Plant Disease 

About: Plant Disease is an academic journal published by American Phytopathological Society. The journal publishes majorly in the area(s): Biology & Medicine. It has an ISSN identifier of 0191-2917. Over the lifetime, 20613 publications have been published receiving 398302 citations.

Mechanisms Employed by Trichoderma Species in the Biological Control of Plant Diseases: The History and Evolution of Current Concepts.

Abstract: Fungal species belonging to the genus Trichoderma are worldwide in occurrence and easily isolated from soil, decaying wood, and other forms of plant organic matter. They are, for the most part, classified as imperfect fungi, in that they have no known sexual stage. Rapid growth rate in culture and the production of numerous spores (conidia) that are varying shades of green characterize fungi in this genus. The reverse side of colonies is often uncolored, buff, yellow, amber, or yellow-green, and many species produce prodigious quantities of thick-walled spores (chlamydospores) in submerged mycelium (8). The potential of Trichoderma species as biocontrol agents of plant diseases was first recognized in the early 1930s (31), and in subsequent years, control of many diseases has been added to the list (1,3,5,7,9,11,19, 23,29,34,37,40). This has culminated in the commercial production of several Trichoderma species for the protection and growth enhancement of a number of crops in the United States (24), and in the production of Trichoderma species and mixtures of species in India, Israel, New Zealand, and Sweden (D. R. Fravel, personal communication). One of the most interesting aspects of the science of biological control is the study of the mechanisms employed by biocontrol agents to effect disease control. Past research indicates that the mechanisms are many and varied, even within the genus Trichoderma. In order to make the most effective use of biocontrol agents for the control of plant diseases, we must understand how the agents work and what their limitations are. We can then develop effective means of culturing, storing, applying, and utilizing biocontrol agents so that we harness their best effort for disease control. The selected research papers cited in this article were chosen because they illustrate what has been learned about mechanisms involved in biocontrol with Trichoderma species.

Scab of wheat and Barley : A re-emerging disease of devastating impact

Abstract: cab can be a devastating disease affecting all classes of wheat and other small grains. This fungal disease, also called Fusarium head blight (FHB), has the ability to completely destroy a potentially high-yielding crop within a few weeks of harvest. Lush, green fields become blighted seemingly overnight (Figs. 1 and 2). Frequent rainfalls, high humidities, and/or heavy dews that coincide with the flowering and early kernel-fill period of the crop favor infection and development of the disease. Damage from head scab is multifold: reduced yields, discolored, shriveled “tombstone” kernels (Figs. 3 to 5), contamination with mycotoxins, and reduction in seed quality. The disease also reduces test weight and lowers market grade. Difficulties in marketing, exporting, processing, and feeding scabby grain are experienced. In North America, Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein.) Petch; synonym = G. saubinetti) predominates among several Fusarium species that can cause scab (4,5,8,40,48,60). Other species may predominate in cooler climates or where crops other than wheat and corn are dominant (8,40,48,60). F. graminearum also is associated with stalk and ear rot of corn and may cause a root rot of cereals. The fungus persists and multiplies on infected crop residues of small grains and corn. The chaff, light-weight kernels, and other infected head debris of wheat and barley, returned to the soil surface during harvest, serve as important sites of overwintering of the fungus. Continued moist weather during the crop growing season favors development of the fungus, and spores are windblown or water-splashed onto heads of cereal crops. Wheat and barley are susceptible to head infection from the flowering (pollination) period up through the soft dough stage of kernel development. Spores of the causal fungus may land on the exposed anthers of the flower and then grow into the kernels, glumes, or other head parts. Excellent descriptions of the disease cycle and spore stages of the causal fungi have been published (4,8,21,40,48). Mycotoxins are frequently associated with the growth and invasion of cereal grains by scab fungi. The most common toxin associated with F. graminearum– infected grain is vomitoxin (deoxynivalenol). Vomitoxin is known to cause vomiting and feed refusal in nonruminant animals and poses a threat to other animals and humans if exposure levels are high (45). The presence of mycotoxins in infected grain further exacerbates the losses that scab can cause. Recent articles have reviewed the epidemiology, management, and history of scab outbreaks in the United States, Canada, Europe, Asia, and South America (5,40,45,48). As these papers indicate, numerous research and survey reports have described the worldwide occurrence and epidemic levels of scab during the past century. Yield loss reports have not always been based on replicated research trials, but extensive surveys of producers’ fields have provided assessments of head blighting severity, which were translated into yield loss estimates. In the United States, scab was found in 31 of 40 states surveyed in 1917, with losses estimated at 288,000 metric tons (10.6 million bushels), primarily in Ohio, Indiana, and Illinois (4). Scab caused an estimated loss of 2.18 million metric tons (80 million bushels) of winter and spring wheat throughout the United States in 1919 (14). Extensive field surveys

First Report of the Cereal Cyst Nematode Heterodera latipons on Wheat in Morocco

Abstract: From May to June 2011, during a survey of the wheat-growing areas in Meknes in the Sais Region of Morocco, several cyst nematode populations were detected. Sampling was performed 1 month before wheat (Triticum durum) harvest, in fields showing patches of stunted plants. Plants were growing poorly, had chlorotic lower leaves, and a reduced numbers of ears. Root systems were short and had a bushy appearance because of increased secondary root production. No cysts were visible on the roots, but were found in the soil. Cysts were collected from soil on 200-μm sieves by the modified Cobb decanting and sieving method (1) and identified by morphology and internal transcribed spacer (ITS)-rDNA sequencing. All isolates were identified as Heterodera avenae except the isolate from Ain Jemâa. From the latter, key morphological features from cysts and second-stage juveniles (J2) were determined. The cysts (n = 10) had the following characteristics: bifenestrate vulval cone, body length without neck 590 μm (551 to 632 μm), body width 393 μm (310 to 490 μm), neck length 75 μm (65 to 90 μm), fenestra length 64 μm (60 to 72 μm) and width 21 μm (18 to 25 μm), underbridge length 96 μm (85 to 115 μm), vulval slit length 8 μm (7 to 9 μm), vulva bridge width 27 μm (24 to 33 μm), and bullae absent. The J2s (n = 10) had the following characteristics: body length 445 μm (412 to 472 μm), body width 19 μm (19 to 21 μm), stylet length 24 μm (23 to 25 μm), four lateral lines, tail length 50 μm (46 to 54 μm), and hyaline terminal tail 28 μm (24 to 31 μm). Values of the morphological characters were within the range of H. latipons reported by Handoo (3). The bifenestrate cysts with a strong underbridge and no bullae and J2 with a tail length greater than 40 μm, a stylet longer than 15 μm, and four incisures in the lateral field were typical for H. latipons. To confirm the identification, molecular observations were made. DNA was extracted from three juveniles from three different cysts separately (4). The ITS-rDNA region was amplified using the primers 5'-CGT AAC AAG GTA GCT GTA G-3' and 5'-TCC TCC GCT AAA TGA TAT G-3' as described by Ferris et al. (2). This resulted in a 1,040-bp DNA fragment. The PCR-products were purified and sequenced (Macrogen, Inc., Seoul, Korea). All sequences obtained (GenBank Accession Nos. per cyst: JQ319035, JQ319036, and JQ319037) were compared with sequences available from the GenBank database ( www.ncbi.nlm.nih.gov ), including several species of Heterodera. This comparison revealed a sequence similarity of 97 to 99% with H. latipons and 89% or lower with any other species of Heterodera. Morphological and molecular identification demonstrated that the population of cyst nematodes from a wheat field in Ain Jemâa, Morocco was H. latipons. In the patches with poor growing plants, 65 cysts per 100 cm3 soil were found. To our knowledge, this detection represents a new record of H. latipons. Since the nematode can cause considerable damage to wheat, one of the main cereals produced in Morocco, care should be taken to prevent the spread to other regions. References: (1) K. R. Barker. Page 19 in: An Advanced Treatise on Meloidogyne. Vol II. Methodology. C. C. Carter and J. N. Sasser, eds. North Carolina State University Graphics, Raleigh, 1985. (2) V. R. Ferris et al. Fundam. Appl. Nematol. 16:177, 1993. (3) Z. A. Handoo. J. Nematol. 34:250, 2002. (4) M. Holterman et al. Mol. Biol. Evol. 23:1792, 2006.

Use of degenerate primers in the polymerase chain reaction to detect whitefly-transmitted geminiviruses

Abstract: Geminiviruses are widely recognised as a serious threat to vegetable production in many tropical and subtropical regions. This has increased the need for accurate identification of these viruses. Geminiviruses are well suited to polymerase chain reaction (PCR) methods because they replicate via a double-stranded, circular DNA form. Degenerate PCR primers were designed to anneal to highly conserved nucleotide sequences identified in the genomes of 10 whitefly-transmitted geminiviruses. The PCR primers were tested for their effectiveness in the amplification of viral DNA fragments from the DNA-A and/or DNA-B components of 15 previously uncharacterized geminiviruses from the Americas, the Caribbean Basin, and Africa (.)