The biotic adversities of poplar in Italy: a reasoned analysis of factors determining the current state and future perspectives

Poplar cultivation in Italy since its early stages has been conditioned and orientated by biotic and abiotic adversities. Spontaneous hybrids between European black poplar ( Populus nigra L.) and Eastern cottonwood ( Populous deltoides W. Bartram (Marshall)) were empirically introduced into cultivation for their suitable characters of branchiness, rooting and tolerance to root rots; nevertheless, the first true scientific programme of genetic improvement began after leaf and shoot blight epidemics from Venturia populina during the second and third decades  of the twentieth century. The resulting selection of resistant ‘I-214’ clone fostered poplar cultivation in Italy, but at the same time «crystallised» it in a condition of delay with respect to other European countries. With the arrival of leaf spot disease from Marssonina brunnea in the Sixties, phytoiatric treatments were introduced rather than diversifying with more resistant genotypes. Similarly, the increased virulence of leaf rusts from Melampsora spp. starting from about twenty years later, did not succeed in undermining the near monopolisation of ‘I-214’. At present, Marssonina leaf spot and leaf rusts are the most incident diseases: fungicide treatments are carried out mainly on the plantation against the former and mainly in the nursery against the latter. The woolly aphid ( Phloeomyzus passerinii ) is the most constant and incident pest in plantations. Besides, persisting problems are associated with new pests mainly of exotic origin, especially with the brown marmorated stink bug ( Halyomorpha halys ). Experiences in other important European poplar cultivation systems highlight the suitability of genetic control, together with a diversification of planted material and efficient agronomic practices. It is advisable to undertake research programmes for vertical and horizontal or quantitative (QTL) resistances, recurring to molecular markers, associated with studies on epigenetics and on microbial communities of various tissues through the new approach offered by metagenomics. The complexity of poplar agrosystems should be increased promoting a homeostatic control of pathogens and pests through antibiotic or competitive features triggered by other microbiota components.