Four species of nematodes have been associated most frequently with, and caused the most damage to, pineapple: the root-knot nematodes, Meloidogyne javanica ((Treub) Chitwood) and Meloidogyne incognita ((Kofoid & White) Chitwood), the reniform nematode, Rotylenchulus reniformis (Linford & Oliveira) and the root-lesion nematode, Pratylenchus brachyurus (Godfrey Filipjev & Schuurmans Stekhoven) (Caswell et al, 1990).
The most obvious symptom of root-knot nematodes, M. javanica and M. incognita, on pineapple is the terminal club-shaped gall resulting from infection of the root tip (Fig. 9.15). Less obvious symptoms include stunting of plants and water stress, with the terminally galled root resulting in poor plant anchorage. Nematode egg masses survive for relatively short periods (hours) in desiccated soils. Egg masses in galls may survive several days. Juveniles may survive several weeks to years in desiccated soils. Second-stage juveniles infect the pineapple root tip and become sedentary after 2-3 days. Vermiform males and saccate, sedentary females go through several moults. Surviving nematodes can tolerate a wide range of soil temperatures and pH.
The reniform nematode, like the root-knot nematode, causes stunting of plant growth,
with infected plants appearing to be under water stress, much the same as in drought, mealybug wilt or root rot. Symptoms are most severe in ratoon crops and may result in the total collapse and death of the plants. As with root-knot, above-ground symptoms are not diagnostic. In contrast to root-knot, however, pineapple plants infected with the reni-form nematode have excellent anchorage because of the lack of terminal galling. Infected primary roots continue to grow but secondary root growth is severely limited. Infected roots appear to have nodules, which are actually soil clinging to the gelatinous matrix of females embedded in the roots (Fig. 9.16; Caswell and Apt, 1989). Reniform nema-tode eggs hatch when stimulated by root exu-dates of host plants. Second-stage juveniles in the soil undergo 3 moults without feeding, ending as either adult males or preadult females. The preadult females infect the root, where they establish sedentary feeding, become swollen mature adults and start producing eggs. The male does not feed.
The infection sites of the root-lesion nema-tode, P. brachyurus, are characterized by a black lesion that progresses along the root as the nematodes move for feeding. Secondary roots and root hairs are also destroyed. Initial inoculum comes from infested root fragments in the soil or infected roots on infested seed material. Once the plant is infected, the entire life cycle can be completed within the pineapple root. Reproduction is by mitotic parthenogenesis, with males being rare. Optimum soil temperatures are 25-30°C and populations do best in acid soils. In the highly acid Ivory Coast soils, the root-lesion nematode displaces the root-knot nematode. A combination of root-lesion nematode and Pythium species results in greater damage than either alone (Guerout, 1975).
Spiral nematodes - Helicotylenchus, Scutel-lonema and Rotylenchus spp., have been reported as problematic in South Africa (Keetch and Purdon, 1979). In Bahia, Brazil, Aorolaimus spp. have been reported to cause stunting (Costa et al., 1998).
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