Branches of field-grown peach cultivars were mechanically wounded and degree of formation of wound tissues or intensity of suberin sampled for histological study after 0, 3, 7, 10, 14, and 17 days. Cell counts autofluorescence. These ranks were compared to cultivar disease and tissue thickness measurements were used to determine the extent of susceptibility ranks, based on field performance history, using Spearman's formation of ligno-suberized boundary tissue and suberized wound rank correlation test. There were no consistent relationships between periderm. Suberin autofluorescence intensity also was measured with a relative susceptibility to disease and phellem cell numbers or suberized microscope equipped with a photometer/fluorometer. The experiments tissue thickness. However, the rate of suberin accumulation during May were

Can. Ent. 119: 195-203 (1987) Principal components analysis was used to assess niche partitioning between four aphid predators on the basis of oviposition strategies. The study was conducted by sampling abundance and position of the eggs of these predators in corn monocultures in two locations of southern Quebec. The results indicated that the chrysopid Chrysopa occulata Say laid its eggs on corn leaves usually without aphid colonies, and late in the season. All other predators reacted to aphid concentrations. The syrphid Sphaerophoria philanthus (Mg.) oviposited close to the ground, early in the season, and among colonies of the aphid Rhopalosiphumpadi (L.). The two coccinellids laid their eggs during July and August with a maximum during tasseling for Coleomegilla maculata lengi (Timberlake) and after pollination for Hippodamia tredecimpunctata tibialis Say. Of these two species, the latter one selected sites at higher levels on the plant, and was more abundant at the edges of the field. It is suggested that the observed niche partitioning cannot be the result of interspecific competition in variable environments such as maize monocultures.L'analyse en composantes p~c i p a l e s est utiliste afin de mettre en Bvidence la kpartition de niches de quatre aphidiphages en utilisant leur stratCgie de ponte. L'Ctude s'est kalisk sur deux monocultures de mdis du sud du QuCbec ou Ctaient BvaluCes l'abondance et la position des pontes des pkdateurs. Les ksultats indiquent que le chrysope Chrysopa occulata Say pond sur des feuilles sans colonies de pucerons, tard en saison.Tous les autres prkdateurs dagissent positivement A la pksence des pucerons. Le syrphe Sphaerophoria philanthus (Mg.) pond sur des feuilles pds du sol, tat en saison et parmi les colonies importantes du puceron Rhopalosiphum padi (L.). Les deux coccinelles pondent en juillet et milt, avec un maximum A la sortie de la panicule pour Coleomegilla maculata lengi (Timberlake) et peu aprks l'anthbe pour Hippodamia tredecimpunctata tibialis Say. De ces deux es@ces, cette demi6re choisit des sites plus haut sur le plant, et est plus abondante en bordure des parcelles. Finalement, il est suggCk que la kpartition de niche observk ne peut etre le ksultat d'une comp6tition interseifique dans un environnement aussi instable que la monoculture de mais.

The effects of the application of 0, 60, and 120 kg N ha-1 and of 0, 25, 50, and 150 kg K ha-1 on final disease severity, standardized area under disease progress curve, and grain yield were investigated at Cedara, South Africa, on a maize (Zea mays) hybrid susceptible to gray leaf spot (GLS), caused by Cercospora zeae-maydis. The trial was a randomized 3 × 4 factor design, split for fungicide treatments, and replicated three times. With increased N and K levels, final percent leaf blighting and the standardized area under disease progress curve were higher. In fungicide-treated maize, grain yields increased with increasing levels of N and K, as expected. In non-fungicide-treated maize, grain yield increased significantly with increased levels of N, despite increased disease severity. This was in contrast to small increases in grain yields from non-fungicide-treated maize with increased K levels, which were not significant. This was probably because grain yield response, which should have occurred at higher K applications, was reduced by increased disease severity. The effect of N, P, and K on GLS wasinvestigated at Ahrens. Maize was grown in a 4 × 4 × 4 N-P-K factorial, in a randomized complete block design. Fertilizer was applied at 0, 60, 120, and 180 kg N ha-1, 0, 30, 60, and 120 kg P ha-1, and 0, 50, 100, and 150 kg K ha-1. No fungicides were applied. A single disease assessment at physiological maturity showed that final disease severity increased with increasing levels of N, P, and K. These results have implications for small-scale farmers who are encouraged to fertilize for increased grain yields but may not have the resources to apply fungicide sprays to control fungal diseases.

No abstract

Phytotoxins from Leucostoma persoonii and Leucostoma cincta were isolated by sequential ultrafiltration of cell-free culture filtrates through a series of exclusion membranes. Phytotoxic activity, characterized by stem necrosis and leaf wilt, chlorosis, and necrosis, was evident when a cold acetone precipitate from the < 1000-Da fraction was tested in a peach shoot tip bioassay. Analytical polyacrylamide isoelectrofocusing of the < 1000-Da fraction in the pH range 3.5–6.0 identified two peptide bands at pH 4.0 and 6.0. Preparative granulated bed isoelectric focusing in the same pH range yielded two fractions with phytotoxic activity against peach shoots. Preliminary characterization studies indicate that the two fractions with toxin activity contain small polypeptides. Key words: Cytospora spp., cytospora canker, Prunus persica, peach.