Diseases of Red clover (2)


Root rot
Causal organism: Rhizoctonia solani Kuhn, Basidiomycota
Fungal disease occurring in roots, causing patch symptom in grasslands. In Japan, the disease was first reported in the Hokuriku region and later in Hokkaido and Kyushu Districts. Firstly root rot occurs in the root near the crown and gradually progress to the lower root. At last, whole tap roots are infected and become blackish brown on the surface, causing plant death. Especially red clover is severely damaged by the disease, if the harvest by cutting the plants is frequent. Damages by soil insects often induce the disease. In Hokkaido, Fusarium solani is also known as the pathogen of the same symptom.

Rust
Causal organism: Uromyces fallens (Desmazieres) Kern, Basidiomycotina
Typical rust disease. The uredinia are reddish brown, round, small and are scattered on the whole leaf. They become oval, continuous lesions of 2-3 mm in length in the stalk. The causal organism can infect subterranean clover and crimson clover.

Sclerotinia crown and stem rot
Causal organism: Sclerotinia trifoliorum Eriksson, Ascomycotina
Important fungal disease which causes plant death occurring in cool and wet regions. The small spots appears at first and then the leaf and stalk turn to yellow and wither. The disease progresses gradually under the snowfall. The stem, leaf and root rot to ash white according to increase of the temperature after snow-melting in the spring of next year. White and fluffy hyphae are produced on the surface of the withering plant and large black sclerotia of irregular types and about 8-10mm in size are produced before long. They germinate in autumn and produce light brown stroma of 3-8 mm in diameter. The ascospores spread from the stroma and the infection happens again. The host range of the causal organism is wide including alfalfa and vetches. DNA markers for the QTL controlling resistance to the disease have been developed.


Sooty blotch
Causal organism: Cymadothea trifolii (Persoon) Wolf, Ascomycotina
Leaf blight causing fungal disease occurring in the cool region. Black sooty molds are produced in the back side of the leaf. These are like black, irregular shaped, small lesions bristly in the leaf. The infected leaf keeps green at first but gradually turns to yellow. It occurs in other clovers.


Stemphylium leaf blight
Causal organism: Pleospora herbarum (Persoon) Rabenhorst, Ascomycotina
Spot-causing fungal disease occurring in leaf. The lesions are at first water-soaked small spots and then become blackish brown lesion devided by leaf veins. The lesion often extends from the leaf rim, fuse with the adjacent lesion, and becomes large. The leaf shrinks and withers in results. The diseased leaf defoliates at the early stage. The species of the causal organism is same with leaf spot fungi of alfalfa, but the pathogenicity is differentiated.


Stemphylium leaf spot
Causal organism: Stemphylium sarcinaeforme (Cavara) Wiltshire, Imperfect fungi
Fungal disease which produces spots in the leaf. It occurs mainly in the rainy season and autumn. The lesions are at first small and drab to brown ones. Then they expand gradually and become brown to dark brown lesions of about 5-10mm in diameter with characteristic zonations. The lesions are often darker and with clearer zonation in red clover than in white clover. The species of the causal organisms of Stemphylium leaf spot are different in red clover and white clover. The white clover fungi does not invade red clover.


Summer black stem and leaf spot
Causal organism: Cercospora zebrina Passerini, Imperfect fungi
Spot-causing fungal disease mainly occurring in the leaf and stalk. The lesions are grayish brown devided by leaf veins, fuse mutually and cause leaf blight. They become purple brown stripes when occurring in the stalk and the damage enlarges. The causal organism can infect other kinds of clovers, but the pathogenicity is considered to be differentiated.


Summer blight
Causal organism: Rhizoctonia solani Kühn AG-1 IA, IB, Basidiomycotina
Important fungal disease which occurs all over the country and becomes a cause of summer depression of grassland. Ash green and water-soaked lesions appears at first and the whole infected plant soften like being boiled before long. Then, the infected stalks and leaves fall one upon another and rot when the disease progresses and hyphae like spider' web appear covering all the infected part. Later light brown to brown sclerotia of about 5 mm in diameter are produced on the infected part. At this point, the infected grass withers forming patches and the grassland gradually becomes bare land. The causal organism is polyxeny and can infect most grasses and legumes of herbage. AG-1 IA and IB of R.solani cause the disease.


Typhula snow blight
Causal organism: Typhula ishikariensis Imai, Basidiomycotina
Important fungal disease which causes plant death and occurs mainly in Hokkaido Dist. The symptom appears just after snow-melting. Stems and leaves become water-soaked and softened like boiled. When they are dry, they discolor to ash brown. Dark brown to black, globular to irregular sclerotia of 0.5-1mm in diameter are produced on them. The biotype A is reported to infect legumes.


Violet root rot
Causal organism: Helicobasidium mompa Tanaka, Basidiomycota
Fungal disease causing plant death. The disease first occurred in Kyushu District, the south region of Japan. In early summer, young leaf begins to wither from leaf tip. And soon, all the leaves come to wither and die in brown. The main root is covered with purple hyphae like felts and the inside of the root rots. Purplish red sclerotia of about 1mm in diameter are occasionally produced on the surface of the infected root. The causal organism is very polyxeny and infect not only many legume crops but also fruit trees. @

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