ABOVE: Stubby, swollen, galled noni roots after infection by root-knot
nematodes (Meloidogyne sp.)
ABOVE: An older noni root with severe galling, distortion and cracking due to infection by root-knot nematodes.
ABOVE: Initial symptoms of root-knot nematode infection of noni: small galls.
ABOVE: Galled root system and cracked and girdled stem associated with
severe root knot disease of noni.
ABOVE: Noni tree killed by root-knot nematodes
ABOVE: Basal stem of noni plant is girdled due to effects of infection by root-knot nematodes (plant is dead)
ABOVE: Foliar chlorosis (yellowing), plant stunting, and root galling
and necrosis associated with noni root knot disease.
ABOVE: Yellowed noni leaves showing deficiency in nutrients (probably iron and other micronutrients) due to infection by root-knot nematodes.
Root-knot nematodes should be avoided at all costs
| Disease: Noni
Pathogen: Noni root knot disease is
caused by a group of plant parasitic nematodes, Meloidogyne
spp., known as the root-knot nematodes. These nematodes have
wide host ranges and are able to infect many plant species.
They can survive for long periods in Hawaii soils, even in the
absence of host plants. The nematodes live in the soil and attack
young noni roots. Their feeding and reproductive activities
cause the noni roots to swell, develop galls and to crack open.
After roots have cracked open, other opportunistic organisms
(fungi, bacteria) can enter the noni roots and cause rotting.
Symptoms: Leaves are golden yellow; plants are stunted
or unthrifty in appearance; root systems are stunted and sometimes
rotten; roots galled, knotty, swollen, distorted, cracked and
rotten; bark along base of stem may split open, leading to stem
girdling by opportunistic fungi and bacteria; plant death is
rare but can occur; low yields; sparse foliage.
Noni root knot can depress noni yields significantly. Replanting
costs may be high in severe infestations and some fields may
have to be abandoned.
Noni root knot nematodes are distributed on all major Hawaiian
islands, especially in older soils and ex-sugarcane lands.
Epidemiology: Disease often begins when seeds or
cuttings are planted in nematode-infested soil. Nematodes are
spread in contaminated soils, media, on tools and shoes and
in water runoff.