Nematological problems of fruit crop

Abstract: The trophic activity of plant parasitic nematodes causes direct damages to plants(various injuries and traumas) leading to synergistic increase of susceptibility to other parasites(fungal and bacterial pathogens) and to environmental stresses. Besides, some nematode speciesare also virus vectors. The average yield losses caused by nematodes to fruit crops, as reported inU.S.A. in 1971 by the Society of Nematologists, is around 10%. This value agrees with recentestimates from other countries. The control of nematodes in orchards must be implementedbefore planting, combining suitable techniques, which may lead to optimal growth conditions.This aspect is particularly important today considering that no registered nematicides exists foruse on established orchards and nematodes eradication is an utopia. The key nematode species offruit trees (apricot, cherry, almond, apple, pear, plum) belong, undoubtedly, to root-knotnematodes of the genus Meloidogyne, mainly M. incognita (Kofoid & White) Chitw. Often thepresence of these nematodes, very common on peach and kiwi, is associated with multiple fungalinfections and Agrobacterium tumefaciens (Smith et Towensend) Conn. In particular, in someItalian localities, especially in the Northern area, M. hapla Chitw. is extremely harmful to kiwitrees. In other countries, other species were found on apple (M. mali Ithoh, Ohshima & Ichinoe)and pear (M. hapla). Also common and harmful, even for the involvement of fungi and bacteria,are root-lesion nematodes (Pratylenchus spp.), the two most representative species beingP. penetrans (Cobb) Chitw. & Oteifa e P. vulnus Allen &Jensen. Widespread and very harmful,especially to peach, is the ring nematode Criconemoides xenoplax (Raski) Luc & Raski). In theU.S.A., the presence of this nematode is closely related to the so-called “Peach Tree Short-Life(PTSL) syndrome. Research conducted in North Carolina showed that nematodes, Cytosporafungus, rootstocks, and low winter temperatures are involved in this syndrome. On Citrus spp.,the most dangerous nematode is Tylenchulus semipenetrans Cobb, which is endemic on Citrusspp. and is also damaging especially grapes in some countries. Among the virus vectornematodes, the key species is Xiphinema diversicaudatum (Micoletzky) Thorne, widespread inItaly especially on peach. It is known as the vector of Arabis mosaic nepovirus (ArMV) and ofStrawberry latent ringspot nepovirus (SLRV); the latter associated to Prune dwarf virus (PDV),causes decline and rasp leaf of the sweet cherry. Very dangerous are also other species of theXiphinema americanum Cobb sensu latu-group (non-European populations). Finally, someLongidorus species may also play a key role in the fruit crop production.