Journal of Plant Pathology & Microbiology

Important Sorghum Diseases and their Management in Ethiopia

Mulatu Gidi^* Department of Agriculture, Ethiopian Institute of Agricultural Research, Holeta, Ethiopia
^*Correspondence: Mulatu Gidi, Department of Agriculture, Ethiopian Institute of Agricultural Research, Holeta, Ethiopia, Email:

Received: 12-May-2023, Manuscript No. JPPM-23-21342; Editor assigned: 15-May-2023, Pre QC No. JPPM-23-21342 (PQ); Reviewed: 29-May-2023, QC No. JPPM-23-21342; Revised: 12-Jul-2023, Manuscript No. JPPM-23-21342 (R); Published: 19-Jul-2023, DOI: 10.35248/2157-7471.23.14.696

Introduction

Sorghum bicolor (L) moench 2n=20 is a major cereal crop grown in arid and semi-arid regions around the world. After maize, rice, wheat, and barley, it is the world's fifth-most important cereal crop. It ranks third among cereals in terms of acreage and production. According to Mindaye, et al., Ethiopia is the world's sixth largest sorghum producer and Africa's third largest, following only Nigeria and Sudan [1]. In Ethiopia, Sorghum production is ranked 4^th next to tef, maize, and wheat. The crop is a main staple food crop in East African countries, including Ethiopia, for most food insecure people where areas are characterized by arid and semi-arid conditions. The crop is cultivated in a wide range of agro-ecological conditions and farming systems, including intercropping, mixed cropping, and drought stressed areas in Ethiopia [2].

Importance of Sorghum

World Sorghum production is approximately 60 million tons per year, with a cultivated area of 46 million ha. The United States, Nigeria, India, Sudan, Ethiopia, Burkina Faso, China, Tanzania, and Niger are the top producers. According to the CSA, Sorghum is Ethiopia's third most important food crop, after maize and tef, in terms of total number of producers, area coverage, and grain production, and is commonly used to make local bread, injera, and various local beverages such as tela and areke. It's also a roasted vegetable and a boiled grain. Sorghum is a self-pollinating monocotyledon crop, with levels of spontaneous crosspollination ranging from 5% to 30% depending on panicle type [3-9]. Furthermore, as a C4 plant, Sorghum is at the heart of dry land agriculture in the current scarcity crisis. Sorghum, in comparison to other food crops, is an ideal crop for dryland agriculture due to its high flexibility and tolerance to adverse conditions. Sorghum stalks are also used as animal feed, building materials, and fencing. However, abiotic and biotic factors, as well as socioeconomic constraints, influence potential Sorghum production. Diseases, insect pests, and weeds are major biotic impediments to Sorghum yield and quality losses [10].

Materials and Methods

Sorghum production constraints

Sorghum production and productivity are affected by both biotic (diseases, insect pests, and weeds) and abiotic (nutrient deficiency, aluminum toxicity, drought, high salinity, water logging, and temperature stress) constraints [11]. Anthracnose, grain mold, turcicum leaf blight, and Sorghum smut are all important Sorghum diseases. Insect pests (stem borer, weevils, shoot fly, termites, and birds) and parasitic weeds (striga) major important biotic constraints on the crop.

Sorghum diseases in Ethiopia

The most important constraint to Sorghum production and productivity is biotic (disease). Anthracnose, grain mold, turcicum leaf blight, and Sorghum smuts are the most common diseases that affect Sorghum crops (Table 1).

Table 1: Important Sorghum diseases in Ethiopia and caused by the pathogens.

Anthracnose

Sorghum anthracnose, caused by Colletotrichum sublineolum Henn, is the most common plant disease in all stages of Sorghum development, resulting in lower yields and grain quality. Anthracnose disease has been observed in all of the world's Sorghum growing areas. It is found in most of Ethiopia's Sorghum producing regions. The disease symptoms vary depending on environmental factors, plant developmental stage, and crop variety. Leaf symptoms appear as circular, elliptical, or elongated lesions of a dark reddish purple to tan color (Figure 1). The lesion's center is straw colored, with reddish brown or reddish orange margins and black acervuli with setae [12]. Under ideal conditions of high humidity and rainfall, the lesions grow in size and number, coalesce, and cover the entire leaf surface. Sorghum anthracnose causes yield losses of up to 70% in susceptible varieties.

Figure 1: Important Sorghum diseases in Ethiopia: A) Anthracnose; B) Cover smut; C) Grain mold; D) Cover kernel smut; E) Turicium leaf blight.

In Ethiopia and most sub-Saharan African countries, anthracnose is a major focus of Sorghum breeding research. Sorghum landraces from the Western and South Western parts of the country were resistant to multiple leaf diseases, including anthracnose these locations are used for Sorghum screening under natural conditions (hot spot area) in the national Sorghum improvement program, particularly for disease resistance breeding [13].

Management

The use of resistant genotypes is the most effective and environmentally sound management strategy for Sorghum anthracnose. Sorghum originated in Africa, with Ethiopia having the highest genetic diversity in native Sorghum as Sorghum is a diverse crop, and this center of diversity could also serve as a center of diversity for host plant resistance to anthracnose [14]. Sorghum originated in Africa, with Ethiopia having the greatest genetic diversity in native Sorghum as Sorghum is a diverse crop, and this center of diversity could also serve as a center of diversity for host plant resistance to anthracnose. As a result, searching for potential sources of resistance and breeding for disease resistance are important tasks for researchers working to develop effective and long lasting methods of controlling anthracnose.

In southern Ethiopia, for example, significant variation in the response of 56 Sorghum accessions collected from different regions of Ethiopia showed significantly lower disease levels compared to susceptible checks, indicating that germplasm from Ethiopia may be useful sources of anthracnose resistance [15]. Similarly, Erpelding discovered 44 lines developed in the United States from Ethiopian germplasm that had a high frequency of anthracnose resistance this suggest that Ethiopian germplasm could be an important source of anthracnose resistant accessions. Chala, et al., found resistant germplasm in Ethiopia, indicating that Ethiopia is an important source of anthracnose resistance for Sorghum improvement. All of these reports indicate that Ethiopian Sorghum germplasm has the potential to serve as a source of resistance in future breeding programs [16].

Covered smut

Among the reported Sorghum disease problems, covered smut disease caused by Sphacelotheca sorghi is the major bottleneck for Ethiopian Sorghum growing areas and requires close attention. Farmers in Nigeria's Sudano-Sahelian savanna recognize covered smut as a major production constraint. For the development of covered smut, an optimal temperature of 25℃ and half moisturized soil during planting are more important. The incidence of cover smut varies from place to place, but it is estimated to be between 50% and 100%. The disease is mainly seed borne, with the smut sori breaking during threshing and releasing spores, which adhere to the surface of healthy seeds and remain dormant until the following season [17]. When farmers use farm saved seed without treating it, it promotes the accumulation of seed borne pathogens, which leads to disease outbreaks and spread.

Management

In Ethiopia, most farmers do not have access to clean seed, so they use seed from other farmers or their own savings from the previous cropping season. This has resulted in the spread and accumulation of seed borne diseases such as covered smut and others. Several studies indicate that seed treatment and seed dressing of Sorghum seed with various types of fungicide is an effective method to control seed borne disease [18].

Results and Discussion

Grain mold

Grain mold is still one of the most common and serious diseases affecting Sorghum grain and quality, particularly in areas with high humidity and temperatures during grain development. Grain mold is defined broadly as a fungal component of preharvest grain deterioration caused by parasitic and/or saprophytic plant colonization. An alternative definition limits grain mold to infection and colonization of the spikelet tissue prior to grain maturity, excluding fungal damage after physiological maturity. All fungal associations with Sorghum spikelet tissue that occur between anthesis and harvest have an impact on grain quality and quantity, so a broader definition may better explain the damage from a practical standpoint. Regardless, grain mold is caused by multiple fungal pathogens and reduces yield and grain quality [19]. Yield reductions are caused by caryopsis abortion, reduced seed filling, and lower grain density, whereas seed quality and market value are affected by surface discoloration, embryo and endosperm deterioration, and contamination by toxigenic fungi and their mycotoxins. Mold affected grains have significantly reduced processing qualities and cannot be used for food. Grain mold is extremely damaging to the quality of Sorghum based foods, so resistance is a major consideration.

Management

The use of resistant genotypes is considered to be the most feasible means to mitigate Sorghum grain damage by grain mold in a climate favorable for fungal invasion and subsequent mycotoxin contamination. But cultural and chemical control methods are also management options.

Covered kernel smut

Covered kernel smut Sphacelotheca sorghi (Link) Clinton (syn. Sporisorium sorghi) is the most common seed borne disease of Sorghum. It is highly found in areas like Sheraro, Northwestern Tigray, in Northern Ethiopia, where untreated seed is sown. Field survey results in Sorghum growing areas in the Northwest, Northeast, Southwest, Eastern Ethiopia, and Tigray regions revealed that covered kernel smut is one of the major Sorghum diseases in the country. In similar studies, Teklay, et al., found that the two smut types (covered and loose smuts) had a combined prevalence of 37% in the southern Tigray Region, with incidence ranging from 0% to 5% and severity ranging from 20% to 100%. Traditional farmers' practices of using unclean and chemically untreated seeds are largely responsible for the continued occurrence of Sorghum smuts in the region.

Management

Several promising alternative options for managing covered kernel smut have been identified and recommended. Although treating seeds with cow or goat urine, bio-pesticide (using plant derivatives), and the use of synthetic seed treatment chemicals had profound effects, none of them were widely adopted to have an impact on disease management. Farmers most likely lack relevant information, or extension services may not have adequately addressed farmers' needs. Nonetheless, none of the management options mentioned above exist to address the covered kernel smut problem in Ethiopia, such as in Sheraro, Northwestern Tigray, and Northern Ethiopia. Notably, farmers frequently use all available varieties without seed treatment, resulting in significant losses.

Turcicum leaf blight

Among fungal diseases, Turcicum Leaf Blight (TLB) caused by Exserohilum turcicum (synonyms: Helminthosprium turcicum (pass.) is one of the most economically important fungal diseases in Sorghum producing countries around the world, including Ethiopia. The disease is widely distributed and problematic in both extensive and subsistence Sorghum producing communities in the producing countries of the world. The disease is widely distributed and problematic in both extensive and subsistence Sorghum producing communities in the producing countries of the world. In Ethiopia as well as the study areas, Sorghum is dominantly produced under mono cropping systems year after year. The disease epidemic's development is favored by high precipitation and relative humidity, mild temperatures (20℃ to 28℃), and the existence of huge amounts of inocula. However, severe epidemic development can arise, even under suboptimal conditions, where highly pathogenic TLB strains infect vulnerable host genotypes. In this situation, the disease can cause significant yield losses in Sorghum production [20]. In addition, loss of yield due to TLB in Sorghum may be noteworthy depending on the severity and host susceptibility, together with the time of disease onset. Yield loss due to TLB of Sorghum was not estimated in the study areas as well as in the country (Ethiopia). However, yield losses of 50% to 70% have been reported elsewhere on highly susceptible Sorghum genotypes for TLB. To this end, effective TLB management alternatives should be focused on the pathosystem elements.

Management

Efforts have been made to characterize TLB epidemic development in order to provide needed information for designing and developing better disease management strategies, as summarized by Ramathani MB and Mayada MB. TLB management strategies have included the use of high quality or disease free seeds, the removal of infected debris and residues, the cultivation of resistant genotypes, crop rotations, and fungicide applications as seed treatments and foliar sprays. The most beneficial way for TLB management is the development and use of resistant Sorghum genotypes with the help of good agricultural practices. As a result, when combined with appropriate agronomic practices, the development and deployment of resistant genotypes is the most cost-effective means of managing TLB. However, few efforts have been made to manage TLB disease in maize crops using resistance genotypes. However, no resistance breeding research in Sorghum genotype improvement has been done so far for TLB under Ethiopian.

Conclusion

Sorghum bicolor (L) Moench is an important food security crop grown by smallholder farmers in Sub-Saharan Africa (SSA), including Ethiopia. Abiotic and biotic factors, as well as socioeconomic constraints, all have a significant effect on potential Sorghum production. Diseases are major biotic impediments to Sorghum yield and quality losses. Management options include biological, cultural, chemical, and diseaseresistant genotypes. However, among the Sorghum disease management strategies, using disease resistant Sorghum genotypes is the most effective.

Acknowledgment

I would like to thank my institution, the Ethiopian institute of agricultural research, and the national agricultural biotechnology research center.

Conflict of Interests

The author has not declared any conflict of interests.

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