Sugarcane is one of the most important crops for sugar production in sugarcane-growing areas. Many biotic and abiotic stresses affected the sugarcane production which leads to severe losses. Pokkah boeng is now playing a very important role due to its economic threats. Currently, the occurrence and rigorousness of pokkah boeng disease have been spread like wildfire from major sugarcane-growing countries. Pokkah boeng is a fungal disease that can cause serious yield losses in susceptible varieties. Infection of the disease is caused either by spores or ascospores. It may cause serious yield losses in commercial plantings. However, there have been many reported outbreaks of the disease which have looked spectacular but have caused trade and industry loss. Fusarium species complex is the major causal agent of this disease around the world, but some researchers have documented the increased importance of Fusarium. Three Fusarium species have been identified to cause the sugarcane pokkah boeng disease in China. Moreover, Fusarium may be accompanied of its mycotoxin production, genomic sequencing, and association with nitrogen application in China. Many studies on disease investigations, breeding of disease-resistant varieties, and strategy of disease control have also been carried out in China.
- pokkah boeng
- Fusarium species complex
- secondary metabolism
Sugarcane is a major crop in Southern China, and it is the third biggest sugarcane producer in the world. Sugarcane is one of the most important crops grown commercially in the tropical and subtropical region. Sugarcane belongs to the genus
Many biotic and abiotic stresses affected the sugarcane production and are known to be one of the oldest cultivated plants in the world. Improving sugarcane production will greatly help in economic prosperity of the farmers and others associated with sugarcane cultivation. Large numbers of sugarcane pathogens have been recorded all over the world. One of the current major diseases affecting sugarcane and sugar production is pokkah boeng. It is caused by
Pokkah boeng disease on sugarcane has been recorded in almost all countries where sugarcane is grown commercially. It normally appears during periods of hot humid conditions when the cane is growing rapidly. This disease was originally described in Java in 1896, denoting a malformed or distorted top. The temperature, light, and fertilizer regimes are optimized for maximal plant growth, but these conditions may also be favorable for pathogens. Walker and Went (1896) were the first ones who describe the pokkah boeng disease on sugarcane. Generally, it appears that slowly growing fungi, which are less efficient than quickly growing fungi at escaping competition by entering specific niches, have a higher prevalence of enmity against competing fungi. Geh  first reported the presence of the disease in Malaysia. It may cause substantial damage to the crop and not severe except in very susceptible varieties.
Pokkah boeng is a reemerging disease of sugarcane—which has been found recently to cause major yield losses—in most sugarcane-producing regions, including South Africa, Malaysia, India, and China [10, 11, 12, 13, 14]. Pokka boeng disease of sugarcane has associated with several diseases of sugarcane such as sett rot, root rot, and wilt . The pathogen is transmitted by air currents, and airborne spores will colonize the leaves, flowers, and stems of the plant . Pokkah boeng causes serious yield losses in commercial plantings. Reported outbreaks of the disease, while looking spectacular, have caused economic losses. The fungus was reported to occur systemically in all plant parts of sugarcane.
Pokka boeng diseases are dependent upon the environmental conditions, quality of setts, and handling of the plants, e.g., exposing sugarcane plants to stress either from water stress, temperature, pH, or soil nutrition. Hail damage can cause cane plants to be easily susceptible to diseases due to the bruised stalks and broken leaves, giving the diseases access to the damaged setts. Some of the favorable conditions for disease development included drenched conditions of the soil, lack of cultural practices that result in the growth of weeds, constant cultivation of same variety in the field, and existence of susceptible varieties in the surroundings. It is very important for a farmer to prevent and control such pests and diseases to avoid losses.
The taxonomy of
Several control measures may be implemented to minimize potential sugarcane yield loss caused by pests and diseases, but an integrated approach is often recommended. Good farming practices are essential but do not guarantee eradication of infections. The planting of resistant cultivars is recommended as the best and most economical approach for controlling pests and diseases, having the least impact on the environment and increasing productivity without the need for other inputs, such as costly chemical applications or labor. Breeding sugarcane that is resistant to multiple pests and diseases is difficult due to the complex genome of sugarcane . Additional genome-scale comparative and functional studies are needed to elucidate the evolution and diversity of pathogenicity mechanisms, which may help inform novel disease management strategies against
2. Manifestation of pokkah boeng
The initial symptoms were easy to recognize the disease since they attack the top parts and are chlorotic areas at the base of young leaves. Heavily infected plants showed a malformed or damaged top, and stalk may occur in highly susceptible varieties. The base of affected leaves is often narrower than that of normal leaves. Ladder-like lesion on the spindle leaves pronounced yellowing, wrinkling of the spindle, twisting or tangling appearance of the spindle, marketing red stripes, and shortening of the leaves accompanied the malformation or distortion of the young leaves. The most advanced and serious stage of pokkah boeng is a top rot phase. Leaf infection sometimes continued to downward and penetrates in the stalk by way of a growing point. The young spindles are killed and the entire top dies. Leaf sheaths may also become chlorotic and develop asymmetrical necrotic areas of reddish color.
The reddish tissue form ladder-like lesions, often with dark edges. These lesions sometimes break through the surface of the rind. Occasionally, the pathogen also attacks the spindle, and from there it moves down the terminal portion of the stalk causing top rot. The pathogen makes its entry into the host tissues through any sort of injury made by insects or borers or natural growth cracks, etc. The severity of symptoms varies with the susceptibility of a variety and with the congenial environmental conditions and governs the development of the causal organism. During fungal penetration and growth inside the plant,
3. Mode of transferal
The pathogens of pokkah boeng disease are transmitted by the movement of spores through airflow. For spores to take off, it depends on the environmental situation that requires different strategies to disperse. Fungal species that dispersed by rain splash are based on the “puff” and “tap” mechanisms that will cause the dry spores to become airborne, and usually the spores are curved like
The growth of sugarcane is the most important factor in the biological control and prevention and land and natural environmental factor. The processes for controlling are limited, and there is an increasing need for novel and environmental strategies to control diseases of sugarcane. There will be four sections in this chapter, including
Fusarium species complex (FSC) and their distribution
To recognize and define species in the FFSC, various operational species concepts have been applied. However, a variety of genetic, ecological, and biological traits and properties may be used for this purpose. Only morphological species recognition (MSR), biological species recognition (BSR), and phylogenetic species recognition (PSR) have contributed significantly to the classification of
3.1.1. Fusarium verticillioides
3.1.2. Fusarium proliferatum
During winter or in dry periods,
3.1.3. The other members of Fusarium fujikuroi species complex (FFSC)
Other FFSC, viz.,
3.1.4. Fusarium oxysporum species complex (FOSC)
Fungal growth initiated with white mycelium which subsequently turned pale violet. Ten isolates were recovered from the single-spore cultivation. The mycelia were floccose, sparse, or abundant. The microconidia were oval, elliptical, or kidney shaped and with 0 septate, while the macroconidia usually had three septa. The apical cell was tapered and basal cell was foot shaped. The morphological features and sporulation pattern were consistent with the description of
3.2. Comparative genomics of
Fusarium species complex (FSC)
Comparative genomics allows investigating many questions of evolutionary and functional significance of sequence features. By associating the species-specific genes with the unique characteristic of that species, researchers can find the potential relationship between genotype and phenotype. Various forward and reverse genetic methods have been developed to explore the repertoire of
The whole genome of three fungal isolates (CNO1, YN41, and BS2–BS6) from the
The development of genomics is allowing the incorporation of new tools and resources to address the important new challenges for agriculture. The commercial sugarcane cultivars used today resulted from crosses of
A comparative genomics approach was effective in resolving the genetic relationship among fungal species and isolates. The
FFC species can produce structurally diverse secondary metabolites (SMs), including the mycotoxins fumonisins, fusarins, fusaric acid, and beauvericin and the phytohormones gibberellins, auxins, and cytokinins.
Secondary metabolites are very important in mediating interactions between fungus and host plant. The genes encoded the secondary metabolite often involve particular types of key enzymes, including polyketide synthase (PKS), non-ribosomal peptide synthetase (NPS), and terpenoid synthase. These key enzymes are clustered along with various combinations of additional enzymes for further metabolite catalyzing and with transporters and transcription factors that are essential for the regulation of most of the clustered genes. Based on the fungal SM analyses by antiSMASH software, some SM biosynthetic gene clusters were shared in all
Modern sugarcane cultivars were derived from the interspecific crosses among a few clones of
Fusarium species complex and nitrogen source
Nitrogen is one of the most important nutrients for crop growth and production. It is a major component in chlorophyll, which is the most important pigment needed for photosynthesis, as well as amino acids, the key building blocks of proteins. Nitrogen accelerates growth, gives vitality to plants, and promotes dark green color in leaves due to better chlorophyll synthesis. Sugarcane is the world’s largest sugar crop and an economically important crop in China. The symptoms of sugarcane pokkah boeng tend to develop during periods in which high concentrations of nitrogen are applied.
Fungi are able to respond to quantitative and qualitative changes in nitrogen availability through complex regulatory mechanisms. The source of nitrogen has been isolated from sugarcane (
Nitrogen availability has significant effects not only on physiological and morphological characteristics of the fungus but also on the biosynthesis of secondary metabolites, such as mycotoxins in
On the other hand, it has been observed that in some plants as the N content is increased beyond sufficient levels, the amount of antifungal compounds decreases. Nitrogen fixation is a biological process that reduces molecular N2 into ammonia (NH3), which can be easily absorbed by plants. During this adaptation, nitrogenase plays a very important role in catalysis. Strains with nitrogenase activity were identified on the basis of their phenotypic and 16S rDNA sequence analysis and concluded that isolates had potential for regulation of plant growth. To synthesize the secondary metabolites of nitrogen molecules, ammonia plays the vital role in plant growth and development.
Nitrogen supply can bang plant-pathogen interactions through consequence on pathogen virulence. The well-established virulence factor of
Biofertilizers are based on effective strains of microorganisms in sufficient numbers, which are useful for nitrogen fixation in plants and synthesis of growth-promoting substances like hormones, vitamins, and auxins. Besides being essential as a source of cheap protein for human nutrition and animal feed, symbiosis with rhizobia is essential in crop rotation to maintain soil fertility. Poultry manure and other animal waste products were used as a source of supplemental nitrogen long before inorganic nitrogen fertilizer came into popular use. The utilization of BNF for agricultural purposes has long been the dynamic force behind N-fixation research. The environmental benefits from using biological N-fixation are seen to be associated with the proxy of chemical-based technologies with a biological system. Some of the main benefits provided through crop rotation include the prevention of soil erosion, increased soil microorganism diversity, decreased pest prevalence, and increased field fertility. The importance of field fertility in the process of growing crop is immense. The process of BNF can be defined as the reduction of dinitrogen to ammonia by means of a prokaryote. BNF is accomplished by a wide variety of prokaryotes; some can accomplish this as free living organisms, while others require a symbiotic association with plants.
The secondary metabolism, also called specialized metabolism, is part of the metabolism of fungi which is not essential for direct survival; such gene will rely on regulatory mechanisms for biosynthesis and their perpetual relations with the nitrogen regulation of other pathways in
3.4. Preventive and control measures
Sugarcane is a highly industrious crop which suffers from numerous diseases caused by different organisms and factors such as environmental and physiological disorders and nutritional deficiencies. Historically, planting susceptible varieties in a large area encouraged the outbreak of a certain diseases in a particular period of time. Several control measures may be implemented to reduce potential sugarcane yield loss caused by pests and diseases, but an incorporated approach is often recommended.
Disease control in sugarcane is based on an integration of legislative control, resistant cultivars, and other management procedures. Short-term spraying options are available, but their economic viability may not be sustained. Machine harvest can also transmit disease. Many sugarcane diseases are also managed through the use of disease-free planting material supplied through Cane Protection and Productivity Boards. The genetical resistant cultivars is the most cost-effective method to control the disease, and the presence of genetic variations against pokkah boeng and its associates is well documented. Because of the more serious disease problem, a progressive effort to socialize and conduct integrated management for controlling the disease.
Several control measures may be implemented to reduce potential sugarcane yield loss caused by pests and diseases, but an incorporated approach is often recommended. To remove and destruct of infected plants on the first appearance of the disease in case of pokkah boeng established that frequent breakdown of varietal resistance against pokkah boeng is due to the appearance of new pathotypes matching the resistance of cane genotypes.
Successive ratoons are characterized by reductions in cane yield due to systemic diseases or physical damage to stools, and the number of ratoons obtained from a single harvest also depends on genotypic and environmental factors. Ratoon productivity has been proved to increase with proper management involving timely agricultural operations, proper nutrition management and integrated pest management, and maintenance of adequate plant population. A number of ratoon management practices currently in use, such as inter-row ripping, burning of crop residues at harvest, harvesting under wet conditions, and using heavy infield transport, were found to be contrary with the substantial, chemical, and biological properties of the soil. The incidence was figured out as five grades (Figure 1).
Based on the disease severity index (DSI) of pokkah boeng disease of sugarcane, the resistance of sugarcane against pokkah boeng was classified into five levels from 0 to 5. Level 0 was defined as highly resistant (HR) with DSI≦1.0, Level 1 as resistant (R) with DSI ranged from 1.1 to 5.0, Level 2 as moderately resistant (MR) with DSI from 5.1 to 10.0, Level 3 as moderately susceptible (MS) with DSI from 10.1to 15.0, Level 4 as susceptible (S) with DSI from 15.1 to 20.0, and Level 5 as highly susceptible (HS) with DSI > 20.0.
The disease severity index (DSI) was calculated as follows:
Conidial suspensions of the isolates (CNO-1 and YN41, 106 conidia mL−1, 100 μL) were dripped into the young spindle of 89 sugarcane germplasm, and the symptoms were observed on the inoculated plants in 6–8 days post-inoculation, respectively. Our results showed that 34 of 89 tested clones (38.2%) were susceptible to both CNO1 and YN41, 32 clones (36.0%) susceptible to CNO-1 but resistant to YN-41, 14 clones (15.7%) susceptible to YN41 but resistant to CNO-1, and only 8 clones (9.0%) resistant to both CNO-1 and resistant YN41. Both these resistant clones included CP84-1198, GT94-40, GT05-3846, ROC1, ROC27, YC58-14, YC64-173, and YT94-128. Moreover, our results also showed that CNO-1 had higher infection than YN-41 by this inoculation with a success of up to 89.8%.
Chemical control is often expensive and has downstream unconstructive effects on the environment. Nine compounds were tested at three concentrations (100, 50, and 10 ppm) for their ability to inhibit mycelial growth of
In the field test, spraying of different fungicides like Bavistin or Blitox or copper oxychloride or carbendazim is efficient for reducing the pokkah boeng disease. Planting of healthy seed, the use of resistant varieties, and following the integrated disease management practices are the best ways to prevent disease incidence. The use of resistant cultivars is particularly useful, as it reduces the use of harmful chemicals which can disturb the balance of nature and result in other pests becoming a problem. Furthermore,
Host plant resistance shows major advantages compared to chemical, biological, and cultural control components for management programmes. However, it needs to be supported with additional management practices to ensure durability in the field. Biological control of plant pathogens is an attractive alternative to the strong dependence of modern agriculture on chemical fungicides, which cause environmental pollution and development of resistant strains. The endophytic bacterial community associated with sugarcane harbors multiple genera with potential for plant growth promotion and disease control.
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