Diseases of Ryegrass (1)

Halo blight

Causal organism: Pseudomonas syringae pv.atropurpurea (Reddy and Godkin 1923) Young, Dye and Wilkie 1978, bacteria

Bacterial disease which causes leaf blight occurring mainly in the warm regions. The disease produces at first water-soaked spots in leaves and then the lesions become brown and oval to spindle-shape or irregular and surrounded with yellow halos. The lesion expand to long sripe when the disease advances and finally it might invade the head spikes and seeds. The causal organism is same with that of fescue halo blight. symptom literature Sakai(1981), Matsumoto and Sugiyama(1983), Isawa(1983d), Sato et al.(1983), (1986), (1988) Mino et al.(1987)

Anthracnose

Causal organism: Colletotrichum graminicola (Cesati) G.W.Wilson, Imperfect fungi

Spot-causing fungal disease which causes summer depression of grasslands in the warm regions. The lesions are at first water-soaked small spots and then expands to ash white to drab, long oval to spindle shaped ones of 5-10mm in length and 2-4mm in width. The fungal tissues, setae, are produced in the center of the old lesion and looks black moldy. Orange masses of spores are formed on the lesion under wet conditions and they disperse by wind and rain. The disease often occurs from the end of the rainy season to summer. The species of the pathogen is same with those of sorghum, orchardgrass and bahiagrass, but the pathogenicity is considered to be differentiated. symptom

Ascochyta leaf spot

Causal organism: Ascochyta desmazieri Cavara, Imperfect fungi
(Undescribed disease in Japan)

Spot-causing fungal disease producing characteristic lesions. The lesions are at first brown spot at the rainy season, but they expands gradually and become indistinct zonate circle ones. When they occur a lot in the leaf, etc., they fuse mutually and become cloud-like pattern. When the pathogen invades the base of leaves and sheaths, the entire leaf withers and the damage grows. When the lesion becomes old, black small grains (pycnidia) are produced on the surface. symptom

Blast

Causal organism: Magnaporthe grisea (T.T.Hebert) Yaegashi et Udagawa, Ascomycotina

Spot-causing fungal disease occurring mainly in the warm regions. The lesions are ash white with brown border and short spindle-shaped. The lesion size is about 2-5mm, but soon they fuse mutually and cause leaf blight of the entire leaf. Causal organism is homogeneous with rice blast fungus, but its pathogenicity is partially differentiated. A resistant variety, "Sachiaoba" has been bred and utilized in Japan. symptom causal organism (conidia) literature Arase et al.(1983), (1984), (1986), Kusaba et al.(1999), (2006), Kato et al.(2000), Fujiwara et al.(2003), Sumida et al.(2003), Mizuno et al.(2003), Miura et al.(2005), Takahashi et al.(2009), (2010), (2014), Tsukiboshi (2011), (2019), Murata et al.(2014), Suzuki et al.(2015b)

Crown rust

Causal organism: Puccinia coronata Corda var.coronata, Basidiomycotina

It is one of the most important disease of the ryegrass and the damage is large. The disease occurs comparatively a lot in the warm regions south of Kanto. The lesions are at first yellow swelling and then become oval ones of 1-2mm in length and 0.5mm in width. The epidermis tears and yellow to orange urediniospores appears from the inside. When occurring severely, the entire leaf looks yellow powdery and then withers. Blackish brown telia are produced later, but the pathogen is considered to overwinter and oversummer by urediniospores. The species of the causal organism is same with that of fescue crown rust, but the pathogenicity is differentiated. The existence of races is not known in Japan. symptom causal organism (urediniospore) causal organism (teleutospores) literature Miyagawa and Inoue(1996a), Sugiyama et al.(1982), Isawa(1982a), Fujimori et al.(2004)

Endophyte

Causal organism: Epichloë festucae Leuchtm., Schardl & M.R. Siegel, Epichloë occultans (C.D. Moon, B. Scott & M.J. Chr.) Schardl, Ascomycotina

Since the causal organism is an endophytic fungus in gramineous plants, the infected plants are usually symptomless and undistinguishable from the non-infected ones. Hyphae of the fungus are colorless, rarely branched and elongate intercellularly in leaves and leaf sheaths. They intrude seeds and intercellular hyphae elongate among starch cells, becoming inocula for the next generation. It has been discovered in the ecotypes of ryegrass since 1990s in Japan. The infected plants acquire tolerance to insects, diseases and environmental stresses. Hyphae in a leaf (stained) literature on E. festucae (=Neotyphodium lolii) (Koga et al. 1993a, 1993b, 1997, Kanda et al. 1994, Sato et al. 1995, Fukami et al. 1997, Yoshimatsu et al. 1998, Maejima et al. 2000, Miyazaki et al. 2001, Saiga et al. 2002, 2003, Sugawara et al. 2004, 2011, Shiba and Sugawara 2009, 2010, Tanaka et al. 2008, 2011, 2013, Takemoto et al. 2011, Kayano et al. 2013, 2018) on E. occultans (=N. occultans) (Sugawara et al. 2006, 2009, 2011, Shiba et al. 2011) on inoculated E. uncinata (=N. uncinatum) (Kasai et al. 2004, 2005, 2006, Shiba et al. 2007, Sugawara 2011, Matsukura et al. 2012)

Ergot

Causal organism: Claviceps purpurea (Fries) Tulasne, Ascomycotina

The ergots (sclerotia) are formed in the head and have toxicity to livestocks. The disease at first produces light-brown honey dew in the head just after flowering, and many spores included in the honey dew disperse and transmit by wind and rain. The black purple, cattle-horn like, ergots covered with white sphacelia of 2-18mm in length and 0.6-2.4mm in width are produced in the infected flowers replacing the seeds. The ergots drop to the ground, germinate in next year, and disperse ascospores as primary inocula. The host range is wide and the pathogen can also infect orchardgrass, timothy, and fescue, etc. The alkaloids in the ergot are strongly toxic such as ergovaline and cause abortion and so on of livestocks. symptom (honey dew) symptom (ergot) causal organism (conidia)

Foot rot

Causal organism: Rhizoctonia cerealis v.d. Hoeven in Boereme et Verhoeven (AG-D), Basidiomycotina

Fungal disease which causes plant withering. The disease occurs from winter to spring. The infected plant shows the symptom like water shortage and looks red in the field. The lesions are especially distinct on the stalk, irregular shaped like rice sheath blight and covered with white hyphae. Brown sclerotia of 1mm in size are produced on the lesion. When the disease advances, the hyphae invades also in the inside of the stalk and cause foot rot from the lower leaf. It occurs severely under wet conditions. The causal organism is one of the binucleate Rhizoctonia and considered to be same with barley foot rot fungi. symptom causal organism (hyphae, nuclei stained) literature Inoue et al.(1994)

Fusarium blight

Causal organism: Gibberella zeae (Schweinitz) Petch, Ascomycotina

Fungal disease that occurs in the heads. The head spikes become red to brown and pink-colored molds grow in the joint of glume. It also occurs in the leaf and produces oval zonate lesions of a rice grain size. The causal organism exists continuously also in the soil and this becomes primary inocula. Besides, the disease occurs in a lot of cereals such as rice and wheat. symptom

Leaf blight

Causal organism: Drechslera noblea McKenzie et Matthews, Imperfect fungi

Spot-causing fungal disease occurring from spring to summer. The lesions are often formed from the leaf rim and become brown and half oval with indistinct border. When occurring after heading, the base of the leaf is invaded and the entire leaf withers and falls. The species of the causal organism is same with that of fescue leaf blight. symptom

Leaf spot

Causal organism: Pyrenophora lolii Dovaston (=Drechslera siccans (Drechsler) Shoemaker), Ascomycotina

Spot-causing fungal disease occurring all over the country. The lesions are blackish brown with yellow surroundings, oval to circle, 5-15mm in length and 3-7mm in width. But The lesions often fuse mutually and become irregular shape. So, it is difficult to distinguish the lesion and the resistance breeding is behind the times in results. The causal organism is one of Helminthosporium fungi, but the species is different from those of leaf spot of orchardgrass and fescues, etc. symptom literature Isawa(1983a)

Net blotch

Causal organism: Drechslera andersenii Lam (=D. dictyoides Drechsler f.sp. perennis (Braverman et Graham) Shoem.), Imperfect fungi

Spot-causing fungal disease occurring a lot in the northern area. At first, the lesions are net blotch of 1-2cm in length and 1-5mm in width. Later they become brown to black stripe of 1-3cm in length and 5-8mm in width. The disease often causes leaf blight when the lesions enlarge. It is often treated collectively with other disease as "spot disease" though the lesion is distinguished comparatively easily. The species of the causal organism is different from that of fescue net blotch, and the pathogenicity is differentiated. symptom causal organism (conidia) literature Isawa(1983a)

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