European and American chestnuts: An overview of the main threats and control efforts

Abstract

Chestnuts are multipurpose trees significant for the economy and wildlife. These trees are currently found around the globe, demonstrating their genetic adaptation to different environmental conditions. Several biotic and abiotic stresses have challenged these species, contributing to the decline of European chestnut production and the functional extinction of the American chestnut. Several efforts started over the last century to understand the cellular, molecular, and genetic interactions behind all chestnut biotic and abiotic interactions. Most efforts have been toward breeding for the primary diseases, chestnut blight and ink disease caused by the pathogens, Cryphonectria parasitica and Phytophthora cinnamomi, respectively. In Europe and North America, researchers have been using the Asian chestnut species, which co-evolved with the pathogens, to introgress resistance genes into the susceptible species. Breeding woody trees has several limitations which can be mostly related to the long life cycles of these species and the big genome landscapes. Consequently, it takes decades to improve traits of interest, such as resistance to pathogens. Currently, the availability of genome sequences and next-generation sequencing techniques may provide new tools to help overcome most of the problems tree breeding is still facing. This review summarizes European and American chestnut’s main biotic stresses and discusses breeding and biotechnological efforts developed over the last decades, having ink disease and chestnut blight as the main focus. Climate change is a rising concern, and in this context, the adaptation of chestnuts to adverse environmental conditions is of extreme importance for chestnut production. Therefore, we also discuss the abiotic challenges on European chestnuts, where the response to abiotic stress at the genetic and molecular level has been explored.

Warming Scenarios and Phytophthora cinnamomi Infection in Chestnut (Castanea sativa Mill.)

“…Temperature has been shown to alter plant secondary metabolism, and this response seems to be species- compound- or context-dependent [ 12 ]. Compounds from the secondary metabolism of plants may directly interact with pathogens (e.g., as antifungal agents) [ 13 , 14 ] or participate in the immune response of plants [ 15 ].…”

“…Ink disease, caused mainly by Phytophthora cinnamomi Rands, is considered the most widespread and destructive disease of C. sativa [ 30 , 31 , 32 , 33 ]. Symptoms include fine root rot, root collar necrosis, obstruction of xylem vessels, leaf chlorosis, rapid or gradual wilting of leaves and dieback [ 14 , 33 , 34 ]. Phytophthora cinnamomi ( Pc ) is a soil-borne pathogen (Stramenopila, Oomycota) that infects almost 5000 plant species, including many that are significant in agriculture, forestry and horticulture [ 30 ].…”

The impact of the Asian chestnut gall wasp (Dryocosmus kuriphilus) on chestnut tree growth may be mediated by site resources

“…Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) is one of the major key insect pests in chestnut orchards and forests (e.g., Fernandes et al, 2022). This pest, commonly known as the Asian chestnut gall wasp, is native to China and can affect species of the genus Castanea and hybrid clones.…”

Defensive patterns of chestnut genotypes (Castanea spp.) against the gall wasp, Dryocosmus kuriphilus

“…Chestnuts cover an area of more than 100,000 ha in northwestern Spain, of which about 45,000 ha are in Galicia (MARM, 2011), where this study was conducted. Spain is considered the second (Fernandes et al, 2022) or third (Freitas et al, 2021) largest producer of chestnuts in the world. The European chestnut has no native fauna of gall makers, but other members of Fagaceae (especially Quercus spp.)…”

“…Castanea sativa in NW Spain has been seriously affected by Phytophthora spp. for the last two centuries (Alcaide et al, 2020;Fernandes et al, 2022). Since some Asian species of Castanea were considered resistant to the disease, a program of hybridization between European chestnut and two Asian chestnut species (C. crenata Siebold and Zucc.…”