Fruit yield

1 Estación Experimental Agropecuaria San Juan, Instituto Nacional de Tecnología Agropecuaria (INTA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), San Juan, Argentina. 2 Ingeniería Agronómica, Facultad de Ingeniería, Universidad Nacional de San Juan. 3 Instituto Multidisciplinario de Biología Vegetal (IMBIV), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad Nacional de Córdoba (UNC), Córdoba, Argentina.

The production potential of olive trees is determined by numerous genetically based characteristics, such as chilling requirements, pollen-pistil incompatibility, ovary abortion and fruit size, among others. The expression of these characteristics is significantly influenced by external factors, such as site location and year of cultivation, planting density and orchard management practices (irrigation, fertilisation, pruning, diseases and pests, etc.). Thus, the productive efficiency of an olive orchard depends on the interaction between the cultivar and these environmental and management factors. Consequently, the range of the olive’s productive potential is very broad, with average yields ranging between 2,000 and 20,000 kg ha⁻¹, depending on the selected cultivar, the site and climatic conditions, age, orchard design and management practices.

When determining the productive potential of varieties, several indices are considered (León et al., 2007): 

• Precocity of bearing (kg/tree): Jointly considering the number of years until the first harvest and the cumulative production over the first three crop years;

• Average or cumulative production (kg/tree): Estimated either from the last four harvests or from the first to the most recent harvest, respectively;

• Productivity index: It can be expressed in different ways, for example, productivity (cumulative yield per cm² of trunk cross-sectional area), productive efficiency (cumulative yield per m³ of canopy volume) or harvest index (cumulative yield per m² of canopy surface).

Precocity of bearing is a desirable trait because it shortens the unproductive phase and accelerates the recovery of planting costs. Various studies (Bellini et al., 2002; Ben Sadok et al., 2012; De la Rosa et al., 2006; Hammami et al., 2021; Moral et al., 2013; Rallo et al., 2008; Santos-Antunes et al., 2005) confirm that this trait is strongly determined by genotype. Nonetheless, some differences between cultivation sites exist; for example, varieties tend to bear earlier in warmer environments. Table 1 shows varietal differences in bearing precocity for most cultivars included in this catalogue (León et al., 2007; Del Río et al., 2005).

Table 1. Precocity categorisation of some olive varieties according to the number of years to first harvest. Source: Compilation based on trials carried out in different countries (Argentina, Spain, Italy, Morocco).

Precocity categories; number of years until first harvest: E (early) = up to 3 years; M (medium) = from the fourth year; L (late) = from the fifth year.

Unlike precocity, average productivity is far more complex to categorise by variety. Although numerous studies exist, their results are not always consistent and can even be contradictory. Recently, productivity indices have been introduced that account for plant vigour (which has a strong genetic component) and consider the trend towards orchard intensification. As shown in Table 2, some varieties are early-bearing but display lower productive efficiency, such as Palomar, Picual and Maurino (highlighted in red). It should be noted that these indices also vary depending on the cultivation environment. When comparing two varieties like Manzanilla and Empeltre, differences in productive efficiency between two Spanish growing regions are very noticeable (Tables 2 and 3, highlighted in blue).

Table 2. Bearing precocity and productivity of olive varieties in Catalonia, Spain, recorded between 1991–2001. Source: Tous et al. (2005).

Table 3. Bearing precocity and productivity of olive varieties in Andalusia, Spain, recorded between 1991–2001. Source: del Río et al. (2005).

If productive efficiency values vary within regions of the same country, differences between countries can be even more dramatic. Tables 4 and 5 show results from comparative productivity trials conducted in Australia and Morocco, respectively. It is remarkable, for instance, that the Koroneiki variety showed the best early performance in Morocco but the worst in Australia (highlighted in green). Similarly, certain varieties show diametrically opposed behaviours in extreme environments, such as Leccino (which has high chilling requirements), when cultivated in a cold area of central Italy (Table 6) versus a warm area in western Argentina (Table 7). This clearly demonstrates that, as noted at the beginning of this chapter, cultivars exhibit different capacities for adaptation to various olive-growing environments (Tables 2–7).

On the other hand, there are few varieties that show stable production across different environments, such as the Spanish Arbequina, which is widely planted worldwide. Given these differences in plasticity, it is crucial to study varietal behaviour in each local olive-growing area.

Table 4. Records of productivity, oleic acid content, fresh fruit weight and pulp-to-stone ratio for different olive varieties in Australia (1998–2004). Source: Sweeney (2005).

Table 5. Precocity, productivity, alternate bearing index and oil content of various olive varieties grown in Meknes, Morocco (planting density: 178 trees/ha). Source: Idrissi and Ouazzani (2003).

* Data collected from three years after planting.

Table 6. Productivity, mechanical harvestability, canopy volume and productive efficiency of different olive varieties grown in Umbria, Italy (2004–2007). Source: Farinelli et al. (2012).

* No data recorded for 2005 due to frost damage to the inflorescences.
For each cultivar and year, means followed by the same letter are not significantly different (P ≤ 0.05).

Table 7. Average yield values of varieties from the World Olive Germplasm Bank in San Juan, Argentina (2012–2019). Source: Own elaboration.

These results highlight the need to evaluate and preserve olive genetic resources, and to promote local and/or regional experimentation as a strategy for better understanding the complex genotype × environment interactions, improving crop productivity, as well as increasing cultivar diversity and product offerings.

References 

1. Bellini E, Giordani E, Parlati MV, Pandolfi, S. (2002). Olive genetic improvement: thirty years of research. Acta Hort 586:105–108.

2. Ben Sadok I, Moutier N, Dosba F, Rebai A, Grati-Kamoun N, Rebai A, Khadari B, Costes E (2012). Genetic determinism of the vegetative and reproductive traits in a F1 olive tree Progeny: evidence of tree ontogeny effect. Tree Genetics and Genome 9: 205–221.

3. De la Rosa R, Kiran AI, Barranco D, Leon L (2006). Seedling vigour as a preselection criterion for short juvenile period in olive breeding. Aust J Agr Res 57:477–481.

4. Del Río, C., Caballero, JM, García-Fernández, MD (2005). Producción (Banco de Germoplasma de Córdoba). In: Variedades de olivo en España (Libro II: Variabilidad y selección). Rallo L, Barranco D, Caballero JM, Del Rio C, Martin A, Tous J, Trujillo I (eds.). Junta de Andalucía, MAPA and Ediciones Mundi-Prensa, Madrid, Spain.

5. Farinelli D, Ruffolo M, Boco M, Tombesi A (2012). Yield Efficiency and Mechanical Harvesting with Trunk Shaker of Some International Olive Cultivars. Acta Hort. 949: 379-384.

6. Hammami SBM, León L, Rapoport HF, de la Rosa R (2021). A new approach for early selection of short juvenile period in olive progenies. Scientia Horticulturae 281: 109993.

7. Idrissi A, Ouazzani N (2003). Apport des descripteurs morphologique à l’inventaire et à l’identification des variétés d’Olivier (Olea europaea L.). Plant Genetic Resources Newsletter 136: 1-6.

8. León L, De la Rosa R, Barranco D, Rallo L (2007). Breeding for early bearing in olive. HortSci 42(3):499–502.

9. Moral J, Diez CM, Leon L, De la Rosa R, Santos-Antunes F, Barranco, D, Rallo L (2013). Female genitor effect on the juvenile period of olive seedlings. Sci Hort 156:99–105.

10. Rallo L, Barranco D, M. Díez C, Rallo P, Suárez MP, Trapero C, Pliego-Alfaro F (2018). Strategies for Olive (Olea europaea L.) Breeding: Cultivated Genetic Resources and Crossbreeding. In: Al-Khayri, J., Jain, S., Johnson, D. (eds) Advances in Plant Breeding Strategies: Fruits. Springer, Cham.

11. Rallo P, Jiménez R, Ordovás J, Suárez MP (2008). Possible early selection of short juvenile period olive plants based on seedling traits. Aust J Agr Res 59:933.

12. Santos-Antunes F, León L, de la Rosa R, Alvarado J, Mohedo A, Trujillo I, Rallo, L (2005). The length of the juvenile period in olive as influenced by vigor of the seedlings and the precocity of the parents. HortSci 40:1213–1215.

13. Sweeney S (2005). National olive cultivar assessment – NOVA- Stage 2. Rural Industries Research and Development Corporation Publication N° 05/155, Project N° SAR-47A.

14. Tous, J, Romero A, Plana J. 2005. Producción (Banco de Germoplasma de Cataluña). In: Variedades de olivo en España (Libro II: Variabilidad y selección). Rallo L, Barranco D, Caballero JM, Del Rio C, Martin A, Tous J, Trujillo I (eds.). Junta de Andalucía, MAPA and Ediciones Mundi-Prensa, Madrid, Spain