A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
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Pests and Diseases <strong>of</strong> Dipterocarpaceae 120<br />
and Sharma 1982, Mohanan and Sharma 1991). Most <strong>of</strong><br />
these fungi belong to Fungi Imperfecti<br />
(Deuteromycetes). Though a large number <strong>of</strong> species are<br />
recorded on dipterocarp seeds, their disease transmission<br />
and seed degradation is not well documented. In general,<br />
poor seed storage conditions affect seed quality and<br />
facilitate fungal infection and spread <strong>of</strong> fungi (see<br />
Chapter 4). There have been few fungicidal studies on<br />
stored dipterocarp seeds and there is a need <strong>for</strong> seed<br />
pathology research to establish suitable control methods<br />
<strong>for</strong> fungal infection both during storage and in nurseries.<br />
Two categories <strong>of</strong> seed fungi can be identified, the<br />
storage fungi and the seedborne fungi. The first category<br />
includes saprophytic fungi growing on the seed testa, and<br />
the second refers to pathogenic fungi developing from<br />
the internal part <strong>of</strong> the seed. Both cause significant<br />
damage during storage.<br />
Storage fungi<br />
Storage fungi grow fast, developing from the ever-present<br />
spores in the air or on the seed testa. They rapidly invade<br />
the embryo, causing damage and decreased germination<br />
(Neergard 1977). These saprophytes do not feed on the<br />
seeds, but their excessive development leads to the<br />
rotting <strong>of</strong> the seeds. The most common species belong<br />
to the genera <strong>of</strong> Aspergillus, Penicillium, Pestalotia,<br />
Pestalotiopsis, Gliocladium, Fusarium,<br />
Cylindrocladium and Lasiodiplodia. Most <strong>of</strong> these fungi<br />
produce enormous quantities <strong>of</strong> spores spreading rapidly<br />
and infecting the whole seed stock.<br />
Aspergillus niger was widely recorded on<br />
dipterocarp seeds (Pongpanich 1988, Singh et al. 1979,<br />
Mittal and Sharma 1981, 1982, Hong 1976, 1981a, Lee<br />
and Manap 1983, Hadi 1987, Elouard and Philip 1994).<br />
In India, fungicidal trials were conducted on fungi<br />
infecting Shorea robusta seeds, namely Aspergillus<br />
niger, Penicillium albicans, P. canadense,<br />
Cladosporium cladosporioides, C. chlorocephalum<br />
and Rhizopus oryzae (Mittal and Sharma 1981).<br />
Brassical, Bavistin and Dithane-45 proved effective. In<br />
Malaysia, Elouard and Philip (1994) tested fungicides<br />
on Hopea odorata seeds, and Benlate 50 and Thiram<br />
were effective without preventing germination or<br />
affecting seedling development.<br />
Seed-borne fungi<br />
Seed-borne fungal infection most probably takes place<br />
during the flowering period or at the early stage <strong>of</strong><br />
fructification. The infection occurs through spores<br />
present in the environment or through inoculation <strong>of</strong><br />
spores or mycelium by pollinating insects or predispersal<br />
insect predators while laying their eggs. Seed-borne<br />
fungi feed on living tissues, destroying the embryo and<br />
the cotyledons. The mycelium develops inside the seed<br />
and eventually covers the whole fruit. In natural stands,<br />
seed destruction is mainly caused by seed-borne fungi.<br />
The most common seed-borne fungi belong to the<br />
genera Fusarium, Cylindrocladium, Lasiodiplodia,<br />
Colletotrichum, Curvularia and Sclerotium (Hong<br />
1976, 1981a, Lee and Manap 1983, Charlempongse et<br />
al. 1984, Pongpanich 1988, Mohanan and Sharma 1991,<br />
Elouard 1991, Elouard and Philip 1994). The<br />
Basidiomyceteae Schyzophyllum commune has been<br />
observed on several <strong>dipterocarps</strong> (Hong 1976, Vijayan<br />
and Rehill 1990, Elouard and Philip 1994), developing<br />
on the cotyledons and embryo and ultimately covering<br />
the whole seed and producing carpophores. Infection<br />
leads to high levels <strong>of</strong> mortality: 70% <strong>of</strong> Shorea<br />
leprosula and S. ovalis seeds were rotted by a Fusarium<br />
species and 90% <strong>of</strong> Shorea glauca seeds were destroyed<br />
by Schyzophyllum commune (Elouard and Philip 1994).<br />
Seedlings and Saplings<br />
Over 40 species have been identified causing seedling<br />
diseases. The most common are in the genera<br />
Colletotrichum, Cylindrocladium, Fusarium and<br />
Lasiodiplodia, which are responsible <strong>for</strong> damping-<strong>of</strong>f,<br />
wilting, root and collar rots, cankers, leaf diseases, thread<br />
blights and gall <strong>for</strong>mation.<br />
Damping-<strong>of</strong>f is the rotting <strong>of</strong> seeds and young<br />
seedlings at soil level (Hawksworth et al. 1983) and is<br />
in most cases caused by seed-borne fungi (Hong 1981a,<br />
Lee and Manap 1983, Pongpanich 1988, Elouard l991,<br />
Elouard and Philip 1994). Collar rot, root rot and wilting<br />
(loss <strong>of</strong> turgidity and collapse <strong>of</strong> leaves (Hawksworth et<br />
al. 1983)) are mainly caused by Fusarium species<br />
(Foxworthy 1922, Thompson and Johnston 1953, Hong<br />
1976, Lee and Manap 1983, Elouard, l991, Elouard and<br />
Philip 1994).<br />
A canker is a plant disease in which there is sharplylimited<br />
necrosis <strong>of</strong> the cortical tissue (Hawksworth et<br />
al. 1983). Though most <strong>of</strong> the time stem cankers are not<br />
lethal, they still can be harmful decreasing the strength<br />
<strong>of</strong> the stem and causing it to fracture. Root and collar<br />
cankers can affect the vascular system <strong>of</strong> the plant and<br />
eventually result in plant death by wilting (Spaulding