Antifungal activity of plant extracts and Silver nano particles against Citrus brown spot pathogen (Alternaria citri)
Abstract
Citrus Brown spot caused by Alternaria citri. Different control strategies should be used for management of disease and for increasing potential yield of citrus. Hence in-vitro potential of Plant extract and Silver Nanoparticles were evaluated for control of Brown spot pathogen in Citrus mangroves of Pakistan. Four different plant extracts garlic, neem, mint and basil leaves extracts were used at concentration of 20%. 40% and 60 %. Their effect on radial mycelial growth was checked with reference to untreated or control petri plate. It was observed that almost all concentrations of plant extracts significantly reduce radial mycelia growth as compared to control. In all treatments of plant extracts it was observed that 60% concentration of neem extracts is effective with radial mycelia growth of 3.96 cm over control petri plate which is 7.73cm, garlic extract@ 60% gave least fungal mycelia growth 5.5cm followed by mint leaves @60% gave 3.16 cm radial growth and Basil leaves extract @60% reduces fungal mycelia growth upto 3.93 cm as compared to control petri plate. Nanoparticles were used for invitro control of brown spot pathogen .Ten different concentration of nanonparticles were used as 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 ppm. The result of study revealed that by increasing concentration of nanoparticles inhibit mycelial growth of pathogen more significantly and 100 ppm concentration of Silver nanoparticles reduce fungal mycelia growth upto 2.63cm as compared to untreated petri plate fungal growth 7.23cm.
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Introduction
Pakistan has wide range of ecological climate, more than thirty one types of fruits has been produced in Pakistan like mangoes, guava, apple, peach, pear that comprises more than 73% of Gross annual production. From all fruits Citrus ( Citrus reticulate) share one third in export[1].It has great export potential almost 250,000 tons of kinnow is exported to Russia, SouthEast Asia and Middle East from Pakistan with foreign exchange of 120 million dollars. Punjabis major citrus growing province and 49% of citrus is produced herein Pakistan [2]. A large number of export & processing units have been established in last two decades in Sargodha. Citrus is attacked by wide range of pathogens include fungi, nematode, bacteria, viruses. Fungi play an important role in decreasing quality and quantity among all pathogens. Citrus is attacked a large number of diseases that includes Anthracnose, citrus scab, citrus decline, citrus canker, citrus scab and blemishes. Anthracnose, melanose, greasy spot and fruit blemishes are important diseases that are caused by fungi. The quality, quantity and market value greatly affected by fruits blemishes [3].
Alternaria citri is the casual organism of brown spot of citrus. Different pathotypes are associated with the diseases that are characterized on the bases of host specificity. Almost all species of citrus is attacked by different pathotypes oranges are not affected by the disease but considerable spotting develops on grapefruit [4]. Spores of Alternaria are found on twigs, leaves and root lesions on the tree and on the ground. Spore germination favored by presence of moisture, spores are disseminated by air and rain splashes. Disease symptoms appear on young leaves after 36 and 48 hours after infection. Fruit is the most susceptible part that continues to develop symptoms even after four months of petal fall [5]. Thousands of phyto chemicals like phenols, phenolic acid, quinonels, flavanoides, flavanoles, pannins have inhibitory activity against wide range of pathogens. Plant extract have antimicrobial properties. Brown spot is managed biologically by application of plant extracts, these extracts have antifungal activity and are used as botanical fungicides and pesticides. Proper agronomic practices also reduces source of inoculum from vicinity/orchard. Timely irrigation and adequate fertlization plays an important role in controlling disease causing pathogens [6]. Nanoparticles consists of nano silver combined with water soluble polymer and manufactured by exposing silver salt solution and silicate radioactive radiations[7]. Nano sized silica silver in concentration of 3.0 ppm has strong antifungal activity against wide range of phytopathogenic fungi however many useful bacterial species were not affected at 10ppm concentration but at 100ppm concentration of nano sized silica silver completely inhibit the activity of plant pathogenic fugi[8]. Now a day’swhole worlds were thinking about debasement of the usage of botanicals as innovative chemotherapeutant in plant protection. Plant products had been widely used as pesticides now a days and some botanicals were used as green pesticide throughout the world. Some plant products like neem oil , pyrethriods and some essential oil has been used of some trees were used as antimicrobial agent against stored grains pests because they were easy to handle and they have no harmful effect fungal hyphal growth is greatly inhibited by using silver nanoparticles in those dependent manner. Efficacy of silver nanoparticles was observed among fungi on the hyphal growth in the following manner Rhizoctonia R.solanae ≥ S.sclerotium ≥ S.minor. Sclerotium germination growth proves that silver nanoparticles significantly inhibit its growth. High concentration of silver nanoparticles was effective in inhibiting sclerotial germination growth of s.sclerotia[9]. When hyphae of fungi that were exposed to silver nanoparticles was observed under microscope shows that nanoparticles severely damage the hyphal and leads to collapse and separation of layers of hyphae [10]. This research suggests using silver nanoparticles and plant extracts as an alternative to fungicides for management of Alternariacitri.
Conclusion
In the present study antifungal activity of plant extracts and Nanoparticles were evaluated against citrus brown spot pathogen Alternaria citri. Neem, garlic, basal, and mint leaves extracts were used in the study for in vitro control of disease it was found that these botanicals are green pesticides for inhibiting the mycelial growth of Alternaria citri. 20 %, 40 % and 60 % concentrations of these extracts were made for mycelial inhibition of pathogen all plant extracts @60% were effective for management of citrus brown spot pathogen. Nanoparticles were also used in study and different concentration of nano sized silver particles which were used includes 10, 20, 30,40,50, 60, 70,80, 90 and 100 ppm. Average decrease in colony growth was maximum at 100 ppm concentration over control at 100 ppm concentration maximum inhibition was up to 63.77 %. Nanoparticles are also used in place of synthetic chemicals for disease management and amount of inoculums in the field is reduced by using plant extracts and nanoparticles as an alternative to chemical control and moreover this is eco friendly method for management of fungal plant pathogens.