The and healthy taproot production which is the most

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. The carrot was reported to be the susceptible
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 the 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 create 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.

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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 the 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 the 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, the 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 persist
for the 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.