EVALUATION OF ANTIFUNGAL EFFICACY OF SOME LEAF EXTRACTS OF SOME PLANTS ON RED ROT PATHOGEN (Colletotrichum falcatum) OF SUGARCANE (Saccharum officinarum)

ABSTRACT

Botanical extracts have shown appreciable achievement in controlling plant diseases. This became evident in this study when the potency of leaf extracts from Azadirachta indica, Carica papaya, Lawsonia inermis, Khaya senegalensis and Ziziphus spina- christi were tested on the mycelia growth of Colletotrichum falcatum, the pathogen of red rot disease of sugarcane. The infected sugarcane used for isolation and identification were collected from National Cereal Research Institute (NCRI) Badeggi. And a total of sixty (60) healthy sugarcane setts planted were collected from  farmers in Wuya rake along Bida Mokwa road in Niger state. The plant leaf materials used in this study were collected from the mountain area at Egubagi village and were identifield at the herberium in the Department of Plant Biology, Federal University of Technology, Minna. After collection, leaves were sterilised using 0.5% sodium hypochlorite and the extraction was done using soxhlet extraction. Tested leaves were subjected to qualitative phytochemical screaming. The isolation and identification of the fungus was done by cutting the transition zone between the rotten tissue and healthy side into 5mm, sterilised and inoculated into potato dextrose agar (PDA) medium. In vitro antagonistic effects of the plant extracts were done using food poison techniques at 75 %, 50 %, and 25 % concentrations while the controls are 0.5g/l (clot) and 0% (sterile distilled water) concentrations with three replicates each. After the in vitro evaluation, the best three plant extracts that had the highest mycelia inhibition were taken to the field to evaluate their effect on the fungus as it affects the growth parameters (plant girth, plant height, number of nodes and internodes length) on the growing sugarcane plants in the screen house (in vivo). The phytochemical analysis of the extractants revealed the presence of alkaloids, flavonoids, phenols, tannins, saponins terpenoids, steroids anthraquinones and cardiacglycosides. The results of in vitro revealed that the percentage mycelia growth inhibition were 100.0±0.00 (Lawsonia inermis ), 53.00±1.15 (Azadirachta indica ), 78.00±0.00 (Carica papaya), 45.00±1.00 (Ziziphus spina- christi ) and 60.60±0.00 (Khaya senegalensis) while controls were 100.0±0.00 (0.5 g/L) and 0.00±0.00 (sterile distile water) positive and negative respectively. The results obtained from the field were promising at 75 % concentration of plant extracts used for the percentage disease reduction with   6.94 %, 15.28 % and 25.8 % Lawsonia inermis, Carica papaya and Khaya senegalensis were used  in that order, while controls had 5.90±0.00 0.5 g/L (clot) 0 % (sterile distile water). The percentage inhibition and reduction in all the treatments used were significantly different (P<0.05). The efficacy of the ethanolic leaf  extracts increase with the increase in concentrations, 75% concentrations of all the plant extracts showed the highest level of mycelial growth inhibition (in vitro) and percentage disease reduction (in vivo). Extracts from Ziziphus spina−christi (45.00±1.00 %) had the least effect on the percentage mycelia growth of C. falcatum (in vitro) while Khaya senegalensis had least (25.8−35.09 %) effect than other plants extracts used (in vivo) in suppressing the disease severity on sugarcane plants. The results were promising and the best plant extracts can go a long way in reducing the red rot disease of sugarcane on the field.

CHAPTER ONE

1.0        INTRODUCTION

1.1       Background to the Study

Sugarcane (Saccharum officinarum), is a perennial grass of the family Poaceae, primarly cultivated for its juice from which sugar can be processed.  It is an important cash crop cultivated in tropical and sub-tropical regions of the world (Dacosta et al., 2011).  Its edible stem is rich in sucrose and used for the production of sugar, ethanol, and important renewable biofuel source (Menossi et al., 2008 and Dacosta et al., 2011). Globally, sugarcane is an important source of commercial sugar accounting for almost two thirds of the world sugar production (Menossi et al., 2008). It is a tropical crop which attains maturity between 8 and 12 months.   Matured cane may be green, yellow, purplish or reddish in color and it consider ripe when sugar content is at is maximum (Imolehin and Wada, 2008).

World production of sugarcane stood at 1.5 billion tonnes as of 2008 (Imolehin and Wada, 2008) Brazil, China, Cuba, Mexico, Pakistan, Thailand, USA, Colombia, Australia and Indonesia are the leading countries in sugarcane production, producing over half of the total world sugarcane production. Africa in the same reporting period has 1.2 million hectares with 72.1 million metric tonnes, respectively (Onwueme and sinha, 1991). Nigeria is one of the most important producers of the crop with a land potential of over 500, 000 hectares of suitable cane field capable of producing over 3.0 million metric tonnes of sugarcane. If processed, it will yield about 3.0 million metric tons of sugar (National Sugar Development Council Policy, 2003).

Nigeria is highly blessed with human, water and environmental potentials for commercial sugarcane. And it was pointed out that most of the areas in the Northern states where water for irrigation is available, sugarcane cultivation in large quantities are feasible. Sugarcane production is widely affected by biotic (microbes) and abiotic factors (climate and drougth), of which the loss to fungal pathogens (Colletotrichum falcatum) causing red rot disease is most critical (Wada et al., 2016). Red rot pathogen (C. falcatum) of sugarcane is a dreadful fungi disease which infects the sugarcane stalk at both the initial and mature stages of growth,  cause discoloration, reduction in cane weight, loos of sugar, sucrose content and juice (Sharma and Tanta, 2015).

Annual loss of revenues to C. falcatum infection is estimated to be between 500 -100 million USD (Viswanathan and Samiyappan, 2002). Chemical fungicides are used to curtail direct  destruction caused by fungi on plants, but the use of these chemical fungicides is toxic to human and cause environmental pollution (Abu-Taleb et al., 2011). Thus, alternative control such as use of botanicals are desired that are eco− friendly and cheap (Gurjar et al., 2012). Botanical extracts are gaining popularity as some plant product are being used globally as green pesticides, in the context of agricultural pest an disease management, botanical pesticides are best suited for use in organic food production in industrilized countries but can play a much greater role in the production and post-harvest production of food products in developing countries (Malkhan et al., 2012). Therefore, the efficacy of Azadirachta indica, Khaya senegalensis, Carica papaya, Lawsonia innermis and Ziziphus spina−christi were determined to ascertain their effeactivenes in the control of red rot fungi (C. falcatum) disease of  sugarcane.

1.2    Statement of the Research Problems

Red rot disease of sugarcane caused by Colletotrichum falcatum is one of the oldest,  broadly distributed, and documented diseases of sugarcane in many countries and a threat to the production and cultivation of sugarcane (Viswanathan and Samiyappan, 2002; Viswanathan, 2012). The pathogen attacks the cane plant from seedling stage till maturity stage causing retard growth and most times extermination of seedling (Viswanathan, 2012). It therefore, observed to be a part of obstacles hindering sugarcane growing in Nigeria according to the recent survey of some states in the country, the disease was observed in states like Niger, Katsina, Benue, Plateau, Adamawa and FCT, Abuja (Wada et al.,1998). The sugar industry in India suffer losses of more than 500 million dollars (US) every year due to red rot disease and this loss is due to the reduction in the sucrose contents and weight of the cane due to red rot disease (Viswanathan and Samiyappan, 2002). It is not only of a huge concern for the global export sector, but also has a great impact on the domestic production, as many locally preferred cultivars are also endangered (Sharma and Tanta, 2015).

Various methods are adopted for red rot disease management, including application of chemical fungicides, breeding and tissues culture methods. All of these have limitations and disadvantages. For instance, chemical methods increase cost of production and contaminate the environment. Whiles tissue culture , the selection  of fungus -resistance cells (Mohanraj et al., 2003; Sengar et al., 2009) is most often associated with somaclonal variations.also breeding methods are laborious and time consuming (Agnihotri, 1996).

1.3     Justification for the Study

Biofungicide botanicals are gaining more significant as they have been used as alternative control in the management of fungal pathogens. The active ingredients in plants may either act on the pathogen directly or induce systemic resistance in the plant, resulting in reduction of disease development (Yulier et al., 2015). They are considered not only as an alternative to chemicals but also less expensive, easily available and also for the eco-friendly  mangement of various plant diseases including red rot (Imtiaj et al., 2007 and Hafiz et al., 2016 ). Plant extracts have opened a new avenue for the control of plant diseases and much attention has been given to the use of secondary metabolites rich plant substances such as; phenols, alkaloids, terpenoids amongst others. These serve as chemical defence against plant disease (Tripathi and Singh, 2015). Plant extracts have also been investigated throughout the world for their antifungal activity against a wide range of fungi (Gupta et al., 2008). Hence, the fungicidal and fungistatic potentials of Lawsonia inermis, Ziziphus spina-christi, Carica papaya, Khaya senegalensis and Azadirachta indica plant extracts on different plant pathogenicfungi previously reported by Hafiz et al. ( 2016 ) motivated this research.

1.4 Aim and Objectives of the Study

The aim of the study was to evaluate the antifungal potential of five plant extracts (Ziziphus spina- christi, Azadirachta indica, Carica papaya, Khaya senegalesis and and Lawsonia inermis) on the red rot pathogen (C. falcatum) of sugarcane.

The objectives of the study are to:

i.         determine the phytochemical constituents of Ziziphus spina-christi, Azadirachta indica, Carica papaya, Khaya senegalensis and Lawsonia inermis extracts.

ii.        characterize the causative organisms of red rot disease of sugarcane.

iii.        determine in vitro antifungal efficacy of the plant extracts of Ziziphus spina-christi, Azadirachta indica, Carica papaya, Khaya senegalensis and Lawsonia inermis on mycelia growth of C.  falcatum.

iv.        determine the efficacy of the selected plant extracts in the control of red rot disease of sugarcane under screen house conditions.

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