Species of Colletotrichum, Botryosphaeria, and Phomopsis causing postharvest rots in avocado (Persea americana Miller) fruits are present in the living and dead branches and twigs of avocado trees, ...and in the living pedicels. They dominate the fungal population within the extra-cambial tissues but are less common within the xylem elements. There is no evidence that invasion of these tissues is pathogenic. With the possible exception of C. gloeosporioides they appear to be discontinuously present and are more properly termed phellophytes rather than endophytes. There was a higher incidence of stem-end rots than of body rots in untreated (control) 'Hass' avocados in New Zealand experiments and most of these stem-end rots were associated with B. parva and Phomopsis spp. A high proportion of stem-end infections appeared to be initiated during harvesting. Picking the fruit by snapping the pedicels instead of clipping, as in commercial practice, resulted in an unusually high level of stem-end rots caused by C. acutatum. Frequently sterilising the clippers used to harvest the fruits reduced the incidence of stem-end infections, in particular those caused by B. parva, indicating that contamination of the clippers is an important source of infection. It is suggested that this contamination is probably present as fragments of infected extra-cambial tissue.
A disease complex, with symptoms that include stem cankers and tip die-back, is reported in New Zealand olives (Olea europaea L.). Bacteria from stem cankers of olive were consistently isolated as ...pale lemon-yellow colonies on King's medium B. On the basis of microbiological, molecular, and pathogenicity tests the bacterium isolated was identified as Xanthomonas sp. The bacterial isolates allowed verification of Koch's postulates on young olive trees. As a result of our findings we suggest that the stem canker on olive is caused by Xanthomonas sp. In addition a fungus identified as Fusicoccum luteum was consistently isolated from stem cankers and tip die-back. In inoculated plants F. luteum occasionally formed cankerous symptoms though not as aggressively as Xanthomonas sp. At this stage it is not clear what role F. luteum has in primary infection.
The time required for potato late blight lesions, caused by Phytophthora infestans (Mont.) de Bary, to produce sporangia during periods of continuous leaf wetness, and for inoculations to produce ...lesions bearing sporangia, was determined over a temperature range of 5-24°C. Equations were derived relating time to sporulate with temperature. A 2-h break in leaf wetness, initiated at any time within the first 3 h of incubation after inoculation, markedly reduced lesion numbers. When the break was initiated later it had less effect, except at the lowest temperature tested (9°C).
The seasonal abundance of ascospores of Sclerotinia sclerotiorum (Lib.) de Bary in the air depended on rainfall moistening the soil sufficiently for apothecia to develop. No other climatic factors ...were found to be related to the trapping pattern. Conidia of Botrytis cinerea Pers. ex Fr. were released in large numbers if the previous day was calm and the night warm, or when rain was falling. Few conidia were released at night unless rain was falling. Ascospores of S. sclerotiorum and conidia of B. cinerea both showed markedly diurnal distribution patterns.
Two major post-harvest diseases have been found in New Zealand avocados (Persea americana Miller): anthracnose, associated with Colletotrichum species, and stem-end rots, associated with ...Botryosphaeria and Phomopsis species. Several Fusarium species have been also isolated from fruit rots. Scab (Sphaceloma perseae Jenkins) is recorded for the first time on New Zealand avocados.
In a fungicide trial to control brown rot of peaches and nectarines (induced by Monilinia fructicola (Winter) Honey) at the Department of Scientific and Industrial Research (DSIR) Kumeu Research ...Orchard, January-March 1987, a number of fruit with unusual lesions were found (Fig. 1). The lesions were observed on all parts of the fruit but occurred most often at the distal end. The lesions were initially small, circular, and covered with white mycelium. They enlarged slowly as the fruit matured, the mycelium changing to an orange-pink colour and becoming less flocculent. Concentric rings of sporodochia developed on the surface of the lesions. Few lesions exceeded 2.5 cm in diameter but occasionally they enlarged to cover the entire fruit. The lesions were relatively dry compared with those caused by M. fructicola and Rhizopus stolonifer (Ehrenberg:Fries) Lind. Severely infected fruit became mummified.
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 susceptible in inoculation studies on cruciferous weeds and on non-vegetable brassica crop plants. Knowledge of the aetiology of light leaf spot is reviewed and the probable disease cycle in New Zealand is described.
SUMMARY
Symptoms of ringspot of brassicas, caused by Mycosphaerella brassicicola, rarely appeared on rapidly expanding leaves of cabbages and cauliflowers but were common on fully expanded leaves. M. ...brassicicola ascospores did not germinate, or germinated poorly, on expanding leaves or on recrystallised wax deposits taken from these young leaves. A high proportion germinated on expanded leaves, on waxes taken from expanded leaves and on various other surfaces in the absence of nutrients.
A volatile metabolite, present in the younger leaves, appears to inhibit ascospore germination.
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