Puccinia komarovii var. glanduliferae var. nov.: a fungal agent for the biological control of Himalayan balsam (Impatiens glandulifera)

Clearly defining the taxonomic identity of a potential biocontrol agent is an essential component of any biological control programme. As part of such a programme against Impatiens glandulifera, a highly invasive annual weed in both Europe and North America, the rust fungus Puccinia komarovii was collected on this host plant in its native Himalayan range. However, current literature indicates that P. komarovii is a pathogen of a number of Impatiens species globally and was described originally from I. parviflora, a species native to Asia and now naturalized in Europe. Morphological comparisons, based on urediniospore and teliospore measurements, were generally inconclusive in showing any clear differences between the accession from I. glandulifera and those from other Impatiens species. Both, nrDNA ITS and ITS2-LSU sequence analyses indicated a difference between the rust infecting I. glandulifera compared to accessions on other hosts. However, the large variations in both ITS and 28S (ITS2-LSU) sequences determined within single accessions in this study, makes a clear separation difficult. Cross-inoculation experiments, using one accession of P. komarovii ex I. glandulifera (from India) and two accessions of P. komarovii ex I. parviflora (from China and Hungary), confirmed the specificity of these strains to their original hosts. Two Himalayan Impatiens species, I. scabrida and I. brachycentra, showed varying levels of susceptibility to these rust accessions, where the former was weakly susceptible to all three accessions and the latter was weakly susceptible only to P. komarovii ex I. parviflora (from China). However, commercial cultivars of I. balsamina proved to be fully susceptible to all rust accessions, although this has not been demonstrated under field conditions in India. Based on these host specificity differences between the rust accessions, we propose a new variety: Puccinia komarovii var. glanduliferae var. nov. associated with I. glandulifera in the Himalayas.