Item

Studies on the pathogens of giant buttercup (Ranunculus acris) and their mycoherbicide potential

Jellyman, Spencer
Date
1991
Type
Dissertation
Fields of Research
ANZSRC::060704 Plant Pathology
Abstract
The disease symptoms produced by the pathogens affecting giant buttercup (Ranunculus acris) were described. The pathogens were isolated into pure culture and their in vitro characteristics described. The fungal isolates were identified as Alternaria alternata, Colletotrichum acutatum and Phoma exigua. The growth and sporulation of these pathogens was investigated on artificial media. The radial growth rate of all the pathogens was greatest at 25°C. With A. alternata and P. exigua, there was a significant increase in growth rate with an increase in temperature from 20°C to 25°C, but not with C. acutatum. P. exigua had the fastest growth rate at 25°C with 16.9mm d⁻¹, followed by A. alternata, 10.8mm d⁻¹, and C. acutatum slowest with 5.7mm d⁻¹ . Light had no effect on the radial growth rate of any pathogen. A. alternata and C. acutatum grew best on V8 5% agar, and P. exigua was best on Malt extract agar (MEA). Sporulation of A. alternata was relatively low, with 6.7 x 104 spores mrl at 25°C. C. acutatum produced abundant conidia, with 1.6 x 107 spores ml⁻¹ at 25°C. Both A. alternata and C. acutatum sporulated best on PDA or V8 5% agar. Pycnidia production of P. exigua was greatest on MEA at 25°C, with 433.3 pycnidia per 90mm plate. Total darkness significantly decreased spore production of C. acutatum and pycnidia production of P. exigua, with no effect on A. alternata. Experiments were designed to investigate pathogenicity of the three isolates. Whole plants and detached leaves of old and young plants were inoculated with each isolate. All three isolates caused some disease, but not sufficient to kill the plants. P. exigua caused sufficient disease on one plant to stunt the plants growth, but the plant recovered. The overall results were inconclusive, because a primary or main pathogen could not be identified.
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