Effects of Rust Fungus and Aphid Infestation on Plant Height and Seed Production of Impatiens parviflora DC

The effects of the rust fungus Puccinia komarovii Tranzschel and the aphid Impatientinum asiaticum Nevsky 1929 on plant height, seed number per capsule, and seed mass were investigated in eight small balsam (Impatiens parviflora DC.) stands in Hungary and one in Poland. Two stands were infected by rust, five by aphids, and two were healthy. The lowest average plant height was 37.5 cm and the highest 94.7 cm, both measured in aphid-infested stands. Examining the stands separately, no relationship appeared with the type of damage. For data pooled across stands, differences were significant: rust-infected plants were the tallest, healthy shoots were the shortest, while aphid-infected plants fell in between. Mean seed number per capsule was the lowest (1.53) in the pest-free Nagybörzsöny stand, and the highest (2.33) in the aphid-infested Bielsko-Biała stand. In pairwise comparison of stands, average seed number did not differ in most cases. Significant positive correlation was found between average plant height and average seed number per capsule. Seeds were the heaviest in the healthy stand, whereas they were lighter in rust-infected and aphid-damaged stands. Regarding the applicability of the studied pests as biological control agents, the results showed that both pests reduce seed mass but not overall performance of the host plant.