Worldwide, concern over the consequences of global warming has resulted in intensified searches for potential plants that couldsupply raw materials for producing renewable fuels. Therein, physic nut (
The existing literature contains various descriptions of the pathogens occurring in culture, most of which are caused by fungi, and of which we address the following:
Although several descriptions of fungi exist, this chapter will discuss the most common and damaging diseases that affect physic nut, and draws on the following descriptions:
2.1. Anthracnose (figure 1)
This disease was first described in physic nut by the USDA (1960) in the USA, in Brazil by Viégas (1961), and later by Freire & Parente (2006) and Sá et al. (2011).Currently, the disease is present in all areas where physic nut is cultivated.
The most commonly observed symptoms are brown to black necrotic lesions that are irregularly shaped and appear on the edges and center of the leaf and which may contain a yellow halo. The lesions appear in the form of small, isolated points that coalesce and subsequently cause the complete destruction of the leaves. The fruit can also become infected, which leads to the appearance of dark brown lesions.
In addition to these symptoms, research in Mexico has indicated that the fungus
So far, there are no recommendations for controlling this disease. Because of the damage it can cause to physic nut, this disease should be studied further.
2.2. Passalora leaf spot
This disease was first described in Brazil by Braun & Freire (2004), and later by Freire & Parente (2006) in leaves of
The primary symptoms of this disease are rounded leaf lesions that are creamy to light brown in color, with a narrow dark brown halo, and later become limited by leaf veins and darken. Lesions measure 1-2 cm in diameter and rarely coalesce (Freire & Parente 2006).
Although it has been reported in several countries, to date this disease has not presented risk to physic nut cultivation.
This disease manifests in the form of leaf spots that consist of well-delimited brown irregular necrotic spots (Dianese et al. 2010).
The genera mentioned above have the following taxonomic characteristics:
Crous & Braun (2003) cite the occurrence of five species of cercosporoid, indicated above, in the culture of physic nut. However, few studies have examined fungi cercosporoid in this crop. As a result, there is no information about favorable conditions, symptoms or disease control. To date, this disease has not presented risk to the cultivation of physic nut.
2.4. Powdery mildew (figure 4)
The powdery mildew caused by the fungus
The most common symptoms of the disease are the production of abundant white or gray mycelia in leaves, petioles, stems, flowers and fruits (Dianese & Cargnin 2008). With the evolution of the disease, infected plants may show necrotic lesions, which cause leaf fall, underdevelopment, death of buds and young fruit deformation (Bedendo 2011).
The fungus that causes this disease is a typical biotrophic pathogen of the phylum Ascomycota, order Erysiphales. This pathogen may be characterized by white or grayish colonies, septate and branched mycelia; conidiophores that are erect or ascending, cylindrical, hyaline, septate and forming conidia singly; conidia that are usually large in proportion to the diameter of the conidiophores, simple, smooth, ellipsoid-ovoid doliiform, hyaline, single-celled (Braun & Cook 2012).
The disease generally favors warm temperatures, humidity of 75-80% and reduced light. Heavy rains are generally unfavorable to the pathogen (Furtado &Trindade 2005). In Brazil, the disease usually occurs in the dry season, apparently without causing extensive losses, because its occurrence coincides with the plants’ period of natural defoliation (Saturnino et al. 2005).
Currently, there are no fungicides recommended for culture, but some studies cite that spraying sulfur fungicides works to control this fungus. Another measure is to control alternative hosts, especially plants of the family Euphorbiaceae (Furtado & Trindade 2005; Saturnino et al. 2005; Dias et al. 2007).
2.5. Rust (figure 5)
The first report of this disease in
The fungus that causes this disease was previously classified as
The symptoms manifest in the leaves, initially in the form of small chlorotic points on the upper surface, which correspond to the underside of the leaf, and then small protruding pustules, which after breaking, release a powdery mass of uredospores of orange color, giving a ferruginous aspect. In severe infections, pustules coalesce to form necrotic spots, which are reddish brown and irregularly shaped and can destroy the leaf (Dias et al. 2007; Carneiro et al. 2009).
Currently there are no fungicides recommended for this culture. However, according to Dias et al. (2007), protective copper fungicides can control this disease.
2.6. Stem canker and dieback (figure 6)
The first report of this disease in Brazil was made byFreire & Parente (2006) and in Malaysia by Sulaiman & Thanarajoo (2012).
The disease manifests in the form of dieback that can progress until it takes over the trunk of the plant. Stem cankers have also been observed, causing necrotic lesions on branches and vascular discoloration. In Malaysia, disease incidence can be as high as 80% of a plantation (Freire &Parente 2006; Sulaiman & Thanarajoo 2012).
Characteristics of the
The identification of the
Control of this disease can be achieved by pruning and destroying affected branches. Later plants should be brushed with copper fungicides or thiophanate methyl for injuries (Furtado & Trindade 2005). Additionally, balanced fertilization, soil analysis and sufficient levels of irrigation in regions with long periods of drought can aid in disease control.
2.7. Collar and root rot (figure 7)
The first report of this disease in Brazil was made by Pereira et al. (2009), who identified it as being caused by
This disease has acquired great importance, because it can reduce productivity by causing the sudden death of plants and making cultivation areas unviable. The symptoms most commonly observed are wilting, leaf yellowing with subsequent fall, and cracks in the collar region. In the collar region, the appearance of black fungal structures in the bark of the plant has been consistently observed. Upon being removed from the soil, plant roots rot and the vascular system is affected by necrotic symptoms, ranging from light brown to black. Due to loss of support, the plants have often already fallen due to the wind.
The common characteristics of
Characteristics of the
In areas prone to prolonged dry seasons, a higher incidence of collar and root rot has been observed. Therefore, it is believed that the water stress is the main factor that predisposes plants to this disease.
The above-mentioned pathogens are difficult to control, due to the fact that they survive in soil. Therefore, to reduce disease incidence, it is first necessary to provide water and fertilizer balanced for proper plant development. When transplanting seedlings to the field, all forms of injury should be avoided. Another control measure would be to use healthy propagative material as well as seed treatments.
2.8. Yellow mosaic
In addition to the several fungal diseases mentioned, there is also yellow mosaic, a disease caused by a strain of the virus
3. Seed associated fungi
Seeds propagate the majority of cultures worldwide. These cultures are vulnerable to infection by several pathogens that can survive in seeds. These pathogens may cause reduction of seed germination, as well as deformation, discoloration, reductions in size and weight, and deterioration during storage. They can further contribute to rotting roots, damping-off, necrosis in leaves, and the spread of diseases across long distances. Consequently, these diseases cause losses valued at billions of dollars (Neergaard 1977; Agarwal & Sinclair 1997). To date, few studies have addressed the seed pathology of physic nut, and there is no information available about the losses that seed pathogens cause in this culture. But, follows below the major pathogens and saprophytic fungi associated with seeds.
Other fungi commonly associated with Jatropha curcas seeds (Figure 13)
Although there are no recommendations for fungicide useon physic nut, treatments can be administered by soaking seeds for 20 minutes in a solution of 1 liter of formaldehyde 40% diluted in 240 liters of water (Massola and Bedendo, 2005). This treatment is indicated for the seeds of
Despite the fact that most literature considered physic nut as resistant to pests and diseases, this review emphasizes the diversity of pathogens associated with this plant and the damage that they may cause. Most of these diseases may become a serious problem for Brazilian farmers, due to its severity and the lack of registered chemical products for these pathogens. Studies should be carried out in order to know the environmental conditions that favor to these diseases on
The authors wish to thank