Cuscuta spp. (Dodder): cA Literature RevieW" of Its Biology and Control Division of Agricultural Sciences BULLETIN UNIVERSITY OF CALIFORNIA 1880 P RINTED AUGUST 1976 This review cites and summarizes lite.rature published for the last 25 years on Cuscuta spp. (dodder) - parasitic plants that attack many commercial crops in California, as well as other plant pests in themselves hard to control. Following the introduction, the review is organized topically in the following sequence: taxonomy, host species, disease transmission, flower and seed formations, dormancy and germination, anatomy and cytology, biology, chemical com­ position, metabolism, translocation, growth and development, chemical control, biological control, and cultural control. 2 Cuscuta spp. (Dodder): A LITERATURE REVIEW OF ITS BIOLOGY AND CONTROL A single dodder plant may cover mum) or swamp dodder (C. gro­ INTRODUCTION several square feet and produce novii), and largeseed dodder (C. thousands of "hard" seeds, the indecora). primary method of reproduction. Cuscuta (dodder) are parasitic Some seeds germinate the season This review summarizes the liter­ plants with slender thread-like, after they are produced, but many ature on dodder that has been yellow-to-orange, twining stems, will remain dormant in the soil for published since Gaertner's (1950) and inconspicuous flowers that coil years. Therefore, once a field publication, "Studies of Germina­ about and fasten to their host plants becomes infested with dodder seed, tion, Seed Identification, and Host with wart-like attachments called it may be a problem for several Realtionships in Dodder, Cuscuta haustoria. About 170 species of this years - even though no additional spp." Occasionally, it is necessary to genus occur; Munz (1963) lists 16 in seed are produced. In the labor­ cite some of the older literature in California. atory, "hard-seed" dormancy of order to put the subject in prospec­ dodder seed can be broken by soak­ tive. Well over a thousand publi­ Tomatoes and alfalfa are the pri­ ing the seeds in concentrated cations have been written in at mary commercial crops parasi­ sulfuric acid or by scarification. Cer­ least a dozen languages since 1950. tized by dodder in California. tain species have been reported to Tomatoes are usually attacked by overwinter in the stems of some Following the introduction, this Cuscuta campestris, but in San Joa­ woody plants, although dodder is review has been topically organized quin County C. californica has also usually an annual. in the following sequence: tax­ been a problem. Alfalfa has been onomy, host species, disease reported to be attacked by C. In the field, dodder seeds germinate transmission, flower and seed for­ campestris, C. indecora, C. epi­ in the soil and are dependent initial­ mations, dormancy and germina­ thymum, C. planiflora, and C. ly upon the food stored within the tion, anatomy and cytology, biol­ racemosa. The first two species are seed. The dodder plant will die if it ogy, chemical corporation, metab­ probably the most serious. Aspar­ does not attach to a suitable host olism, translocation, growth and agus, clovers, cucurbits, and plant within several days after ger­ development, chemical control, bio­ onions are also parasitized by dod­ mination, since it cannot produce logical control, and cultural con­ der; C. campestris and/or C. the food necessary to sustain its trol. californica and perhaps other dod­ growth. Once a dodder plant has at­ der species are involved. Citrus tached attached to a host plant, orchards and citrus nursery stock the part of the dodder stem between TAXONOMY plantings have been invaded by C. the point of attachment and the soil subinclusa. This species has also dies. Then the dodder plant is total­ Gaertner (1950) reviewed the tax­ been found in a number of naturally ly dependent on the host plant for onomic history of Cuscuta. The occuring woody species including its food, inorganic salts, and water. genus Cuscuta was first established Ceanothus, Rhus, Prunus, Sal'ix, Consequently, the host plant has by Tournefort in 1700 and has since Aesculus, Sambucus, Eriogonum, less food for its own growth and been monographed four times, most and Quercus. Many common her­ yields of crop plants are reduced. recently by Yuncker (1932). Be­ baceous annual and perennial cause of the ecotylendonous na­ weedy species also are hosts for cer­ Some of the common names used for ture of the embryo, Cuscitta was tain dodder species; i.e., C. Cuscuta, besides dodder, are tangle first believed to be a monocot. campestris has been found in gut, love vine, strangle gut, devil's However, taxonomist now consider knotweed, pigweed, lambsquarters, gut, witch's shoelaces, and angel's Cuscuta to be a member of the field bindweed, cheeseweed, mal­ hair. In general, we have used the · Dicotyledoneae. low, and alkali mallow. The fact scientific names given by the that many of the hosts of dodder authors for these species. However; Although there is some controversy species that are problems to for a few species that are mentioned on whether the genus belongs in the agriculture are also parasitic on frequently, we have used the com­ Convolvulaceae or in the Cus­ naturally occuring plants makes mon names - field dodder ( C. cutaceae, most taxonomists place eradication impossible and control campestris ), flax dodder (C. ep­ it in the Cuscutaceae. Munz and most difficult. ilinum), clover dodder (C. epithy-. Keck (1959) place heavy taxonomic 3 emphasis on cuscuta's parasitic reduction before developing new of three groups: (1) as a good food habit and considers the Cuscutaceae adaptations peculiar to its peculiar provider for dodder; (2) as a host on to be composed of the single genus, parasitic habit (Searcy, 1970; Sear­ which dodder can survive; (3) as a Cuscuta. cy and Macinnis, 1970). plant serving only to support dod­ der. Gaertner also praises Dean Yuncker's (1965) final contribution The possibility of polyploidy as an (1934, 1935) for his species-host list to the study was published post­ influence in the development of this of the United States. Although humously and is the only signifi­ genus is an intriguing question in Yuncker's (1932) monograph is an cant recent publication on the need of additional study. Moreover, excellent taxonomic addition, it con­ taxonomy of Cuscuta. Most of the as indicated in other sections of this tains no new relevant data on host information reviewed here is de­ review, data from field observations species. rived from Yuncker's two publica­ of floral biology, host relationship, tions. and general biology will no doubt in­ The results of Gaertner's study are fluence taxonomic judgements. compiled into two lists. The names The genus Cuscuta has a sub­ of 609 species parasitized by dodder cosmopolitan distribution. Al­ are presented by family in the first though some species are found in list. There is some experimental Africa, Australia, New Zealand, HOST SPECIES data for 55 of the 609 species. The Polynesia, Asia, and Europe; most names of 118 species immune to of the 170 species are found primari­ dodder are presented in a second ly in the Americas from Canada to list. Argentina. The seeds of some spe­ Since Gaertner's review of the lit­ erature in 1950, few publications cies, such as C. campestris, C. suaveolens, C. epilinum, C. epi­ have expanded our knowledge on From her literature review and ex­ thymum and C. approximata are host species of dodder; further­ periments, Gaertner concludes believed to have been accidently more, her suggested lines of in­ that: vestigation have not been fol­ dispersed along with the seeds of (1) Data on species parasitized their economic hosts. lowed. Gaertner (1950) has re­ viewed the literature on host by and species immune to species. With her 1950 review, she dodder are generally lacking; Taxonomic characters are primarily presented data from her exper­ (2) According to preliminary in­ limited to the flowers and in­ iments using material from the vestigation using nine po­ florescence. Moreover, on the following species: Cuscuta camp­ tential hosts, no species of basis of style and stigma characters, es tris, C. epilinum, C. epi­ dodder is limited to one host the genus is divided into three thymum, C. epithymum var. alba, species; subgenera. Gram mica has the C. glomerata, C. europaea, C. (3) Succulents are frequently widest distribution and is believed gronovii, C. lupuliformis, C. pen­ parasitized by dodder; to have given rise to the two other tagona, and C. suaveolens. (4) The age of the host as it af­ subgenera, Cuscuta and Monogyna. fects its growth may pro­ However, all native American spe­ According to Gaertner, problems in vide mechanical obstruc­ cies are members of the subgenera rearing both the parasite and poten­ tion to parasitism; Gram mica. tial host reduced the amount of (5) Survival and reproductive new experimental data she could capacities of the parasite are Although chromosome numbers for present. Field dodder ( Cuscuta dependent on the physio­ a few species have been reported, campestris), for example, was found logical condition of the neither of Yuncker's publications at various times to be thriving or host. (1932, 1965) contained this data. dying on tomato (Lycopersicon Three of the sixteen Californian esculentum). In this example, she cuscutas have chromosome numbers suggested that the varying results Host-parasite Relationship of 2N = 50 and 2N = 60 (Munz and were due to imbalances in the age of Keck, 1959). These numbers are the parasite and potential host. Olifirenko (1961) has compiled a list similar to the chromosome numbers Hence, Gaertner's conclusions re­ of 68 host species parasitized by first reported by Gaertner (1950) in lied heavily on reports in the Cuscuta arvensis. He is one of the her review of Cuscuta taxonomy. literature with supplements of her few individuals who has made field Gaertner suggested that the basic own research.