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Occurrence of Root Lesion Nematodes (Pratylenchus spp.) in wheat and barley crops in the high rainfall region of Victoria

Grant Hollaway¹, Jackie Nobbs², Graham Exell¹ ,Vivien Vanstone³ and Michelle Russ³

¹Victorian Institute for Dryland Agriculture, Agriculture Victoria, Private Bag 260 Horsham, Victoria 3401
²Field Crops Pathology Unit, South Australian Research and Development Institute, GPO Box 397, Adelaide, South Australia 5001, Australia
³Department of Plant Science, University of Adelaide, Waite Campus

Summary

A survey of wheat and barley crops in south-west Victoria was conducted to determine the occurrence and species of root lesion nematodes infecting plant roots. Pratylenchus neglectus was found to be the most prevalent nematode, with the species P. thornei, P. crenatus and P. penetrans also identified. The importance of these nematodes in the high rainfall cropping region is not known.

Introduction

In the higher rainfall regions of south-west Victoria there is a rapid expansion in the area of cereal production occurring with the decline in wool prices. Since this is a relatively new production area it is important to know the diseases that may limit production. The root lesion nematodes Pratylenchus thornei and P. neglectus have been shown to reduce the yield of wheat crops in the more traditional cropping areas in south-eastern Australia (Hollaway et al. 2000, Vanstone et al. 1998 ). However, the distribution of these nematodes in the higher rainfall cropping zones, or the presence of other root lesion nematode species is not known.This survey of wheat crops in south-west Victoria was undertaken to establish the distribution and species of root lesion nematodes present.

Methods

In 1999, 43 wheat crops and 3 barley crops were selected at random to be inspected for the severity and cause of disease during the growing season. The cropping history of each paddock was obtained from the grower. During September 1999, a total of 18 plants from five locations on a 150 m transect were dug from each paddock. The soil was washed from the roots and the plants delivered to the University of Adelaide for nematode extraction Roots were chopped into 1 cm lengths, and placed in a misting chamber. Nematodes were extracted from each set of 18 plants over 96 hours. Roots were sprayed with a fine mist of water at 25°C for a duration of 10 seconds at 10 minute intervals. Nematodes in 1 ml of the mister extract were counted, and average number of Pratylenchus per plant calculated.Identification of the Pratylenchus species extracted from the wheat roots was conducted on 13 of the samples. Measurements and diagnostic characters were used to identify the species of root lesion nematode present. Characters used to identify the different species included a) tail shape, b) whether the tail was smooth or crenate/annulated, c) the number of head annules, and d) type and number of lateral lines. Measurements included a) length of stylet, b) body length, c) position of vulva as a percentage of body length, and d) ratio of tail length to tail width (c’).

Results

The number of nematodes extracted from the plant roots was related to the cropping history (Table 1). The higher numbers of root lesion nematodes were extracted from paddocks with a history of crops (such as canola and wheat) susceptible to the root lesion nematode P. neglectus (Taylor et al. 2000). The lowest numbers were extracted from roots sampled from paddocks with a history of resistant crops (such as oats, barley or lupins) and pastures.

Table 1. Relationship between paddock history and number of nematodes extracted from the root system of plants collected from paddocks in south-west Victoria in 1999

The results from identification of nematodes from the 13 paddocks are shown in Table 2. The predominant nematode identified was P. neglectus. P. thornei, P. crenatus and P. penetrans were also identified in some of the samples.

Table 2. Identification of nematodes extracted from 13 of the paddocks from the survey of cereal paddocks in south-west Victoria in 1999

Discussion

In most paddocks, only low numbers of root lesion nematodes were extracted from the plant roots, suggesting that these nematodes are not causing a major problem to cereal production in the higher rainfall region of Victoria. However, growing a number of susceptible crops in sequence was shown to result in higher nematode numbers, and therefore has the potential to cause yield loss to intolerant crops. The identification of species of root lesion nematode other than P. neglectus and P. thornei in the high rainfall area is of significance. The effect of these nematodes on cereal crop yield in the high rainfall region of southern Victoria is not known. P. penetrans occurs in higher rainfall regions and has many hosts (Corbett, 1973), although it is more common in horticultural crops than in broad-acre crops. There is a possibility that several pathotypes of P. penetrans exist (Loof, 1991). P. crenatus causes damage to cereals in light sandy soils in Europe (Loof, 1991) and also attacks vegetable crops. It has been associated with the poor establishment of pastures on old meadow sites (Loof, 1991). Further studies are required to determine the economic importance and host range of these other species of root lesion nematode in the higher rainfall regions of Victoria. Their identification using both morphological and molecular criteria may also need to be investigated, as complications may arise using the current diagnostic methods.

Acknowledgments

This work was supported by the Grains Research and Development Corporation through projects DAV428, DAS229 and DAS281.

References:

• Corbett, D.J.M. (1973). Pratylenchus penetrans. CIH Descriptions of plant parasitic nematodes, Set 2, Number 25.
• Hollaway, G. J., Burns, R., Exell, G., Ward, D., and Ophel-Keller, K (2000). Yield loss in wheat caused by Pratylenchus thornei in the Wimmera region of Victoria. Australasian Nematology Newsletter 11 (2): 12-15.
• Loof, P.A.A. (1991). The family Pratylenchidae Thorne, 1949. In Manual of Agricultural Nematology ed Nickle pp. 363 – 421.
• Taylor, S.P., Hollaway, G.J., and Hunt, C.H. (2000) Effect of field crops on population densities of Pratylenchus neglectus and P. thornei in south-eastern Australia; Part 1: P. neglectus. Supplement to the Journal of Nematology. 32 (4) (In Press).
• Vanstone, V.A., Rathjen A.J., Ware A.H., and Wheeler, R.D. (1998). Relationship between root lesion nematodes (Pratylenchus neglectus and P. thornei) and performance of wheat varieties. Australian Journal of Experimental Agriculture 38:181-188.