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Dwarf Mistletoe (Arceuthobium Oxycedri ) and Damage Caused by Dwarf Mistletoe to Family Cupressaceae

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Dwarf Mistletoe (Arceuthobium Oxycedri ) and Damage Caused by Dwarf Mistletoe to Family Cupressaceae Pure Appl. Bio., 4(1):15-23, March- 2015 Review Article Dwarf mistletoe (Arceuthobium oxycedri) and damage caused by dwarf mistletoe to family Cupressaceae Humaira Abdul Wahid, Muhammad Younas Khan Barozai, Muhammad Din* Department of Botany, University of Balochistan, Sariab Road Quetta, Pakistan *Corresponding author email: [email protected] Citation Humaira Abdul Wahid, Muhammad Younas Khan Barozai, Muhammad Din. Dwarf mistletoe (Arceuthobium oxycedri) and damage caused by dwarf mistletoe to family Cupressaceae. Pure and Applied Biology. Vol. 4, Issue 1, 2015, pp 15-23 Received: 11/11/2014 Revised: 10/12/2014 Accepted: 12/12/2014 Abstract Mistletoe is an angiospermic plant famous for its shoot hemi-parasitizes activity of higher plant species. It parasitize thousands of vascular plant species and depend almost entirely on their tree hosts for water and nutrients. Their damaging effects are growth reduction, branch distortions, and decreased longevity. All mistletoes take water and nutrients by tapping the host xylem but differ in their dependence on the host for carbon. Dwarf mistletoes (Arceuthobium spp.) are considered to be mainly heterotrophic, tapping the host phloem for carbon compounds. It is an obligate parasite with an endophytic 'root' system that infects trees and shrubs of the family Cupressaceae. The aim of this review is to cover the basic concepts of dwarf mistletoes and its host range for family Cupressaceae. Key words: Angiospermic parasite; Cupressaceae; dwarf mistletoe Mistletoes are angiosperm shoot Mistletoes hemiparasites of higher plant species [2, 6] Parasitic plants are common in many natural parasitize thousands of vascular plant and seminatural ecosystems from tropical species and depend almost entirely on their rain forests to the high Arctic [1]. It has been tree hosts for water and nutrients [7]. They estimated that 1% of all angiosperm species are considered to be pathogens of trees are parasitic [2,3] and about 40% of plant because of their damaging effects, parasites are shoot parasites, parasitizing the particularly growth reduction, branch above ground parts of their host plants, distortions, and decreased longevity [8]. All while the other 60% are root parasites [4]. mistletoes take water and nutrients by Angiosperm parasites are confined to dicot tapping the host xylem but differ in their subclasses Magnoliidae, Rosidae and dependence on the host for carbon [9]. Asteridae and represents approximately 22 These plants have also complex associations families, 265 genera and 4000 species [5]. with animals that pollinate their flowers and disperse their seeds [2, 10]. Published by Bolan Society of Pure and Applied Biology 15 Wahid et al. Mistletoes as polyphyletic group parasites parasitic on Pinaceae and Cupressaceae. includes species in the Loranthaceae, Plants glabrous, variously colored from Viscaceae, Eremolepidaceae, greenish yellow to orange, reddish or black, Misodendraceae and Santalaceae [11, 12]. dioecious. Stems with variant (anomalous) Among these families two major families, patterns of secondary growth. Branches are Loranthaceae and Viscaceae. The dichotomous or verticillate, stem internodes Loranthaceae is the largest family within the terete. Leaves reduced to scales, decussate, mistletoes with 950 species [13] while the in 4 ranks, connate. Flowers axillary or Viscaceae contains 365 species [12]. terminal on branchlets, decussate or Dwarf Mistletoes whorled, peduncle absent, pedicel short to Dwarf mistletoes (Arceuthobium spp.) are nearly absent. Male flower subglobose or one the important genus of the Viscaceae. ovoid in mature bud, perianth lobes 3 or 4, ± They are considered to be mainly rotate. Anthers sessile, inserted on perianth heterotrophic, tapping the host phloem for lobes, circular, 1-loculed, dehiscence carbon compounds [14, 15] other mistletoes transverse, central nectary present. Pollen are usually considered as autotrophic, grains subprolate, 3-lobed to circular in depending on their host for water and polar section. Female flower ovoid to inorganic nutrients only [12]. The ellipsoid in mature bud, epigynous; perianth chromosomes number of all species of tube short, 2-lobed, adnate to ovary, Arceuthobium examined are n=14 [16]. No persistent . Placentation free, central. Style natural hybridization or polyploidy is short; stigma obtuse. Berry ovoid or present in the genus. The absence of ellipsoid, apex different in texture from hybridization and polyploidy has apparently base, exocarp smooth, explosively dehiscent resulted in relatively clear, dendritic lines of at maturity. Seeds without true integuments, evolution and well-defined species [17]. usually 3 to 5 mm long, ovate-lanceolate, Dwarf mistletoes can attack on all ages and containing one (rarely two) distal, sizes of trees. Mostly the larger trees are cylindrical embryo, with copious endosperm usually infested, while lesser proportions of [17]. the younger trees are infested [18]. Dwarf Dwarf mistletoe life cycle mistletoes spread by way of pressure- The dwarf mistletoe life cycle (Fig. 1) released seeds, with spread occurring both begins with the seed. Fruit normally from tree to tree and within the crowns of contains a single seed with one embryo, but individual trees [19]. Plants tend to build up fruits may rarely contain two seeds or a initially in the lower portion of the crown single seed with two embryos [22]. Dwarf and gradually spread upward. Tree growth mistletoes possess one of the most effective and vigor usually decline only when more hydrostatically controlled, explosive than half the crown is parasitized. Most mechanisms of seed dispersal known in infected trees can survive for several flowering plants [23, 24]. Local dispersal decades; generally the smaller trees decline occurs when seeds are shot from mistletoe and die more quickly than the larger ones plants at velocities as high as 100 kph. Seed [20]. Infection centers tend to expand at a dispersal range is usually 6 to 11 m, but rate of 1 to 2 feet per year [21]. some seeds may travel as far as 15 m. Long distance dispersal occurs through birds or Description of Dwarf mistletoes rodents to initiate new infection centers. Dwarf mistletoes are herbs or shrubs from Seeds have a viscous coating (viscin) that 0.5 cm to approximately 70 cm high easily adheres to any object they strike, 16 Pure Appl. Bio., 4(1):15-23, March- 2015 especially conifer needles [25, 26]. All mistletoes are dioecious, and female Intercepted seeds usually remain on the plants have flowers that produce seed while needles until the first fall rain wets the male plants have small inconspicuous hygroscopic viscin. Gravity then pulls the flowers that produce pollen. Aerial shoots well-lubricated seed to the base of an are only a few inches long. Several clumps upright needle. As the viscin dries, the seed may appear on one branch, and witches’ is cemented to the shoot surface. Seeds broom and dieback may develop in older intercepted by downward-pointing needles infections [30]. Male flowers have three or generally fall to lower branches or to the four “petals”that open to expose the pollen ground [27].To achieve infection, seeds sacs, but female flowers are inconspicuous must lodge on shoot segments usually less and remain closed. Most flowers are than 5 years old, only this portion of the host pollinated by insects. Fourteen to 18 months can be considered a "safe-site," i.e., a place after pollination, the fruit, or fleshy berry, where a seed can germinate and establish an matures, with each berry containing a single infection. Seeds are not deposited at safe- seed. From infection to seed production sites, and a high proportion of those that do takes 4 to 5 years. Spread is from tree to arrive at safe-sites are lost to disease, tree, and infection centers in young stands predation, or removal by rain. Seed typically develop around larger and older interception rates, however, are highly infected residual trees [15]. variable and depend on stand structure and Arceuthobium oxycedri composition, position of the dwarf mistletoe Genus Arceuthobium have 42 recognized on the host, and needle characteristics of the species [31]. Among these species host tree [28]. Arceuthobium oxycedri is an obligate The first visible symptom of dwarf mistletoe parasite with an endophytic 'root' system. is swelling of host tissue at the site of Arceuthobium oxycedri infects trees and infection. The radicle produced by the seed shrubs of the family Cupressaceae and grows until it reaches a suitable bark distinguished from other species primarily crevice, bud, or needle base. A holdfast by its deep green colour, higher frequency of forms that completes the infection process whorled branching. elongated internodes by wedging into the host tissues and (especially in staminate plants) which are of producing an extensive haustorial absorptive approximately equal wirth from the base to system. These “sinkers” penetrate the xylem near the apex. The younger portions of of the host and are sub-sequently embedded plants including the fruit are glaucousin live by additional growth of xylem tracheids to plants, but glaucousness tends to disappear which they are connected [29]. The on drying. expanding network of sinkers eventually Shoots mostly 5-10 cm high, but can grow breaks through the surface to form new up to 20 cm high, green, verticillate aerial shoots, buds, flowers, and seeds. branching common basal shoots 1-4 mm Aerial shoots typically range in height from across. Third internode
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