Showing papers in "Plant Disease in 1993"
TL;DR: Degenerate PCR primers were designed to anneal to highly conserved nucleotide sequences identified in the genomes of 10 whitefly-transmitted geminiviruses, and 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.
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 (.)
763 citations
TL;DR: The 1984 report of A2 mating types of Phytophthora infestans (Mont.) de Bary in western Europe was the first indication of new and dramatic developments in populations of that Fungus, indicating changes were not restricted to western Europe but, rather, were worldwide.
Abstract: The 1984 report of A2 mating types of Phytophthora infestans (Mont.) de Bary in western Europe (20) was the first indication of new and dramatic developments in populations ofthat Fungus. This discovery stimuiated plant pathologists aH over the world to analyze local populations, since previously only the A 1 mating type had been detected outside of central Mexico (Fig. I). The analyses of a large number of dispersed Eocal populations indicated, surprisingly, that the changes were not restricted to western Europe but, rather, were worldwide (Fig. 2) [3,10,23,26,36,41). The recent wortdwide changes in populations mOSK certainly result from migration. Indeed, migration has played an essential role in the entire history of potato late blight. In this article we illustrate that role. To provide context, however, we first present background concerning the basic biology/pathology of P. infestans, the genetic tools used to investigate populations of P. infesrons, and the char. acteristics of the source population of P. infestans.
408 citations
TL;DR: This article will focus on the use and the potentials of molecular genetics, monoclonal antibody technology, and microbial taxonomy to clarify the taxonomy of the pathogenic, describe the pathogen population structure in single plants or fields, and investigate the molecular events occurring in the hostparasite interactions.
Abstract: Bacterial blight of rice, caused by Xanthomonas orpw. aryzap (37), was first reported in Japan over a century ago. Since hen, considerable research on the disease and its causal agent has been reported and reviewed ( 1 8,19,24,29). In the past 10 years, advances in the area of molecular genetics, monoclonal antibody technology, and microbial taxonomy have been made. Now these technologies are being used to characterize the pathogen, reevaluate the ecology and epidemiology of the disease, and study host-parasite interactions. In this article, we will focus on the use and the potentials of these technologies to clarify the taxonomy of the pathogen, describe the pathogen population structure in single plants or fields, and investigate the molecular events occurring in the hostparasite interactions.
253 citations
TL;DR: Leaves of the rapeseed cultivar Jupiter used as a soil amendment effectively reduced Meloidogyne chitwoodi population densities at the zone of incorporation.
Abstract: Leaves of the rapeseed (Brassica napus) cultivar Jupiter used as a soil amendment effectively reduced Meloidogyne chitwoodi population densities at the zone of incorporation. Soil in the zone of incorporation was protected from nematode colonization for 6 wk. Stem and root tissues of rapeseed were also effective when homogenized before being used as an amendment. Greenhouse-grown plants accumulated more glucosinolates and became more effective in suppressing M. chitwoodi with age (.)
184 citations
TL;DR: The strain from wheat infected gramineous plants of five tribes: Hordeae, Festuceae, Aveneae, Chlorideae, and Agrosteae, but not Japanese differential or Brazilian lowland and upland rice cultivars.
Abstract: Isolates of Pyricularia grisea collected from wheat in regions of Brazil were inoculated on various gramineous plants to determine their host range. A set of 42 different gramineous plants belonging to nine tribes was analyzed by plant reactions and sporulation potential. The strain from wheat infected gramineous plants of five tribes: Hordeae, Festuceae, Aveneae, Chlorideae, and Agrosteae, but not Japanese differential or Brazilian lowland and upland rice cultivars
179 citations
TL;DR: There is considerable interest in determining mechanisms accounting for the natural resistance of unripe fruits to fungal pathogens and extending its effectiveness to fruits after harvest.
Abstract: Fungal pathogens must perform precise functions and overcome several barriers before they are able to initiate disease in plants. First, the pathogen must locate and adhere to suscept tissue and then initiate infection (10,12,14). The first plant barriers encountered are generally the cuticle and cell wall, which may be breached by enzymatic (6) or physical (12) assault, or the pathogen may infect through wounds (27). Contact with underlying plant tissues presents the invading pathogen with a different set of barriers, most notably preformed antibiotic compounds and/ or morphologic barriers and phytoalexins induced by the plant (13,25,26). Pathogens that infect fruits are confronted by several problems not normally facing pathogens of vegetative plant tissues. Fruits are generally protected by differentiated integumentary structures, and their physiology changes markedly during development, particularly when ripening occurs. Pathogens frequently infect unripe fruits but cause relatively minor damage until ripening, when they may cause extensive decay. Such quiescent infections have been observed in tropical (l5), subtropical (8), and deciduous fruits (9). The resultant decays have great economic importance, since they reduce the shelf life of fruits during storage and transport (27). These disease problems have been further exacerbated by the development of pathogen resistance to fungicides and the withdrawal of pesticides on environmental grounds. Consequently, there is considerable interest in determining mechanisms accounting for the natural resistance of unripe fruits to fungal pathogens and extending its effectiveness to fruits after harvest. One of the possible mechanisms that may account for such differential
167 citations
TL;DR: Lettuce yield was significantly increased by most solarization treatments in successive fall and spring crops at both locations, but an inhibitory effect on lettuce growth and yield in the fall crop was observed in the plots that were amended with compost after solarization.
Abstract: Two field experiments were conducted to determine effects of commercial chicken compost, ammonium phosphate fertilizer, and solarization, alone or combined, on several soilborne pathogens and the growth and yield of lettuce (Lactuca sativa). Southern root-knot nematode (Meloidogyne incognita) present at one of the sites was effectively controlled by the combination of these treatments, whereas solarization alone gave only partial control. Pythium ultimum was controlled by both solarization alone and combined with chicken compost. Lettuce yield was significantly increased by most solarization treatments in successive fall and spring crops at both locations. However, an inhibitory effect on lettuce growth and yield in the fall crop was observed in the plots that were amended with compost after solarization
157 citations
123 citations
Journal Article•
115 citations
TL;DR: Bacterial canker of tomato (Lycopersicon esculentum Mill.), caused by Clavibacter michigansensis subsp.
Abstract: Bacterial canker of tomato (Lycopersicon esculentum Mill.), caused by Clavibacter michiganensis subsp. michiganensis (Smith) Davis et al, has caused major economic losses in commercial tomato production worldwide. Losses from canker are caused primarily by wilting and collapse of plants, but fruit spotting, also known as bird's-eye spot, reduces the value of f resh-market tomatoes. The disease can occur on pepper and several other members of the Solanaceae, but tomato is the only crop on which it is economically significant. Since its discovery in a Michigan greenhouse in 1909, canker has been reported from virtually all tomatogrowing regions of the world (40). In North America, epidemics have occurred in the U.S. Midwest (1930s and 1980s), Ontario (1960s and 1980s), and North Carolina (1960s), causing yield losses of up to 80% for individual growers and 5-1094 regionally (40). Erwin F. Smith (38) first named the pathogen Bacterium rnichiganense, then Aplanobacter michiganense. After additional attempts at renaming, including Pseudomonas michiganensis, Phytomonas michiganensis, Erwinia michiganensis, and Mycobacterium rnichiganense, the accepted nomenclature became and stayed
115 citations
TL;DR: Pseudomonas cepacia strain AMMD applied as a seed treatment has been used for biocontrol of Pythium damping-off and Aphanomyces root rot of peas and it was found that this strain was effective on four pea cultivars that differed in susceptibility to Aphanomics root rot.
Abstract: Pseudomonas cepacia strain AMMD applied as a seed treatment has been used for biocontrol of Pythium damping-off and Aphanomyces root rot of peas. We tested the biocontrol efficacy of this strain on four pea cultivars that differed in susceptibility to Aphanomyces root rot. In 1990 and 1991, seedling emergence, Aphanomyces root rot severity, and pea yield of biocontrol-treated and nontreated controls were compared in a field naturally infested with Pythium spp. and Aphanomyces euteiches f. sp. pisi
TL;DR: The effectiveness of adult-plant resistance (APR) in protecting grain yields in winter wheat grown in Virginia under varying levels of intensity of powdery mildew obtained with different fungicide treatments in field experiments in two crop years is studied.
Abstract: We studied the effectiveness of adult-plant resistance (APR) in protecting grain yields in winter wheat grown in Virginia under varying levels of intensity of powdery mildew (caused by Blumeria graminis f. sp. tritici) obtained with different fungicide treatments in field experiments in two crop years. Mildew severity was assessed at three to four plant growth stages, and the data were used to calculate mean mildew severity (MMS) and area under the mildew disease progress curve. The susceptible cultivar Saluda had an average MMS of 5.3%. MMS and grain yield for Saluda were significantly negatively correlated in both years, and yield loss averaged 13.4% in untreated plots relative to full-season control plots (.)
TL;DR: Forty-five international races of Pyricularia grisea, representing all nine race groups, were identified in a «hot spot» breeding site (Santa Rosa) in Colombia, with the largest number included in the IA group.
Abstract: Forty-five international races of Pyricularia grisea, representing all nine race groups, were identified in a «hot spot» breeding site (Santa Rosa) in Colombia, with the largest number included in the IA group. The international race system did not fully describe the virulence spectrum of the isolates, since several races could be further differentiated into different pathotypes when local commercial cultivars were used as differentials. Compatibility was present in the pathogen population for at least 13 known resistance genes and resistance sources tested. Frequency of virulent phenotypes on the 42 cultivars tested ranged from 0.0 to 0.86, with no cultivar susceptible to all isolates. The lowest compatibility frequencies were associated with combinations of resistance genes
TL;DR: This report describes concepts concerning reference points for yield and crop loss as well as a hierarchy for threshold terms, then presents a list of terms and definitions to standardize terminology for crop loss assessment.
Abstract: The initial report (14) of a subcommittee of the APS Plant Disease Losses Committee dealt with terms and concepts relating to the measurement of disease intensity to obtain accurate and precise quantitative information on the relationship between disease intensity (stimulus = X) and yield or yield loss (response = Y). In addition to standardizing the terms and concepts for the measurement of disease intensity, members of the full committee identified a need to clarify and standardize terms and concepts pertaining to yield, crop loss, and disease thresholds. A second subcommittee was formed to accomplish this task. This report describes concepts concerning reference points for yield and crop loss as well as a hierarchy for threshold terms, then presents a list of terms and definitions to standardize terminology for crop loss assessment.
TL;DR: Genetic association between the gene Bdv1, which confers slow yellowing to barley yellow dwarf in adult plants, and genes Lr34 and Yr18, which confer partial adult plant resistance to leaf rust and stripe rust, respectively, was investigated.
Abstract: Genetic association between the gene Bdv1, which confers slow yellowing to barley yellow dwarf (BYD) in adult plants, and genes Lr34 and Yr18, which confer partial adult plant resistance to leaf rust and stripe rust, respectively, was investigated. Nearly 115 random F 3 and F 5 lines, derived from the crosses of susceptible cultivar Jupateco 73S with resistant (symptomatically tolerant for BYD) cultivars Jupateco 73R and Condor, and the parents were evaluated for reaction to the three diseases in separate experiments. Resistance to each disease in Jupateco 73R and Condor is conferred by a single gene
TL;DR: The leaf mesophyll susceptibility of 54 citrus species, cultivars, and relatives to Xanthomonas campestris pv.
Abstract: The leaf mesophyll susceptibility of 54 citrus species, cultivars, and relatives to Xanthomonas campestris pv. citrumelo, the cause of citrus bacterial spot, was evaluated in Hastings, Florida, during 1989 and 1990. A similar host range of 53 citrus species, cultivars, and relatives was tested in Beltsville, Maryland, during 1991 to compare their differential susceptibility to X. c. citri, which causes citrus canker, and to X. c. citrumelo by inoculations on foliage of the same trees in replicated field plots. Field-grown trees were pruned to stimulate synchronous leaf flush for inoculation by a modified pinprick method. Lesion size at 60 days (Hastings plots) or 45 days (Beltsville plots) postinoculation was used to quantify leaf mesophyll susceptibility. For X. c. citrumelo inoculations, lesion expansion was greatest on cultivars of trifoliate orange and trifoliate orange hybrids. Smaller lesions formed on Citrus spp. such as grapefruit, sweet orange, sour orange, mandarin, lemon, and their hybrids, with the exception of Key lime, which developed lesions similar to those formed on trifoliate hybrids. Susceptibility of most citrus types to X. c. citri was more general. Lesion sizes resulting from pinprick inoculations with X. c. citri were not significantly different among Citrus spp. and hybrids, indicating a general susceptibility of leaf mesophyll. Smaller lesions generally formed on citrus relatives, including some cultivars of trifoliate orange. Because pinprick inoculations cause wounds and open the leaf mesophyll to direct colonization by bacteria, this method bypasses stomatal infection and does not consider other factors that may affect field resistance.
TL;DR: An electron micrograph showed that the bacterium was rod-shaped with rippled cell walls, and measured from 0.23 1to 0.5 × 1.1 to 3.4 μm (.)
Abstract: Leaf scorch symptoms occurred in 12-20.6% of the pear trees (Pyrus pyrifolia) in the low-altitude areas of central Taiwan in 1990. Symptoms appeared on leaves in early July and stayed until the leaves dropped in winter. If unchecked, dieback of twigs and branches, and finally death of the infected trees occurred within a few years. The disease was closely associated with a xylem-limited bacterium. An electron micrograph showed that the bacterium was rod-shaped with rippled cell walls, and measured from 0.23 1to 0.5 × 1.1 to 3.4 μm (.)
TL;DR: The host range and serological properties of several of these isolates were compared to a PVY N strain from Scotland and other PVY strains from the United States that had been reported to cause necrosis in tobacco.
Abstract: A tobacco veinal necrosis strain of potato virus Y (PVY N ) was detected in tobacco production in Ontario in 1989. Subsequent surveys of potato production in Ontario, Prince Edward Island, New Brunswick, Nova Scotia, and Quebec and of table potatoes imported into Canada from California yielded similar isolates of PVY N . The host range and serological properties of several of these isolates were compared to a PVY N strain from Scotland and other PVY strains from the United States (PVY-NN, PVY-MN, and PVY-36) that had been reported to cause necrosis in tobacco (.)
TL;DR: Holding inoculated mature green and pink tomato fruits for 3 days at 38 C completely inhibited decay caused by Botrytis cinerea, one of the main postharvest pathogens of tomatoes in Israel.
Abstract: Holding inoculated mature green and pink tomato fruits for 3 days at 38 C completely inhibited decay caused by Botrytis cinerea, one of the main postharvest pathogens of tomatoes in Israel. Conidial germination was more sensitive than mycelial growth to 38 C, but inhibition of both processes increased with duration of treatment. The prophylactic effect of heating on decay of tomatoes caused by B. cinerea appeared to be by direct interaction with the fungus rather than by inhibitory effects on fruit ripening. Carbon dioxide production by tomatoes increased and ethylene production decreased during heating, but when fruit were moved to 20 C, gas evolution rates returned to those of nonheated fruit
Journal Article•
TL;DR: Field samples of annual and perennial grasses were tested to determine which can be alternate hosts to wheat streak mosaic virus (WSMV) and can survive and sustain the virus from wheat harvest to fall wheat emergence in Kansas.
Abstract: Field samples of annual and perennial grasses were tested to determine which can be alternate hosts to wheat streak mosaic virus (WSMV) and can survive and sustain the virus from wheat harvest to fall wheat emergence in Kansas. Sites sampled included Conservation Reserve Program (CRP) hectares, government set-aside fields, wheat stubble fields, and waterways. Samples were collected in August of 1988 and at four approximately monthly intervals in 1989 and were tested for the virus by indirect ELISA. None of the perennial grasses sampled were infected, but five annual grass species - Setaria viridis, S. taberi, Eriochloa contracta, Echinochloa crusgalli, and Panicum capillare - plus volunteer wheat were infected throughout this period (.)
TL;DR: The Biolog GN MicroPlate system was evaluated for accuracy in identifying gram-negative and gram-positive phytopathogenic bacteria to genus, species, and pathovar.
Abstract: The Biolog GN MicroPlate system was evaluated for accuracy in identifying gram-negative and gram-positive phytopathogenic bacteria to genus, species, and pathovar. Approximately 1,000 strains of Agrobacterium, Clavibacter, Erwinia, Pseudomonas, and Xanthomonas were compared. Of 79 cultures representing 77 P. syringae strains and eight pathovars, identification to species and pathovar was correct in 100 and 2% of cases, respectively. Of 603 cultures representing 537 X. campestris strains and 28 pathovars, identification to species and pathovar was correct in 97 and 20% of cases, respectively. With E. carotovora and E. chrysanthemi, 22 and 62% of the strains, respectively, were correctly identified to species (.)
TL;DR: A wilt disease was observed in one commercial lettuce field (Lartura sativa «Empire») in Fresno County, California, and in the fall of 1991 in two nearby fields (cvs. Empire and Desert Queen).
Abstract: A wilt disease was observed in the fall of 1990 in one commercial lettuce field (Lartura sativa «Empire») in Fresno County, California, and in the fall of 1991 in two nearby fields (cvs. Empire and Desert Queen). The disease is characterized by the death of some plants in the seedling stage, accompanied by a red streak through the cortex of the crown and upper root. Older affected heads show a tan-to-yellow tipburn with black streaks in the vascular system of some affected leaves, brown streaks in the vascular system of the crown, and a reddish brown discoloration of the cortex of the crown and upper root, Fusarium oxysporum was readily isolated from all affected plants, and in greenhouse inoculations this fungus caused a wilt disease of lettuce but not of any other crop species onto which it was inoculated
TL;DR: Initial screening of citrus tristeza virus isolates under glasshouse conditions on West Indian lime hosts showed that growth was not a good criterion for differentiation among isolates; however, differences in stem pitting symptoms were more distinct.
Abstract: Citrus tristeza virus isolates were collected during 1976 and 1977 from healthy-appearing old grapefruit trees in different climatic areas of South Africa. Initial screening of citrus tristeza virus isolates under glasshouse conditions on West Indian lime (Citrus aurantifolia) hosts showed that growth was not a good criterion for differentiation among isolates; however, differences in stem pitting symptoms were more distinct. This varied greatly, from 2.5 to 76.0 pits per square centimeter. Significant differences occurred among isolates from the same orchard, indicating the presence of multiple strains within an orchard (.)
TL;DR: Four tomato lines, an F 1 hybrid tolerant to tomato yellow leaf curl virus, and the susceptible cultivars 1651, 1630, 614-1, and 199-2 were compared for accumulation of viral DNA in TYLCV-infected plants.
Abstract: Four tomato lines (M-60, M-54, 1970, and 2950), an F 1 hybrid (TY-20) tolerant to tomato yellow leaf curl virus (TYLCV), and the susceptible cultivars 1651, 1630, 614-1, and 199-2 were compared for accumulation of viral DNA in TYLCV-infected plants. DNA was analyzed by either alkaline transfer or dot spot hybridization using a cloned viral DNA as a probe. Results obtained with either procedure indicated that in all tested lines viral DNA accumulation peaked at 12-15 days after inoculation. At this time, accumulation of viral DNA in the tolerant genotypes was 10-50% lower than in the susceptible ones. Viral DNA then decreased up to 50% in both the tolerant and the susceptible lines, and it remained at that level (.)
TL;DR: The barley (Hordeum vulgare) accession Cebada Capa has been used extensively as a source of resistance to the leaf rust pathogen (Puccinia hordei) in the Virginia barley breeding program, and in the mid-Atlantic region of the United States, cultivars derived from it have remained resistant to P. hordei since 1968.
Abstract: The barley (Hordeum vulgare) accession Cebada Capa has been used extensively as a source of resistance to the leaf rust pathogen (Puccinia hordei) in the Virginia barley breeding program, Cebada Capa possesses the resistance gene Rph7; and in the mid-Atlantic region of the United States, cultivars derived from it have remained resistant to P. hordei since 1968. In 1990, outbreaks of leaf rust were observed in Virginia on cultivars carrying Rph7. Isolates of P. hordei collected from these cultivars were found to possess virulence on Cebada Capa in greenhouse and growth chamber experiments. In addition to Virginia, P. hordei isolates with Rph7 virulence were identified in Pennsylvania and California
TL;DR: Standard postharvest handling practices for fresh market carrots grown in organic soils in the Fraser Valley of British Columbia were monitored during 1990-1992 at two grading and packaging operations and disease was not detected on carrots harvested by hand from fields infested with the pathogen.
Abstract: Standard postharvest handling practices for fresh market carrots (Daucus carora) grown in organic soils in the Fraser Valley of British Columbia were monitored during 1990-1992 at two grading and packaging operations. Root samples were obtained from 29 loads over the harvest season (July to November) at various stages after carrots were washed, sized, graded, and packaged; and the samples were assessed for the development of black root rot, caused by Chalara elegans (Thielaviapsis basicola). Disease was not detected on carrots harvested by hand from fields infested with the pathogen, and was less than 5% on carrots sampled from the truck following mechanized harvesting