ABSTRACT
The fungi isolated from infected castor leaves were Fusarium sp, Helminthosporium sp
and Curvularia sp. Pathogenicity tests was conducted on the fungi and Fusarium sp was
pathogenic on castor and its pathogenicity was confirmed using Koch’s postulate. The
Fusarium sp was later identified to be Fusarium pallidoroseum by International
Mycological Institute (IMI) Egham, London. Plants at different ages (11, 18 and 25 days
old) were inoculated using three methods (spray, smear and soil inoculation). Twenty one
day old castor plants were inoculated with inoculum at different densities (103, 105, 107,
1010 conidia / ml and water) and assessed in order to determine at what density the
pathogen can induce infection. Six fungicides were evaluated in vitro at three
concentrations (one and half the recommended, recommended and half recommended
rates) for their effect on growth and regrowth of mycelia, sporulation and conidia size of
Fusarium pallidoroseum. Five of the fungicides tested in the laboratory were further
evaluated at two concentrations (recommended and half recommended rates) for their
efficacy in the management of leaf blight induced by Fusarium pallidoroseum in vivo.
Effect of three sowing dates on disease incidence and severity was assessed on two castor
types during the 2006 wet season. During the pathogenicity tests it was observed that,
younger plants were more susceptible to infection than older plants. For the in vitro
evaluation of fungicides, it was observed that all the fungicides (benomyl, benomyl +
thiram, mancozeb, metalaxyl-M + thiomethoxam + difenoconazole, tricyclazole and
carbendazim + mancozeb) at all the concentrations tested inhibited mycelial growth,
sporulation, and reduced conidia size and mycelial regrowth of the fungus. Benomyl,
benomyl + thiram and tricyclazole completely inhibited mycelial growth and sporulation
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of the fungus at the three tested rates. Metalaxyl-M + thiomethoxam + difenoconazole,
carbendazim + mancozeb inhibited mycelial growth and sporulation only at one and half
rate but not at recommended and half recommended rates. Inhibitory effect of all the
fungicides on mycelial growth and sporulation were greatest at one and half
recommended rate. Benomyl, benomyl + thiram, mancozeb, carbendazim + mancozeb
and tricyclazole reduced the rate of disease development on 21 – day- old inoculated
castor plants in the screenhouse at recommended than at half the recommended rate.
Large seeded castor sown on July 27 had less disease severity and higher yield compared
with plants sown in August 3 and August 11. For the small seeded type, August 3 sown
plants had high disease severity and more yield than those sown on other dates. F.
pallidoroseum is the cause of leaf blight, seedling rot and wilt of castor in Samaru. The
younger plants (11 days old) were more susceptible to infection. The evaluated
fungicides can be used to control F. pallidoroseum on castor. Sowing late, resulted in
poor seed germination thereby affecting bean yield negatively.
TABLE OF CONTENTS
Title page………………………………………………………………………………………………….. i
Declaration………………………………………………………………………………………………. ii
Certification …………………………………………………………………………………………..iii
Dedication………………………………………………………………………………………………. iv
Acknowledgement …………………………………………………………………………………… v
Abstract …………………………………………………………………………………………………..vi
Table of Contents……………………………………………………………………………………viii
List of Tables…………………………………………………………………………………………… xi
List of Figures …………………………………………………………………………………………xii
List of Plates…………………………………………………………………………………………..xiii
List of Appendices………………………………………………………………………………….xiv
CHAPTER ONE
1.0 Introduction………………………………………………………………………………….. 1
1.1 Justification of study …………………………………………………………………….. 2
1.2 Objectives of study………………………………………………………………………… 2
CHAPTER TWO
2.0 Literature Review……………………………………………………………………………. 3
2.1 Origin and Distribution of Castor …………………………………………………….. 3
2.2 Ecology of Castor…………………………………………………………………………….. 3
2.3 Botany of Castor………………………………………………………………………………. 4
2.4 Production and Yield of Castor ………………………………………………………… 4
2.5 Economic Importance of Castor ………………………………………………………. 5
2.6 Insect Pests and Diseases of Castor………………………………………………….. 5
2.7 Taxonomy and Characteristics of Fusarium sp………………………………….. 7
2.7.1 Nomenclature and taxonomy of Fusarium sp……………………………………. 7
2.7.2 Morphological and cultural characteristics of Fusarium sp ……………….. 8
2.8 Disease Inducement as Influenced by Inoculum Concentration ………. 8
2.9 Chemical Control of Some Diseases Induced by Fungi……………………… 9
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CHAPTER THREE
3.0 Materials and Methods…………………………………………………………………. 12
3.1 Isolation and Identification of Pathogen…………………………………………….. 12
3.1.1 Pathogenicity test in the screen house ………………………………………….. 12
3.1.1.1 Raising of seedlings ……………………………………………………………………. 12
3.1.1.2 Inoculum preparation and inoculation of plants………………………………….. 13
3.2 Determination of Inoculum Density Capable of Disease
Inducement …………………………………………………………………………………… 14
3.3 Evaluation of Fungicides for the Control of Pathogen …………………… 15
3.3.1 In vitro evaluation of fungicides …………………………………………………… 15
3.3.2 Evaluation of fungicides in vivo…………………………………………………….. 17
3.4 Leaf blight Incidence and Severity on Castor Sown at Different
Dates …………………………………………………………………………………………….. .17
3.5 Statistical Analysis…………………………………………………………………………. 19
CHAPTER FOUR
4.0 Results…………………………………………………………………………………………… 20
4.1. Isolation, Identification and Symptoms of the Pathogen …………………. 20
4.1.1 Symptoms ……………………………………………………………………………………. 20
4.1.2. Morphological and cultural characteristics of F. pallidoroseum on
PDA ……………………………………………………………………………………………. 20
4. 1.3 Incidence and severity of leaf blight induced by F.
pallidoroseum on castor of different ages inoculated using
different methods ………………………………………………………………………… 25
4.2 Effect of Inoculum Density on Disease Incidence and Severity……….. 30
4.3 Evaluation of Fungicides………………………………………………………………. 32
4.3.1 Effects of fungicides on the mycelial growth, sporulation,
spore size and mycelial regrowth of F. pallidoroseum in vitro…………… 32
4.3.2 Efficacy of varying fungicide concentrations on F.
pallidoroseum in vivo ……………………………………………………………………… 51
4.4 Effect of Sowing Dates on Incidence and Severity of Leaf
Blight…………………………………………………………………………………………… 55
4.4.1 Effect of sowing dates and disease severity on yield of two
castor types in 2006 ……………………………………………………………………… 58
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CHAPTER ONE
1. INTRODUCTION
Castor, Ricinus communis L., a monotypic genus belongs to the family Euphorbiaceae.
The plant varies greatly in growth habit, colour of foliage, stem, seed size and colour, oil
content and many other characteristics. It is widely cultivated in the tropics, sub tropics
and warm regions for its seed from which castor oil is extracted (Purseglove, 1968;
Weiss, 1971). Castor can thrive well in dry arid climate as well as areas of heavy rains
and floods (Weiss, 1971). It requires low temperature (15 – 18 oC) for emergence. A
moderate temperature of 20 – 26 oC is favourable for flowering. In its natural growing
area, the plant is perennial forming a tree stature but commercially treated as annual or
biennial and exhibits a bushy appearance (Atsmon, 1989; Moshkin, 1986; Weiss, 1971).
Seed colours ranges from light to dark brown, with various mottling patterns. High
rainfall and humidity favours leaf diseases (Hiruy and Alemaw, 1989). The important
part of the crop is the seed which contains 50-55 % oil (Duke, 1983; Adefris and
Nigussie, 1993; Gobin et al., 2001).
Traditionally, castor oil is used in lamps lightening and in medicine. The oil is used in
industries as cosmetic base, pharmaceuticals, high grade lubricant and protecting coatings
in paints (Purseglove, 1968; Gobin et al., 2001; Duke, 1983).
Castor is attacked by many pests including insects, nematodes, fungi, bacteria and viruses
(Duke, 1983). The major insect pests are the semi lopper (Achoea janata), capsule borer
(Dichrocrocis punctiferalis) (Patel et al., 1991; Nanda and Prasad, 1974). The most
important bacterial disease is leaf spot caused by Xanthomonas ricini (Anon. 1971).
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Fungal diseases include wilt caused by Fusarium oxysporum f. sp ricini, root rot
(Macrophomina phaseolina), gray rot (Botrytis ricini) which caused yield loss of 80 –
100 % in India (Anjani et al., 2004), seedling blight caused by Phytophthora palmivora
in Hawaii (Uchida and Aragaki; 1988), leaf spot induced by Cercospora ricinella and
Alternaria leaf spot caused by Alternaria ricini (Duke, 1983; Anon. 1971).
1.1 Justification of Study
Castor oil which is very important in industries as cosmetic base, high grade lubricant
and as water resistant and protective coating in paints have suffered some set backs due
to diseases. In India, yield loss of 80 – 100 % has been attributed to fungal diseases
(Anjani et al., 2004) and these have caused economic loss to farmers in terms of foreign
exchange. In Nigeria, with the recent demand for castor oil in industries and the Federal
Government in its effort to diversify the economy is encouraging its production for local
industries and as a source of foreign exchange.
In view of the emerging importance of the crop and with little or no information on the
various diseases affecting its growth and reproduction in Nigeria there is need to identify
fungi associated with castor and the management of diseases induced by them.
1.2 Objectives of Study
The objectives of this study are to:
Isolate and identify fungi associated with castor and ascertain their pathogenicity.
Determine minimum infectious inoculum density of fungi on castor.
Evaluate in vitro and in vivo effects of some fungicides on the pathogen.
Determine the effect of sowing dates on disease incidence and severity.
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