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.

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

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

Incidence and Severity of Southern blight in Uganda

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

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

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)

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

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)

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

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

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

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

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

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

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

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

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