Didactic orchard

History of fruit culture

 

The specialized cultivation of fruit trees is a modern practice since the ancient world did not adopt the notion of an orchard. Instead in the ancient world, a hortus was the norm. The hortus was a confined area bordered by walls where an assortment of fruits, such as vines, olive trees, and a variety of vegetables, were grown in a multifunctional approach (Sereni, 1997). The presence of the wall was necessary to preserve the plants from attacks by animals in the wild, but also to protect them from potential damage caused by unfavorable climatic conditions (e.g. high winds).

 

During the sixteenth century, the cultivation of fruit trees continued to form an integral part of gardens. Nevertheless, French castles commenced to recognize distinct and functional areas, including the jardin potager or vegetable garden, the jardin fruitier or orchard, and the jardin médicinal or medicinal plant garden. In the Jardin fruitier of Versailles, the emergence of rational agriculture was facilitated through the activity of superintendents such as Jean Baptiste de la Quintinie. This marked a crucial turning point in the evolution of fruit cultivation techniques and exemplified the early adoption of contemporary farming methods (de La Quintinie, 1690).

 

However, it was in California, in the early twentieth century, that the premises were laid for an “industrial” development of fruit growing with the adoption of more rational cultivation techniques. In the same period, on the Italian front the situation was very backward. Molon, an important Italian pomologist, attributed the delay to the multiplicity of varieties without authentic qualities, to irrational breeding methods and archaic commercial circuits (Saltini, 1988). The possibility of bridging the gap with other nations was seen in the training of fruit growers. Pursuing this view, the agricultural schools received a great boost and, consequently, the foundations were laid for modern Italian fruit culture.

 

Fruit trees morphology

In modern fruit culture, it is common to join two individuals: the scion and the rootstock which constitute the aboveground and underground parts of a tree, respectively.

Scions and rootstocks are joined by using grafting. Grafting is a common horticultural technique used to improve plant growth, yield, and resistance to pests and diseases. Several studies highlighted that these effects result from different patterns of gene expression, alteration in water and nutrient absorption, and changes in hormone signalling pathways occurring in grafted plants (Habibi et al., 2022).

The aerial part of a tree is formed by the crown, the trunk, and the root collar, whilst the subterranean component encompasses all underground ramifications forming the root system. The crown of a tree includes the entire network of ramifications located above the trunk (the main woody stem without ramifications) which, depending on the season, carry lignified organs (branches and lignified shoots), leaves, buds, flowers, and fruits. The aboveground part is connected to the underground one through the root collar. In grafted plants the crown results from the activity of one or multiple buds.

 

According to the botanical terminology, the bud is considered as the primordium of a vegetative axis (vegetative bud) or a reproductive organ (flower bud) or both (mixed bud). In spring, the sprouting of a vegetative or mixed bud results in not lignified developing shoot. The lignification of the shoots occurs at the end of summer (August), originating a one-year-old shoot. Shoots older than one year are called branches. Branches directly inserted on the trunk are defined as primary scaffold branches, while those inserted laterally on these will be secondary branches, and so on.

The flower, the structure encapsulating the reproductive organs of angiosperms, derives either from a flower or a mixed bud. The regulation of bloom time in deciduous fruit trees is an area of increasing interest due to the negative impact of climate change on fruit production, therefore a better understanding of flower development is necessary for minimizing fruit crop loss (Goeckeritz and Hollender, 2021).

The nature and location of the buds differs between the various species. In apple trees vegetative and mixed buds are present, with the latter found terminally on shoot, while in the peach tree there are vegetative and flower buds. In peach, the shoot terminates in a vegetative bud, whilst in peach the flower buds, combined with the vegetative buds, are positioned along the shoot.

 

 

The reproductive buds-bearing shoots are generally in terminal part of fruiting branches and can be classified based on their length and diameter into mixed shoots (from 35 to 80 cm long), slender twigs or sprigs (up to 20 cm long) and spurs (up to a few cm long). Pome fruits, likes apple and pear, often present other short spurs called bourse arising from a mixed bud that has already fruited. Bourses are enlarged at the base due to starch accumulation, grown only a few millimeters per year and can remain active for several years.

More detailed information is reported in the Principles of Modern Fruit Science. Sansavini, S., Costa, G., Gucci, R., Inglese, P., Ramina, A., Xiloyannis, C., and Desjardins,Y., eds. (2019) (Leuven, Belgium: ISHS), pp.421. ISBN 978-94-6261-204-4.

 

Training systems

The morphological and functional characteristics of fruit-bearing tree plants are the result of the interaction of the genetic binomial (rootstock-scion) and environmental (soil-climate). Through pruning practices, the fruit grower can control the shape and size of the plant and the quantity and quality of the fruiting organs.

The traditional training systems, historically, were made up of large bulky trees at low planting density, and in which trees were often associated with annual and perennial herbaceous crops. The modern orchards are intensive and specialized with small tress and production guidelines and management methods aimed inducing an early fruiting, facilitating mechanization, minimizing costs, and reducing the use of labor per unit of product.

To reach this goal a strong reduction in plants size was pursued.  The architecture of the canopy was modified acting on the free arrangement of the branches and by limiting the tree pruning aimed at obtaining pre-ordered geometric shapes. The essential objective of modern pruning has therefore become the achievement of an early, balanced, and autonomous development of the tree, in the context of specific plant designs and training methods. For this reason, plant densities have progressively increased (up to the limits compatible with the quality and quantity of production), the use of rootstocks capable of reducing the plant size (weak or dwarfing rootstocks) has spread.

The influence of rootstocks on scion growth and dwarfing mechanisms is induced by multiple factors, including hormone signaling, photosynthesis, mineral transport, water relations, anatomical characteristics. The study of these relationships requires a system biology approach for providing a framework that would simplify future rootstock selection for diverse agro-climatic conditions as well as for different varieties (Shrivan et al., 2022).   In the didactic orchard, a clear demonstration of the effect of dwarfing rootstocks is the grafting of the same apple scion (Golden Delicious) on different rootstock of the M and MM series (Wang et al., 2019).

In the didactic orchard are present different species trained with different systems such as open vase, fusetto, bi-axis and Superspindle.

More detailed information is reported in the Principles of Modern Fruit Science. Sansavini, S., Costa, G., Gucci, R., Inglese, P., Ramina, A., Xiloyannis, C., and Desjardins,Y., eds. (2019) (Leuven, Belgium: ISHS), pp.421. ISBN 978-94-6261-204-4.


Orchard design

The agronomic and economic success of orchard is mainly due to a series of entrepreneurial and technical choices that are made when planting it. Each choice is the result of a careful analysis of the environmental suitability (climate and soil) and the presence of the infrastructures (transportation system and supply chain logistic) according to the purpose pursued (the destination of the product).

 

The choices at the time of planting concern the plant material (cultivars and rootstock), the preparation of the soil (hydraulic arrangements), pre-planting operations (pre-planting fertilization), the design of the plant (training system, lay out planting, stakes and anti-hail or anti-insect nets). The orchard design has the purpose of determining the distribution of plants in the field to optimize the use of resources (light, water, …), and facilitate cultivation management.

 

It is important to choose the planting density and planting distances so that the plant can quickly get to a size where they can intercept the maximum radiation, while maintaining adequate separation between the plants to avoid self-shading and reciprocal shading phenomena. For this reason, in the typical latitudes of temperate species, the orientation of the rows should be, if possible, in a North-South direction since this alignment guarantees a uniform distribution of solar radiation on the canopy.

 

The plant layout gives rise to regular designs of different geometric shapes, such as the square, with equally spaced trees on the row and between the rows, and the rectangular, with trees closer together on the row and more distant in the inter-row. The separation of the inter-rows is normally chosen to guarantee the best machine operation. The didactic orchard being promiscuous does not have different planting densities for the various species as happens in industrial orchards. This choice was made to simplify the orchard design by reducing stakes and the design solution for installing the net. For the latter an anti-insect net, named Alt’Carpo, was adopted. The mesh size of this net is 2.2×5.4 mm, and this characteristic allows the exclusion of Cydia pomonella, a moth whose larvae feed on fruits (Manja and Aoun, 2019).

 

More detailed information is reported in the Principles of Modern Fruit Science. Sansavini, S., Costa, G., Gucci, R., Inglese, P., Ramina, A., Xiloyannis, C., and Desjardins,Y., eds. (2019) (Leuven, Belgium: ISHS), pp.421.

The orchard ecosystem

The growing interest in carbon budgeting on a global scale is due to the well-documented impact of increasing atmospheric carbon dioxide concentration on earth temperature.

 

Forests and, to a lesser extent, grasslands by sequestering significant amounts of carbon from the atmosphere are considered an important strategy for mitigating global warming.

 

Conversely, agricultural systems are often viewed as potential sources of atmospheric carbon dioxide. However, orchards have structural characteristics that could help maintain long-term storage of soil carbon as:
i) their long life cycle, which allows them to accumulate carbon in permanent organs such as trunk, branches, and roots and in the soil through rhizodeposition;
ii) a low or null soil tillage, which preserves soil organic matter from mineralization;
iii) the frequent presence of herbaceous vegetation in the alleys, which can contribute to the buildup of soil organic matter.

 

This result is very important since generally the orchards are closer to areas where large quantities of CO2 are produced, such as those in which are present industries and urban settlements.

 

Recent studies have established that apple orchards and vineyards are capable of sequestering respectively 4.30 and 7.5 tons of carbon per hectare per year. This result pointed out that orchards and vineyards positively contribute to alleviate this greenhouse gas emissions into the atmosphere (Scandellari et al., 2016).

 

In orchards the fruit trees are associated with herbaceous plants and hedges (shrubs/other trees) forming an integrated and complex biological framework. The presence of herbaceous plants together with the roots of fruit trees reduces soil erosion by increasing the soil stability. Hedges are very important natural areas as they contribute to the increase in biodiversity and can host insects useful for the life cycle and defense (as predators of potential pathogens) of the fruit trees.

Suggested readings

de La Quintinie, J.B. (1690). Instruction pour les jardins fruitiers et potagers: avec un traité des orangers, suivy de quelques réflexions sur l’agriculture.

https://archive.org/details/instructionpourl02laqu/mode/2up?ref=ol&view=theater.

Goeckeritz, C., Hollender, C.A. (2021). There is more to flowering than those DAM genes: the biology behind bloom in rosaceous fruit trees. Cur Opin Plant Biology, 59: 101995, https://doi.org/10.1016/j.pbi.2020.101995.

Habibi, F., Liu, T., Folta, K., Sarkhosh, A. (2022). Physiological, biochemical, and molecular aspects of grafting in fruit trees. Hortic Res, 9: uhac032. doi: 10.1093/hr/uhac032.

Manja, K., Aoun, M. (2019). The use of nets for tree fruit crops and their impact on the production: A review. Scientia Hortic, 246: 110-122. https://doi.org/10.1016/j.scienta.2018.10.050.

Saltini, A. (1988). Il viaggio in America: la frutticoltura nel confronto mercantile mondiale”, in Girolamo Molon 1860-1937. L’ampelografia e la pomologia, Vicenza.

Scandellari, F., Caruso, G., Liguori, G., Meggio, F., Palese, A., Zanotelli, D., Celano, G., Gucci, R., Inglese, P., Pitacco, A., Tagliavini, M. (2016). A survey of carbon sequestration potential of orchards and vineyards in Italy. Eur J Hortic Sci,  81:106-114. 10.17660/eJHS.2016/81.2.4

Sereni, E.  History of the Italian Agricultural Landscape, Princeton: Princeton University Press, 1997. https://doi.org/10.1515/9781400864454

Shivran, M., Sharma, N., Dubey, A.K., Singh, S.K., Sharma, N., Sharma, R.M., Singh, N., Singh, R. (2002). Scion–Rootstock Relationship: Molecular Mechanism and Quality Fruit Production. Agriculture 12: :2036. https://doi.org/10.3390/agriculture12122036

Wang, Y., Li, W., Xu, X., Qiu, C., Wu, T., Wei, Q., Ma, F., Han, Z. (2019). Progress of Apple Rootstock Breeding and Its Use. Hortic Plant J, 5: 183-191. https://doi.org/10.1016/j.hpj.2019.06.001.