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INTRODUCTION
Guava is a species native from Tropical America, specifically, from México and Peru. It belongs to the family of Myrtaceae that is constituted by more than 133 genera and 3800 species (Bandera and Pérez, 2015). At present, the production and commercial exploitation of guava is widespread in many countries of the world, highlighting Australia, Brazil, Colombia, Egypt, United States, Mexico, Philippines, India, South Africa and Venezuela. It is a natural source of vitamins and minerals, which makes it one of the most valuable and appreciated fruits (Lakpathi et al., 2013). It is well known throughout the world for its varied qualities, especially for its high content of vitamin C, digestibility coefficient and the amount of calories (Yam et al., 2010; Lakpathi et al., 2013; Sangerman et al., 2013).
Cuban agriculture is working in a program to increment and diversify fruit trees to augment offers to the population and exportation and guava production is an important part to achieve this objective. In 2015, Cuba had 12 109 ha of harvested of guava, 991 ha belonged to the state sector and 11 118 ha to the private sector, which represented 91,8% of the area total (ONEI, 2016).
In guava tree, the pruning production is very important, since fruits are born in the new sprouts. Besides, it makes possible the use of high densities of plantation, the control of weeds and pests and the efficient execution of the harvest (Boora et al., 2016). On the other hand, the pruning constitutes the initial step in the works for the re-graft of the plantations (change of a tree’s canopy). Quijada et al. (2009), Yam et al. (2010), Singh (2011) and Vento (2011), established that pruning consists in the elimination of lively parts of the plant with the aim of modifying the habit of growth. Definitively, with the pruning it is pursued to contribute to establish the shape of the plant in order to achieve the biggest operability and efficiency of the characteristic cultivation works, and to reduce the aging of the plant by the renewal of its parts to maintain adequate and uniforms productions. The conformation of the canopy of a tree is essential to control the pattern of growth, the shape of the tree and maintaining a high yield (Singh, 2011). Besides, the pruning is indispensable in frames of plantation with very high density to maintain the vigor, yield, and the fruit quality in the final years (Bhagawati et al., 2015). The main types of pruning on the guava tree are: formation, sanitary, conformation or in hedge, of fructification and rehabilitation (Mederos, 1988; Peña et al., 1996). The pruning of formation and fructification must be made by manual form since they require major precision during the cut, however, the pruning of rehabilitation and conformation can be realized of mechanized form.
Several researches were carried out using different types of guava pruning, changing in intensity, schedule, plantation frames, and the evaluation of the effect of these variables on the agricultural yield and guava quality(Singh et al., 2001; Quijada et al., 2005; Serrano et al., 2008, 2009; Mehta et al., 2012; Madhubala et al., 2013). These works show how the pruning influences the crop yields. Due to the importance that this agricultural operation has and the lack of scientific information on the pruning of guava in Cuba, it is necessary to review the researches that have been done on this subject. Based on the need of the information, the present paper has the objective to analyze the research conducted on pruning of the guava tree and its influence on its yield.
DEVELOPMENT
A bibliographic review was accomplished related with the pruning, the intensities, epoch and frequency of pruning and the productive results achieved with this. The consulted materials comprehended the results from the past XX century up to present days, from papers of Cuba, Brazil, India, Mexico and Venezuela.
In the guava tree, the time elapsed between the appearance of the flowers and the maturation of the fruit fluctuates between five or six months, according to the climatic conditions and the availability of water and nutrients. In conditions of hydric deficit, the reduction of the yield and a decrease of the life cycle of the plant are produced (depending on the kind of soil and growing). In high-temperature zones with precipitations well distributed during the whole year, it gets a continuous production (Vento, 2011).
Guava tree can maintain the flowering throughout the year, manifesting two periods of maximum flowering. The first occurs between March and April, in which the highest number of flowers is reached and the fruits are harvested in greater volume in the months of August-September and are of lower quality and sweetness. A second peak of flower production occurs from October to November with a lower intensity of flowering than the first one. In this case, fruits are harvested from March to April and fruits are of higher quality and sweetness (Peña et al., 1996)). Singh et al. (2001), describe a similar behavior in the production of guava in India. In that country, the highest production is reached from July to October, in the rainy season, but with lower quality of the fruit. Production in smaller quantity, but with higher quality of the fruit is obtained from November to February, during the winter. Also in Venezuela, there are two periods of production, the first one from June to August, with almost 50% of the harvest. The second period is from November to January with close to 30% production, associated with the physiological response of the plant to the degree of soil moisture, which is directly associated with the fructification potential (Quijada et al., 2009).
The flowers of guava tree grow mainly in the new emerging terminal sprouts. Agricultural operations such as irrigation, fertilization, defoliation and the pruning can be used to stimulate the growth and fructification of this plant (Singh et al., 2001). Researchers like Bhagawati et al. (2015), Singh et al. (2001), Serrano et al. (2008, 2009), Quijada et al. (2009), Mehta et al. (2012) and Lakpathi et al. (2013), among others, have reported increases in yield, fruit size and quality attributes of guava as a result of different periods, intensities and types of pruning. Singh et al. (2001) attribute the improvement in fruiting to a better penetration of light inside the tree canopy after pruning. Another aspect to consider with regard to the benefits of pruning and its effect on the yield of guava, is the possibility of sowing a greater number of plants per hectare reducing the plantation frame, reaching a higher density of plants per hectare (Mehta et al., 2012; Kumawat et al., 2014)
Quijada et al. (2005) and Quijada et al. (2009), conducted research with the purpose of evaluating the effect of pruning on guava production. They used different treatments evaluating different types of pruning and their effects on production. The results showed that, in most of the evaluated months, the pruned trees increased their production with respect to the treatment without pruning, observing larger volumes of fruits in the treatments in which the monthly pruning and with the central pruning were done. In general, the pruning modified the guava production curve of this region. For other regions in Venezuela, the pruned trees reached the highest values of productivity and productive efficiency indices. These authors recommend combined pruning (monthly pruning plus central pruning) for the study area because it presented better productive yield and higher fructification and productive efficiency indexes. On the other hand, they state that pruned trees have a lower ratio of plant height versus crown radius, which allows higher planting densities.
The period of the crop phenologic stage during pruning, modify the productive results of guava plants. Hojo et al. (2007), determined, for the variety Pedro Sato in Brazil, show that the period of pruning has influence in the physical chemical characteristics of the fruits and it allows getting yields with high quality of the fruits in not usual periods or in others of minor production. Besides, they outline that the fructification pruning allows harvesting fruits in the periods desired by the producer, making possible to carry out the harvest when the presence of this fruit in the markets is minor.
Researches of Serrano et al. (2008), in guava Paluma, in the state of Espírito Santo in Brazil, report that since the pruning to the beginning of the harvest concentrated would have about 189 to 203 days, according to the epoch of realization of the fructification pruning. These authors determined that the pruned plants in February present bigger production and number of fruits per plant and that the plants pruned in January and February present peak of harvest in the period of the best prices of the product.
Mehta et al. (2012), carried out researches in guava Sardar cultivar, in India, cultivated at a garden with ultra-high density of plantation 1 m x 2 m. They evaluated the effect of pruning three times a year (March, May, and October), once a year in May and once a year in October. They measured diameter of the trunk, number of flowers per plant, number of fruits per plant and yield per plant. The diameter of the trunk did not vary in any treatment researched, but the pruning three times a year proved to have the maximum number of flowers per plant and the biggest yield of fruits per hectare.
The growth of the new sprouts is largely influenced by the date of pruning. Singh et al. (2001) found that the sprouts from branches pruned in February and March were bigger than the ones in unpruned trees. The response of the vegetative growth of guava tree to the pruning seems to vary with the month of operation and cultivar. In general, these authors found that May was the best month for the pruning, given that it caused a shortening of the sprouts growth (24,0 to 21,0 cm and of 16,5 to 12,0 cm) in the cultivars Sardar and Allahabad Safeda, respectively. The percentage of formation of flowers buttons in the new sprouts was affected by the different dates of pruning. The trees pruned in May produced maximum sprouts of flowering from July to September in Sardar (70%) and Allahabad Safeda (73%) compared with unpruned trees (26%). The total yield was major in the trees pruned in May and June than the not pruned or the pruned in February or March.
Serrano et al. (2009), evaluated the phenology, yield and quality of guava, cultivar Paluma, according to different pruning dates. They shortened the guava branches to 1/3 of the original length, without consideration for the branch diameter. The research was carried out on a nine-year plantation, with a planting frame of 6 x 4,5 m; in orchard without irrigation. The pruning took place in four different dates of the year, on August 27, September 11, September 26 and October 11. The results showed that the pruning date significantly influenced the duration of the phenological phases of the guava trees. The pruning carried out in August caused the phenological phases to spread more than when the pruning was carried out in October, due to a greater rain fall and higher average temperature in October (20,1 °C), with respect to August (18 °C). The time since the pruning to the beginning of fruit maturation was greater also in the pruning carried out in August. The trees pruned in August and at the beginning of September showed a higher index of fruit fixation, higher yield and better physical characteristics of the fruits.
Peña et al. (1996), indicate that some authors report the date of pruning like influential in the percentage of fallen fruits and when the pruning is later, the yield increases. These aspects reveal the importance of establishing the dates of pruning with precision and of carrying it out in the optimal periods to achieve bigger production of fruits.
The pruning intensity is another of the factors that have influence over the yield and the fruit quality of the guava tree. In India, Lakpathi et al. (2013), accomplished researches in guava, cultivar Allahabad Safeda, under high density of plantation. They determined the effect of three pruning intensities in the yield and the fruit quality, leaving 10 cm, 20 cm and 30 cm from the base to the sprout. Their results evidenced that the number of days until the appearing of the first vegetative sprout was significantly influenced only for the pruning intensity. When the tree was pruned to 10 cm the sprout of the new buds was produced faster, it got the bigger diameter, average weight and yield of the fruits in harvest. However, the fruits quality was not different in no one of the researched treatments. Bigger entrance of solar light within the canopy of the trees, because of the pruning, can influence the vegetative growth, the efficiency of the photosynthesis, the floral initiation, and the color, size and quality of the fruit.
Bhagawati et al. (2015), reported that in studies accomplished with three intensities of pruning (light, moderated and severe) and without pruning, to gardens with guava trees of many years, the yield, size and fruits weight increased with the pruning intensity and they were the lowest in the treatment without pruning. These authors propose, besides, that the complete pruning of the tree has rejuvenating impact at old plantations, due to a better use of the light in the process of photosynthesis.
Kamal et al. (2016), determined that in plants of 10 years in production, the utilization of different intensities of pruning (15 cm, 30 cm, 45 cm and 60 cm) induced more production of new sprouts than the treatment without pruning, increasing the flowers production and later on bigger fruit yield. The pruning influences the process of metabolism of the plant, which determines the yield. The pruning treatment at 45 cm was the one that provoked the biggest growth, early flowering and very good fruit yield. Authors like Lötter (1989) and Serrano et al. (2008, 2009), refer that in severe pruning the production of fruits in guava Sardar and Fan Retief decreases. Serrano et al. (2008b) evaluated the effect of three intensities of fructification pruning and classified them according to the distance at which branches were pruned from their base. The classification established severe pruning (branches pruned at 1 cm from their base), average pruning (branches pruned at 1/3 of their length from their base) and light pruning (branches pruned at 2/3 of their length from their base). All branches of growth of the plants were pruned without taking into account their diameter, besides all fruits and flowers were eliminated. These authors found that plants with light pruning presented the biggest number of sprouts and established branches and that plants that were pruned of severe form presented the minor number of sprouts, of branches, of fruits and yield per plant.
Mehta et al. (2012), determined than the maximum yield, in guava Sardar in ultra-high density of plantation (1 m x 2 m), was achieve by pruning the plants to 50% of the length of the sprouts, unlike when the 60% and 80% of the canopy height were pruned. Authors recommend this type of pruning, accomplished three times a year like standard to achieve high agricultural yield in this plantation frame.
Kumar y Rattanpal (2010), researched several treatments of pruning of the guava tree (elimination of 1/3 and 1/2 of the vegetative growth) for several plantation frames (6 m x 5 m, and 6 m x 4 m). They found that the pruning had a significant effect in the height of the plant and in the volume of the canopy because of the different kinds and intensities of pruning utilized. Other authors (Madhubala et al., 2013) evaluated the effect of seven pruning treatments with different intensities, in the fruit yield. They obtained that all treatments with pruning had bigger results than control or treatment without pruning.
It was found in all researches reviewed that the pruning of the guava tree was made by hand, which is an inconvenience for the pruning in the dates and periods for large plantations of this crop and the big expenditures that this manual operation represents, within the operating costs of crop.
The absence of published information on the pruning of the guava tree, for the conditions of Cuba makes it necessary to undertake research that allows standardizing the pruning procedures, according to the cultivar planted and that recommends the dates and pruning intensities that produce higher yields and fruit quality.
CONCLUSIONS
The pruning is one of the most important cultural practices to perform in the guava tree. It favors the renewal of the biological material and bigger action of the solar light. The pruning allows managing the plant height and the form of the canopy. It is a very important operation in plantations of high density and enables bigger efficiency of the crop.
The results reviewed evidence increments of the guava production with the pruning; however, is not an obvious tendency with regard to the intensity of this practice to generalize, because the obtained results were different in terms of the researched cultivar, plantation density, season and climate. Several authors propose the monthly pruning all the year, as well as, pruning at least three times a year. Regarding the pruning intensity, several authors agree in that pruning of the end of the branch can be beneficial in terms of fruit production and quality, since severe pruning reduces fruit production, however, other authors recommend the use of severe pruning for obtaining higher yield.
