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EFFECT OF WATERING REGIME AND SOIL

TEMPERATURE ON INFECTION OF POTATO

ROOTS BY SPONGOSPORA SUBTERRANEA F.

SP. SUBTERRANEA

Chris Slabbert, Jacquie van der Waals

Department of Plant and Soil Sciences,

University of Pretoria

Potato Pathology Programme @ UP

INTRODUCTION

Soil-borne inoculum important, but environmental factors are most important in determining final disease intensity

Soil temperature (?)

Soil moisture – very important for motility of

zoospores

IMPORTANT TEMPERATURES FOR INFECTION OF POTATOES BY SPONGOSPORA SUBTERRANEA F. SP. SUBTERRANEA

Minimum temp.

Optimal temp.

Maximum temp.

≈9⁰C 12-16⁰C ≈25⁰C

Temperature Reference

Optimal temperature 14-20°C Kole, 1954

12-13°C Hims, 1976

>20°C Hughes, 1980

12.5°C de Boer et al., 1985

12°C van de Graaf et al., 2005

9-17°C Wale, 2005

12-16°C Carnegie et al., 2010

16-17°C (root hairs) Kole, 1954

17°C (root gall formation) van de Graaf, et al., 2007

Maximum temperature 22-25°C Kole, 1954

Minimum temperature <11°C Kole, 1954

9°C van de Graaf et al., 2005

12°C (root galls) Van de Graaf, et al., 2007

IRRIGATION MANAGEMENT

Most important environmental factor for infection is free soil moisture

Avoid over-irrigation or water logging during tuber initiation

M. Steyn M. Steyn

SIGNIFICANCE OF PROPOSED PROJECT

Powdery scab previously considered disease of cool, wet climates

FOUND IN MOST POTATO GROWING REGIONS IN SOUTH AFRICA

Cannot extrapolate data from elsewhere to SA

Is the pathogen is able to adapt to prevailing environmental conditions?

Imperative to conduct studies in South Africa, with South African Sss samples

Collection of

infected tubers

Inoculum

preparation

Inoculate soil (CRD)

Control pots uninoculated

Plant with mini-tubers of

susceptible cultivar

Incubate at

10, 15, 20,

25 and

30˚C

Wilting point,

saturation point and

fluctuating water

content

Sample roots two

weeks after

emergence

DNA Extraction

Microscopy

Spongospora subterranea f. sp. subterranea DNA in the roots of potato plants grown at different

temperatures, samples taken 14 days after inoculation.

Spongospora subterranea f. sp. subterranea DNA in the roots of potato plants grown at

saturation point, samples taken 2-12 days after inoculation.

Spongospora subterranea f. sp. subterranea DNA in the roots of potato plants grown at field

capacity, samples taken 2-12 days after inoculation.

Spongospora subterranea f. sp. subterranea DNA in the roots of potato plants grown at

fluctuating soil moisture, between field capacity and soil saturation, samples taken 2-12

days after inoculation.

Field capacity Fluctuating wilting point Saturation point

DAP Incidence

DNA

Quantity

(pg/µl) DAP Incidence

DNA

Quantity

(pg/µl) DAP Incidence

Quantity

(pg/µl)

2 0% 0,0000 2 0% 0,0000 2 50% 0,0028

4 50% 0,0033 4 0% 0,0000 4 50% 0,0077

6 0% 0,0000 6 100% 0,0068 6 100% 0,2965

8 100% 0,0034 8 50% 0,0102 8 100% 0,0071

10 50% 0,6109 10 50% 0,0011 10 100% 0,0191

12 50% 0,0051 12 100% 0,9314 12 100% 0,0039

Optimal temperature and soil

moisture for root infection

Temperature:

• Most infection at 15⁰C, then 20⁰C (literature: 17⁰C)

• Least root infection: 30⁰C < 25⁰C < 10⁰C

Soil moisture:

• Earliest and greatest infection at Saturation point > Fluctuating soil moisture > Field capacity

• Applications: • Choose planting date so that temperatures during initial root development are >20⁰C

• Use irrigation scheduling – allow soil moisture content to fluctuate

IMPORTANCE FOR INDUSTRY

Knowledge of conditions favourable for disease development = integral part of risk assessment

Ultimate goal: Better disease management and more sustainable potato production