IntroductionTop

Spanish citriculture occupies a significant place worldwide not only because of its production, but also because it ranks first among the exporting countries of fruit for fresh consumption, maintaining this global leadership in oranges, mandarin oranges and lemons, with an average of 33%, 55% and 28% respectively in the 1994-2013 period (FAO, 2018). In the 2016-17 season, the Spanish cultivated area amounted to 295,331 ha, of which 48% accounts for sweet oranges, 37% for mandarin oranges and 14% for to lemons. The remaining area is divided between grapefruit, bitter oranges and other citrus fruits (MAPA, 2018). National citrus fruit production in the 2016-17 season amounted to 7,085,819 tonnes (tn), with oranges accounting for 51.7% of production, followed by mandarin oranges with 33.4%, while lemon production is 13.5% and that of grapefruit only 1.02%.

Taking all varieties as a whole, or groups of orange varieties, the navel group stands out which, with a production of 2,705,332 tn in the aforementioned season, accounts for 73.86% of the total for oranges. This is followed by the late varieties, which account for 13.88%; select white varieties for 10.97% and the rest of the groups (common whites and blood oranges) for only 1.29%. Orange cultivation mainly covers the area between the Region of Valencia and Andalusia, with respectively 49.31% and 41.45% of the national orange tree area; the Region of Murcia is the third-largest region in orange production, with 7,952 hectares, i.e. 5.61%.

In Spanish citriculture, the varietal composition, the qualities obtained in production, and the marketing calendar coinciding with peak demand periods in the main markets are the characteristics that contribute the most to placing Spain in the top position among the exporting countries for fresh consumption. Al­though the exported proportion varies between different seasons, over the years, competitiveness determined by the degree of specialization and dependence, trade balance, analysis of market share, quality, national efforts and product differentiation (Ben-Amor et al., 2015), presents a growing trend among Mediterranean countries, where Spain has not lost its primacy as the main orange exporter to the European Union (EU), positioning itself ahead of its traditional competitors (Ben-Amor & de-Miguel, 2018).

The success of the competitiveness and stability of Spanish citriculture is due to: (i) the geographical situation, close to the main importing countries of fruit and vegetables; the climate, which varies from region to region and production area and is highly suitable for the production of quality citrus fruit; the range of varieties, which is very broad and comprehensive, with a marketing calendar running from September with the early clementines to June, and which even extends to the summer, with sales to the domestic market and exports of the ‘Valencia’ variety drawn from cold storage, or the ‘Verna’ lemon; (ii) the abundant availability of well-equipped packing and degreening warehouses, and an efficient logistics network; (iii) the existence of an ensemble of plant nurseries with a good technical standard, regulated by legislation that ensures the production and supply of healthy plants and the availability of technological research and dissemination to facilitate obtaining new varieties and rootstocks, improvements in cultivation techniques and the optimal use of natural resources such as water among producers.

However, against these characteristics that favour competitiveness, we should also point out shortcomings in the productive structure and difficulties in marketing. With regard to the productive structure, the division of the property has fewer drawbacks in Andalusia and Murcia than in the Valencian Region, where the greater proportion of smallholdings leads to an unfavourable situation (Fernández-Zamudio et al., 2006). However, in order to maintain the sector’s professionalisation, actions promoting associated or collective management are increasing in a quest to encourage larger and more viable management units both in the technical and commercial aspects (Cajamar, 2018; BOE, 2018; UPA, 2018).

Spanish citriculture is characterised by high-quality production, although its costs are also higher than other competitors, which requires proper management and economic planning of production (Caballero et al., 2001).

As for marketing, the main difficulties faced by the citrus sector are the result of market liberalisation. There is a decrease in trade protection, especially through tariffs. The measures adopted by the EU lead to the increased openness of EU markets, with a significant reduction in export aid and the questionable effectiveness of control mechanisms, as there are insufficient measures to prevent the penetration of new pests and diseases. Fresh fruit and vegetable markets are well supplied, are demanding in terms of quality, with little response to novelty and prone to price collapse if oversaturation is reached.

There is no seasonality in prices due to the ease with which Southern Hemisphere productions can access the European market, and the positive effect that used to occur at the end and beginning of each season has diminished. In recent years, too, the quality has been established in the calibre, colour and a blemish-free skin, with the market not clearly appreciating organoleptic quality. This prevents the real value of the fruit from being recognised, which could otherwise favour growth in consumption (Hagenmaier & Baker, 2004). In the commercial stage, the concentration and dominance of mass distribution has led to very marked change. Trade relations between wholesaler and customer are usually reached through prior agreements, with product and service security guarantees. Sale prices in superstores are not always fairly related to production costs in the field and often do not take sufficient remuneration for the farmer into account. In some cases, abusive behaviour has even been detected, especially towards the source link in the chain (Caballero, 2009). In addition, increased consumer awareness of product health and pesticide residue levels requires traceability throughout the production and marketing process, which mass distribution does not compensate for.

Given the commercial perspectives of Spanish citriculture, exports are expected to increase, as the latest countries to have joined the EU offer possibilities of increasing their consumption and shipments to third countries continue to grow. In addition, there will be an increase in demand for quality fresh juice, which will result in a higher proportion of industrialised fruit.

Lastly, it is essential for Spanish citriculture to maintain varietal restructuring. This strategy has been implemented in every era and is one of the foundations underpinning current and future competitiveness, by improving existing varieties and introducing new ones. The adoption of new varieties offers advantages by filling the gaps that the season commercially accepts. However, there is no need to modify varietal supply-demand because there is no phase difference.

In this context, and based on the dynamic structure of varietal composition, the objective of this study was to explain the survival of different orange varieties on the market, identifying the attributes inherent to the variety or environmental factors that affect the survival period of the varieties over time. Survival refers to the length of the variety’s commercial life, which may adopt two types of cycles: (i) long cycle, corresponding to the accumulation of one or more useful life periods with their corresponding plantations; in this case we could say that introducing the variety was a success; (ii) short cycle, shorter than normal biological duration; the introduction of the variety is then unfavourable and does not cover the businessperson’s expectations. In both situations, in the former case commercial obsolescence usually occurs in the last plantation period and, in the latter, in the first and only period (Caballero et al., 1992).

Knowing the survival of varieties on the market and identifying which factors affect them will help improve decision-taking for both growers and breeders of new varieties, thus allowing for an increase in economic efficiency.

Material and methodsTop

Situation and characteristics of orange varieties

In the last 40 years, most of Spanish production tonnage comes from the range of sweet orange varieties which, given their common characteristics with regards to morphology, ripening time and fruit properties, are made up of the following groups: navel, mid-season white, blood and late white. The number of varieties with commercial importance grown and introduced on the market since the mid-20th century is 33, with representatives of the four groups among them (Table 1). In addition, Table 1 shows whether the characteristics of the variety have allowed for a commercial life with a duration equal to or longer than a useful biological life, whether or not the variety is currently extinct and the current situation of the varieties. Current situation categories, associated with the growing area, are: (i) fully extinct, when no product can be found in the market; (ii) starting cycle indicates the recent novelty of the variety; (iii) surface area refers to the growing area trend, that could be growing, decreasing or maintained.

In accordance with the start of ripening, the most precocious group is that of ‘Navelina’ and ‘Newhall’, both from the Navel group, identified by their navel, both of them very similar to each other, with medium-size or large trees of open and rounded growth (Soler, 2014). The fruits differ because the ‘Navelina’ ones adopt a more reddish and glossy hue. The ‘Navelina’ was introduced in Spain in 1933, the ‘Newhall’ in 1966, and both have a long harvesting period spanning from October 20 to January 20 (Soler & Soler, 2006). Both varieties are very widespread, accounting for 32% of Spanish orange production. In Spanish citriculture, except for ‘Navelina’ and ‘Newhall’, there have been no precocious varieties for marketing at the start of the season. Both sufficiently cover the first stage of the Spanish marketing calendar, and do so with quality.

Less widespread than the above ones is the ‘Fukomoto’ variety detected in Japan by spontaneous mutation of a tree bud from the ‘Washington Navel’, with a harvesting period similar to the ‘Newhall’ (Soler, 2014). In recent years, the company CGM Citrus has introduced ‘Navelina M7’, which is an ultra-early mutation of the ‘Navelina 7.5’ detected in Australia, from which it was imported. It is notable for the rounded shape of its fruits, and because it can be harvested over a long period of time.

The navel group also includes the ‘Washington Navel’ (‘W. Navel’), introduced in Spain in 1910, which was one of the most representative varieties and in the 1970s accounted for as much as 36% of domestic production. A few years after the introduction of the ‘W. Navel’, the ‘Thomson Navel’ became widespread in Spain, with slightly earlier ripening and a smaller-sized fruit (Gonzalez-Sicilia, 1968). Its cultivation came to cover an appreciable area but was displaced by more precocious and better-quality varieties and has almost disappeared today. The ‘Caracara’ variety has identical morphological characteristics and harvesting calendar to the ‘W. Navel’; it differs from the group by the red colour of the pulp (Soler, 1999).

Following the ‘W. Navel’ there appeared the ‘Navelate’ and the ‘Lane Late’, together with ‘Ricalate’ and other even less important ones because of the area they covered, such as the ‘Powell Summer’, ‘Rohde Summer’, ‘Barnfield Late’ and the ‘Chislett’, this last one with a later ripening date. This group has a harvesting period extending from January to May in ideal commercial conditions. The ‘Navelate’ became widespread in Spain from 1957 onwards, and the ‘Lane Late’ became known in the 1987/88 season. Plantations were started from 1990 onwards.

Also very important is the group of whites which, due to their time of ripening, are divided between mid-season and late-season. With regard to the mid-season ones, it should be noted that the ‘Comuna’ was the first variety introduced in Spain in the mid-15th century. It has many seeds; however, it continued to be cultivated for centuries thanks to its juice yield. It is currently deemed to be extinct. The ‘Cadenera’ is a variety known since 1870, virtually seedless and with high juice yield. Today, however, the most important mid-season orange is the ‘Salustiana’, which by 1960 already had an appreciable presence, with fruits that remained long on the tree and were high in juice content. Of lesser importance and now extinct were the ‘Castellana’ and ‘Vicieda’ varieties (seeded) and the ‘Macetera’ with few seeds, which was important in the mid-20th century.

For their part, late whites dominate the citrus fruit calendar in the last period of the season. The most relevant one is the ‘Valencia Late’, introduced in Spain by the Levante Orange Station and disseminated in the first half of the 20th century. Also in the group of late whites is the Valencia subgroup, which inclu­des ‘Barberina’, ‘Midknight’, ‘Late Frost’ and ‘Delta seedless’.

Virtually all the fruits are seedless and feature good conditions for conservation and transport. They are in demand by the juice industry. Late whites also include the ‘Berna’, of unknown origin, which is practically seedless.

Finally, the blood orange group enjoyed an era of being of interest to farmers in the ‘60s. The 1970-71 season accounted for 14% of Spanish citrus fruit production. This was followed by a dizzying decline and is currently only testimonially represented. The varieties ‘Doblefina’, ‘Entrefina’ and ‘Moro Catania’ were important in this group. Today, the scant surface area corresponds to the ‘Sanguinelli’, which originated from spontaneous mutation of the ‘Doblefina’ and was detected in 1929 (Bono, 1991).

Within the complex web existing between commerci­al varieties and the similarity some of them may present, it should be noted that not all are clearly reflected in the existing statistical series. In addition, the most important varietal groups tend not to have a single differentiated variety and, in some cases, statistics may group similar varieties together. Sometimes, not enough years may have elapsed for a new variety to become consolidated and consequently they do not have their corresponding section in the statistical information.

The estimated useful life of an orange tree is 40 to 45 years when grafted on a bitter orange tree, and 25 to 30 years if the rootstock is a citrange. Under this scenario, according to the information on plants marketed by nurseries, 22 of the varieties analysed have exceeded one or two periods of useful life, while 18 varieties have ceased to be in demand among farmers (Table 1).

However, the attributes of the varieties, and the environmental factors that lead to improving the competitiveness of productions, are behind the decision to adopt one or another variety.

One of the attributes that the farmer values is qua­­lity, in which there are different points of view in terms of appreciation since it is thought to play a decisive role in the introduction of new varieties. Firstly, health quality has been taken into account, which legislation enforces, especially in the case of pesticide residues. Secondly, the morphological quality of the fruit which consumers demand in terms of shape, colour, fine skin and calibre. Thirdly, organoleptic quality, which can include, in addition to taste, aroma, the proportion of juice, the sugar-acid ratio, pulp softness (Hagenmaier & Baker, 2004; López-Carmona, 2011; Bello, 2015).

The presence of seeds also affects quality. Harvest precocity has held considerable appeal for farmers because of higher prices obtained.

The location of the plantation may condition the adoption of one or another variety. This may be due, on one hand, to there being varieties that are more sensitive to frost than others, and on the other, to the varieties that are being grown in the area. The imitation effect has a strong influence on the adoption of innovations in agriculture (Alcon et al., 2011).

Duration analysis

The study was conducted on the main Spanish production regions, which are Andalusia, Valencia and Murcia.

The duration or survival analysis allows us to explore the fact that a certain event occurs (market entry or exit of a product or service, adoption of a technology, etc.) and the time elapsed until this event takes place (Fuentelsaz et al., 2004). Therefore, the interest lies in identifying the event as well as its causes, and the relationship between the causes and the timing of the event. Recently, works such as those of Alcon et al. (2010); Abebe & Menale (2015); Hina & Melinda (2016), and Robertson et al. (2018), have applied duration analysis to explain the attributes and factors influencing the adoption of innovations in agriculture.

In this regard, the likelihood that a variety will continue to be cultivated over time based on the variety’s attributes and the environmental factors can be expressed as:

where Ps is the variety’s survival, A are the variety’s attributes, and B are the environmental factors that can influence the length of time the variety remains on the market but are common to all varieties.

Unlike other econometric methods which statically determine the conditioning factors of a particular event, without taking into account the time in which it occurs (e.g. Logit or Probit models), survival analysis explores the event through a dynamic approach based on a given observation period.

Formally, duration analysis explains the time period, T, between the start and end of a process in which a particular event occurs to learn the sign and magnitude of the effects exerted by the explanatory variables on T (Kiefer, 1988; Lancaster, 1990). In each case, survival, i.e. the likelihood of a variety of oranges surviving on the market over a period of time, dt after t, would be defined by a risk function.

If F(t) is the density function of the continuous probability of variable T and where t indicates the end of the period, cumulative function may be defined as:

Likewise, the distribution of T may be expressed by survival function S(t), which defines the probability of survival over time, in other words, that T is greater than or equal to t. This function offers the likelihood of surviving t, i.e. the probability that the variety has not disappeared in each period of t.

Therefore, the risk function h(t) defining survival to time t is defined as:

The risk function reflects the effects of the explanatory variables (X) and the baseline. The risk function h0, which can be semiparametric or follow a specific functional form h0(t) (Kiefer, 1988; Cleves et al., 2002), allows parameters to be estimated β, by maximum likelihood, assuming the observed durations ti together with the right-censored observations, which last at least until the end of the observation period, which in this case corresponds to the survival of each variety of orange tree θj. Thus, the resulting risk function would be (Burton et al., 2003):

To ensure that the risk function is not negative, with­out imposing restrictions on parameters, proportional risk models use an exponential specification q (X, B). Therefore, the estimated coefficients and their sign represent the impact on the risk function and should be interpreted as eβ. β values equal to 1 would have no impact on the risk function, higher (lower) values than 1 would indicate a positive (negative) impact on the risk function.

Data collection

The study period used ranged from 1972 to 2016. The time range analysed started, for each variety of orange tree, in the year when the sale of seedlings begun, or in the year in which the analysis period started if its sale was earlier, and ended in the year in which the sale of seedlings was completed. For cases where the variety remained on the market at the end of the analysis period, the length of the survival period was right-censored.

The collection of the information needed for measuring the attributes of varieties was set up in two phases. In the first one, the attributes of the varieties were identified through expert interviews and, in the second phase, assessed by a panel of 10 experts, who evaluated the existence of the attributes listed in Table 2 for 30 orange tree varieties. Despite other attributes that could affect the variety survival, were identified by experts in the first phase, they have not been considered due to their association with the variables included in Table 2, following Pearson's chi-squared criteria, whose values are shown in Table 2.

In the second phase, environmental factors (prices, productions, cultivation areas and sale of seedlings) were quantified from historical data series available from 1971 to 2016, for the different varieties of orange trees.

Most varieties ripen late within their group (only 17% are precocious), 50% of the varieties are large in calibre within their group, 47% are seedless, 83% are frost-sensitive, 90% have sufficient commercial quality, and 50% are not affected by fruit fly.

With regard to environmental factors, Figs. 1 and 2 show the evolution of prices1 and cultivation areas for the most representative varieties within the four major groups of orange trees included in this study, namely: the navel group (‘Navelina’, ‘Washington Navel’ and ‘Navelate’), whites (‘Salustiana’), blood oranges (‘Sanguinelli’ and ‘Entrefina’) and late varieties (‘Berna’ and ‘Valencia Late’).

Figure 1. Price evolution (€2017 /kg) of the main varieties of orange trees in Spain from the 1969/70 season to the 2016/17 season. Source: Own compilation based on data from MAPA (2018), CAPA (2018), CARM (2018) and Junta de Andalucía (2018).

Figure 2. Evolution of the cultivated area for the main orange tree varieties in Spain for the 1972-2016 period (in hectares). Source: Own compilation from MAPA (2018).