Uromyces heliotropiiis an autoecious rust fungus with a macrocyclic life cycle (Hasan, 1984: 4) meaning that it produces different spore types (Kolmer, Ordonez & Groth, 2009: 1).It is native to the Mediterranean and Middle East but has been found in southern Russia, as well (Hasan, 1984: 617).U. heloptropiican survive in a wide temperature range and reproduces faster in the presence of moisture (Hasan and Aracil, 1991: 559).
Species of theHeliotropium, a summer-growing annual weeds originally found in Iran and Iraq, were accidentally introduced in Australia (Hasan, 1984: 617-18).These plants contain pyrrolizidine alkaloids that cause crop poisoning and they effectively compete for water which affects crop yield (Hasan, 1984: 617).This has become a major problem in Australia and researchers have experimentally introduced numerous pathogens to help solve this problem (Hasan, 1984: 617).U. heliotropiihas proved to be successful in attacking this weed in all stages of its life cycle (Hasan, 1984: 618).
At the beginning of its life cycle in early spring,U. heliotropiiis a short, small, yellow aecidia forming rings on the underside of the leaves of early seedlings (Hasan, 1984: 618). The aecidia contain aecidiospores, which are dikaryotic spores (Kolmer, Ordonez & Groth, 2009: 2).They rupture the epidermis of the host plant and produce a dark brown, round uredinia (Hansan and Aracil, 1991: 559).These uredinia become large and abundant on both surfaces of the leaves and stem and produce urediniospores (Hasan, 1984: 618).Urediniospores are dikaryotic spores (Kolmer, Ordonez & Groth, 2009: 2).Researchers have found that urediniospores germinated successfully in both light and darkness, but germinated twice as fast in the dark (Hasan, 1984: 620).Urediniospores also germinate best between the temperatures of 18 and 30oC and do not germinate at all below 15oC (Hasan 1984: 620). The urediniospores are present in the spring and summer and rapidly spread to nearby plants (Hasan, 1984: 618).This stage can kill the host plant or stop its growth (Hansan and Aracil, 1991: 559).Next, round telia appear on the leaves and stems (Hasan, 1984: 618).Teliospores are diploid spores found within telia (Kolmer, Ordonez & Groth, 2009: 2).Researchers have also found that teliospores must germinate in a cycle of light and darkness; no teliospores germinated in continuous light or darkness under experimental conditions (Hasan and Aracil, 1991: 561). Teliospores usually appear in the fall when the helioptrope season is ending and can infect dead plants. The cycle then begins again by producing spermagonia and aecidiospores (Hasan, 1984: 618).
U. helioptropiiinfectsHeliotropiumspecies in all four of its spore stages and does great damage to the seedlings as well as mature plants (Hasan, 1984: 622).Infection will reduce seed production and thus serve as a biological control to manage weed infestation (Hasan, 1984: 622).WhenU. heloptropiiwas used as an infectious agent forHeliotropium in the greenhouse, all infected plants died within 7 weeks and all uninfected control plants survived (Hasan and Aracil, 1991: 561).When the same experiment was conducted in the field, all infected plants died within a month and 95.5% of the uninfected control plants survived (Hasan and Aracil, 1991: 561).If no other environmental limitations are present, Uromyces heliotropii will be a valuable agent for controlling the invasive Heliotropium.
