Calophoma clematidina

The asexual stage (anamorph) of the fungus was first described by the German botanist and mycologist Felix von Thümen in 1880 as Ascochyta clematidina. Based on new scientific insights into the differences in spore formation between species, it was reclassified as Phoma clematidina by the Dutch mycologist Gerhard Boerema in 1978. More recently, multi-locus phylogenetic analyses led to the fungus being reclassified again as Calophoma clematidina. Both mating types of Calophoma clematidina are known to occur in Europe, and yet no sexual stage (which is most likely to be a Didymella species) has ever been described. Unlike Calophoma clematidina, the two closely related Didymella species (and their anamorphs) have not been found on large-flowered Clematis varieties. and has in the past been implicated in cases of clematis wilt in the Netherlands. ==Biology==

The biology of Calophoma clematidina is now reasonably well understood thanks to research into clematis wilt at the University of Canterbury in New Zealand and the University of Derby and ADAS in the UK. A full overview of its life cycle was first produced in 1999. Within a nursery or garden, the fungus is mainly spread through splash dispersal of its asexual spores (conidia) which are formed in bulbous fruiting bodies called pycnidia. Pycnidia can be formed on any infected part of the plant showing symptoms, including leaves, stems and roots. The pycnidia exude the spores in a sticky mass which is splash dispersed to other plants nearby during rain or irrigation. Contact, such as with pruning tools, may also spread the spores and, in addition, it is suspected that certain insect species may act as contact vectors. Movement of infected plant material forms an important method of spread to previously unaffected nurseries or gardens. Unlike many other plant pathogens, Calophoma clematidina is not a biotroph which means that it can infect plants but does not need them to survive. The fungus can live saprophytically on dead plant material or organic matter as well. In addition, it forms thick-walled resting spores (chlamydospores) which increase its survival in plant debris and soil during unfavourable conditions. ==Disease development==

Many publications report Calophoma clematidina to be a wound pathogen. However, although wounding may aid infection, scientific trials have shown that, in susceptible Clematis varieties, the fungus can cause extensive leaf spotting and wilt without any previous damage to plant tissues. Relatively recently, it was discovered that Calophoma clematidina can also infect the roots of Clematis and be a cause of black root rot. In practice, this has been found to be a particular issue in containerised plants. ==Host susceptibility==

Many gardening publications express a view on the susceptibility of different Clematis varieties and species to clematis wilt based on observations in practice, but very few comment on their susceptibility to disease caused by Calophoma clematidina in particular compared with other causes of wilt. Scientific trials have shown that large-flowered varieties are especially susceptible to disease caused by Calophoma clematidina in line with their vulnerability to wilt observed in practice. It is believed that hybrids which have Clematis lanuginosa in their ancestry are most susceptible to wilt. Such hybrids include many cultivars in the early flowering, large-flowered group (such as C. 'Nelly Moser' and C. 'Elsa Späth') and, to a lesser extent, cultivars in the late flowering, large-flowered group (such as C. 'Jackmanii' and C. 'Perle d'Azur'). Clematis viticella and related varieties are also susceptible to infection with Calophoma clematidina, yet are reported to wilt less often than large-flowered varieties, possibly because they are very vigorous and outgrow infections quite rapidly. Most other cultivated Clematis species and their varieties are largely resistant to both infection with Calophoma clematidina and wilt in general. Reported isolations from wild C. vitalba in Europe have proven to be an unnamed Didymella species rather than Calophoma clematidina. == As biological control ==

This fungus has been reported as having been successfully used as a biological control agent of Clematis vitalba, which is seen as an invasive plant in New Zealand. However, further genetic studies of the isolates used in those trials have revealed that the fungus released as biocontrol agent had been misidentified and was not Calophoma clematidina, which thus far has never been found on Clematis vitalba. == Management ==

Benzimidazole fungicides are used. Benzimidazole resistance has occurred. == References ==