Pyrenopeziza Brassicae Research Articles

Disease cycle in New Zealand of light leaf spot of brassicas, induced byPyrenopeziza brassicae

Abstract This paper discusses the role of a pothecia of Pyrenopeziza brassicae Sutton & Rawlinson in the disease cycle of light leaf spot of brassicas. Apothecia survived for up to 27 weeks on the soil surface under a weed canopy but for less than 4 weeks when buried in the soil. Apothecia stored for up to 50 weeks on dry cauliflower residues in the laboratory discharged ascospores when wetted. Ascospores discharged on to glass slides remained viable for up to 8 weeks at about 20°C and 70% RH. Less than 1% of conidia incorporated into unsterilised volcanic loam remained viable after 10 days as determined by direct counts, but bioassay showed that some conidia remained viable for up to 10 weeks. Seeds from severely diseased cauliflower seedheads contained the pathogen but tests indicated that the disease was not seed-transmitted. P. brassicae was not found on any of the common cruciferous weeds present in vegetable brassica crops in the Pukekohe district. Only summer-grown plants of oilseed rape were susce...

Fungicide effects on light leaf spot, canker, crop growth and yield of winter oil-seed rape

SummaryField experiments with rape ovs Primor, Jet Neuf and Norli during 1979–83 tested the effects of benomyl, prochloraz, imazalil, thiabendazole, metalaxyl or triadimefon sprays applied at different times on disease, crop growth and yield. The principal disease in all experiments was light leaf spot (Pyrenopeziza brassicae).A single spray in autumn of benomyl or prochloraz at 0·5 kg a.i./ha consistently decreased incidence and severity of light leaf spot and sometimes decreased stem canker (Leptosphaeria macvlans). Under severe disease conditions in cv. Primor an autumn spray of fungicide contributed more to disease control than a spray in spring; a decrease in light leaf spot incidence was detectable up to 8 months after application. The autumn spray maintained plant population density, increased leaf area index, dry matter, crop growth rate, earliness of flowering, and yield by up to 0·69 t/ha; an autumn + spring spray increased yield by up to 0–83 t/ha. Effects on crop growth and yield were due to disease control not direct chemical stimulation of growth. Measurements of crop growth and population per unit area revealed the effects of fungicides more clearly than traditional disease assessments based solely on randomly selected plants.Triadimefon sprayed on rape stubble at high dose rate (1 kg a.i./ha) decreased incidence and severity of light leaf spot throughout the growing season of a subsequent rape crop, with beneficial effects on plant population density, growth, flowering and yield.Electrostatically charged rotary atomizer and conventional hydraulic spray applications of fungicide were equally effective in disease control. A reduction to one quarter in dose rate of prochloraz and 100–fold reduction in amount of water carrier (125 g a.i. in 4·3 1/ha) when applied electrostatically in autumn or autumn + spring had similar effects on disease, crop growth and yield to those obtained with a conventional sprayer delivering 500 g a.i. prochloraz in 410 1/ha.Fungicides, spray timing and methods of application are discussed in relation to the epidemiology of light leaf spot and canker and the economics of disease control.

Some effects of climate and plant growth on the development of light leaf spot in cauliflowers

Abstract In laboratory and climate chamber studies with Pyrenopeziza brassicae Sutton and Rawlinson, most conidia germinated at l6°C, mycelial growth was most rapid (about 1 mmjday) over the range 15–20°C, and symptom development on cauliflower leaves was greatest at 18°C. High relative humidity (98–100%) was required for conidial germination but symptom development was inversely proportional to atmospheric saturation. Results of field studies are discussed in the light of these findings. Conidia rarely germinated on newly emerged leaves, but the proportion germinating increased as the leaves expanded and was optimum on fully expanded leaves. Symptoms did not usually appear on leaves during the early stages of leaf expansion.

Heterothallism in Pyrenopeziza brassicae, cause of light leaf spot of brassicas

The control of sexual reproduction in Pyrenopeziza brassicae was investigated by pairing single-spore isolates in conidial suspensions and culturing these on nutrient agar. The results demonstrated that P. brassicae is heterothallic, with two mating types. Experiments in which ascospore progeny of fertile pairings were crossed with the parental isolates supported this, and suggested that the mating types may be determined by two alleles at a single locus, as in many other ascomycetes.

Control of light leaf spot of brassicas (Pyrenopeziza brassicaeSutton & Rawlinson) with fungicides

Abstract A poisoned-media technique was used to test and rank the efficiency of 23 fungicides in controlling growth of Pyrenopeziza brassicae. Tests were done separately using conidia, ascospores, and mycelium. Several protectant fungicides strongly inhibited germination of conidia and ascospores. Many systemic fungicides did not prevent spore germination, yet prevented mycelial growth. In field trials with seven selected fungicides, benomyl + oil, prochloraz, and fenapanil gave best control of the disease on cauliflowers. Although there were no significant differences in crop yield between sprayed and unsprayed plots, the presence of scarred petioles on unsprayed plants depressed their market value. In a further trial, benomyl + oil and prochloraz controlled the disease at the three rates tested. In a timing of application trial, the first three benomyl applications were the most effective, but additional applications further reduced the number of plants with scarred petioles. In both the rate and timing...

Resistance of cultivated brassicas to Pyrenopeziza brassicae

A survey of resistance and susceptibility of cultivars of commercial brassicas to three isolates of Pyrenopeziza brassicae, the cause of light leaf spot disease, showed that all the major forms of cultivated brassicas are potential hosts. A considerable heterogeneity of resistance was found between different brassica varieties and sub-species, between cultivars within these groups, and between individuals of a single cultivar. Differences in virulence were also found between the isolates of P. brassicae in terms of the ability to infect and the rate and extent of subsequent development. In the survey and in additional experiments these differences were not related to the host plant from which the isolates were obtained. Differential interactions between cultivars and isolates were also shown, though they were not sufficiently defined to distinguish clear physiological races of the pathogen.

Studies of the perfect stage of the light leaf spot pathogen of brassicas, Pyrenopeziza brassicae

Studies of the perfect stage of the light leaf spot pathogen of brassicas, Pyrenopeziza brassicae

Studies of survival and longevity of the light leaf spot pathogen of brassicas, Pyrenopeziza brassicae

Experimental studies showed that conidia of Pyrenopeziza brassicae, cause of light leaf spot of brassicas, can remain infective for at least 10 months, and can germinate at 19 months after storage in a dried state. The pathogen was isolated from viable seed up to 2 months after harvest, but survival for longer periods on seed and natural infection of plants grown from contaminated seed was not demonstrated. Artificial inoculations indicated that susceptibility amongst species closely related to the cultivated brassicas is limited to certain species within the genus Brassica. The significance of these findings to an understanding of the epidemiology of light leaf spot is discussed.

First report of the natural occurrence ofPyrenopeziza brassicaeSutton et Rawlinson, the apothecial state ofCylindrosporium concentricumGreville, in brassica crops in New Zealand

Abstract In May 1978 a severe epidemic oflight leaf spot occurred in crops of cauliflowers (Brassica oleracea L. var. botrytis L.), cabbages (B. oleracea L. var. capitata L.), and sprouting broccoli (B. oleracea L. var. italica Plenck) in parts of the Pukekohe district. Conidia produced on lesions associated with the disease were typical of those of Cylindrosporium concentricum Greville, previously reported to be the causal pathogen. Three months later numerous small black apothecia were found on decaying petioles, veins, and occasionally lamina tissue of fallen leaves from these crops. When vegetable brassica seedlings were inoculated with ascospore suspensions obtained from these apothecia typical symptoms oflight leaf spot developed 11-14 days later. The apothecia were identified as those of Pyrenopeziza brassicae Sutton et Rawlinson. This is the first record of the natural occurrence of the teleomorph (perfect state) of the species in New Zealand.

Diseases of winter oil-seed rape: occurrence, effects and control

SUMMARYThe results of observations begun in 1973 and of disease surveys carried out on winter oil-seed rape crops on ten farms in Hertfordshire and Bedfordshire between 1975 and 1978 are reported. The major diseases encountered in the surveys, namely downy mildew (Peronospora parasitica (FT.) Tull.), canker (Leptosphaeria maculans (Desm.) Ces. & de Not.), light leafspot or scorch (Pyrenopeziza brassicae Sutton & Rawlinson) and grey mould (Botrytis cinerea Fr.) are discussed in relation to diseases of rape grown elsewhere and the results of experiments on disease control reported. Symptoms of virus infection and root disease were rare.Early (before stem extension) use of two applications of benomyl (1·2 kg a.i./ha) decreased the incidence and severity of light leaf spot and canker and increased yield by up to 33%. Benomyl plus thiram seed treatment (5 and l·5ga.i./kg) was less effective than a benomyl foliar spray. In field experiments differences in severity of light leaf spot and canker explained a substantial part of variation in yield but downy mildew did notaccount for further variation.

Effect of herbicides on epicuticular wax of winter oilseed rape ( Brassica napus) and infection by Pyrenopeziza brassicae

Foliar sprays of the herbicides dalapon, carbetamide and propyzamide on winter oilseed rape (Brassica napus L. ssp. oleifera) can decrease the amount and alter the form of epicuticular wax on leaves. This effect was most marked with dalapon where it occurred on sprayed leaves and those affected by translocated herbicide. It was evident under controlled environment and field conditions up to at least 3 months after treatment. Decreased wax on leaves was associated with increased wettability which favours spore deposition and encouraged infection by Pyrenopeziza brassicae (Cylindrosporium concentricum). Benomyl gave useful but incomplete control of this fungus on rape when applied in winter and early spring before stem extension. The use of herbicides and fungicides on winter rape is discussed in relation to disease control and yield.

Cylindrosporium concentricum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Cylindrosporium concentricum [Pyrenopeziza brassicae] . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Brassica spp. (cabbage, cauliflower, broccoli, brussel sprouts, oil seed rape, swedes). DISEASE: Light leaf spot of Brassicae . GEOGRAPHICAL DISTRIBUTION: Europe (UK, Ireland, Netherlands, Germany, Denmark, Norway, Portugal, Rumania, Latvia); Asia (Japan, Philippines); Australia (South Australia, Tasmania); New Zealand. (CMI Map 193, ed. 2, 1975). TRANSMISSION: By splash-dispersed air-borne conidia. No seed transmission has been demonstrated.