Alternative methods of carrot (Daucuscarota) protection against the northern root knot nematode (Meloidogyne hapla)

Abstract

The presence of northern root knot nematode (Meloidogyne hapla) has considerably increased in the Czech Republic during the last 10 years. The management of this pest is difficult; thus, the aim of this study was to test two alternative pest management techniques on carrots under field conditions. When Indian mustard (Brassica juncea) was ploughed and the treated area was then covered with polyethylene sheets to prolong effect of the treatment, the root gall numbers decreased; whereas a nitrolime application combined with plastic covering had a positive effect on the experimental plants’ fresh weight.

Keywords:

• Alternative management
• biofumigation
• Brassica juncea
• nitrolime application
• soil covering

Introduction

Sedentary root knot nematodes (Meloidogyne sp.) are major pests of field crops and horticulture. Global economic losses caused by Meloidogyne sp. nematodes were evaluated at 100 billion USD per year (Oka et al., 2000); according to Sasser and Carter (1985), root knot nematodes cause approximately 5% of global crop loss. The management of the root knot nematode is difficult because of its rapid reproduction (one female is capable of laying approximately 1000 eggs during its life cycle) and wide range of host plants (Natarajan et al., 2006). Most of the Meloidogyne sp. nematodes occur in tropical and subtropical areas; however, some species have adapted to the temperate zone climate (Siddiqi, 2000).

In Central Europe, the northern root knot nematode (Meloidogyne hapla) has become an important pest during the last 10 years. Crop losses are regularly reported from the field cultures of carrot, parsley and parsnip on the sandy soils of the Elbe lowlands. The low initial awareness of this nematode species led to its uncontrolled spreading; the pest moved into new locations via agricultural mechanization and crop residues.

Currently, there are no nematocides registered for use especially against M. hapla in the Czech Republic; the sole available chemical treatment is the application of Basamid Granular (BASF). However, the use of this chemical is prohibited in areas under water sources protection. This situation, together with the prohibition of methyl bromide, leads to a lack of means for M. hapla management. In the case of phytoparasitic nematodes, it is often possible to utilize resistant cultivars; however, this is impossible with M. hapla and root vegetables because there are presently no cultivars of carrot, parsley or parsnip that are resistant to this nematode.

Thus, finding new means and procedures for root knot nematode management should be a priority for the scientific community. This study shows the effects of biofumigation and nitrolime fertilization on experimental plants; the effects on infestation and yield of the common carrot (Daucus carota), the economically most important host of M. hapla in Central Europe were measured. Evaluated methods were selected as simple, cheap and environmentally friendly and easily applicable by farmers; both methods utilize soil covering to prolong the effect of treatment.

Materials and methods

A carrot field that was naturally infested with M. hapla in Litol (in Lysá nad Labem, Central Bohemia, 50°11′3.288″N, 14°50′16.429″W) was chosen for the trials. The area was mapped with coordinates using a network of squares with sides measuring 10 m. Samples of carrot were taken from the cross points, and the presence of M. hapla nematodes was evaluated by evaluation of root galling. A total of 154 samples were recovered by this manner, and the homogeneity of the plot infestation was assessed. Moreover, 37 soil samples were taken in a zigzag pattern; carrots were sown in the soil samples, and the root galls on the emerging plants were evaluated. The data were used for establishing the presence of M. hapla on the plot and for choosing the area best suited for the experimental seedbeds.

The northeast part of the plot was selected for the parallel establishment of two experimental variants and one control. The area was divided into three belts that were 21 m long and 3 m wide; each area was traced out and prepared for the experiment.

The screening of biofumigation effectiveness against M. hapla nematode was performed as follows: Indian mustard (Brassica juncea L., Czern. et Coss) was sown in one of the experimental sites at the beginning of July; Indian mustard was chosen because it contains the highest amount of glucosinolates from all mustard species. The sowing rate was 11 kg ha⁻¹. After reaching heights of 30 to 50 cm in mid-September (a vegetation period of 13 weeks), the mustard plants were plowed with a disc stubble plough; the depth of ploughing was 12 cm. Immediately after ploughing, the ploughed site was covered by transparent polyethylene sheets (thickness 0.2 mm). Transparent sheets were used because they transfer heat to the soil better than an opaque plastic can. The effect of nitrolime was tested in a similar way; nitrolime (CaCN₂) was applied in a dose of 800 kg ha⁻¹ on the second experimental site, and the soil was covered in clear plastic sheets. The control site was left untreated.

The plastic sheets were removed at the beginning of March of the next year, the whole plot was fertilized with NPK (250 kg ha⁻¹), and carrots (cultivar Darina; Moravoseed) were sown in the field. The signs of possible phytotoxicity were scored regularly during vegetation. The experiment was terminated and evaluated on 29 October. Using a method of random selection, three equal parts of each experimental variant were harvested. The plants were counted; the fresh weight and gall indexes were assessed. The gall index was designated according to Taylor and Sasser (1978): index 0 indicates a root system without galls; 1=1 −2 galls; 2=3−10 galls; 3=11−30 galls; 4=31−100 galls and 5<100 galls. The acquired data of the fresh plant weight were subjected to an analysis of variance (ANOVA) and the treatment means were separated by Tukey's test (p<0.05). Gall indexes were subjected to Kruskal–Wallis test. All statistic calculations were performed using STATISTICA software.

Results and discussion

No negative effects of treatment were observed during vegetation. In the case of the variant treated with biofumigation, 156 plants were harvested; 152 plants were acquired from the nitrolime variant; and 182 came from the control.

After weighing the harvested plants and applying statistical analyses, significant differences were discovered among the control and treated plots, plants were smaller following the biofumigation treatment (Table I). Nevertheless, biofumigation was effective in decreasing gall number, which is important for improving the commercial potential of the carrots (Table I).

Table I. Summary of numbers of the plants harvested and effect of the treatment on fresh weight and gall index of the experimental and control carrots. In the case of fresh weight and gall index the mean value is followed by the standard deviation; variants with the same number are not significantly different at p ≤ 0.05.

Variant	Number of plants harvested	Fresh weight (g)	Gall index
Indian mustard	156	42.2±27.8a	3.1±1.0a
Nitrolime	152	73.3±40.8b	3.6±0.9b
Control	182	53.2±30.3c	3.4±0.8b

The results show that both tested methods were effective in different degrees. The carrots from the nitrolime plot weighed more, probably because of higher nitrogen dose, because nitrolime did not reduce gall number. The findings and the effect of biofumigation may relate to the time of year when the Indian mustard was sown. Given the climatic conditions of Central Europe, it is necessary to sow biofumigation crops early enough to make the most of the high temperatures of July and August. According to Wang et al. (2006), one disadvantage of biofumigation can be the shortness of the effect. Nematodes return to treated plots in a few months. However, solarization prolongs biofumigation, so combining biofumigation with solarization seems appropriate. It is also important to account for the negative effects of solarization on saphrophagous nematode species and other soil organisms that act as a decompositors of the dead organic matter. It is possible to utilize solarization for the sanitation of greenhouse substrate, especially in southern Europe. In soil batches covered by polyethylene sheets, the number of Meloidogyne sp. eggs can be reduced by 95% during three weeks of solarization (Nico et al., 2003).

New research on alternative means for M. hapla management should target the efficiency of different mulches; testing the application of different manures may also be important. Promising results were achieved when chicken manure (López-Pérez et al., 2005) or diverse composts were used; composts have also been effective against cyst-forming nematodes (Renčo et al., 2007).

Results obtained in this study seem to be promising. Application of the tested methods will not lead to eradication of M. hapla nematode on treated areas; however it can decrease the inflicted damage significantly.

Acknowledgements

This work was supported by the Czech Ministry of Agriculture, project numbers QH81163 and MZE0002700604, and Czech Ministry of Education, grant number MSM6046070901. The authors are grateful to Mr Jan Procházka for collaboration during trials.