Annuals and Herbaceous Perennials Tolerant or Resistant to Phytophthora Species in the Landscape1
Authors: Henson M. S. , Sharpe S. R. , Meadows I. M. 
Published: September 2020

Plants of one or two cultivars of 16 annuals and 14 herbaceous perennials were evaluated based on desirability and anecdotal evidence of resistance to Phytophthora root or crown rot. Six plant cultivars served as susceptible controls. Three landscape beds were established in North Carolina and each was infested with three species of Phytophthora: P. nicotianae, P. drechsleri, and P. tropicalis. Plants were regularly rated for disease incidence and symptomatic plants were assayed to determine the presence of Phytophthora species. Ten cultivars of annuals and seven cultivars of herbaceous perennials did not exhibit symptoms of Phytophthora root or crown rot or other disease throughout the season (June 4 to October 15, 2018). Phytophthora spp. were recovered from seven and six cultivars of the evaluated annuals and herbaceous perennials, respectively. Phytophthora nicotianae, P. drechsleri, or P. cryptogea were recovered from a susceptible host in each landscape bed. P. tropicalis was recovered from one plant cultivar evaluated. Phytophthora cryptogea was recovered from three plant cultivars, although this species was not intentionally introduced in the landscape beds. We identified 22 plant cultivars within 13 herbaceous plant species that grew vigorously in landscape beds infested with species of Phytophthora.

Index words: bedding plants, disease resistance, herbaceous perennials, landscape plants, Phytophthora nicotianae, Phytophthora drechsleri, Phytophthora tropicalis.

Species used in this study: yarrow (Achillea millefolium L. ‘Desert Eve Red'), fernleaf yarrow (Achillea filipendulina Lam. ‘Moonshine Yellow'), angelonia (Angelonia angustifolia Benth. ‘ArchAngel Pink', ‘Serenita White'), annual vinca (Catharanthus roseus (L.) G. Don ‘Cora Apricot', ‘Cora Strawberry', ‘Pacifica Raspberry'), celosia (Celosia argentea L. ‘New Look'), tickseed (Coreopsis auriculata L. ‘Nana', ‘Yellow Jethro Tull'), purple coneflower (Echinacea purpurea (L.) Moench ‘Cheyenne Spirit', ‘PowWow Wild Berry'), blanket flower (Gaillardia x grandiflora Hort. ‘Goblin', ‘Mesa Bi-color'), Barberton daisy (Gerbera jamesonii Bolus ex Hooker f. ‘Crazy Daisy'), verbena (Glandularia canadensis ‘Homestead Purple'), &gt;dusty miller (Jacobaea maritima (L.) Pelser & Meijden ‘Silver Dust'), New Guinea impatiens (Impatienshawkeri W.Bull ‘Hamony', ‘Sunpatiens Compact Orchid', ‘Sunpatiens Lilac'), sweet potato vine (Ipomoea batatas (L.) Lam. ‘Ace of Spades', ‘Bright Idea Tri-color'), West Indian lantana (Lantana camara L. ‘Miss Huff'), lantana (Lantana x hybrida ‘New Gold'), shasta daisy (Leucanthemum x superbum (Bergmans ex J.W. Ingram) Bergmans ex Kent. ‘Becky', ‘Snow Lady'), bee balm (Monarda didyma L. ‘Petite Delight', ‘Jacob Cline'), ornamental grass (Panicum virgatum L. ‘Rotstrahlbusch', ‘Shenandoah'), geranium (Pelargonium x hortorum L.H. Bailey (pro. sp.) ‘Bullseye Cherry', Calliope Dark Red'), calibrachoa (Petunia x calibrachoa ‘Super Cal'), petunia (Petunia x hybrida (Hooker) Vilmorin ‘Easy Wave Red', ‘Easy Wave White', ‘Wave Purple', ‘Yellow Madness', Violet Picotee'), annual phlox (Phlox drummondii Hook. ‘Intensia Red Hot', ‘Phlox Star'), garden phlox (Phlox paniculata L. ‘Amethyst True Gal'), black-eyed susan (Rudbeckia hirta L. ‘Indian Summer', ‘Prairie Sun'), mealy blue sage (Salvia farinacea Benth. ‘Victoria Blue'), African marigold (Tagetes erecta L. ‘Inca Yellow', ‘Proud Yellow'), French marigold (Tagetes patula L. ‘Disco Mix', ‘Disco Yellow'), narrowleaf zinnia (Zinnia angustifolia Kunth. ‘Star Orange', ‘Star White'), Phytophthora nicotianae Breda de Haan, Phytophthora cryptogea Pethybr. and Laff, Phytophthora drechsleri Tucker, Phytophthora tropicalis Aragaki and J.Y. Uchida, zinnia (Zinnia elegans Jacq. ‘Magellan Orange').