Challenges for expanding pear production

The pear is among the temperate fruits of greatest interest worldwide, being the most imported by Brazil. Domestic market consumption is around 210 thousand tons, of which approximately 90% originate from Argentina, Chile and Portugal (FAO, 2017). This is due to low Brazilian production, which is around 22.108 tons in an area of ​​1.305 hectares, making the country occupy 46th place in the world ranking of pear producers.

Brazilian productivity and fruit quality are considered low, not presenting an adequate standard to meet the demands of the consumer market. The low production of pears in Brazil has been attributed mainly to the lack of cultivars that adapt to climatic conditions that are not favorable to the crop.

In this way, pear production ends up being concentrated in regions that present the minimum conditions required by the crop, with five being the main producing states, where harvests occur from February to April: Rio Grande do Sul, Santa Catarina, Paraná and São Paulo .

ROCHA AND SANTA MARIA CULTIVARS      

Among the main European pear cultivars that are presenting high production and quality with greater adaptation to the climatic conditions of the producing regions in the south of the country are Santa Maria and Rocha.

The Santa Maria and Rocha cultivars are increasingly widespread worldwide due to the attractive characteristics that make up their fruits, presenting excellent resistance to handling and transportation, in addition to not losing their quality when stored, with indications for cultivation mainly in the southern region of the country. The cultivation of European pear trees can become an alternative to diversify the production of temperate and subtropical fruit crops in the South region.

ROST ROOT FOR PEAR TREES

For good performance of pear cultivars, it is necessary to use rootstocks that contribute to efficient vegetative and productive growth. However, the lack of rootstocks suitable for the soil and climate conditions of the southern region of the country is among the biggest obstacles to the expansion of the crop.

In the country, the majority of orchards are formed by pear trees grafted onto quince trees (Cydonia Mill.), however, some European cultivars present incompatibility when grafted onto this species, making it necessary to deepen the understanding of new possible combinations between cultivars and rootstocks.

Compatibility within and between species depends on the healing and regeneration of tissues at the union site. When incompatibility occurs, the formation and functionality of vascular bundles is impeded, affecting sap translocation and, consequently, the growth and development of the plant.

EDAPHOCLIMATIC CONDITIONS FOR CULTIVATION

The pear tree is a temperate climate crop. Due to this, it is recommended for regions with higher altitudes and which have homogeneous cold hours, with temperatures below or equal to 7,2ºC. These regions are more conducive to the development of the species, providing the hours of cold necessary to overcome dormancy. This period of dormancy comprises the necessary time for cold to accumulate so that the buds formed in autumn sprout properly in spring; Therefore, selecting the most suitable cultivar for each soil and climate condition is very important for the success of pear tree cultivation.

CULTIVATION LIMITATIONS

The choice of cultivar is a limiting factor for production, as the cold requirements of each cultivar and other aspects of management and marketing must be considered, which will depend on each production region.

The rootstock has influences on the vegetative and productive characteristics of the scion, having great importance in adapting to environmental factors, due to the connection between the soil and the cultivar, which can interfere with the absorption of nutrients, adapting to the physical-chemical characteristics of the soil. . The appropriate choice of rootstock makes it possible to modify the size and vigor of the plant. The reduction in vegetative growth allows for denser plantings, improving and facilitating orchard management. Selecting the correct rootstock guarantees better characteristics of size, vigor and overcoming stress conditions.

In addition to the quince tree, in some orchards the pear trees are grafted onto rootstocks Calleryan Pyrus (Decne), which provide plants with high vigor and later entry into production. With the high vigor of the rootstocks, European pear cultivars take around six to seven years to begin production and require drastic intervention in crown management, characteristics undesirable by the fruit grower.  

NEW ROOT STOCKS FOR PEAR TREES

 In the rootstock selection process, it is important to take into account its affinity with the scion cultivar, as well as the adaptation of the scion/rootstock set to climate and soil conditions. In the search for new options for pear cultivation, new selections of quince (Cydonia oblonga) were offered, as well as P. communis L., such as the Old Home x Farmingdale (OHF) hybrids in the USA, which may be options to improve productivity, precocity and fruit quality of some European pear tree cultivars. The rootstocks of the OHF series stand out for presenting a high degree of tolerance to fire blight, considered one of the most serious diseases in pear trees, tolerant to frost, medium resistance to aphids and their vigor classified as semi-dwarf. 

The selection of P. communis L. was also used to obtain the CAV 3 rootstock, developed by the CAV/Udesc Fruit Culture group in 2012, obtained from commercial seeds, through the mass selection technique, in a population of 320 seedlings established in 2008.

The introduction of some new rootstocks requires knowledge of the extent and nature of compatibility reactions. After the grafting process, that is, throughout the period of tissue healing and regeneration, a cascade of events and signaling occurs in the plant that culminate in different responses and physiological effects.

One of the possibilities to verify scion/rootstock compatibility would be by studying characteristics linked to the initial development of the plant, with the percentage of bud sprouting being considered one of the most important.

RESULTS AND INDICATIONS

An experiment was conducted in the experimental area of ​​the Agronomy Department of the Central-West State University (Unicentro) on the Cedeteg Campus, located in Guarapuava, Paraná. The treatments consisted of combinations of pear cultivars (Santa Maria and Rocha) with rootstocks (OHF 69, OHF 87 and CAV 3), totaling six treatments. The experimental design was randomized blocks in a 2 x 3 factorial scheme, with four replications and five plants per experimental plot.

 Sprouting percentage assessments were carried out in two vegetative cycles, the first and second year of planting implementation, respectively. The evaluations began in the second half of September 2017 and the first half of September 2018, when the plants began to sprout. Firstly, total buds were counted and from the beginning of budding (green tip phenological stage) evaluations were carried out weekly until budding stabilization, which occurred in the first fortnight of October in 2017 and October in 2018, totaling six evaluations. in 2017 and five evaluations in 2018. The results were expressed as a percentage of sprouted buds.

The results of the sprouting percentage evaluation demonstrate that there was a positive linear effect as a function of time in the first year of evaluation, for both cultivars (Figures 1A and 1B). The beginning of sprouting (BI – 5%) occurred in the second half of September, being later for the Rocha/CAV 3 combination (Figure 1B).

In the first year of evaluation (2017), the highest final sprouting rates recorded were in the combination Rocha/OHF 69 (92,28%) (Figure 1B) and Santa Maria/OHF 69 (96,47%) (Figure 1A) at 35 days after the start of sprouting.

According to the equations of the proposed model (Figures 1A and 1B), the OHF 69 rootstock, in both cultivars, reached 50% of sprouting in the shortest period of time, which was 16,5 and 12,6 days for the cultivars Santa Maria and Rocha, respectively. The OHF 87 rootstock obtained this percentage at 16,7 days, for both cultivars; and the CAV 3 rootstock only reached 50% of sprouting at 23,5 and 18,8 days, for the Santa Maria and Rocha cultivars, respectively.

In the second cycle of evaluation of the sprouting percentage, the final sprouting percentage values ​​were lower compared to the previous period, however, the sprouting speed was higher (Figures 2A and 2B). As can be seen, the OHF 69 rootstock reached 50% of sprouting on the sixth day after initiation, for both cultivars, representing an average reduction of eight days. 

Budding stabilization occurred at 35 days (Figures 1A and 1B) after the beginning of sprouting in the first year of evaluation, while in the second year it occurred at 28 days (Figures 2A and 2B). This reduction in the number of assessments carried out in the second year was probably due to differences in climatic conditions after the start of sprouting. 

In the second evaluation cycle, a linear increase in sprouting as a function of time was again observed for both cultivars (Figures 2A and 2B). 

The formation of shoots, reproductive structures and productive efficiency are strongly influenced by the translocation of sap via xylem and phloem, which can be affected by the rootstock used. In this context, it is noted that the CAV 3 rootstock, in both cultivars evaluated, did not perform well in both evaluations.

It can be seen that the CAV 3 rootstock was the one that provided the slowest budding percentage in both cultivars evaluated, and at 35 days after the beginning of budding in the first evaluation, the Santa Maria cultivar showed 86,15% and the cultivar Rocha, 82,24% of sprouting (Figures 1A and 1B), and 28 days after the beginning of sprouting, in the second evaluation, the cultivar Santa Maria presented 68,48% and the cultivar Rocha, 61,25% of sprouting (Figures 2A and 2B).

During the entire evaluation period, which ran from September/2017 to November/2018, it was clear that the climate conditions were favorable to the initial development of the plants, with average minimum and maximum temperatures of 11,9ºC and 22,5ºC. °C, respectively, with accumulated precipitation of 1.275,9mm and 834,6mm, totaling 2.110,5mm accumulated during the 14 months of the experiment.

After a year of plants adapting to soil and climate conditions in the region under study, the number of cold hours accumulated during the months of May to September 2018 was 481,3 UF (Cold Units), calculated according to the Carolina Method of the Modified North, which corresponded to 276 hours of cold (≤ 7,2ºC) accumulated by plants during the winter period.

As observed, among the six combinations evaluated, only the Rocha/OHF69 (92,51%), Santa Maria/OHF (90,28%) and Rocha/OHF87 (86,53%) combinations reached maximum sprouting (BM ≥ 80 %). This fact indicates that these combinations better adapted to the edaphoclimatic conditions in this first development cycle and that possibly the rootstock OHF 69, both for the cultivar Rocha and for the cultivar Santa Maria, as well as the rootstock OHF 87 under the cultivar Rocha, provided a reduction in the number of chilling hours required by these cultivars, classified as European.

Assessments of initial vegetative development, as well as the phenological phases of the crop, represent an important tool for verifying adaptation to climatic conditions. This makes it possible to select the best combination of scion cultivar and rootstock, since pear tree cultivation is an excellent alternative for the diversification of fruit growing in the region.

Bud sprouting tends to be more uniform after the plants have supplied the necessary cold for each genotype. In view of this, the slow evolution of budding on the CAV 3 rootstock, in both cultivars and in both years, may possibly have occurred due to the greater cold requirement of the rootstock in relation to the others. This probably resulted in a lower percentage of sprouted buds, despite the uniformity observed.

The choice of rootstock must therefore take into account the adaptability of the combination between scion and rootstock to soil and climate conditions, in addition to its effect in reducing the vigor of the scion cultivar, in order to guarantee better development and greater productivity. 

Laís Cristina Bonato Malmann Nedilha, UFPR; Janaina Marek, Agricultural Engineer, PhD in Agronomy, (Plant Production) and Researcher; Leo Rufatto, Udesc; Renato Vasconcelos Botelho, Unicentro

Growing Vegetables and Fruits November 2019

With each new edition, Cultivar Hortaliças e Frutas publishes a series of technical content produced by renowned researchers from all over Brazil, which address the main difficulties and challenges encountered in the field by rural producers. Through research focused on controlling the main pests and diseases in vegetable and fruit cultivation, the Magazine helps farmers in the search for management solutions that increase their profitability. In the November 2019 edition you can also see: 

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