Role of bacterial and fungal endophytes in the expression of defense genes against leaf rust of wheat and their activities as a biofertilizer

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Wheat (Triticum aestivum) is the most widely grown crop in the universe. Wheat is one of the most domestic food crop in Pakistan and other many countries of the world from 8000 years. It is the most consumed food grain and its productions leads almost all agriculture products like maize, rice and vegetables.  Wheat as the staple food is valued due to its good taste and rich source of vitamins, minerals, calories and proteins in all over the world. Its importance is due its utilization, as its large quantity used in the bread making, chapatti in Pakistan and India, in biscuits and many more products are formed by the wheat. A minor amount of wheat is also used in the coffee making while low grade of wheat used in feed stock for the domestic animals.

Production status of wheat in Pakistan

In Pakistan, wheat has the status of staple food and cover the large area as compared to other any crops. Pakistan categorized into ten major wheat producing countries of the world in term of yield per acre, total production and area for cultivation. The sixty (60) percent daily diet of the public man in Pakistan depend upon the wheat. Wheat share 2.2 GDP and 10.1 % value added in the agriculture products of the Pakistan. Area under cultivation of wheat increased 0.5 % from 8.650 to 8.693 in the year of 2012-13. The production graph in the year 2012-13 was 24.3 million tons, while the target was 25.5 million tons in this year, so its production decrease from the target but 3.2 % increase from the production of previous year which was 23.5 million tons. The 2.7 % yield per hectare increased from the previous year. The wheat production and area under cultivation also increased from the last year.

Diseases of wheat crop

There are many factors which influence the wheat crop at various phases, which causing a great reduction in germination percentage, growth rate and quantity and quality as well as. Pathologically point of view, wheat plant is attacked by many diseased which are caused by nematode, bacteria, fungal and viral pathogens in the universe, but prevalence of fungal diseases are most important in the Pakistan, particularly rust, bunt and smut due to very conducive environmental conditions. However, the all fungal pathogen cause highly losses but rusts are more deleterious and ubiquitous pathogen in all over the world and in Pakistan.

Brown rust of wheat is more deleterious amongst other two rust diseases of the wheat which cause highly losses in wheat production. Mostly, the yield losses depend upon the strength level of the respective cultivar. For example, in highly susceptible cultivars losses may reach up to 80%. Other two rust diseases are stripe rust (Puccinia striiformis f.sp. tritici) and stem rust (Puccinia graminis tritici) of wheat, however under favorable condition these diseases cause highly losses.

The Puccinia recondita tritici affects morpho-physiological and grains of the wheat crop under severe condition. The infected crop produces shrinking grains which reduce the weight of the grains. Additionally, proteins contents, carbohydrates, nutrients, vitamin, minerals, flag leaf area, chlorophyll contents, relative membrane permeability, sugar contents, spike length, spike weight, plant height and number of tillers per plants are badly affected by the wheat rusts. The market value of the infected grains is reduced due to unhealthy and shriveled grains. Leaf rust of wheat cause epidemic during 1978 and cause 10 % yield losses at that year. Therefore, leaf rust of wheat is the permanent threat for the wheat production in Pakistan and other wheat growing countries of the world.

Role of endophytes in the expression of defense genes  

Certain defense genes in wheat activated by the application of endophytic bacteria and fungi against Puccinia recondita f.sp. tritici, but until their mode of action is not understood. The different families of the resistant genes like PR1 and PR5 are famous by the name of thaumatin because amino acids of these proteins show wide homology with thaumatin. It is recorded that PR5 genes which have more molecular weight are present in the cell vacuoles of the plants that show antifungal response. While PR5 proteins which have low molecular weight are present in the extracellular and also showed antifungal response, because the amino acid sequence of small molecular weight proteins associates small grade of homology with thaumatin. The research which will be focus on the various resistant genes like PR1, PDF1.2 and PR5 have a status of “hot spot” in the plants resistant.

Leaf rust effect the health status of the wheat crop, which ultimately reduce the quality and quantity of the wheat grains and reduce the market value as well. Therefore, proper management of leaf rust of wheat is very compulsory for the avoidance of highly losses. Proper management relied on the adopting of various combined approach which reduce the inoculum of the Puccinia recondita f.sp. tritici. Using of resistant cultivars is the best option against leaf rust of wheat, but after a few years these resistant cultivars become susceptible due to the changing in the genetic makeup of the pathogen. But, using of resistant cultivars, various bacterial and fungal endophytes and applying fungicides which have a lowest residual effects is one of the best option for the leaf rust of wheat. In this scenario, resistant cultivars have resistant genes against leaf rust of wheat, endophytes have a great potential in the improvement of plant health by providing the solubilized sulfur to the plants and also act as a biocontrol against the different soil and air borne pathogens while fungicides reduce the inoculum which is present small quantity on the upper surface of the leaves. But various fungicides have soaring prices which are not affordable by the common farmer.  Therefore, against leaf rust of wheat using of fungal and bacterial endophytes and resistant varieties are the most suitable and environmentally friendly approach.

Role of endophytes in the Morpho-physiological attributes

Use of plant growth promoting endophytes (PGPEs) is a technique which act as a bio fertilizer that improve host capacity for nutrient uptake, enhanced production, reduce the cost of fertilizer and eco-safe nature due to reduction in nitrogen leaching. These are asymptomatic microbes found in almost all living plant species. They form colonies in living tissue of plants without causing any deleterious effect on plants. They can also help plants for fixing atmospheric nitrogen and production of siderophores which have the potential to convert inorganic iron into organic form for the easily assumption of the plants.  Similarly, plant growth promoting bacteria and fungi produce many growths stimulating hormones like Indole acetic acid (IAA), gibbrelic acid (GA) and abscisic acid (ABA) and cytokinin which play a very vitalrole in the plant growth promotion and alleviation of biotic stresses. Many researchers also reported that PGPEs protected the plants from many deleterious abiotic stresses like salt, over irrigation i.e. flooding, and drought. They also increase directly or indirectly water use efficiency, fresh and dry weight and different physiological responses of the plants i.e. increase in proline concentration which act as an osmoregulation agent.

Bacillus subtilis are endophytic bacteria which improve plant growth directly or indirectly by production of many phytohormones and antibiotics which kill other plant pathogenic bacteria. Plants induce systematic resistant against different types of pathogens by the process of mobilization and solubilization of phosphate. In some studies, it is reported that Bacillus subtilis bacteria enhance the root and shoot length of plant, number of grains and size of the grains, fresh and dry weight, flag leaf area and chlorophyll contents of the treated plants. Similarly, Trichoderma harzianum is a plant growth promoting fungus which belongs to Ascomycetes. It is used as a biofertilizer, biocontrol agent and promotes the growth of the plants against various biotic and abiotic stresses. It also play an important role in nutrient absorption by colonizing the roots and enhance the chlorophyll content, fresh and dry weight of the plant leaf, increase flag leaf area, grain yield and plant height.

The potential of Bacillus subtilis has been exploited to control plant diseases under control and natural field conditions. However, very few information’s are present on the combined use of Bacillus subtilis and Trichoderma harzianum for improving plant growth and disease suppression in wheat. Therefore, the present study was designed to evaluate the synergistic use of Bacillus subtilis and Trichoderma harzianum for enhancing growth, yield attributes, expression of defense genes and traits expressing the moisture status in Galaxy-2013 and disease suppression in wheat. Moreover, the role of endophytic bacteria and fungi in the expression of defense related genes like PR1, PR2 and PDF1.2 was also checked.

However, the using of bacterial and fungal endophytes is best approach to control leaf rust of wheat (Puccinia recondita f.sp. tritici). This approach also reduces the mutation process in the pathogens against various fungicides which are in used from many years. The using of endophytes against rust diseases also provide environmental friendly approach.

This article is collectively authored by Ghulam Muhae-Ud-Din*, Muhammad Amjad Ali, Muhammad Jabran, Farhan Goher, Zuniara Akash and Mehwish Naz ,Department of Plant Pathology, University of Agriculture, Faisalabad-Pakistan.


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