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ABSTRACT

During the 1997 and 1998 cropping seasons, studies on turcicum blight of maize
(Zea mays L.) induced by Helminthosporium turcicum Pass were carried out in
Zaria using selected early and extra-early maize lines. The pathogenicity test
carried out in the glass house confirmed Helminthosporium turcicum as the
causative agent of the disease.
Field and glasshouse screening of fifteen early and eleven extra-early maize
lines for their resistance to turcicum blight was conducted in 1997 and 1998.
Seven early lines (AK 9331-DMSR, SynE2, ACR 92TZE Comp. 5-W, Dorke-SR,
Farakoba 90 pool 16DT (HD), NAES pool 16DT, DT-E-Y SR) and five extra-early
lines, TZE-W-SRBC5, CSP-SRBC5, KEB, TZEF-Y-SR, 95.TZEE-W1 were
moderately resistant while CSP x local Raytiri, CSP-SR x TZEE-Y among the
extra-early lines and AB 11, Kamboinse 88 Pool 16DT RE among the early lines
were moderately susceptible.
Sowing date trials at 14-day intervals were conducted in 1997 and 1998 using
early line AB 11 and extra-early line CSP-SR x TZEE-Y. The sowing dates were
June 26, July 10, July 24 and August 7 in 1997; June 29, July 13, July 27 and
August 10 in 1998. In both lines, disease incidences were recorded at 30, 45
and 60 days after sowing (DAS) while severity were recorded at 50, 60 and 70
(DAS). The maximum disease severity (12.71 % and 26. 04%) was recorded on
early maize lines planted on July 24 and 27 (i.e. third sowing date) in 1997 and
1998 respectively. The highest grain yields in both years (1997 and 1998)
(2592.6kg/ha and 1592.6kg/ha) respectively were recorded on maize planted on
June 26 and 29 (i.e., first sowing date) that were least affected with turcicum
blight. For the extra – early lines, the maximum disease severity (9.68% and
38.34%) were recorded on maize planted in July 24 and 27 in 1997 and 1998
respectively. Least severity (7.61% and 17.08%) was recorded on maize planted
7
on June 26 and 29 in both years with subsequent significantly (p= 0.05) highest
yield (2555.6 kg/ha) in 1997.

 

 

TABLE OF CONTENTS

 

Chapter Title Page
8
1.0
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.2.1
Declaration
Certification
Dedication
Acknowledgement
Abstract
Table of contents
List of Tables
List of plates
List of Appendices
INTRODUCTION
LITERATURE REVIEW
History and Nomenclature of the Organism
Distributions and Host Range
Symptoms
Description of the Fungus
Disease Development
Factors Affecting Disease Development
Host Resistance/Biological Races of the Pathogen
Seasonal Persistence, Spread and Control
Economic Importance
IDENTIFICATION OF CAUSAL ORGANISM
Introduction
Materials and Methods
Observations on symptoms Development and collection of
Samples
i
ii
iii
iv
v
vi
ix
xii
xiii
1
4
4
5
6
7
9
9
11
13
15
16
16
16
16
9
3.2.2
3.2.3
3.2.4
3.3
3.3.1
3.3.2
4.0
4.1
4.2
4.2.1
4.2.2
4.2.2.1
4.2.2.2
4.2.2.3
4.3
4.3.1
4.3.2
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.5
4.5.1
4.5.2
Preparation of Media: Potato dextrose agar (PDA) Medium
Isolation Method
Purification and Examination of Culture
Results and Discussion
Symptomatology
Isolation and Morphological studies of the Pathogen
SCREENING OF EARLY AND EXTRA-EARLY MAIZE LINES
FOR RESISTANCE TO TURCICUM BLIGHT
Introduction
Materials and Methods
Field Screening
Turcicum blight assessment
Incidence
Severity
Yield assessment
Glass House Screening
Inoculation of the plants in the screen house with conidial
suspension
Turcicum blight assessment
Results and Discussion of Field Screening
Early Maize Lines 1997
Early Maize Lines 1998
Extra-early Maize Lines 1997
viii
Extra-early Maize Lines 1998
Glass House Screening
Extra-early Maize Lines
Early Maize Lines
16
17
18
19
19
23
27
27
27
27
28
28
29
30
30
31
32
32
32
36
40
42
46
46
46
10
5.0
5.1
5.2
5.2.1
5.2.2
5.3
5.3.1
5.3.2
5.3.3
5.3.4
6.0
7.0
SOWING DATE EXPERIMENT
Introduction
Materials and Methods
Turcicum blight Assessment
Yield Assessment
Results and Discussion
Extra-early Maize Line 1997
Extra-early Maize Line 1998
Early Maize Line 1997
Early maize Line 1998
SUMMARY AND CONCLUSION
REFERENCES
APPENDICES

 

CHAPTER ONE

1.0 INTRODUCTION
Maize, Zea mays L., is an annual plant of the family Gramineae like all the other
cereal crops. Cultivated maize is a fully domesticated plant (Dowswell et al.,
1996), and very high in grain yielding capacity probably exceeding all other
cereal crops.
Maize is susceptible to numerous diseases and pests all over the world.
Variation of these diseases and pests as noted by Effron (1985), is a major
cause of yield instability with yield losses reaching 100% under epidemic
conditions. Ullstrup (1977), had noted that parasitic diseases which may be
caused by bacteria, fungi, viruses and mycoplasma provide severe constraints
on tropical maize production frequently causing 30-40% yield loss.
According to Effron (1985), maize diseases are categorized as follows:
i. Local-spot foliar diseases;
ii. Systemic foliar disease; and
iii. Stalk and ear rots.
Local-spot foliar diseases: These affect primarily the leaves and sometimes
other green tissues. Notable examples are Puccinia rust (Puccinia spp),
Helminthosporium leaf blights (Helminthosporium spp), Curvularia leaf spot
(Curvularia pallenscens) and brown leaf spot (Physoderma maydis). The local
spot foliar diseases destroy the leaves and result in significant yield reduction
when susceptible plants are infected early in their growth stage. Amongst these,
Helminthosporium turcicum blight is most destructive as the disease can develop
into epiphytotic proportions under favourable environmental conditions such as
cool to moderate temperatures and adequate moisture (Purseglove, 1976; El-
Shafey, 1978).
4
Systemic foliar diseases: These include maize streak and maize mottle
viruses and downy mildew. The first two are caused by two different viruses
but are transmitted by the same insect vector, Cicadulina sp. Downy mildew
caused by fungus Peronosclerospora sp. is a threat to maize production in
some countries of tropical Africa including Nigeria, Ivory Coast and Sudan
(Effron, 1985).
Stalk and ear rots: Bacteria stalk rot incidence is low; attacks maize during
the active growth stage causing losses usually. Fungal stalk rots are incited
by Fusarium moniliforme, Diploidia maydis, Cephalosporium maydis,
Botriodiploidia and Rhizoctonia sp. The later two are most important in low
land rainforest and moist savanna. All the stalk rot pathogens cause kernel
rot, resulting in grain deterioration and loss of quality especially in soft
endosperm genotypes (Effron, 1985). Development of resistant varieties is
the best means of controlling stalk and ear rots.
West and Central Africa Maize Research Network (WECAMAN) have released
early and extra-early maize lines that could fit into the semi arid tropics. These
lines are generally susceptible to foliar diseases in the tropics (Misovic, 1985).
They are also very stable over years under low rainfall and dry land conditions
with insufficient precipitations.
The interest on the studies on turcicum blight of maize in Samaru – Zaria was
elicited due to:
a. Introduction of these early and extra early maize line vis-à-vis the short
period of rainfall experienced in the northern savanna regions;
b. The severity of turcicum blight consistently reported by Adeoti (1982,
1995, and 1996) with other previous report by Fajemisin and Osunlaja
(1977) and Cammack (1956);
5
c. High yield potential reported by Adeoti and Iwuafor (1997) in the
regional trial experiment with the early and extra early maize lines from
(WECAMAN) in Zaria and Minjibiri research stations.
The specific objectives of this study are as follows:
i. To confirm the identity of the causal organism;
ii. To screen early and extra-early maize lines in the glass
house and on the field for their reaction to turcicum blight.
This will help in identifying sources of resistance;
iii. To study the effect(s) of sowing date on the incidence and
severity of turcicum blight with a view to determining the most
appropriate time for sowing to avoid high incidence and
severity of the disease; and
iv. To identify those germplasm that are high yielding which may
be useful for breeding programme in future.

 

 

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