DEVELOPMENT OF 'TETRAZYG' ROOTSTOCKS TOLERANT OF THE DIAPREPES/PHYTOPHTHORA COMPLEX UNDER GREENHOUSE CONDITIONS

摘要

Diaprepes (Diaprepes abbreviatus L.) root weevil has become an increasingly important pest affecting Florida citrus production. No known citrus rootstock germplasm appears to be resistant to weevil larvae feeding. Mechanical wounds on tap and scaffoldroots caused by weevil feeding create opportunities for invading fungi, especially ubiquitous Phytoph-thora spp. Our strategy for dealing with this problem is to develop complex rootstock hybrids that have the capacity to tolerate mechanical root damagecaused by weevil feeding and then recovery by exhibiting vigorous root growth in challenging soils inoculated with both Phytophthora nicotianae and P. palmivora. Crosses were made of superior allotetrap-loid somatic hybrid rootstocks and resulting seedwere planted in a high pH calcareous 'Winder' depressional soil inoculated with both Phytophthora spp. in greenhouse flats. Vigorous healthy "tetrazyg" seedlings were selected and propagated by grafting to vigorous rootstocks and subsequently rooted cuttings. New mandarin + pummelo somatic hybrids were also included in the assays. Replicated Diaprepes no-choice feeding assays were conducted in conetain-ers~R, and hybrids selected for reduced root damage were replanted in the 'Wmtier'I Phytophthora mix to assess recovery potential. Several hybrids showed excellent capacity for complete recovery in this greenhouse test and are now being propagated for more extensive field evaluation. Citrus rootstock breeding and selection at the tetraploid level maximizes genetic diversity and selection efficiency, and shows great promise for generating new rootstocks that can tolerate the existence of Diaprepes and Phytophthora in clay loam soils.