Bipolaris victoriae (Victoria blight of oats).

A disease almost unknown prior to 1944 (Romanko, 1957), Bipolaris victoriae is a potentially destructive disease of oats (it reduced the Iowa oat crop by 32% in 1947) (Anon, 1965) that currently has a limited host range and geographical spread. It has been reported from several continents and associated with several crops, however its status as a pathogen on crops could be questioned in all cases with the exception of oats, timothy grass and switch grass. It is seedborne and thus any trade in seed both for cultivation or for livestock feed is a potential means of spread. The virulence of the fungus is due to the production of a peptide often called a host-specific toxin 'victorin'. The disease has generally been controlled through the use of genetically resistant lines but the resistance gene which confers resistance to victorin actually causes plants to become susceptible to crown rust, caused by Puccinia coronata (Lorang et al., 2007).

Bipolaris victoriae (Victoria blight of oats).

A disease almost unknown prior to 1944 (Romanko, 1957), Bipolaris victoriae is a potentially destructive disease of oats (it reduced the Iowa oat crop by 32% in 1947) (Anon, 1965) that currently has a limited host range and geographical spread. It has been reported from several continents and associated with several crops, however its status as a pathogen on crops could be questioned in all cases with the exception of oats, timothy grass and switch grass. It is seedborne and thus any trade in seed both for cultivation or for livestock feed is a potential means of spread. The virulence of the fungus is due to the production of a peptide often called a host-specific toxin 'victorin'. The disease has generally been controlled through the use of genetically resistant lines but the resistance gene which confers resistance to victorin actually causes plants to become susceptible to crown rust, caused by Puccinia coronata (Lorang et al., 2007).

Molecular interactions of victorin and oats

We have been investigating a disease called victoria blight of oats, which is caused by the fungus Cochliobolus victoriae. The fungus is pathogenic because of its ability to produce the host-selective toxin, victorin. Victorin is composed of a group of structurally related cyclized pentapeptides. The most abundant component of victorin in culture filtrates, victorin C, has a molecular weight of 814 and is composed of glyoxylic acid, 5,5-dichloroleucine, threo-β-hydroxylysine, erythro-β-hydroxyleucine, α-amino-β-chloroacrylic acid, and 2-alanyl-3,5-dihydroxy-⌂2-cyclopentenone-1. Sensitivity to victorin, and thus, susceptibility to the fungus, is controlled by a dominant allele at the Vb locus. Furthermore, the Vb gene is either closely linked or identical to the Pc-2 gene, which confers resistance to the crown rust pathogen Puccinia coronata. Thus, it is anticipated that identification of the product of the Vb gene, a putative toxin receptor, will simultaneously identify the product of the Pc-2 rust resistance gene. We have identified two proteins, referred to as victorin binding proteins (VBP), which bind biologically active, radiolabelled victorin in vivo. One protein, a 100-kDa VBP, binds victorin in vivo only in toxin-sensitive, susceptible genotypes. The other VBP, a 15-kDa protein, binds victorin in vivo in both susceptible and resistant genotypes. We have isolated and characterized the 100-kDa VBP and have recently identified, in vitro, a 15-kDa VBP. Both of these proteins are components of the multienzyme complex, glycine decarboxylase. Current investigations center on the role of this enzyme complex in toxin sensitivity. Key words: victorin, oats, toxin, glycine decarboxylase, resistance, susceptibility.

Cochliobolus victoriae. [Descriptions of Fungi and Bacteria].

A description is provided for Cochliobolus victoriae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Oats (Avena) and other Gramineae (57, 2062, 4012). DISEASE: Victoria blight of oats. GEOGRAPHICAL DISTRIBUTION: Australia, Brazil, Canada, Netherlands, Switzerland, UK (Scotland) and USA (CMI Map 267, ed. 2, 1968). Records not yet mapped: India, Irish Republic, Malaysia, Zambia and Zimbabwe. TRANSMISSION: Presumably air dispersed (no detailed studies apparently reported); the fungus also occurs on seed.

Pyrenophora avenae. [Descriptions of Fungi and Bacteria].

A description is provided for Pyrenophora avenae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Oats (Avena spp.). DISEASE: Leaf stripe, blotch or spot and seedling blight of oats. Seed-borne infection produces a range of seedling symptoms from pre-emergence death to slight spotting or streaking of coleoptiles. Mycelial infection of emerging leaves causes distortion and spotting. Inoculum from primary leaves causes secondary spread to upper leaves, producing light reddish-brown irregular streaks or blotches. Spikelet drop (42, 543) and stem-break (36, 641) may also occur when the disease is severe. GEOGRAPHICAL DISTRIBUTION: Widespread; occurs throughout most oat-growing areas. CMI Map 105, ed. 2, 1966, and in addition in Queensland, Egypt, Angola and Colombia. TRANSMISSION: Primary infection appears to be entirely by seed-borne inoculum, either as conidia or more particularly as mycelium in the outer layers of the seed. Secondary infection is by air-borne conidia. Soil-borne inoculum appears to be unimportant.

Pseudomonas coronafaciens. [Descriptions of Fungi and Bacteria].

A description is provided for Pseudomonas coronafaciens. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Avena sativa and very rarely Secale cereale. Also infects the following when spray inoculated without wounding: Hordeum vulgare, Triticum aestivum (Elliott, 1920), Bromus catharticus, Festuca elatior, Hordeum stenostachys, H. bulbosum, Lolium multiflorum and L. perenne (Tessi, 1949). Briza maxima, Bromus hordaceus and B. rubens are reported as slightly susceptible when artificially inoculated (Tessi, 1953). DISEASE: Halo blight of oats. Lesions usually appear on leaves, but may occur on sheaths or glumes occasionally. They are oval and light green at first and centred around the stomata, which are the points of infection. The centres become slightly depressed, one to several mm diam., greyish and dry, with a pale green to yellowish halo-like margin that often is 1 cm wide. The tissues are not water-soaked and exudate is not usualy produced. GEOGRAPHICAL DISTRIBUTION: Probably occurs in most oat-growing areas (CMI Map 356, ed. 2, 1968). An additional record not included is Argentina (Tessi, 1949). TRANSMISSION: Within the field transmission by wind and rain occurs, with infection usually taking place through stomata or wounds. It is seed borne (Elliott, 1920). Dickson (36: 259) states that insects are important in distribution, but gives no reference to support this.