Rotylenchulus reniformis
Encyclopedia
History and significance
Rotylenchulus reniformis is a plant parasite nematodeNematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
with a worldwide distribution in the tropical and subtropical regions. This nematode has a wide host range infecting plants in many species around the word. It belongs to the Family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Hoplolaimidae
Hoplolaimidae
Hoplolaimidae is a family of plant pathogenic nematodes. It has two subfamilies, Hoplolaiminae and Rotylenchulinae. Typically hoplolaimids are ecto- or semi endoparasites of higher plants.-Type subfamily :Hoplolaiminae Filip'ev, 1934....
; it was first observed on the roots of cowpea in Hawaii. The reniform nematode was described as new species in 1940 by Linford and Oliver after four years of investigations [8]. It is called the reniform nematode because of the distinct kidney-shaped appearance of the mature female [2, 5]. R. reniformis is the only species of major economic importance to agriculture of the 10 Rotylenchulus species described [8].
Distribution and host range
R. reniformis has been found associated with hundreds of species of plants in tropical and subtropical areas. It has been reported in thousands of localities in South America, Central America, North America, the Caribbean Basin, Africa, Europe, India, Southeast Asia, Australia, China, Japan and the Philippines [8, 11]. Its wide distribution is due to the wide range of host it infects; including fruit trees, lentil, cotton, cowpea, pigeonpea, tea, tobacco, soybean, pineapple, bananas, okra, coconut, cabbage, sweet potato, alfalfa, corn, asparagus, palm, cucumber, tomato, pumpkin, squash, cassava, radish, eggplant, guava, melon and ginger [2, 5, 8].Certain species of plants such as wild barley, mustard, oats, barnyard grass, pangola grass, red-hot and sweet pepper, spinach have been reported as non-host to reniform nematode [2, 5].
Morphology
Reniform nematodes have esophageal glands overlapping the intestine, short stylet, a strongly developed framework; the dorsal esophageal gland orifice is located posterior to the stylet knobs [5, 10]. Immature females are slender, free in the soil. The body often assumes an open spiral or ‘C’ shape when killed by heat [2]. Mature females have a swollen kidney-shaped body with a short tail, slender and short stylet, rounded knobs; with a three-part esophagus, a long and narrow isthmus, and well-developed metacarpus. The vulva is just behind the mid-portion of the body [10].Males are vermiform; they have a weak stylet and knobs, curved spicules and pointed tail; the esophagus is degenerate, with a reduced median bulb [2, 10].
Life cycle
R. reniformis is sedentary semi-endoparasite on roots of many plants [2, 3, 4]. Mature females penetrate partly into roots, leaving the posterior portion of their bodies projecting at the surface [2, 8]. Juveniles, males and immature females are found in soil [10]. The immature female is the infective stage penetrating roots [2, 4]. Males are not parasites, they do not feed but they are important for reproduction [10]. Under drought conditions, R. reniformis can survives 1–2 years without host by entering an anhydrobiotic state [11].R. reniformis is sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
; its life cycle is completed in 17 to 23 days under favorable temperatures [6]. The developing juvenile (J1) molt once while still inside the egg shell [3, 8]; the eggs hatch in 8–10 days, then a J2 develops molting 3 times (J3 and J4) in the soil to become immature males and females [3, 6]. The anterior one-third of the young female body penetrates roots and forms a feeding site (syncytium
Syncytium
In biology, a syncytium is a large cell-like structure; filled with cytoplasm and containing many nuclei. Most cells in eukaryotic organisms have a single nucleus; syncytia are specialized forms used by various organisms.The term may also refer to cells that are connected by specialized membrane...
) in the endodermis. The female continue to develop, swelling and becoming kidney-shaped [3]. The female deposits eggs in a gelatinous matrix containing about 50 eggs on surface of the root after 7–10 days [6, 10].
Host-Parasite relationship
Infective stage penetrates the epidermis and cortical parenchyma of the host rootRoot
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
, only the anterior part of the body is embedded within root tissue. Penetration is stopped when lips reach the endodermis
Endodermis
The endodermis is the central, innermost layer of cortex in some land plants. It is made of compact living cells surrounded by an outer ring of endodermal cells that are impregnated with hydrophobic substances to restrict apoplastic flow of water to the inside...
, resulting in formation of a trophic site that consist of a syncytium
Syncytium
In biology, a syncytium is a large cell-like structure; filled with cytoplasm and containing many nuclei. Most cells in eukaryotic organisms have a single nucleus; syncytia are specialized forms used by various organisms.The term may also refer to cells that are connected by specialized membrane...
structure, which forms from an endodermal cell and enlarge by incorporation of adjacent parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
cells of the pericycle and vascular parenchyma [8]. A feeding tube forms from stylet secretions [2].
R. reniformis can induce symptoms resembling those of moisture and nutrient deficiencies on above ground plant parts. Reniform nematode can causes hypertrophy in the pericycle cells of root seedlings and in the periderm cells of the roots of 4-5 week old plants [7]. Generally root growth is reduced with limited secondary root development. It can produce root necrosis in pineapple and banana. Shoot growth suppression is observed and reduction of fruit quality in infected crops such as pineapple [4]. Infected plants can become severely stunted and chlorotic, and may wilt. Wilting is often caused by opportunistic parasites such as the Fusarium and Verticillium wilts on cotton [10, 11]. Root decay can be caused by secondary fungi infection.
Damage from R. reniformis is directly related to the number of nematodes present when the crop is planted. Variation among nematode populations, host, environmental conditions and soil types may alter the threshold or economic injury level across the geographic distribution of this nematode [3, 11].