Jujube (Zizyphus jujuba Mill.) witches' broom (JWB) is the most important disease in the areas of jujube cultivation in China, where it occurs every year. Micropropagated shoots of the three most important cultivars (`Lizao', `Junzao', and `Muzao') in the National Jujube Gene Pool, collected at the Pomology Institute of Shanxi province, were tested for the presence of phytoplasmas. Phytoplasma ribosomal (16Sr) general and specific primer pairs were used in direct or nested polymerase chain reaction (PCR). Positive results were obtained only from symptomatic micropropagated samples of `Lizao' and from phytoplasma controls. Restriction fragment length polymorphism (RFLP) analyses of PCR products with several restriction enzymes revealed that the phytoplasmas infecting the symptomatic plants belong to the 16SrRNA group V subgroup B. The positive correlation between symptoms and the presence of phytoplasmas was verified in tissue culture. Samples from apparently healthy shoots of `Junzao', `Muzao', and `Lizao' were free of phytoplasmas.
J.B. Tian, H.P. Guo, A. Bertaccini, M. Martini, S. Paltrinieri, and M. Pastore
J. Steven Brown, R.J. Schnell, J.C. Motamayor, Uilson Lopes, David N. Kuhn, and James W. Borrone
A genetic linkage map was created from 146 cacao trees (Theobroma cacao), using an F2 population produced by selfing an F1 progeny of the cross Sca6 and ICS1. Simple sequence repeat (SSR) markers (170) were used principally for this map, with 12 candidate genes [eight resistance gene homologues (RGH) and four stress related WRKY genes], for a total of 182 markers. Joinmap software was used to create the map, and 10 linkage groups were clearly obtained, corresponding to the 10 known chromosomes of cacao. Our map encompassed 671.9 cM, approximately 100 cM less than most previously reported cacao maps, and 213.5 cM less than the one reported high-density map. Approximately 27% of the markers showed significant segregation distortion, mapping together in six genomic areas, four of which also showed distortion in other cacao maps. Two quantitative trait loci (QTL) for resistance to witches' broom disease were found, one producing a major effect and one a minor effect, both showing important dominance effects. One QTL for trunk diameter was found at a point 10.2 cM away from the stronger resistance gene. One RGH flanked the minor QTL for witches' broom resistance, implying possible association. QTLs mapped in F2 populations produce estimates of additive and dominance effects, not obtainable in F1 crosses. As dominance was clearly shown in the QTL found in this study, this population merits further study for evaluation of dominance effects for other traits. This F2 cacao population constitutes a useful link for genomic studies between cacao and cotton, its only widely grown agronomic relative.
Seedlings obtained from mutations on conifer trees exhibit populations of dwarf shrubs. The general characteristics of the shrubs often differ from progeny to progeny. The most obvious difference between progenies is in annual rates of growth, with some showing growth rates 10 or more times greater than the slowest growing group. Differences that appear within each progeny include needle length, foliage coloration, branching habit and plant form. As a consequence, many interesting forms have been produced and named that are miniature, dwarf, and intermediate in size.
Variations in form include plants that are columnar, rounded, spreading, and weeping. Whereas variation in foliage color include blue-green, green, and gold.
H. Brent Pemberton, Kevin Ong, Mark Windham, Jennifer Olson, and David H. Byrne
Rose rosette disease is incited by a negative-sense RNA virus (genus Emaravirus ), which is vectored by a wind-dispersed eriophyid mite ( P. fructiphilus ) ( Di Bello et al., 2015a ; Laney et al., 2011 ). Symptoms on roses include witches broom
Edward J. Boza, Juan Carlos Motamayor, Freddy M. Amores, Sergio Cedeño-Amador, Cecile L. Tondo, Donald S. Livingstone III, Raymond J. Schnell, and Osman A. Gutiérrez
limited genetic base. In the 1930s, Ecuadorian cacao production suffered a steep decline attributable mainly to a combination of aging plantations and damage caused by disease, specifically witches’ broom disease, frosty pod or moniliasis disease
Jane M. Marita, José Luis Pires, W. Martin Aitken, and James Nienhuis
An increased need to understand the genetic relationships among cacao (Theobroma cacao) germplasm exists to identify cultivars that possess resistance to witches' broom disease (caused by Crinipellis perniciosa). Loss of production due to witches' broom disease in important cacao-growing areas, such as Bahia, Brazil, has generated a strong demand for disease-resistant varieties. Varieties based on single sources of resistance have been released; however, other genotypes are needed to enlarge the genetic diversity of cultivars in breeding programs. A core collection has been created to represent the range of genetic diversity available among the more than 600 cacao accessions at Centro de Pesquisa do Cacau (CEPEC). The cacao core facilitates access to the collection and is intended to enhance its use. This core collection was created from RAPD marker-based estimates of genetic distance among a subset of 270 accessions from the entire collection. The subset was sampled based on 1) witches' broom disease resistance data, 2) random sampling of the collection, and 3) random sampling of recently acquired accessions. Differences in RAPD marker frequencies were used to identify accessions in a witches' broom disease breeding program that contribute to the genetic diversity of the collection as a whole. In addition, differences in RAPD marker frequency allowed the comparison between accessions in the original collection and those acquired from new geographic regions that may expand the collection's genetic diversity.
C.M. Ronning, D.M. Harkins, R.J. Schnell, and L.H. Purdy
Cacao is an important crop in the tropics, but its breeding has been hampered by a lack of understanding of its genetics. One result of this has been the introduction of “hybrid” trees which did not perform predictably under various environmental conditions. We are studying the inheritance of isoenzyme, RFLP, and Random Amplified Polymorphic DNA (RAPD™) markers in order to estimate the genetic relationships among and between populations. Our objectives include determining if any linkage exists between these molecular markers and witches' broom (Crinipellis perniciosa) resistance, a major disease of cacao.
A. Gera, L. Maslenin, A. Rosner, M. Zeidan, S. Pivonia, and P.G. Weintraub
Yellows diseases in ornamental crops have become more common in Israel, and phytoplasmas have been detected in several crops. Recently, symptoms typical of a phytoplasma infection were observed on a large number of Limonium hybrids grown in commercial fields in Israel. Examination of samples from diseased plants by electron microscopy revealed the presence of pleiomorphic membrane-bound bodies in the phloem cells. Diseased plants were additionally analyzed by PCR using universal and nested primers and revealed upon sequencing products of 1143, 788 and 722 bp (Li-IL, Li-b2-IL, Li-v3-IL, respectively). Analysis of the PCR products, associated with infected Limonium, clustered within two major groups of phytoplasmas (16SrV and 16SrIX), elm yellows and almond witches broom. This is the first published record of these phytoplasmas in Israel.
Assunta Bertaccini, Robert E. Davis, and Ing Ming Lee
A collection of mycoplasma-like organisms (MLOs) was maintained in plant tissues micropropagated in vitro. MLO-infected plants included Chrysanthemum frutescens L. with chyrsanthemum yellows disease, Gladiolus sp. L. with “germ fins,” Hydrangea macrophilla (Thunb.) DC. with virescence, Rubus fruticosus L. with rubus stunt, and periwinkle [Catharanthus roseus (L.) G. Don] singly infected by the following MLOs: Italian periwinkle virescence, chrysanthemum yellows, North American aster yellows, Italian periwinkle stunt, American periwinkle little leaf. Shoots micropropagated in vitro exhibited symptoms of little-leaf and/or abnormal proliferation of axillary shoots resulting in “witches' broom” appearance that resembled symptoms in grafttransmitted greenhouse-grown or naturally infected field-collected plants. These symptoms, typical of infection by MLOs, were not observed in micropropagated healthy shoots of the same plant species, and, compared with the healthy ones, varied with MLO strain and host plant species. Dot hybridizations with a nonradioactive cloned DNA probe provided evidence for the presence of MLOs in propagated tissues through serial subcultures.
John M. Ruter*
Mouse ear (leaf curl, little leaf, squirrel ear) has been a problem for growers of container-grown river birch (Betula nigra L.) since the early 1990's. Mouse ear has been noticed in several southeastern States as well as Minnesota, Ohio, Oregon, and Wisconsin, making it a national problem. The disorder is easy to detect in nurseries as the plants appear stunted. The leaves are small, wrinkled, often darker green in color, commonly cupped, and have necrotic margins. New growth has shortened internodes which gives plants a witches-broom appearance. Plants growing in native soil rarely express the disorder. Several common micronutrients have been evaluated with no results. A trial was initiated in June, 2003 to determine if nickel deficiency was the cause of mouse-ear. Symptomatic river birch trees growing in a pine bark substrate in containers were treated with foliar applications of nickel sulfate and a substrate drench. Topdress applications of superphosphate (0-46-0) and Miloroganite, products known to contain nickel, were also applied. At 16 days after treatment (DAT), up to 5 cm of new growth occurred on plants sprayed with nickel sulfate and foliar concentrations of nickel in the new growth increased five fold compared to control plants. At 30 DAT, shoot length increased 60%, leaf area increased 83%, and leaf dry mass increased 81% for trees receiving a foliar application compared to non-treated control plants. Treating trees with a substrate drench alleviated symptoms, whereas treatment with superphosphate and Milorganite did not. Trees receiving a foliar or drench application had normal growth for the remainder of the growing season. Additional studies are underway to refine methods of application, rates, and sources of nickel suitable for use.