Development of "Tetrazyg" rootstocks tolerant of the Diaprepes/Phytophthora complex under greenhouse conditions.

Surveys conducted in the late 1990s of groups with an ex- pressed interest in ecolabels indicated approximately 60% of respondents ranked fresh fruit and vegetables as foods most in need of ecolabels, with only 10% ranking juice products as most in need (Hartman Group, 1997), suggesting a greater market potential for fresh than processed citrus. Convention- al growers who are already committed to sustainable practices and who are already managing a range of production, har- vesting, packing, processing, labor and environmental regula- tions but who do not seek organic certification might also Abstract. 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 scaffold roots caused by weevil feeding create oppor- tunities 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 damage caused by weevil feeding and then recovery by exhibiting vigorous root growth in chal- lenging soils inoculated with both Phytophthora nicotianae and P. palmivora . Crosses were made of superior allotetrap- loid somatic hybrid rootstocks and resulting seed were plant- ed 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 subse- quently rooted cuttings. New mandarin + pummelo somatic hybrids were also included in the assays. Replicated Dia- prepes no-choice feeding assays were conducted in conetain- ers®, and hybrids selected for reduced root damage were replanted in the 'Winder'/ Phytophthora mix to assess recovery