Influence of waterlogging on growth of pyrethrum plants infected by the crown and root rot pathogens, Fusarium oxysporum, Fusarium avenaceum and Paraphoma vinacea

Abstract

Yield decline in pyrethrum fields of northern Tasmania was thought to be due to an interaction between soil-borne pathogens and abiotic stresses. Glasshouse trials were conducted to assess the influence of a 4-day waterlogging period on growth of pyrethrum plants already infected with the crown and root rot pathogens, Fusarium oxysporum, F. avenaceum and Paraphoma vinacea. In plants grown at optimum soil water capacity, F. oxysporum and P. vinacea significantly reduced the below-ground and total biomass of plants before waterlogging (0 bw = 2 months after inoculation, 2 mai), at 2 months after waterlogging (2 maw = 4 months after inoculation, 4 mai) and 6 months after waterlogging (6 maw = 8 months after inoculation, 8 mai) but had little effect on above-ground biomass. Although F. avenaceum was pathogenic it only had a significant effect on below-ground biomass at 4 and 8 mai. At 7 days after waterlogging treatment, plants infected with P. vinacea had more severe wilting, necrosis and chlorosis of the basal leaves and petioles than plants infected with the other two pathogens or non-infected plants. Significant interaction between pathogen treatments and waterlogging occurred at 2 maw, whereas at 6 maw plants had recovered and no significant interaction was observed between the pathogen treatments and waterlogging. The effect of waterlogging on below-ground dry weight of the plants infected with F. oxysporum and P. vinacea at 2 maw was more severe than those infected with F. avenaceum. There was no significant interaction between waterlogging and pathogens on photosynthesis 2 maw however, plants infected by each of the pathogens had the lowest photosynthesis rate in both waterlogged and the non-waterlogged treatments. At 6 maw the number of flowers, flower stems, petioles and leaves were significantly reduced by waterlogging however, there was no significant effect by pathogens nor an interaction between pathogens and waterlogging on these growth parameters. Overall, waterlogging exacerbated the effect of F. oxysporum, F. avenaceum and P. vinacea on below-ground dry weight and total biomass of the root-dip inoculated pyrethrum plants 2 maw and affected the flower and flower stem production.