT-601	46.50	31.30
CT-602	44.37	30.30
CT-603	45.43	31.24
CT-605	47.99	30.84
CT-607	46.78	30.53
CT-608	44.26	30.61
CT-609	46.70	31.21
SE ±	1.11 NS	0.49 NS
Dry season
CT-115	46.23^b	45.39^b
CT-600	43.86^b	44.86^b
CT-601	44.81^b	44.81^b
CT-602	34.28^a	38.72^ab
CT-603	51.19^c	37.86^ab
CT-605	34.87^a	42.30^ab
CT-607	45.55^b	42.70^ab
CT-608	37.79^a	39.79^ab
CT-609	36.04^a	36.22^a
SE ±	0.86***	1.91**

^abcValues with uncommon letters differ at P<0.05 (^Duncan1955)

** P<0.01 *** P<0.001 NS: Not significant

Reyes-Perez et al. (2021) when evaluating five varieties of C. purpureus (Verde, Morado, Maralfalfa, CT-115 and Elefante) in Ecuador, found that leaves yield increased with fertilization and regrowth age and each variety showed a characteristic response pattern. Tulu et al. (2022) studied the effect of the year, the date and the cutting height in Napier and determined that the leaf/stem ratio decreased with the years of study and the cutting height, while the cutting date (month) had a varied effect. The mentioned authors relate these results to the performance of climatic factors, the plant age, the type of soil and the management of grass, among other aspects.

The stem content (table 5) showed an inverse performance to that mentioned above. However, this aspect can be unfavorable from the point of view of animal intake , since they, in the process of selecting food, first intake the leaves and ultimately the stems, but from the point of view of Plant Physiology, they favor the storage of soluble carbohydrates, especially in the lower parts of the stem, to facilitate the plant regrowth even in the absence of sufficient leaf area and, in addition, it allows the storage of appreciable amounts of water, which guarantees the metabolism and plant survival under stress conditions.

Table 5 Stems content (%) during the evaluation 

Varieties	Years
	1	3
Rainy season
CT-115	52.00	52.28
CT-600	54.03	53.76
CT-601	53.50	54.20
CT-602	55.64	55.64
CT-603	54.07	52.71
CT-605	52.01	52.01
CT-607	53.22	54.07
CT-608	55.74	54.97
CT-609	52.63	53.47
SE ±	1.28 NS	1.00 NS
Dry season
CT-115	53.77^b	54.61ª
CT-600	56.14^b	55.14ª
CT-601	55.19^b	55.19ª
CT-602	65.73c	61.28^ab
CT-603	48.81ª	62.22^ab
CT-605	65.13^c	57.70^ab
CT-607	54.45^b	57.30^ab
CT-608	62.21^c	60.21^ab
CT-609	63.96^c	63.79^b
SE ±	0.86***	1.91**

Values with uncommon letters differ at P<0.05 (^Duncan1955)

** P<0.01 *** P<0.001 NS: Not significant

On the other hand, ^{Arias et al. (2018}, ^{2019a b}) when evaluating some of the drought-tolerant varieties of C. purpureus (CT-601, CT-603, CT-605, CT-608 and CT-609) in the eastern region of the country, showed that the regrowth age increased the length, thickness and number of stem nodes, being these responses specific for each variety.

With the exception of the dry season of the first year, there were differences between varieties in yield for each seasonal period and for the annual total (table 6). The absence of differences in the first year of exploitation in the dry season is not easy to explain, especially if it is takes into account that in the rainy season there was. In the second year, in this same period, there were differences and the values tended to be lower when compared to the first year, which could be determined by the decrease in soil fertility due to the extraction of mineral elements that these plants make, especially nitrogen and potassium. This could be an indicator to carry out a strategic or maintenance fertilization using chemical fertilizers (if available) or organic from the second year of exploitation. The lowest values were recorded in the third year.

Table 6 Yields (tDM/ha) in the evaluation period 

Variety	Rainy season	Dry season	Total
First year
CT-115	12.14^b	3.24	15.38^b
CT-600	11.44^b	3.32	14.76^b
CT-601	12.68^b	3.01	15.69^b
CT-602	12.63^b	2.09	14.72^b
CT-603	13.05^b	2.48	15.53^b
CT-605	19.15^c	2.67	21.82^c
CT-607	7.61^a	2.56	10.17^a
CT-608	13.59^b	3.20	16.79^b
CT-609	13.81^b	2.50	16.31^b
SE ±	0.74***	0.42 NS	1.05***
Second year
CT-115	11.26^ab	3.59^d	14.85^ab
CT-600	10.53^ab	2.59^abc	13.12^ab
CT-601	11.93^b	3.36^cd	15.26^b
CT-602	12.70^b	2.18^a	14.88^ab
CT-603	11.64^b	2.94^abcd	14.58^ab
CT-605	12.89^b	3.48^d	16.37^ab
CT-607	8.55ª	3.01^bcd	11.56^a
CT-608	13.42^b	3.37^cd	16.79^ab
CT-609	11.11^ab	2.28^ab	13.39^ab
SE ±	0.68***	0.18***	2.55*
Third year
CT-115	3.06^a	0.44^b	3.50^a
CT-600	4.47^ab	0.51^b	4.98^c
CT-601	4.92^b	0.39^b	5.31^d
CT-602	10.00^c	0.15^a	10.15^f
CT-603	3.92a^b	0.57^bc	4.49^b
CT-605	8.65^c	0.40^b	9.05^e
CT-607	4.30^a	0.51^b	4.81^c
CT-608	10.00^c	0.75^c	10.75^f
CT-609	4.31^ab	0.44^b	4.75^c
SE ±	0.41***	0.05***	0.07***

^abcdValues with uncommon letters differ at P<0.05 (^Duncan1955)

* P<0.05 *** P<0.001 NS: Not significant

Reyes et al. (2021) found in four varieties of C. purpureus that the yield of green biomass and dry matter increased with fertilization and age. Sinche et al. (2021), when evaluating a population of Napier hybrids, found that indicators such as height, stem diameter, flowering, and yield varied among the hybrids. Ventra Rios et al. (2022), when they studied the response of Taiwan (C. purpureus) grass to cutting frequency, reported that yields increased with the regrowth age. ^{Arias et al. (2019a)} when evaluating some of the drought-tolerant varieties in the eastern region of Cuba reported increases in yields with the regrowth age. All this information has in common the specific and individual response of each of the studied plants.

All of the above is confirmed by the results published by ^{Arias et al. (2019b)} when studying physiological indicators such as absolute and relative growth rate, leaf area and leaf area index, leaf area duration and biomass duration in C. purpureus varieties with drought tolerance. The six varieties showed values that individually characterized each of them and confirmed their biochemical and physiological individuality.

In the evaluated period (table 7), there were no significant differences for the population of the varieties and the values at the end of the experiment were similar to those registered in the first year, since the varieties did not suffer depopulation. This is positive if it is taking into account that during the three years of research both irrigation and fertilization was used.

Table 7 Performance of the population (tillers/5m) during the evaluation 

Variety	Years
	1	3
Rainy season
CT-115	(10.73)3.22	(11.18)3.34
CT-600	(8.52)2.99	(8.85)2.98
CT-601	(9.85)3.16	(10.30)3.21
CT-602	(9.36)2.99	(9.25)3.04
CT-603	(8.78)2.99	(9.13)3.02
CT-605	(9.40)3.10	(9.55)3.09
CT-607	(9.53)3.07	(9.73)3.12
CT-608	(9.60)3.10	(9.78)3.13
CT-609	(10.43)4.21	(10.90)3.30
SE ±	0.56	0.08
Dry season
CT-115	(10.17)3.19	(10.70)3.27
CT-600	(8.94)2.99	(8.63)2.94
CT-601	9.67)3.11	(9.23)3.07
CT-602	(8.18)2.86	(8.78)2.96
CT-603	(8.82)2.97	(8.58)2.93
CT-605	(9.18)3.03	(9.23)3.04
CT-607	(9.42)3.07	(9.20)3.03
CT-608	(8.94)2.99	(9.15)3.02
CT-609	(22.56)4.75	(9.93)3.15
SE ±	0.50	0.08

( ) Real values

These varieties were evaluated (^{Díaz 2007}, ^{Arias et al. 2018}, ^{2019a b} and ^{Ray et al. 2018}) in the pasture station of Instituto de Investigaciones Agropecuarias Jorge Dimitrov, located in Cauto Valley, Bayamo, Granma and that area is characterized by soils with low fertility and rainfalls regimes that reach 700-800 mm of rain and drought periods that extend up to seven months). The results showed the adaptability of the varieties and, above all, the yields achieved in the dry season, where rainfalls did not exceed 50mm, so their performance against drought stress is unquestionable. In addition, promising results were obtained when evaluating the ruminal passage rate and ruminal degradability of these varieties (^{Ledea et al. 2016}, ²⁰¹⁷).

However, this was not the response found in the varieties in this study, which was determined by the high rainfalls that occurred in the second and third year of research (table 2), which limited the plants from expressing their production potential under drought stress conditions. However, in the first year of research, the value of rainfalls was lower than the rest of the experimental years and below the historical value, which could influence on the yields obtained that year. The previous determines the need to carry out future researches under of water stress conditions, as well as to use strategic fertilization in the rainy season in the western region of Cuba.

Acknowledgments

Thanks to the technicians M. García and Ana M. Cruz for their attention to the experiment, the sampling, the processing of samples and the analysis of the results.

References

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Received: January 23, 2022; Accepted: April 15, 2022

^*Email: [e-mail]

Conflict of interests: There are no conflicts of interest between the authors

Authors contribution: R. S. Herrera: Conceptualization, Investigation, Formal analysis, Writing - original draft