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(1996). Genotypic variability in seedborne infection of field pea by Mycosphaerella pinodes and its relation to foliar disease severity. Canadian Journal of Plant Pathology: Vol. 18, No. 4, pp. 370-374.

Oospores of Peronospora ducometi, the causal agent of downy mildew of buckwheat (Fagopyrum esculentum), were found in the calyx remnant attached to the seed, on the inside of the seedcoat and in the spermoderm layer between the seedcoat and the endosperm. This constitutes a first report documenting the location of oospores in buckwheat seed. Systemic infection of seedlings occurred from oospore-infested seed. Conidial germination was greater at 14°C than 25°C. Systemic infection also occurred as the result of conidial infection of leaves. It is proposed that primary infection of buckwheat occurs by the germination of seed-borne oospores resulting in systemic invasion of the seedling by the germtubes, and followed by conidial formation on the cotyledons. Secondary infection occurs initially from conidia produced on the cotyledons as a result of the systemic infection from seed and subsequently as the result of repeated infections by conidia produced on leaf lesions as the disease progresses up the plant.

Field studies were conducted over 5 yr to determine the effect of seeding date on agronomic characteristics and disease reaction of buckwheat (Fagopyrum esculentum Moench). Two large-seeded, mid-season buckwheat cultivars, Manor and a semi-dwarf line, G410 or G474, and a small-seeded early-maturing cultivar, CM 169, were grown at Morden and Portage la Prairie during the period 1983–1985 at early, mid- and late June or early July seeding dates. In 1986 and 1987, Manor was grown at three seeding dates, with and without a fungicide treatment to control downy mildew (Peronospora ducometi Siemaszko and Jankowska). In the 1983–1985 experiments, seed yield generally declined with delay in seeding. The smallest decline occurred in the early-maturing cultivar CM 169. From first to last seeding, yield decreases were 38, 44 and 18% for Manor, the semi-dwarf lines and CM 169, respectively. In 1985, downy mildew infection increased linearly to a small degree with delay in seeding and was negatively correlated with seed yield. However, it was considered a minor factor in the response of yield to seeding date. In 1986 and 1987, mildew infection was minimal. The fungicide treatment had no effect on seed yield. Seed yields decreased with delay in seeding as in the previous tests. It was concluded that seed yield declined markedly with delay in seeding from early to late June, more so in the later-maturing cultivars and the declines were independent of mildew infection.Key words: Buckwheat, Fagopyrum esculentum Moench., seeding date, downy mildew, Peronospora ducometi Siemaszko & Jankowska

Une technique a ete developpee pour determiner rapidement la reaction au blanc (Erysiphe polygoni) des pois (Pisum sativum) cultives aux champs. Des folioles ou des stipules detachees ont ete inoculees avec des conidies, incubees pour trois jours et ensuite evaluees pour leur reaction au blanc. Les resultats obtenus avec cette technique sont en tres bonne correlation avec l'intensite de la maladie sur les plants. Cette technique a ete utilisee pour demontrer qu'un gene recessif, de la variete AC Tamor, est responsable de la resistance au blanc.

Yellowhead is a yellow seeded cultivar of field pea with high yield and high edible fiber content. In national Cooperative Tests, Yellowhead yielded 19–20% higher than the commonly grown cultivars Century and Trapper. Its fiber content, as measured by percent seed hull, was 17% higher than the average fiber content of Century or Trapper.Key words: Field pea, dry pea, cultivar description, edible fiber

Field plots of Century and Trapper, two cultivars of field pea (Pisum sativum L.) commonly grown in Manitoba, were mechanically inoculated with pea seed-borne mosaic virus (PSbMV) when plants were at the 6-, 8- or 13-node stages. Growth stage at time of inoculation did not significantly affect seed yields or levels of virus transmission through seed of either cultivar. Average yields of plots inoculated at all three stages were reduced 8 and 10% in Trapper and Century, respectively. In both cultivars, yield reductions were attributable mainly to reductions in seed weight. Transmission of PSbMV through seed from inoculated plots of Century and Trapper averaged 0.5 and 5.8%, respectively. In both cultivars, cracked seed coats were most prevalent in seeds from plots inoculated at the two youngest stages of growth. The preceding yield loss values are probably lower than those actually attributable to PSbMV infection, since the virus infected a substantial proportion of control plants (presumably as a result of aphid transmission) and did not infect all inoculated plants. Consequently, an equation was derived for estimating the average yield loss of infected plants. According to this equation, PSbMV infection reduced yield by 11% in Trapper and 36% in Century.

The structure of traversianal, a tricyclic diterpenoid fungal metabolite of Cercospora traversiana, has been elucidated through detailed 1H and 13C magnetic resonance studies, including homo- and heteronuclear correlation spectra of the natural product and examination of 13C-labelled material obtained by [1,2-13C2]acetate incorporation experiments. Its stereochemistry was established from a series of nuclear Overhauser effect difference spectra. The tricyclic carbon skeleton of traversianal is that of the fusicoccin/cotylenin and ophiobolane terpenes although the oxygenation pattern closely resembles the latter. Incorporation experiments with [2,2,2-2H3, 1-13C1]acetate revealed that traversianal arises by a sequence that differs substantially from that established for the fusicoccanes but rather resembles that previously shown for the ophiobolanes, in the retention of hydride at C-2, -10, and -14. However, the opposite configuration of the methyl group at C-3 suggests that the route to traversianal involves a terminal trans-geranylgeranyl unit instead of the cis unit implicated in ophiobolin generation.

Pea seed-borne mosaic virus (PSbMV) was first identified in Canadian field pea (Pisum sativum L.) breeding lines in 1974. Since then, an extensive program has been underway to eradicate this virus from the breeding lines. At the Morden Research Station, nearly 2000 breeding lines were evaluated. The virus was assayed by infectivity tests using the local lesion host Chenopodium amaranticolor, and by a gel immunodiffusion test. PSbMV was detected in 1361 lines. The level of infection within lines varied from 1 to 3%. Due to the restricted extent of the virus in the breeding lines, it was possible to continue the breeding program without a serious loss in germplasm.

The structure of a diterpene aldehyde isolated from a fungus provisionally identified as Cercospora traversiana Saccardo was elucidated as (1) mainly by extensive 1H and 13C n.m.r. studies and confirmed by the labelling patterns of the substance enriched with [1,2-13C2]acetate.