Lasiodiplodia carlesii — a new canker pathogen

The genus Castanopsis, in the beech family, dominates the evergreen broadleaved forests of South and Southeast Asia. It carries ecological and economic weight, supplying timber, firewood, food and materials for traditional medicine, and China is a centre of its diversity, where plantation area has been rising for decades.

In 2021 severe outbreaks of canker and dieback struck plantations of Castanopsis carlesii and C. hystrix. Yong Zhang's team isolated fungi from the diseased tissue and, on the basis of morphology and multi-locus phylogenetic analysis of ITS, tef1-α, tub2 and rpb2, described a new species: Lasiodiplodia carlesii.

The pathogenicity tests are the most important part of the work, because they separate a culprit from an incidental resident of diseased tissue. They showed that L. carlesii causes canker and dieback symptoms on several Castanopsis species, including C. carlesii, C. hystrix and C. faberi. It also produced water-soaked brown lesions on the fruits of the wax apple, Syzygium samarangense — a different plant family altogether.

A broad host range and infection across families are the traits that raise an alarm in plant pathology. A pathogen confined to one genus can be held back by changing what is planted; one that crosses families offers no such option, and gains a reservoir in plants nobody is monitoring.

The genus Lasiodiplodia is known for opportunists that attack trees weakened by drought or injury. Describing a new species in it is therefore also a warning about plantations established under increasingly frequent water stress.

Some family context is worth adding. The Botryosphaeriaceae, to which Lasiodiplodia belongs, is known for latent species: the fungus lives in the tissue of a healthy tree for years without symptoms and turns pathogenic only once the plant weakens. Drought, transplanting, mechanical damage or overly dense planting are enough as a trigger.

For a plantation that has an organisational consequence. Planting stock can be infected and entirely symptomless, so visual inspection in the nursery detects nothing. Detection requires isolation from tissue or a molecular test, which means cost and time that mass production usually does not carry.

What the paper establishes

Lasiodiplodia carlesii was described during a severe 2021 canker-and-dieback outbreak in Castanopsis carlesii and C. hystrix plantations in China, using morphology with ITS, tef1-α, tub2 and rpb2. Crucially, pathogenicity tests caused cankers and dieback in inoculated C. carlesii, C. hystrix and C. faberi, while necrotic lesions formed on Syzygium samarangense fruit. This is stronger evidence than DNA detection or isolation from symptomatic tissue alone. The experiment demonstrates infection potential in tested hosts and conditions, but it does not establish landscape disease frequency, dispersal routes or risk to every related tree. Claims about nursery movement or drought-driven outbreaks require separate surveillance and epidemiological evidence.