The use of biofumigant plants to control Cavity Spot in carrots

IntroductionCavity Spot• Cavity Spot is a disease in carrots caused by a number of species of the fungus-like organism Pythium. In the U.K it is primarily caused by Pythium violae. • This disease causes lesions on carrots, these carrots cannot be sold due to their unappealing appearance. This is a problem in carrot crops of temperate countries and can cause large financial losses to farmers.

Biofumigation• Biofumigation is a technique that can be used to control levels of disease in the soil.• Crops, usually Brassicas, are processed and incorporated in to the soil. They then release chemicals that are toxic to some fungi and bacteria.• Brassicas and other crops contain chemicals called glucosinolates,

these can be converted to toxic isothiocyanates when they come in to contact with water.

AIM: Investigate the effect of biofumigant crops on Pythium violae as a potential means of controlling Cavity Spot in carrots

MethodI was involved in two experiments, one was based in the lab and the other in the field:

Field experiment• There is an on going field trial set up at Warwick Crop Centre. Carrots

have been planted in a field and soil samples taken at regular intervals. • Samples were taken before and after incorporation of various biofumigants. They were tested for the presence of Pythium violae.• The plants used in this experiment were: Brown mustard, white mustard, forage rape, rye/clover mix and wheat.

Lab experiment• Pythium violae was grown on agar at the bottom of a petri dish.

Crushed, dried biofumigants were then placed in the lid of the petri dish and 15ml of water

was added. The dish was then sealed and the growth of P. violae along the x and y axis was measured over 7 days.• The plants used for this test were three varieties of brown mustard (Pacific Gold, Vittasso and Caliente 99), white mustard (Brisant), radish (Terranova), rocket (Nemat) and rapeseed (Temple). There was also a control plate that only contained water.

Results

• The field trial has not given clear results, it showed natural fluctuations in P.violae levels throughout the year. The level of P.violae before biofume incorporation was low and remained low after the biofumigant plants were incorporated. • The lab experiment gave clearer results. It showed that all varieties of biofumigant plants tested inhibited growth of P.violae significantly. At the high concentration used in the experiment, all varieties of mustard completely prevented growth of P.violae.

Victoria WoolleySchool of Life Sciences, University of Warwick

V.Woolley@warwick.ac.uk

Conclusions• The lab test showed that Brassicas, in particular mustard, inhibit the growth of P.violae. This is likely due to their high glucosinolate content.• Other crops such as radish and rocket also contain glucosinolates and inhibit the growth of P.violae. • Rapeseed (variety Temple) has been bred to contain low levels of glucosinolates, however it inhibited growth of P.violae. This may be due to other chemicals such as phenols which can have anti-microbial properties. The chemical content of these biofumigant plants may be tested in future research.• The levels of Pythium in the field were found to fluctuate throughout the year.

AcknowledgementsThank you to my supervisors Dr John Clarkson and Dr Andrew Taylor who made my URSS project really

enjoyable and informative.

The field trial at Warwick Crop CentreA petri dish used in the lab experiment. The

lid is on the left and base is on the right.

A culture of Pythium violaeCarrots from the field trial

A plate showing the growth of Pythium violae in the presence of ‘Nemat’

Control Temple Terranova Nemat Brisant Caliente 99 Pacific Gold Vittasso LSD 0

5

10

15

20

25

30

35

40

45A graph showing the growth of P.violae cultures after

treatment with biofumigants

X growthY growth

Variety of biofume

Size

aft

er 7

day

s (m

m)