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Plantwise Technical Factsheet

Philippine downy mildew (Peronosclerospora philippinensis)

Host plants / species affected
Avena sativa (oats)
Saccharum officinarum (sugarcane)
Saccharum spontaneum (wild sugarcane)
Sorghum bicolor (sorghum)
Sorghum halepense (Johnson grass)
Zea mays (maize)
Zea mays subsp. mexicana (teosinte)
List of symptoms/signs
Inflorescence  -  twisting and distortion
Leaves  -  abnormal colours
Leaves  -  fungal growth
Whole plant  -  dwarfing
Symptoms
Systemic symptoms may be observed in the first true leaf stage as chlorotic stripes or a pale yellow colour throughout the entire leaf. Local symptoms (long, chlorotic streaks with a downy growth of conidia and conidiophores) may be present from the two-leaf stage until the appearance of tassels and silks. Sporulation of the fungus was observed on both upper and lower leaf surfaces, but was more abundant on the lower.

Tassels may be malformed and produce less pollen, and ears may be aborted. Early-infected plants become stunted and many die.

There are no external symptoms on seeds. The fungus becomes established in the pericarp layer in the form of mycelium. The fungus is also present in the embryo and endosperm. There are no reports on the effect of P. philippinensis on seed quality.

There are no external symptoms on stems but early-infected plants may be stunted. The fungus invades the stem, moving upward and downward, becoming established in the shoot apex.

The fungus invades the shoot apex and may be found there throughout the life of the infected plant. Invasion of the shoot apex produced chlorotic areas which were at first confined to the base of the lower leaf. These chlorotic areas later increased in size in succeeding leaves. The youngest leaf emerging from the whorl became completely chlorotic (Exconde, 1976).
Prevention and control
Cultural Control and Sanitary Methods

High levels of nitrogen increase the susceptibility of susceptible cultivars, but have less effect on the resistance of resistant cultivars (Yamada and Aday, 1977).

Host-Plant Resistance

Resistant varieties of maize have been developed (Exconde, 1976; Raymundo and Exconde, 1976; Schmitt and Freytag, 1977). Studies of the inheritance of resistance indicate that resistance is under polygenic control and is governed mainly by additive gene effects (Leon et al., 1993; Carpuno and Carpena, 1982). Quantitative resistance was expressed in a study in which resistant inbred lines showed extended duration of local infection, delayed onset of systemic infection, and slow rate of downy mildew development with the area under the disease progress curve remaining low. Patterns of systemic symptoms varied among lines. These resistance components were correlated with one another (Ebron and Raymundo, 1987).

Chemical Control

Fentin hydroxide and maneb provide effective control (Exconde, 1975; Exconde, 1976; Raymundo and Exconde, 1976). Metalaxyl was also effective, when applied as a foliar spray (Cordero and Tangonan, 1988).
Impact
Philippine downy mildew is confined to parts of Asia. It is a major problem in the Philippines where losses in maize were estimated at 8% nationally in 1974-75 (Exconde, 1976). One yield loss study showed losses of 100% (Exconde and Raymundo, 1974). The disease is generally less severe in India, but losses of up to 60% have been reported (Bonde, 1982; Payak, 1975).

An experimental plot study with sugarcane Clone Phil.6723 showed yield losses of 36% associated with P. philippinensis (Husmillo, 1982).
Related treatment support
 
External factsheets
CIMMYT Plant Pest and Disease Factsheets, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) (International Maize and Wheat Improvement Center), English language
PlantVillage disease guide, PlantVillage, English language
East West Seed Crop Disease Factsheets, East West Seed, 2013, English language
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