**1. Introduction**

The African oil palm (*Elaeis guineensis* Jacq.) is a palm tree originally from the West Coast of Africa and currently distributed in three regions of the equatorial tropics; Africa, Southeast Asia, and Central and South America, where it exists in the wild, semi-wild, and cultivated form [1]. Among the oilseeds, it is the one with the highest average yield, producing 4 to 6 tonnes per year of vegetable oil [2]. The fruit palm oil (mesocarp) and the palm kernel oil (almond) are the raw material for several products in the food industry, in the cosmetic and personal hygiene industry, and the biofuels industry [3, 4]. Palm oil provides 36% of the global supply of

vegetable oils with a considerable increase, from crude palm oil (CPO) production from 5.3 million tonnes in 1981 to 71.45 million tonnes in 2018 [2].

The Asian continent concentrates most of the CPO production, led by Indonesia and Malaysia, which together accounts for 85% of the world's CPO production [4]. However, the limited availability of areas for cultivation in Southeast Asia has opened new frontiers for expansion, culminating in the growth of Latin America's share in the global production of oil palm [5]. Latin America has the largest suitable area for oil palm cultivation, notably led by Brazil (2,283,000 km<sup>2</sup> ), Peru (458,000 km2 ), and Colombia (417,000 km2 ) [5]. Among Latin countries, Colombia is the world's fourth-largest producer of CPO and the first in the Americas, with an estimated production of 1.67 million tonnes in 2020, followed by Guatemala with 852 thousand tonnes and Honduras with 580 thousand tonnes [4].

Unfortunately, oil palm plantations in this geographical area are affected by a wide variety of pests and diseases that negatively affects productivity and discourage investment in this sector [1]. Notably, "bud-rot type" diseases pose the greatest threat to oil palm plantations in Latin America [6]. Among them, *Pudrición del Cogollo* (PC) and Fatal Yellowing (FY) are the diseases that cause most of the damage, both presenting a common symptom: rotting of the spear leaf that evolves until reaching the apical meristem system leading to the death of individuals [6, 7]. By far, the FY exhibits the most dramatic scenario because, in contrast to PC, its causal agent remains unknown, hindering effective sanitary control practices [8].

Fatal Yellowing was first identified by Reiking in 1928 in oil palm plantations in Panama, with cases reported in Colombia, Ecuador, Peru, Costa Rica, Venezuela, Suriname, Nicaragua, and, reportedly, in Central Africa, after that [6]. In Brazil, it was only in 1974 that the first symptomatic individuals were identified and, from the epidemiological explosion that occurred in the 1980s, FY started to represent the greatest threat to oil palm in the country [9]. As a result, several studies began to search for the possible biotic causal agent behind it and its putative vectors [8]. However, the research efforts made for more than 30 years have not exactly pointed out organisms directly linked to FY's cause [10–16]. Some studies also looked for possible abiotic causes, with inconclusive results so far [17–19]. Recently, techniques such as metabolomics, proteomics, and metagenomics started to be applied to provide insights into the possible FY etiology, initiating a new phase in the process to solve this problem [20–22].

Although Brazil has more than 30 million hectares with an aptitude for oil palm production, it currently has less than 1% of this area destined for this purpose [23]. Fatal Yellowing is the main contributor to hinder the expansion of the oil palm industry in Brazil, and the attempts to control the emergence of sick plants have not been successful, and its nature remains a mystery [10]. This review intends to analyze descriptively the studies carried out to investigate the FY problem in Brazil, besides pointing out new strategies employed for understanding the development of the disease, confirm the real cause behind it, and develop tools for early diagnostics.

### **2. The oil palm industry: social and economic importance**

#### **2.1 In the world**

Oil palm is originally from West Africa and adapted to the intertropical areas of Africa, Asia, South and Central America [1]. It is the most profitable oil crop, as it presents a higher yield with a lower production cost [24]. Its oil yield is of the order of 4-6 tonnes per hectare per year of CPO, much higher than that presented by other crops, such as rapeseed (0.69 t), sunflower (0.69 t), and soybeans (0.44 t) [3]. Another positive point is that this crop uses only 6% of the area to produce 36% of

#### *Oil Palm Fatal Yellowing (FY), a Disease with an Elusive Causal Agent DOI: http://dx.doi.org/10.5772/intechopen.98856*

the global oil supply, while soy, for example, occupies 40% of the land to generate 26% [4, 24]. Because of that, oil palm stands out as a player fundamental to help the world meet the growing global demand for vegetable oil in 2050 that will be around 240 million tonnes [25, 26].

The expansion of the oil palm industry has been strongly encouraged by governments and private sectors in Southeast Asia [27]. It is by far the most productive region in the world, supplying 85% of the CPO produced, reflecting the rapid expansion of the cultivated area that started in the middle of the last century [25]. The commercial oil palm plantations in Indonesia, for instance, went from 70 thousand hectares in 1961 to 6.78 million hectares in 2018, with a considerable increase of 9.582% during this period [2]. As a result, Southeast Asia production rose to 63.26 million tonnes in 2018, or a 22,378% increase in the period [2, 3].

Africa has not seen an expansion of the oil palm industry as significant as Southeast Asia in the last 60 years [3, 28]. The area occupied by oil palm increased from 3.55 million hectares in 1961 to 4.55 million hectares in 2018 in the African continent, representing an increase of only 33% (**Figure 2**) [2]. Meanwhile, the Americas now occupy 6% of the international market, producing around 4.89 million tonnes of palm oil in 2018, a 273% increase in the last two decades [2].

The considerable increase in oil palm production was supported mainly by the advances in genetic breeding programs that increased oil productivity more than 2 folds since 1960 [1].

Most of the CPO and its derivatives produced stays in the Asian markets that absorb 51% of the total, led by India, which imports 19.4%, and China 13.0% [29]. The European markets, which import 26%, have the Netherlands (6.1%) and Italy (4.3%) as the leading importers [23]. Africa (12%), the Middle East (4%), and Latin and North America (7%) also have a consumer market for vegetable oils, and palm oil from Southeast Asia helps to supply the demand [29]. The global vegetable oil market allocates 70% of total production to food and 30% to non-food industrial purposes, such as, for example, the production of cosmetics and personal hygiene products (24%) and as a raw material for the production of biofuels (5%) [26].

### **2.2 In Latin America**

The increase in global palm oil production in the 21st century is due mainly to new plantations in producing countries, especially in Malaysia and Indonesia [27]. However, due to a reduction in the areas available for expanding cultivation in Southeast Asia, an opportunity opened up to expand to new frontiers to meet the growing global demand for palm oil [5]. As a result, Latin America became one of the most promising regions for oil palm cultivation, as it has one of the largest areas suitable for cultivation, notably represented by Brazil, Peru, and Colombia [5].

Brazil, Colombia, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Peru, and Venezuela produce together 4.65 million tonnes of palm oil, representing 6% of world production in 2020 [2]. Colombia is the largest oil palm producer in this region and ranks 4th in the World, with 1.61 million tonnes produced in 2018, or 33% from the annual palm oil of Latin America (**Figure 1**) [2, 30]. Guatemala produced a total of 875 thousand tonnes in 2018 what places the country in the 2nd position in Latin America [2, 31]. Honduras is in the 3rd, followed by Ecuador, Brazil, Costa Rica, and Venezuela [2].

#### **2.3 In Brazil**

The first oil palm plants arrived in Brazil in the 16th century, adapting very well to the Northeast region of the country [32]. The oil palm industry in Brazil stayed as

#### **Figure 1.**

*Land use for oil palm cultivation in central and South America since 1980, in hectares. Source: adapted from our wold in data [2].*

#### **Figure 2.**

*Fatal yellowing (FY) disease in oil palm. (a) Oil palm plantation affected by FY; (b) individual showing signs of yellowing and necrosis of the intermediate leaves; (c, d, e) evolution of yellowing and dryness of the spear leaf with the presence of necrotic tissue, and (f) root section of an individual with signs of rot. Source: by authors.*

a small industry until 1960, when, due to increasing demand for oil for cooling steel sheets in the national steel park, it started to experience significant growth [33]. In 1967, the oil palm cultivation expanded to the Pará State, in the North region of Brazil, with the first commercial-scale plantations comprising about 3.000 hectares [32].

*Oil Palm Fatal Yellowing (FY), a Disease with an Elusive Causal Agent DOI: http://dx.doi.org/10.5772/intechopen.98856*

Driven by technical advances and growth in demand for vegetable oils, there was a significant increase in the cultivated area of oil palm in Brazil, which went from 11 thousand hectares in 1980 to more than 236 thousand hectares in 2008 [3]. Brazil has large areas with the aptitude for oil palm production, favored by climatic conditions similar to the most productive regions in the world [1]. However, until 2014, less than 1% of this area was occupied by commercial plantations [34, 35]. Brazil's position as the 13th, and 23rd, in palm oil production and on the productivity scale, respectively, in the world, is due mainly to this under-utilization of available areas [3, 32].

Oil palm production is concentrated in Pará state, which accounts for 97.19% of the cultivated area and 97.99% of the national palm oil production, followed by Bahia (1.98%), Roraima, and Amazonas [36]. The expansion of cultivation to already deforested areas in the Amazon and other regions in Brazil is an opportunity to reduce pressure on forests and supply the palm oil demand from the food and energy sectors [35]. To make the plantations more environmentally sustainable, the Brazilian Government launched the agro-ecological zoning (ZAE) program in 2010, a legal mechanism to delimit the oil palm cultivation area [37]. This area include Acre, Amapá, Amazonas, Mato Grosso, Pará, Rondônia, Roraima and Tocantins, part of Maranhão and five municipalities in Goiás state, comprising about 59% of the Brazilian territory [35].
