paparu, p., nkalubo, s., acur, a., kato, f.,...
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Pathogenecity of Sclerotium rolfsii sacc. and Identification of Resistance
Sources in Common Beans
Paparu, P., Nkalubo, S., Acur, A., Kato, F., Acam, C., Musoke, S., Nakibuule, J. and Mukankusi, C.
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Significance of Common Beans
• The common bean (both dry and snap beans)is an important legume crop world wide
• The most important legume crop in Uganda
• Cheapest and most readily available source of high content protein food
• Food security Crop – Quick maturing
• Source of household income (domestic, export markets)
• Farming system friendly i.e fixes nitrogen, acts as ground cover and can easily be intercropped
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Sclerotium Root Rot (Southern Blight) of Common Beans
• Caused by Sclerotium rolfsii Sacc. • Pathogen causes disease in important crops such as
Common beans, Ground nuts, Chick peas, Soya,etc.
Images of Southern Blight of Common Beans
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Incidence and Severity of Southern blight in Uganda
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Isolation and Characterization of S. rolfsii
• >200 isolates were collected from 7 bean agroecologies in Uganda
• These were morphologically grouped using Growth rates
Sclerotia production
Mycelia texture and colour
• Initially genotyped using RAMs, but GBS characterization on-going at Cornell University
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Screening Protocol for Southern blight Inoculum on millet grain
S. rolfsii culture on PDA Inoculum Mixed in Soil
Differential Reaction of Lines Lines Planted in Rows
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Data Collected • Germination data collected 14 days after planting • Southern blight Incidence and Severity assessed 28
days after planting • Severity assessed using a scale of 1-5 (Le et al.
2012; Plant Disease 96: 389-397)
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Southern blight Severity Assessment Scale 1 = No Disease symptom, 2= Disease symptoms without visible fungal outgrowth, 3 = Disease symptoms with visible fungal outgrowth, 4 = Partial wilting of plant and 5 = Complete wilting and death
1 2 3 4 5
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Pathogenecity of S. rolfsii Isolates
• Study conducted to 1) determine the virulence of isolates, and 2) identify isolates for use in germplasm evaluation
• 78 isolates were selected based on origin and morphological grouping
• Lines used included RWR 719 MLB49-89A ALB 123 NABE 15 CAL 96 (K132)
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Effect of S. rolfsii Isolates on Seed Germination
0
5
10
15
20
25
30
35
40
45
ALB 123 NABE 15 CAL 96 MLB 49-89A RWR 719
Num
ber o
f Iso
late
s
Lines Screened
0
1 to 25
26 to 50
51 to 75
76 to 100
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Effect of S. rolfsii Isolates on Southern blight Incidence
0
5
10
15
20
25
30
35
40
45
ALB 123 NABE 15 CAL 96 MLB 49-89A RWR 719
Num
ber o
f Iso
late
s
Lines Screened
0
1 to 25
26 to 50
51 to 75
76 to 100
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Effect of S. rolfsii Isolates on Southern blight Severity
0
5
10
15
20
25
30
35
40
45
ALB 123 NABE 15 CAL 96 MLB 49-89A RWR 719
Num
ber o
f Iso
late
s
Lines Screened
1.0 to 2.0
2.1 to 3.5
3.6 to 5.0
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Nurseries Screened
Origin Number of Lines
Andean Diversity Panel (ADP)
Accessions and released lines from East and South Africa, CIAT, North America, Ecuador, Angola and Caribbean
104
ALB Interspecific Hybrid (SER 16 x G35346)
129
Kenyan Root Rot Nursery
Developed for Pythium resistance 28
Local Germplasm
Land races and released lines from Uganda
31
Root rot Checks
Pythium resistant and susceptible lines
3
Total Number Screened 295
Identification of Resistance Sources
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Effect of S. rolfsii on Seed Germination Lines Seed Germination
0% 1 to 25% 26 to 50% 51 to 75% >75%
ADP 0 2 12 44 46
ALB 0 19 37 43 30
Pythium Root Nursery
2 16 3 3 4
Local Germplasm
0 1 1 8 21
Root Rot Checks
3
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Incidence of Southern Blight Lines Southern blight Incidence
0% 1 to 25% 26 to 50% 51 to 75% >75%
ADP 0 0 15 48 41
ALB 0 2 19 45 63
Pythium Root Nursery
0 0 0 10 15
Local Germplasm
0 0 8 15 8
Root Rot Checks
RWR 719 MLB49… CAL 96
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Lines Southern blight Severity (Scale 1-5)
1 to 2 2.1 to 3.5 3.6 to 5
ADP 9 72 23
ALB 16 52 61
Pythium Root Nursery
0 13 12
Local Germplasm
2 27 2
Root Rot Checks
RWR 719 MLB49-89A
CAL 96
Severity of Southern Blight
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Way Forward
• Confirm reactions of promising lines (high germination and low disease severity being the most desirable combination)
• Continue screening additional nurseries to identify clear-cut resistance sources
• Map Southern blight resistance in common beans
• Incorporate Southern blight resistance in Ugandan Market-class varieties
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Acknowledgements Funding from the Biotechnology and Biological
Sciences Research Council (BBSRC), the Department for International Development (DFID) and (through a grant awarded to BBSRC) the Bill & Melinda Gates Foundation, with additional funding from the Department of Biotechnology (DBT) of India’s Ministry of Science and Technology
USDA – NIFA for funding
Partners Michigan State University, USA and the University of Reading, UK