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Indian Journal of Nematology
Year : 1981, Volume : 11, Issue : 1
First page : ( 132) Last page : ( 133)
Print ISSN : 0303-6960.

Population estimation of citrus nematode, Tylenchulus semipenetrans Cobb, 1913

Sharma S. B., Chawla M. L.

Division of Nematology, Indian Agricultural Research Institute, New Delhi-12.

Presented at Nematology Symposium held at Coimbatore, India in February, 1981

Abstract

For developing diagnostic and advisory services as guides to effective control of nematode diseases, accurate estimation of population is the foremost necessity in the field of applied research in nematology. However, the complete census on the nematode population in a given area is not possible because of their high number as they constitute a major portion of the metazoans inhabiting soil. It is therefore, imperative that sampling and processing techniques, which are basic tools for reliable estimation of popultions, be developed and standardized atleast for nematode problems of economic importance. With this objective and taking into consideration the almost universal distribution of the citrus nematode, Tylenchulus semipenetrans and its association with the citrus die-back complex, the present studies were under taken to analyse factors influencing recovery of the nematode from soil as well as roots so that precise informations are obtained which may be ultimately helpful in the understanding of host-parasite relationship. Attempts were made to evaluate i) sampling methods (distance and depth of sampling from tree trunk, root and soil sample size. ii) storage conditions of the sample, iii) extraction procedure and iv) effect of temperature on the recovery of second stage larvae through modified Baermann funnel technique.

Cobbs decanting and sieving followed by 0.2% separan treatment or 2% detergent treatment or 2% ferric chloride treatment or modified Baermann funnel technique; Seinhorst two flask method and sugar centrifugal floatation method were evaluated. Five soil sample size (50, 100, 150, 200 and 250 cc); six temperature conditions (15, 20, 25, 27, 30 and 35°C); period of storage of soil samples (7, 17, 27, 37, 47, and 57 days) under six temperature conditions (5, 15, 20, 25, 27 and 30°C) and one room temperature, three different root weights (3, 7 and 10g) treated with four different concentrations of hydrogen peroxide and exposed to four different temperature conditions were evaluated also. All the tested methods were at par with each other with maximum recovery between temperature range of 15–27°C. The higher temperatures ono and 35°C were not conducive for the recovery of nematode population. Sample size, foot weight and storage of samples had a marked effecf on the recovery larvae, 50 cc of soil sample size was found to be optimum. Storage of soil samples below 20°C for seven days did not change the population but storage at 25°C for seven days resulted in higher recovery. Size of 3 g of cbopped feeder roots immersed in 30 ml of 5% hydrogen peroxide and incubated at 20°C for 48 bours was the most effective size for the maximum recovery of nematode larvae. Sampling at 120 cm radial distance from tree trunk at a depth of 30 cm was an ideal combination for maximum recovery. These studies bave clearly indicated that not only temperature at the extraction time but also the sample size, the condition of storage of samples, the root weight and also the sampling sites are important deteqnining factors in proper eyaluation, of the population dynamics of citrus nematode.

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