EFFECT OF NUTRIENT STATUS pH TEMPERATURE AND WATER POTENTIAL ON GERMINATION AND GROWTH OF RHIZOPUS STOLONIFER AND GILBERTELLA PERSICARIA
A. Amiri, W. Chai, G. Schnabel
Understanding the impact of environmental factors favouring natural niches of plant pathogens is a key component toward designing efficient management strategies. Rhizopus stolonifer (Ehrenb.:Fr.) Vuill. and Gilbertella persicaria (E.D. Eddy) Hesseltine are two economically important pathogens that are commonly associated in simultaneous infections of many stone and pome fruits. The ability of R. stolonifer and G. pesicaria to assimilate diverse carbon (C) and nitrogen (N) sources and the effect of pH and the interaction temperature/ water potential (?) on their conidial germination and growth were investigated. The fungi were grown on a liquid medium containing D-glucose, sucrose, fructose, maltose, or raffinose as C sources and urea, NH4NO3, NaNO2, glycine, or glutamine as N sources. The biomass production of R. stolonifer was the greatest when sucrose and fructose were used as C sources, respectively, whereas biomass production of G. persicaria was greater on fructose and glucose than on other sources. Glutamine and sodium nitrite (NaNO2) used as N sources yielded the highest biomass for R. stolonifer and G. persicaria, respectively. Sporangiospore germination and mycelial growth of R. stolonifer and G. persicaria were optimal between pH 3 and 10 and were totally inhibited at pH =2.5. The two fungi were affected by the interaction of temperature and ?. Both R. stolonifer and G. persicaria were sensitive to low temperatures (<10°C) and were completely inhibited at ? levels of -17 and -18.3, respectively. The nutrients utilization, pH, and ? x temperature profiles for sporangiospore germination and mycelial growth were to some extent similar between the two species corroborating that R. stolonifer and G. persicaria occupy similar ecological niches. Identifying ecophysiological determinants of these commercially important pathogens will contribute to our understanding of their physiology and epidemiology and will aid in developing appropriate models for disease prediction.