(Phaseolus vulgaris) angular leaf spot

224 Pages·2016·3.97 MB·English

Management of common bean (Phaseolus vulgaris) angular
leaf spot (Pseudocercospora griseola) using cultural practices
and development of disease-weather models for prediction of
the disease and host characteristics

by

David Icishahayo

A thesis submitted in partial fulfillment
of the requirements of the degree of
Doctor of Philosophy

Department of Crop Science
Faculty of Agriculture
University of Zimbabwe

September 2014
ABSTRACT

Bean seed collected from 82 households growing beans in Chinyika Resettlement Area
indicated that sugar (sweet) bean type was the most preferred and cultivated by 84.1 % of
farmers. The most common seed source was home-saved seed as indicated by 73.2 % of
the farmers. Common seedborne fungi isolated from the different seed lots using the
blotter method included; Fusarium oxysporum (73.2 %), Alternaria alternata (70.7 %)
and Colletotrichum lindemuthianum (51.2 %). The major sources of inoculum identified
for Pseudocercospora griseola were; infected seed, concomitant infected plants in the
field, the soil at the end of the growing period, the air, rainfall and irrigation water. The
north and south facing slides on the local trap were the most efficient in conidia trapping
and the north conformed to the main wind direction which was north-north-east.

A field study conducted on the control of common bean angular leaf spot
(Pseudocercospora griseola) during two years (2002/3 and 2003/4) indicated that, as a
consequence of unfavourable weather conditions for disease development, winter and
early planting in summer associated with any irrigation method can be adopted. To target
high yield, early planting can be complemented with any irrigation method, whereas the
winter crop worked best with sprinkler irrigation. However, the high amounts of water
received and high humidity conditions that prevail during maturity when beans are
planted early might interfere negatively with harvesting operations and seed quality. This
situation will require harvesting at physiological maturity, and putting in place facilities
for drying plants/pods and seed after processing.

The variables estimated at the start of the disease and leaf disease variables from 4 to 8
weeks after planting (WAP) [incidence, severity and defoliation], pod disease variables
[incidence and severity], and weather variables from 4 to 10 WAP [duration of humidity
and temperature, and daily mean humidity) were positively correlated with the main
disease variables and negatively correlated with yield. Days to first disease infection and
daily mean temperature were correlated negatively with the main disease variables and
positively with yield. Duration of water and daily mean water were the most variable
across evaluation periods, and correlations were specific to evaluation periods.

For each one of the dependent variables, one most appropriate equation was developed
and the number of predictors was reduced to 7 - 10. The most important predictors
included in the equations developed; disease incidence and severity, mean daily humidity
and water, duration of humidity and water, were associated with specific evaluation
periods. Consequently, decisions can be made early enough to permit disease control
measures and warn farmers. As soon as the conditions of water received and humidity
favourable to the disease are recorded, farmers should be warned and control measures
should be applied when necessary. The critical periods for disease infection were 4, 6 and
10 WAP.

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ACKNOWLEDGMENTS

I am grateful to my supervisor, Dr S. Dimbi for her advice and guidance. Her patience
and understanding were a source of strength during difficult moments. I would like to
thank Dr J. Sibiya, my former supervisor from the start of the research work, who offered
a tremendous support, and constantly shared her knowledge. I also gratefully
acknowledge invaluable guidance and advice from Mr B. Chipindu in agrometeorological
data management, analysis and modeling. Dr S. Kageler, enthusiastically and freely gave
me specialist biometrics advice especially in modeling. I would like to thank Prof. B.V.
Maasdorp for having finalized the final proposal.

Doctor E. Ngadze and Mrs E. Masenda should be commended for their guidance in
research methodology and assistance in the laboratory work. Many useful comments
were received from Drs W. Manyangarirwa, I. Makanda, A. B. Mashingaidze, R. and C.
Madakadze. I am grateful to Dr A. Murwira for his help in the estimation of the distances
between stations, Dr S. Dzikiti in weather data calculations, Dr E. Mashonjowa for his
advice in the management of wind direction data, and Dr A. Senzanje for his contribution
in sprinkler and furrow irrigation weather data adjustment.

I am grateful to Dr C. Mguni who allowed me to use Mazowe Quarantine laboratory
facilities and to the personnel of the institution especially Mrs M. Mabika, D. Mukwena
and A. Semani. I thank also A. Matikiti, G. Ashley, M. Cavill and A. Mare for their
assistance in laboratory work. I am also grateful to Agricultural and Rural Development
Authority Muzarabani (ARDA Mz) staff, to P. Kambidzi, L.Tumbare and R. Tumbare for
their contribution in field experimentation. Givemore Parirenyatwa was the key person in
the Chinyika seed collection. I would like to thank Agricultural Technical and Extension
Services (AGRITEX) personnel, S. Marimo, N. Gachange and all the people who assisted
in seed collection. I would like to thank Dr S. Dimbi and Mrs T. Sigobodhla for having
provided the Burkard trap used in this research. I thank A. Chirwa, M. Mlambo and R.
Cikotosa of the Engineering Department for their contribution in making the local trap,
installing and maintaining the traps used in the study.

I am grateful to Belvedere weather station staff especially Mr T. Gwaze, and to Mr T.
Soko of Seed-Co Rattray Arnold Research Station for sourcing meteorological data used
in this study.

Financial assistance from The Rockefeller Foundation, the Southern Africa Bean
Research Network and the Crop Breeding Institute is gratefully acknowledged.

I thank Fr F. Chanterie, Mr M. Triest, Miss T. Masekesa and Mrs S. Svova for their
contribution in this study.

There are many others who directly and indirectly contributed to the success of this
study, and to you all, I say: thank you. Lastly I thank the Virgin Mary and Christ.

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TABLE OF CONTENTS

ABSTRACT ..................................................................................................................................... i
ACKNOWLEDGMENTS .............................................................................................................. ii
TABLE OF CONTENTS ............................................................................................................... iii
LIST OF TABLES ....................................................................................................................... viii
LIST OF FIGURES .........................................................................................................................x
LIST OF APPENDICES .............................................................................................................. xiii
LIST OF ABBREVIATIONS ...................................................................................................... xiv
CHAPTER 1: INTRODUCTION AND JUSTIFICATION ............................................................1
1.1 General introduction ................................................................................................1
1.2 Objectives of the study.............................................................................................6
1.3 Study hypotheses .....................................................................................................7
CHAPTER 2: GENERAL LITERATURE REVIEW ....................................................................9
2.1 Introduction….. ........................................................................................................9
2.2 Angular leaf spot ......................................................................................................9
2.2.1 Sources of inoculum, survival and symptom development .......................10
2.2.2 Control of angular leaf spot disease in beans.............................................11
2.3 Effect of weather factors on plant disease development ........................................15
2.3.1 Temperature ...............................................................................................15
2.3.2 Moisture .....................................................................................................16
2.3.3 Combination of weather variables .............................................................17
2.4 Conditions suitable for disease-free bean production ............................................17
2.5 Irrigation……. .......................................................................................................19
2.5.1 Sprinkler irrigation .....................................................................................20
2.5.2 Effect of irrigation systems on diseases infection and yield ......................20
2.6 Date of planting......................................................................................................22
2.7 Overview of modeling possibilities .......................................................................23
2.7.1 Simulation models .....................................................................................24
2.7.2 Statistical models .......................................................................................24
2.7.3 Modeling for yield .....................................................................................26
2.7.4 Decisions in disease management ..............................................................27
2.7.5 Forecasting .................................................................................................28
2.8 Implication of literature review key issues in the conception of the
study………… .......................................................................................................29
CHAPTER 3: ASSESSMENT OF QUALITY OF FIELD BEAN SEEDS HOME-
SAVED BY SMALLHOLDER FARMERS .....................................................................31
3.1 Introduction…. .......................................................................................................31
3.2 Materials and methods ...........................................................................................34
3.2.1 Study area...................................................................................................34
3.2.2 Seed collection ...........................................................................................35
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3.2.3 Identification of fungal pathogens .............................................................37
3.2.4 Data analysis ..............................................................................................38
3.3 Results………. .......................................................................................................38
3.3.1 Seed types, sources and quality ....................................................................38
3.3.2 Seed health .................................................................................................39
3.4 Discussion…… ......................................................................................................39
3.5 Conclusion….. .......................................................................................................43
CHAPTER 4: STUDIES ON SOURCES OF INOCULUM OF
PSEUDOCERCOSPORA GRISEOLA ...............................................................................44
4.1 Introduction…. .......................................................................................................44
4.2 Materials and methods ...........................................................................................46
4.2.1 Field evaluation ..........................................................................................46
4.2.2 Environmental data ....................................................................................47
4.2.3 Seed health evaluation ...............................................................................48
4.2.4 Detection of soilborne inoculum ................................................................48
4.2.5 Detection of airborne inoculum .................................................................49
4.2.6 Detection of rainfall and irrigation waterborne inoculum .........................51
4.3 Data analysis… ......................................................................................................52
4.3.1 Environmental data ....................................................................................52
4.3.2 Field evaluation ..........................................................................................52
4.3.3 Seed health .................................................................................................53
4.3.4 Data management, summaries and analysis ...............................................53
4.4 Results………. .......................................................................................................53
4.4.1 Weather data ..............................................................................................53
4.4.2 Field evaluation ..........................................................................................54
4.4.3 Seed health .................................................................................................56
4.4.4 Soilborne inoculum ....................................................................................57
4.4.5 Airborne inoculum .....................................................................................57
4.4.6 Waterborne inoculum.................................................................................57
4.5 Discussion…… ......................................................................................................57
4.6 Conclusion….. .......................................................................................................62
CHAPTER 5: THE EFFECTS OF TYPE OF IRRIGATION AND PLANTING
DATE ON ANGULAR LEAF SPOT DISEASE, SEED YIELD AND
SEED INFECTION ...........................................................................................................63
5.1 Introduction…. .......................................................................................................63
5.2 Materials and methods ...........................................................................................68
5.2.1 Background to sites selected ......................................................................68
5.2.1.1 University of Zimbabwe Farm .......................................................68
5.2.1.2 Agricultural and Rural Development Authority
Muzarabani ....................................................................................68
5.2.1.3 Comparison of weather conditions between sites ..........................69
5.2.2 Land preparation and crop husbandry........................................................69
5.2.3 Treatments and experimental design .........................................................70
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5.2.4 Characteristics of the furrrow ....................................................................70
5.2.5 Data collection ...........................................................................................72
5.2.5.1 Weather data ..................................................................................72
5.2.5.2 Disease incidence ...........................................................................72
5.2.5.3 Disease severity .............................................................................72
5.2.5.4 Defoliation .....................................................................................73
5.2.5.5 Seed yield .......................................................................................73
5.2.5.6 Testing for Pseudocercospora griseola .........................................73
5.2.6 Data management.......................................................................................74
5.2.6.1 Irrigation ........................................................................................74
5.2.6.2 Weather missing data .....................................................................75
5.2.6.3 Changes in rainfall, temperature and relative
humidity associated with evaporation ............................................76
5.2.6.4 Adjustment of weather data with irrigation methods .....................76
5.2.6.5 Selection of weather variables .......................................................77
5.2.6.6 Calculation of the integral variables ..............................................77
5.3 Data analysis… ......................................................................................................78
5.3.1 Weather data ..............................................................................................78
5.3.2 Angular leaf spot variables, seed yield and seed infection ........................79
5.4 Results………. .......................................................................................................80
5.4.1 Weather ......................................................................................................80
5.4.2 Disease incidence at UZ Farm ...................................................................82
5.4.2.1 Number of days to the start of the disease .....................................82
5.4.2.2 Leaf disease incidence at the start of the disease ...........................82
5.4.2.3 Relationship between number of days and leaf
disease incidence at the start of the disease ...................................84
5.4.2.4 Leaf disease incidence during the growing period ........................84
5.4.2.5 Area under disease progress curve leaf incidence .........................87
5.4.2.6 Progression of disease incidence ...................................................87
5.4.2.7 Pod disease incidence ....................................................................89
5.4.3 Disease incidence at ARDA Muzarabani ..................................................89
5.4.4 Disease severity at UZ Farm ......................................................................91
5.4.4.1 Leaf disease severity at the initial development of
the disease ......................................................................................91
5.4.4.2 Relationship between number of days and leaf
disease severity at the start of the disease ......................................91
5.4.4.3 Leaf disease severity during the growing period ...........................91
5.4.4.4 Area under leaf disease severity progress curve ............................94
5.4.4.5 Progression of disease severity ......................................................94
5.4.4.6 Pod disease severity .......................................................................97
5.4.5 Disease severity at ARDA Muzarabani .....................................................97
5.4.6 Defoliation at UZ Farm ..............................................................................97
5.4.6.1 Defoliation at the start of the disease .............................................97
5.4.6.2 Relationship between number of days and disease
defoliation at the start of the disease ............................................102
5.4.6.3 Defoliation during the growing period ........................................102
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5.4.6.4 Area under disease progress curve defoliation ............................103
5.4.6.5 Progression of leaf defoliation due to disease..............................103
5.4.7 Defoliation at ARDA Muzarabani ...........................................................104
5.4.8 Seed yield at UZ Farm .............................................................................104
5.4.9 Seed yield at ARDA Muzarabani ............................................................106
5.4.10 Seed health at UZ Farm ...........................................................................106
5.4.10.1 Seed planted ...............................................................................106
5.4.10.2 Seed harvested ...........................................................................106
5.4.11 Seed health at ARDA Muzarabani ............................................................109
5.5 Discussion…… ....................................................................................................109
5.6 Conclusion…. .....................................................................................................116
CHAPTER 6: CORRELATION STUDIES BETWEEN DISEASE, HOST AND
WEATHER VARIABLES...............................................................................................118
6.1 Introduction…. .....................................................................................................118
6.2 Materials and methods .........................................................................................119
6.2.1 Data analysis ............................................................................................120
6.3 Results………. .....................................................................................................120
6.3.1 Relation between main characteristics .....................................................120
6.3.2 Relation between disease characteristics with the main
variables ...................................................................................................120
6.3.3 Relation between characteristics recorded at the start of
disease infection, pod incidence and severity with the main
variables ...................................................................................................121
6.3.4 Relation between weather and the main variables ...................................122
6.4 Discussion…… ....................................................................................................124
6.5 Conclusion….. .....................................................................................................127
CHAPTER 7: PREDICTION OF ANGULAR LEAF SPOT EFFECT IN
COMMON BEAN USING WEATHER AND DISEASE PREDICTORS .....................128
7.1 Introduction…. .....................................................................................................128
7.2 Materials and methods .........................................................................................131
7.2.1 Conceptual method ..................................................................................131
7.2.2 Calibration................................................................................................131
7.2.3 Models development and selection ..........................................................132
7.2.4 Models validation.....................................................................................133
7.3 Results………. .....................................................................................................134
7.3.1 Disease and weather predictors associated with final leaf
disease characteristics at 10 WAP ...........................................................134
7.3.2 Disease and weather predictors associated with area under
disease progress curves ............................................................................135
7.3.3 Disease and weather predictors associated with seed yield
and seed infection ....................................................................................136
7.3.4 Validation of the models ..........................................................................136
7.3.4.1 Comparison of different models obtained by data
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splitting and removal....................................................................136
7.3.4.2 Regression between responses and fitted values .........................138
7.3.4.3 “Leave out more than one observation” approach .......................139
7.3.5 Assumptions and considerations ..............................................................139
7.4 Discussion…… ....................................................................................................145
7.5 Conclusion….. .....................................................................................................147
CHAPTER 8: GENERAL DISCUSSION AND RECOMMENDATIONS ................................150
8.1 An assessment of quality and health of field bean seeds home-
saved by smallholder farmers ..............................................................................150
8.2 Studies on sources of inoculum of Pseudocercospora griseola ..........................151
8.3 Effect of cultural practices on common bean angular leaf spot
disease characteristics ..........................................................................................152
8.3.1 Weather variables.....................................................................................152
8.3.2 Leaf characteristics ..................................................................................153
8.3.3 Seed yield .................................................................................................154
8.3.4 Seed health ...............................................................................................155
8.4 Correlation….. .....................................................................................................156
8.5 Prediction of angular leaf spot effect in common bean using
weather and disease predictors .............................................................................156
8.6 Recommendations ................................................................................................158
REFERENCES ............................................................................................................................162
APPENDICES .............................................................................................................................189

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LIST OF TABLES

Table 3.1: Characteristics of sweet bean types collected from Chinyika Resettlement
Area in November 2002/3 season (n = 82). .............................................. 41
Table 3. 2: Levels of seedborne fungal pathogens in sweet bean seed samples
collected from 82 farmers in Chinyika Resettlelement Area in November
2002/3 season. ........................................................................................... 41
Table 4.1: Prevailing wind direction recorded during dry and wet days, and water
characteristics recorded during rainy and irrigated days during the growing
period in 2009/10 and 2010/11 respectively at the Crop Science
Department site. ........................................................................................ 54
Table 4.2: Prevailing wind direction and means of other weather characteristics
recorded at the Crop Science Department site during two years. ............. 54
Table 4.3: Seed infection of planted and harvested seed during summer season
obtained from two years data sets. ............................................................ 56
Table 5.1: Effect of planting date on the percentage of common bean plants with
leaves infected with ALS (transformed by sqrt) at 6 weeks after planting in
2002/3 and 2003/4 seasons. ...................................................................... 85
Table 5.2: Effect of irrigation and planting date on the percentage of common bean
plants with leaves infected with ALS (transformed by sqrt) at 8 weeks in
2003/4 and 10 weeks after planting in 2002/3 and 2003/4. ...................... 85
Table 5.3: Effect of planting date on the AUDPC-N (transformed by sqrt) calculated
from the percentage of common bean plants attacked by ALS from 4 to 10
WAP in 2002/3 and 2003/4....................................................................... 87
Table 5.4: Effect of irrigation and planting date on the percentage of leaf area
(transformed by sqrt) attacked by ALS at the start of disease infection at
UZ Farm in 2002/3 and 2003/4. ................................................................ 92
Table 5.5: Effect of planting date on the percentage of common bean leaf area
(transformed by sqrt) affected by ALS obtained at UZ Farm in 2002/3. . 93
Table 5.6: Effect of irrigation and planting date on the percentage of common bean
leaf area (transformed by sqrt) attacked by ALS observed at UZ Farm, 4
WAP with LPD and 8 WAP in 2003/4 with all planting dates. ................ 93
Table 5.7: Effect of irrigation and planting date of common bean on the AUDPC-V
(transformed by sqrt) calculated from the percentage of leaf area attacked
by ALS observed at UZ Farm in 2002/3 and 2003/4 from 4 to 10 weeks
after planting. ............................................................................................ 96
Table 5.8: Effect of irrigation and planting date of common bean on the relative rate
of defoliation (transformed by sqrt) obtained at UZ Farm at 10 WAP in
years 2002/3 and 2003/4. ........................................................................ 101
Table 5.9: Effect of irrigation and planting date of common bean on the AUDPC-L
obtained at UZ Farm in 2002/3 and 2003/4. ........................................... 106
Table 5.10: Effect of planting date and irrigation system on common bean seed yield
(kg/ha) obtained at UZ Farm in 2002/3 and 2003/4. .............................. 108
Table 5.11: Effect of year and irrigation system on common bean seed yield (kg/ha)
obtained at ARDA Muzarabani in 2002/3 and 2003/4. .......................... 108
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Table 6.1: Correlation between main variables of common bean ALS obtained at UZ
Farm and ARDA Mz in 2002/3 and 2003/4............................................ 121
Table 6.2: Correlation between main variables and disease characteristics of common
bean ALS recorded at UZ Farm and ARDA Mz from 4 to 8 WAP........ 121
Table 6.3: Correlation between common bean ALS characteristics recorded at UZ
Farm and ARDA Muzarabani from 2002/3 to 2003/4 at the start of the
disease and pod filling with the main variables. ..................................... 122
Table 6.4: Correlation between common bean ALS leaf incidence, severity and
defoliation recorded at 10 WAP; area under disease progress curve for
incidence, severity and defoliation with weather variables recorded from 4
to 10 WAP at UZ Farm and ARDA Mz in 2002/3 and 2003/4. ............. 123
Table 6.5: Correlation between seed infection and yield of common bean, and
weather variables recorded from 4 WAP to maturity at UZ Farm and
ARDA Mz in 2002/3 and 2003/4. ........................................................... 124
Table 7.1: Relationship between dependent and independent variables from the
common bean trial conducted at UZ Farm and ARDA Muzarabani in
2002/3 and 2003/4 with the percentage calculated from the number of
dependent variables in which the independent variable is significant. ... 137
Table 7.2: Coefficients of determination (R2s) (significant at P < 0.001) and standard
deviations of the residuals (Ss) (between brackets) of the models
developed with combined data for both years, individual data for each year
with data splitting and removal. .............................................................. 138
Table 7.3: Comparison made in each year (2002/3 and 2003/4) of responses and
estimated values of final disease incidence [sr(li )], severity [sr(ls )] and
10 10
defoliation [sr(rrdef )] by multiple regression equations by paired t-test
10
after removal of one observation in each planting date repeated three
times. ....................................................................................................... 144
Table 7.4: Comparison made in each year (2002/3 and 2003/4) of responses and
estimated values of final area under disease progress curve incidence
[sr(dcn)], severity [sr(dcv)] and defoliation (dcl) by multiple regression
equations by paired t-test after removal of one observation in each
planting date repeated three times. .......................................................... 144
Table 7.5: Comparison made in each year (2002/3 and 2003/4) of responses and
estimated values of final seed yield (yd) and seed infection [sr(iv)] by
multiple regression equations by paired t-test after removal of one
observation in each planting date repeated three times. ......................... 144

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