Some factors affecting the development and biocontrol of cotton seedling disease

The effects of temperature and cultivar on disease development in cotton were investigated in addition to the duration of susceptibility to infection and the timing of infection by Pythium ultimum and Rhizoctonia solani. Symptom development was also monitored. Disease was more severe at day/night temperature regimes of 20/15, 25/20, and 30/25°C than at 35/30°C. Disease development differed significantly between cotton cvv. Deltapine 90 and Siokra 1-4 at 30/25°C and 35/30°C. In glasshouse trials in field soil, both R. solani and P ultimum were isolated from seeds as early as 2 h after inoculation, although most seeds were not infected with P. ultimum until 10 h after inoculation and with R. solani until 24 h after inoculation. Increasing the duration of exposure to inoculum increased the number of seeds infected and reduced the number of plants surviving. Seedlings were resistant to P. ultimum infection by 14 days after sowing but were not resistant to infection by R. solani until 28 days after sowing

Effect of rust (Phakopsora pachyrhizi) on soybean yield and quality in south-eastern Queensland

In a field trial conducted at the University of Queensland Research Farm, Redland Bay in 1976, plots of soybeans were protected from rust, Phakopsora pachyrhizi, with mancozeb sprays for varying periods after sowing. Seed yield losses were 60-70% in the most severely rusted plots. In a glasshouse trial, rust inoculations were commenced at regular intervals during growth, and yield was reduced by 95% in plants inoculated immediately prior to flowering. In both trials, reduced yield was associated with reductions in the number of filled pods per plant, the number of filled seeds per plant and seed weight. The oil but not the protein content of the seed was also reduced in the more severely rusted treatments in the field trial

Pathotypes of Cochliobolus sativus on barley in Australia

Pathotypes of Cochliobolus sativus have been reported overseas but variation in the Australian population has not been investigated nor have the optimum conditions for the identification of variation been established. Preliminary experiments showed that maximum separation of infection responses of seedlings to infection by C. sativus conidia was obtained at 21°C using inocula containing 104 conidia/mL and a dew period of 40 h. Under these conditions, the existence of pathotypes in the Australian population of C. sativus was demonstrated. Using 20 lines, six pathotypes were identified among 34 isolates of the fungus. A differential set consisting of 12 barley cultivars is proposed

Pathotypes of Cochliobolus sativus on barley in Australia

Pathotypes of Cochliobolus sativus have been reported overseas but variation in the Australian population has not been investigated nor have the optimum conditions for the identification of variation been established. Preliminary experiments showed that maximum separation of infection responses of seedlings to infection by C. sativus conidia was obtained at 21°C using inocula containing 104 conidia/mL and a dew period of 40 h. Under these conditions, the existence of pathotypes in the Australian population of C. sativus was demonstrated. Using 20 lines, six pathotypes were identified among 34 isolates of the fungus. A differential set consisting of 12 barley cultivars is proposed

Preliminary investigations into the influence of Pseudomonas cepacia on infection and survival of proteas in Phytophthora cinnamomi infected potting mix

The potential for biological control by a strain of Pseudomonas cepacis, selected in vitro for antagonism to the growth of Phytophthora cinnamomi, was tested for both seedling and cutting propagated proteas. Eight species of protea were grown from seed in a modified University of California (UC) potting mix under growth cabinet and glasshouse conditions. In the absence of Pseudomonas cepacia, root infection was recorded in all species 2 months after pot inoculation with Phytophthora cinnamomi. In five species, 60% or more plants died during the 150 day trial period. Inoculation with Pseudomonas cepacia reduced disease incidence with no root infection being recorded in three species and no deaths in five species. In the remaining three species, plant mortality was reduced, varying from 20 to 40%. For cuttings propagated under mist in UC potting mix or wedges of Oasis Grow, the presence of Pseudomonas cepacia significantly (P < 0.05) reduced root infection levels in three of the four species tested in both propagation media. Plant mortality varied from 0 (two species) to 40% during the 60 day trial period. In the absence of Pseudomonas cepacia, all plants of two species died with no plant deaths occurring in the remaining two species

The rust Puccinia abrupta var. partheniicola, a potential biocontrol agent of parthenium weed: environmental requirements for disease progress

The rust fungus Puccinia abrupta var. partheniicola, a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20 degrees C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26 degrees C or 18/13 degrees C; day/night). Urediniospores germinated best at 12 +/- 1 degrees C, with lower germination rates at 5 degrees C or above 20 degrees C. No infection occurred when the plants were exposed to dew periods of less than or equal to 3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 +/- 1 degrees C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13 degrees C) than when exposed to a warm-temperature regime (30/26 degrees C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected. (C) 1999 Academic Press