Introduction

Polianthes tuberosa L., commonly known as tuberose, belongs to the Asparagaceae family. This bulbous plant features pale green leaves and thrives under specific agronomic conditions crucial for its successful cultivation. Tuberose flourishes predominantly in warm, humid climates with temperatures ranging from 16 °C to 30 °C, although it can also be grown in hilly regions at elevations around 1500 meters. Tuberose propagation is typically achieved through seeds and bulbs, with bulb propagation involving the division of bulbs into segments. Root-knot nematode infestation can be a significant issue for tuberose, impacting the health and yield of this ornamental plant. Meloidogyne spp. are the most common and damaging nematodes for tuberose. They cause the formation of galls or knots on roots disrupting nutrient uptake and leading to decreased plant growth and lower flower yield. Infected roots may also show reduced branching and appear stubby or Nematode-infected tuberose plants produce fewer and smaller flowers, reducing their commercial value. (Khan 2020) reported that the root-knot nematode, M. incognita is one of the critical limiting factors affecting commercial cultivation of Tuberose. It reduces the flower yield of root-knot nematode. It reduces the flower yield by up to 10% (Khan and Reddy 1992). Root-knot nematode problem in Tuberose is widespread root. The majority of the Tuberose growing areas in North and South India are heavily damaged by this nematode (Rao et al., 2004).

All commercially grown varieties of Tuberose have been reported to be susceptible to M. incognita. Tuberose bulbs procured from root-knot nematode-infested fields, when planted in pots containing sterilized soil, showed the symptoms of root-knot nematode infection with these issues in recent eras, our current study aims to document the nematode infestations in major tuberose growing regions of Tamil Nadu. Also, the study documented the nematode distribution and prevalence in three different regions.

Materials and Methods

Survey for root -knot nematode, M. incognita on Tuberose in Tamil Nadu

            A comprehensive survey was carried out in diverse locations within the primary Tuberose cultivation districts of Tamil Nadu, specifically Coimbatore, Erode, and Dharmapuri. The objective was to document nematodes associated with tuberose plants prior to harvest. Identification of fields harbouring root-knot nematode infestations was based on observable above-ground symptoms such as stunted growth, daytime-wilting, and chlorosis, complemented by below-ground symptoms like root galling and bulb decay. The tuberose varieties predominantly cultivated by farmers in these districts were identified as Prajwal. Confirmation of the nematode species was established through the observation of adult females, egg masses, and perineal patterns. 

Collection of soil and root samples

            Soil sampling involved the collection of 250g samples from the rhizosphere region, including feeder roots up to a depth of 15-20 cm, while maintaining a 1m peripheral area as a subsample. Employing a zig-zag pattern, five sub-samples per field were gathered and pooled into a 250 g composite sample, securely placed in a small zip-lock polythene bag, and fastened with a rubber band (one sample per field). Also, roots exhibiting gall formation, decay, or related tissues in tuberose plants were collected. Each collected sample was meticulously labelled with details such as sample number, sampling site, date of sampling, farmer’s name, crop stage, and GPS coordinates (Barker and Campbell 1981). The roots were then examined for infestation, with the assessment based on the number of galls, and the incidence of root-knot nematode was subsequently calculated.

RKN incidence =                         Number of samples infested with Meloidogyne spp.   × 100

                                                      Number of samples collected

Extraction of nematodes from soil

            The second stage juveniles (J₂) of the root-knot nematode and other co-existing nematodes were extracted from the soil through the utilization of the decanting and sieving technique (Cobb 1918), coupled with the Baermann’s funnel technique as described by (Viggiano et al., 2014).

Extraction of nematodes from roots

The nematode-infected roots were gently washed with water, followed by exposing them to running tap water   to remove the adhering soil particles. Then, the washed roots were cut into pieces of 1-3cm in length. The root bits were stained with a mixture of boiling acid fuchsin + lactophenol solution and de-stained with plain lactophenol, overnight. The adult root -knot nematode and egg masses were picked from the roots using forceps and needle under binocular stereo zoom microscope (Bridge and Page 1982).

Results and Discussion

Findings from the survey

                The current study spanned three distinct locations in Tamil Nadu, namely Coimbatore, Erode, and Dharmapuri districts (Table 1a, 1b, 1c). In Erode, observations revealed root-knot nematode (RKN) infestation along with the presence of other nematodes, including Helicotylenchus dihystera, Helicotylenchus spp., Pratylenchus spp., Aphelenchus spp., and Filenchus spp. Similarly, the survey in Coimbatore exhibited root-knot nematode infestation and the presence of Helicotylenchus spp. (Fig 4). Dharmapuri survey mirrored the same trend, with M. incognita identified as the predominant species. The collected samples underwent thorough examination, and nematode populations were assessed. Above-ground symptoms of root-knot nematode infestation, such as gall formation and stunted growth, were evident in the plants.

(Mani 1996) previously demonstrated the efficacy of Pasteuria penetrans (Thorne) Sayre and Starr and Pseudomonas fluorescens against Meloidogyne incognita Chitwood in Grapevine (Vitis vinifera Linn.), aligning with the current research utilizing the potential bacterium Pasteuria penetrans. (Sumangala 2018) documented the distribution of plant parasitic nematodes on tuberose in four districts, highlighting major nematodes associated with flower crops in different poly houses, and open field conditions. This is consistent with the present research, emphasizing the distribution of nematodes in flower crops across Tamil Nadu.

The current study revealed the prevalence of root-knot nematode, M. incognita infestation in tuberose in most surveyed areas. These observations were in accordance with the findings               of (Jothi et al., 2018), who reported the population dynamics of root-knot nematode, M. incognita, on tuberose under varied irrigation systems by conducting field experiment. This also helped in the current study to analyze the population and distribution of M. incognita in Tamil Nadu and recorded the presence of few plant parasitic nematodes viz., M. incognita, Helicotylenchus sp, Pratylenchus sp, Filenchus sp, Psilenchus sp, H. dihystera, Aphelenchus sp.

Conclusion

The survey results across the three major tuberose growing districts in Tamil Nadu have highlighted the widespread prevalence of root-knot nematodes (RKN) particularly Meloidogyne incognita, as a significant threat to crops in these regions, and the findings indicate that RKN infestation is consistently accompanied by other nematode species such as H. dihystera, Helicotylenchus spp., Prtaylenchus spp., Aphelenchus spp., and Filenchus spp., suggesting a complex nematode community affecting crop plants. A brief conductance of the survey indicated that M. incognita was prevalent across the surveyed districts and was the dominant species found in nearly all the tuberose cultivated crops.

References

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Bridge, John, and SLJ Page. 1982. "The rice root-knot nematode, Meloidogyne graminicola, on deep water rice (Oryza sativa subsp. indica)."  Revue de Nématologie 5 (2):225-232.

Chawla, Gautam, Krishan P Singh, and AN Srivastava. 2006. "Study on propagation of root knot nematode, Meloidogyne incognita (Kof oid & White) Chitwood, through tuberose (Polianthes tuberosa Linn.) bulbs."  Journal of Ornamental Horticulture 9 (1):73-74.

Cobb, Nathan Augustus. 1918. Estimating the nema population of soil, with special reference to the sugar-beet and root-gall nemas, Heterodera schachtii Schmidt and Heterodera radicicola (Greef) Müller: and with a description of Tylencholaimus aequalis n. sp. Vol. 1: US Government Printing Office.

Jothi, Naga, P Vetrivelkalai, and M Kannan. 2018. "Population Dynamics of Root Knot Nematode, Meloidogyne incognita (Kofoid and White) Chitwood on Tuberose (Polianthes tuberosa L.) under varied irrigation systems."  Pest management in horticultural ecosystems 24 (2):150-153.

Khan, Ali, Shehzad Iqbal Aiman, Yusra Baber, Farazia Hassan, Hafiz Muhammad Usman, Muhammad Aamir Sohail, and Aqleem Abbas. 2021. "An overview of root-knot nematodes and their management."

Khan, Matiyar Rahaman. 2020. "Nematode Pest Problems of Tuberose." In Advances in Pest Management in Commercial Flowers, 119-136. Apple Academic Press.

Khan, RM, and P Parvatha Reddy. 1992. "Nematode pests of ornamental crops."  Nematode pests of crops.:250-257.

Mani, MP. 1996. "Effect of Pasteuria penetrans (Thorne) Sayre and Starr and Pseudomonas fluorescens (Migula) against Meloidogyne incognita (Kofoid and White) Chitwood in grapevine (Vitis vinifera Linn.)."  M. Sc.(Agri.) thesis, Tamil Nadu Agri. Univ., Coimbatore.

Rao, MS, M Shylaja, and PP Reddy. 2004. "Bio-management of Meloidogyne incognita on tuberose using a formulation of Pochonia chlamydosporia."  Nematologia Mediterranea.

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Viggiano, José R, Leandro G de Freitas, and Everaldo A Lopes. 2014. "Use of Pochonia chlamydosporia to control Meloidogyne javanica in cucumber."  Biological control 69:72-77.

Table 1a. Distribution of plant parasitic nematodes in Tuberose in Erode district

                       Table 1b. Distribution of plant parasitic nematodes in Tuberose in Coimbatore district

Table 1c. Distribution of plant parasitic nematodes in Tuberose in Dharmapuri district