Effect of three control treatments on the survival of Quercus ilex seedlings infected with Phytophthora cinnamomi

A. Acedo; E. Cardillo; I. Núñez Institute of Cork, Wood and Charcoal (IPROCOR)

C/ Pamplona s/n. Apdo. 437. Mérida. Badajoz

Phytophthora cinnamomi (Pc) is an invasive root pathogen that causes decline and mortality in main evergreen oaks species in Spain. This pathogen causes significant

environmental and economic loss in semi-natural forest systems in Extremadura.

Several fungicides treatments have been tested both in vitro [1] and in vivo [2] against Pc and chemical treatment could play a major role in future control strategies for

Phytophthora root rot.

Phosphite is effective in controlling Pc in several plant species and low pressure trunk injection reduced the disease severity in Spanish Quercus woodlands.

The suppressive effect of silicon has been reported in Phytophthora root rot avocado under greenhouse and field conditions and gypsum has been proposed to

decrease Phytophthora root rot incidence.

Materials and Methods

Holm oak (Quercus ilex subsp. ballota) seedlings 15 month-old cultivated in greenhouse

were previously treated with:

1. Potassium phosphonate applied to the stem (300 µL 2.5%/plant+ surfactant).

2. Soluble silicon (K2SiO3) soil drench (75 ml 2% SiO2/plant).

3. Gypsum (CaSO4·2H2O) amendment (5% wt/wt).

4. not treated plants (control)

before being inoculated with an axenic chlamydospore suspension in V8 agar (7.5 x 104

u. /ml, 20 ml/plant) of a Pc isolate with proven virulence. Potting media were kept moist for

optimal infection and eventually flooded with tap water during 5 days. Mortality was

registered during 12 weeks.

Mortality was modeled with generalized linear model and treatment effects were

compared by deviance analysis.

Results

No mortality occurred before the plants were flooded. Inoculation with Pc reduced survival of plants from

95% to 78%, however none of the treatments used was able to reduce the mortality and survival time in

the inoculated plants.

Pc was only recovered from soil samples and roots of inoculated plants.

No phytotoxic effects were observed in treated control plants.

Conclusions

None of the preventive treatments applied was able to exert a protective effect on the holm oak under

greenhouse conditions.

The amount of phosphite translocated by direct application to the stem seems to be insufficient even

using a surfactant.

The lack of response of gypsum may be due to a lack of control of calcium on the pathogen in the soil

conditions of the experiment.

Higher doses and repeated applications may be needed in the case of soluble silicon.

Most Pc treatments only delays the appearance of symptoms and the development of the disease, there

being at present no clearly effective treatments for these stocks. So that, any chemical treatment must

necessarily be accompanied by measures to prevent the spread and setting of the pathogen.

Figure 1. Production of sporangia by P.c. strain used in the trial

References Bekker T. F., Kaiser C., Labuschagne N. (2006) Efficacy of water soluble silicon against Phytophthora cinnamomi root rot of avocado: A progress report. South African Avocado Growers' Association Yearbook 29, 58-62. Fernandez-Escobar, et al. 1999. Treatment of oak decline using pressurized injection capsules of antifungal materials. European Journal of Forest Pathology 29, 29–38. Serrano M. S., De Vita, P., Fernández-Rebollo, P. & Sánchez, E. Calcium fertilizers induce soil suppressiveness to Phytophthora cinnamomi root rot of Quercus ilex. European Journal of Plant Pathology, 132(2) 271-279 (2012).

Acknowledgement We thank the following for their collaboration in this trial: Pedro Antolín, Ana Alvarado, Alonso Diaz, Eusebio Dorado, Borja Durán, Emi Galván, Luis Sánchez and Ernesto Trías. This work received aid for Research of the Autonomous Community of Extremadura (PRI09A141).

Fig. 4. Pc recovered from treated and infected plants in NARPH medium

Fig. 3. Pc inoculum production in V8.

Left: survival of inoculated (I) and non-inoculated plants (N); right:

survival of different treatments on plants inoculated with Pc. C (inoculated

control), F (phosphite), S (soluble silicon) and Y (gypsum).

Fig.2. Holm oak seedlings