The genus carrot (Daucus carota L.) is a member of family – Apiaceae, one of the important vegetables commercially grown worldwide. Its edible part is fresh taproot which can be eaten as raw or cooked. Carrot taproots contain large amounts of alpha- and beta-carotene and also an important source of vitamin A (Heinonen, 1990), host of other impressive health benefits including fairy skin, cancer prevention and anti-aging. Carrot is one among the top 10 important economically grown vegetables after potato, tomato, lettuce, onions and sweet corn celery (Bassett, 1986). Globally, the rate of carrot production significantly checked due to different plant-parasitic nematodes, out of which more than 90 species have been found significantly associated (Davis and Raid, 2002). FAO (2016) reported that the world production of carrots and turnips (typically examined together) was almost 42.71 million tons, out of which 0.545 million tons was contributed by India and ranked at14th. Carrot was reported to be the most sensitive crop to root-knot nematodes with yield reduction as high as 45% in commercial fields of USA (Widmer et al. 1999). Carrot is commonly cultivated for the fresh and healthy taproot production which is the most consumed part. The quantitative and qualitative production degraded due to the infection induced by some soil-borne plant pathogens such as bacteria, fungi and nematodes (Korean Society of Plant Pathology, 2009). The quantity as well as quality of the marketable taproot is deteriorated due to forking and galling symptoms which resulted in significant yield losses observed in carrot cultivation (Roberts, 1987). Anita and Selvaraj (2011) reported the unavoidable yield losses up to 35.95% due to infestation of M. hapla in Nilgirs. The worldwide shift towards the production of healthy food and protection of ecological environment has evolved an increased attention in ecology-based protocols for enhancement in plant productivity. The cultivation of carrot is endlessly affected by both biotic and abiotic soil elements.
Plant parasitic nematodes are among the most destructive soil pathogens of cultivated crops which causes severe economic losses to agriculture throughout the world, estimated to $US 121 billion per year (Chitwood DJ, 2003). These tiny parasites consist of ectoparasites as well as endoparasites which feed on the cytoplasm of living plant cells. Functionally, nematodes creates metabolic sinks in infected plants by utilizing photo assimilates prepared to roots through metabolic activity of gall tissues. The intensive cultivation of vegetable crops is becoming particularly at risk due to a group of root-knot nematodes. Among the plant parasitic nematodes, most of the vegetable crops are dangerously attacked by Meloidogyne species, resulting in major yield losses. In India, its infestation is also a serious problem and commonly linked with the cultivation of carrot.
Root-knot nematodes are polyphagous and virulent obligate endoparasites found across the globe especially in tropical, subtropical and warm temperate areas and cause major economic losses in yield of many crops. Due to formation of characteristic ‘root galls’ or ‘root-knots’ over the several hosts, Meloidogyne species are called as root-knot nematodes and infest a wide range of plant species. They parasitize thousands of different plant species including monocotyledons, dicotyledons, herbaceous and woody plants (Sikora and Fernandez, 2005). Despite, crops of economic importance, hundreds of weed plants are also infected by the root-knot nematode, Meloidogyne incognita (Mahmood 1988). Sasser (1989) appropriately defined them as the “hidden enemy” because, they cause huge economic losses and most importantly, one cannot see these pests through naked eyes as they sheltered in roots of crop plants. Meloidogyne species infestation is a limiting factor in the production of carrot in India and thus there is need of the hour to search sustainable control measures which engage the attention of many growers and researchers across the globe.
The nematode population in infested fields can be checked by the use of several approaches like treatment with nematicides, application of biocontrol agents (Vagelas and Gowen, 2012), soil amendments (Asif et al., 2016, 2017), cultural practices in terms of crop rotation and the use of antagonistic plants (Hussain et al., 2011; Kayani et al., 2012). The application of chemical nematicides has been found to be a potent and effective means of controlling root-knot nematodes but the harmful impact of their residues on the environment and especially on non-specific organisms urgently require efficient and feasible alternative methods for the root-knot nematode control. Among all the management tactics, the use of resistant cultivar is an ideal option for controlling the nematodes on carrot in a cheaper way or little extra cost is required for the management (Kinlock and Hinson, 1972; Ansari et al., 2018). For hampering the development of root-knot nematodes, practice of resistant cultivars could be an effective, economic and eco-friendly attempt (Linlin Dong et al., 2012, Ansari et al., 2018). The rotation of resistant cultivars and non-host crops is one of the important methods to minimize the nematode level in the soil (Mukhtar et al., 2013). The cultivars resistant to plant parasitic nematodes considered as the initiative of an integrated nematode management programme for all economically important vegetable crops. Also, the genetically resistant cultivars display various different problems. There is no resistance recognized in different crops or is present only in wild species or undeveloped genotypes against these agriculturally important nematodes. Resistance is a highly specific characteristic and acts against a single or a few nematode species and may not be persist for longer time because of the selection of “resistance-overcoming” populations that deliver the resistance inadequate in specific locations (Starr and Roberts, 2004).
The main objective of this work is to explore the magnitude of disease resistance in 13 carrot cultivars for root-knot nematode, M. incognita under greenhouse conditions that can be further used in nematode management programme.
Material and methods
Collection of carrot cultivar and nematode inoculum
Seeds of thirteen commercially available carrot cultivars Lali, Super red, Rose red, Red king, Desi red, Golden rosy, Noorie, Kamini, Sindhuri, Pearl red, Kamboj, Surbhi, and Selection 80 were collected from Chola Seed Store, Aligarh (U.P.), India.