Effect of temperature and pH onin vitro growth rate and sclerotial density ofColletotrichum coccodes isolates from different VCGs

The radial growth rate and sclerotial density ofColletotrichum coccodes isolates representing four major vegetative compatibility groups (VCGs) were determined at three temperatures (21,25, and 30 C) and three pH levels (pH 5, 6, and 7). This is the first report indicating thatC. coccodes isolates characterized to the same VCG share common physiological traits. The optimal temperature for growth of isolates from all four VCGs was 25 C, except for VCG1 isolates, for which growth at 21 and 25 C was equivalent. The growth rate of all isolates, of all VCG groups was decreased at 30 C, whereas sclerotia development was enhanced. The optimal pH level for growth of all isolates was pH 6 and pH 7. Interactions between VCGs and temperature or pH were observed in relation to radial growth rate and sclerotia density. At 25 C, isolates from VCG1 and 2 demonstrated the most rapid growth rate. At 21 and 30 C, VCG1 isolates demonstrated the fastest growth compared with all other VCGs. In response to pH, VCG1 and 2 demonstrated the fastest growth rates at all pH levels. VCG3 and 4 demonstrated the highest sclerotial density at 25 C and at pH 6; and VCG2 and 4 demonstrated the highest sclerotial density at 30 C.     

Recovery ofVerticillium dahliae from North American certified seed potatoes and characterization of strains by vegetative compatibility and aggressiveness

Samples of tubers collected from commercial potato seed lots produced across North America were assayed forVerticillium dahliae. V. dahliae was successfully isolated from 65 of 224 seed lots tested, a successful isolation rate of nearly 30%. Vegetative compatibility of the isolates was assessed through complementation tests using nitrate non-utilizing mutants. AllV. dahliae isolates belonged to vegetative compatibility group (VCG) 4. Of the 162 isolates recovered, 64% belonged to VCG 4A, 33% to VCG 4B, and 3% to VCG 4AB. All 39 of the isolates tested in the greenhouse on potato cv. Superior were pathogenic to potato. Disease symptoms developed earlier, were more severe, and plants died earlier when inoculated with VCG 4A compared to 4B isolates. As a group, AUSPC values were significantly higher (p=0.05) for VCG 4A than for 4B isolates. These data suggest that (1) commercial certified seed tubers from diverse locations are commonly infected withV. dahliae and thus may serve as primary sources of the pathogen; (2) potato isolates ofV. dahliae in North America belong to VCG 4A and 4B and these strains are widely distributed via seed tubers; and (3) VCG 4A and 4B are distinct pathotypes ofV. dahliae that vary in their aggressiveness to potato.     

Response ofColletotrichum coccodes to fungicidesin vitro

Black dot is an important disease of potato that affects all plant parts. The causal agent,Colletotrichum coccodes, is commonly found on potato tubers used for seed. Our objective was to determine thein vitro sensitivity ofC. coccodes to the fungicides maneb, thiabendazole, imazalil and CGA 173506, a phenylpyrrole. These fungicides are currently used, or are being tested for use, as potato seed treatments in the United States. All four fungicides reduced radial growth, sclerotial germination and spore germination ofC. coccodes at 10 μg/ml and higher. The fungicide concentrations that inhibited radial growth by 50% were 2 μg/ml, 5 μg/ml, 35 μg/ml, and 40 μg/ml for imazalil, CGA 173506, maneb and thiabendazole, respectively. TBZ was less inhibitory than the other three fungicides and stimulated sclerotial productionin vitro. Isolates ofC. coccodes differed in their sensitivity to maneb, thiabendazole and imazalil in radial growth, but not spore and sclerotial germination, assays. On CGA 173506, radial growth of fourC. coccodes isolates was inhibited, but these isolates produced sectors which grew normally. Germination of most sclerotia from these isolates was inhibited, but some germinated and produced normal colonies in the presence of CGA 173506. OneC. coccodes isolate was resistant to this fungicide in all assays.     

Population structure ofGibberella pulicaris (AnamorphFusarium sambucinum) from potato tuber dry rot in North America and Europe

Gibberella pulicaris is the sexual stage ofFusarium sambucinum, the major cause of potato tuber dry rot in North America and Europe. In a previous study 42 strains from dry-rotted tubers in North America were analyzed for genetic diversity by mating type and vegetative compatibility group (VCG) tests. In the present study, an additional 96 strains from North America, 21 strains from Europe, and six strains from other geographic areas were analyzed. Both mating types, MAT1-1 and MAT1-2, occur widely outside North America. In contrast, all but two, Canadian, strains of the 138 North American strains analyzed to date are MAT1-1. VCG analysis provides additional evidence that genetic diversity ofG. pulicaris from potato tubers is high in Europe but low in the United States. These results suggest that the potential for pathogen change due to sexual recombination is low in the United States, but may be higher in Europe. Limited genetic diversity ofG. pulicaris in the United States indicates that there are likely to be few barriers to heterokaryon formation and asexual recombination in the field. Thus, the potential exists for rapid spread and persistence of advantageous mutations throughout theG. pulicaris population, which may have contributed to the recent proliferation of strains resistant to the fungicide thiabendazole which has been widely used to control tuber dry rot.     

Infection of aerial parts of potato plants byColletotrichum coccodes and its effects on premature vine death and yield

Collectotrichum coccodes, the pathogen causing black dot disease of potato, was investigated to determine its potential for causing symptoms on the aerial parts of potato plant, premature vine death, and reduction in yield under greenhouse and field conditions. Spray inoculations with conidial suspensions (10⁶ colony forming units/ml) ofC. coccodes caused sunken, dark, necrotic lesions on stems, leaves and petioles, vein and leaf necrosis, dieback and premature vine death under growth chamber and greenhouse conditions. Field inoculations in 1986 and 1987 provided evidence for an increased incidence of premature vine death in seven potato genotypes (Russet Burbank, Norgold Russet, Superior, Butte, NDA 8694-3, A68113-4 and A66107-51). Late season application of metribuzin at 0.84 kg/ha significantly increased the incidence of stems with black dot symptoms in cv. Russet Burbank at one location. Field inoculations in 1987 at two locations resulted in yield reduction in the late-maturing cv. Russet Burbank (6.3 and 6.5 t/ha) and clone A68113-4 (5.0 t/ha), but not in the early maturing cv. Norgold Russet. Similar results were obtained in greenhouse studies following soil inoculations withC. coccodes: yield reduction was observed in cv. Russet Burbank but not in cvs. Norgold Russet, Superior and Katahdin. Colonization of stem ends of tubers byC. coccodes from spray inoculated field plots was higher than in tubers from uninoculated plots at one of the two locations. These results point to a much broader potential ofC. coccodes as a potato pathogen, than hitherto documented. Colletotrichum coccodes (Wallr.) Hughes (syn.C. atramentarium (Berk. & Br. Taub.) was described in 1825 (21) and has a wide host range (5). Potato and tomato are the more economically important hosts. This fungus has been variously referred to as an unspecialized, minor pathogen or secondary invader (18), weak pathogen (22), specialized parasite (5), or superficial colonizer and widespread epiphyte (19). The symptoms produced by this pathogen on potato have been described as black dot (10, 14) on stems, stolons, tubers and roots, sometimes associated with leaf scorch or wilt (24), rubbery tuber wilt (1), and tuber skin necrosis (17). The fungus is commonly associated with senescent, decaying root and stem tissue, especially at the end of the season. In Idaho, instances of premature death of potato without typical symptoms of Verticillium wilt, but accompanied by a high incidence of stems with black dot symptoms, have been observed in potato crops grown on fields fumigated with metam sodium. Additional observations by growers have also implicated the possible interaction of the herbicide metribuzin with the incidence of black dot. Although it was observed by some workers to accelerate leaf senescence (12, 22), Schmiedeknecht (21) concluded thatC. coccodes was unable to infect the green leaves of potato plant. Even thoughVerticillium dahliae is generally considered the major factor in potato early dying (20), several workers (7, 11, 13, 19, 22) have investigated the possible role ofC. coccodes in causing premature death of potato (8). However, these studies examinedC. coccodes only as a soilborne, root and tuber pathogen of potato; its effects on shoot portions (aerial parts) of the plant were not considered. In addition to causing anthracnose of fruits of tomato, pepper and squash (18), recent reports indicate thatC. coccodes causes foliage blights on eastern black nightshade (2) and velvetleaf (25). The objectives of this study were: (1) to examine the potential ofC. coccodes to cause symptoms on aerial parts of potato plant, (2) to investigate the effect of spray inoculation in the field withC. coccodes on incidence of premature vine death, tuber colonization and yield of potato, and (3) to document the effect of soil inoculation withC. coccodes alone or in combination withV. dahliae on potato varieties under greenhouse conditions.     

Colonization of rotation crops and weeds by the potato black dot pathogenColletotrichum coccodes

The rotation crops wheat, barley, oat, maize, soybean, rye, yellow mustard, alfalfa, and spring canola and weeds eastern black nightshade, velvetleaf, timothy grass, orchard grass, and Giant foxtail common to potato-growing areas in North America were used to study the host range ofColletotrichum coccodes, the causal agent of potato black dot. The fungus was isolated from nine of 14 rotation crops and weeds that were inoculated: yellow mustard, soybean, spring canola, alfalfa, oat, eastern black nightshade, velvetleaf, giant foxtail, and timothy grass. In all, colonization was highest in black nightshades (87%) and velvetleaf (80%). Among the rotation crops, colonization was highest on yellow mustard (59%) followed by spring canola (33%) and soybean (30%).Colletotrichum coccodes was not isolated from wheat, barley, rye, maize, or orchard grass. The results indicated that crops used for rotation with potato should be selected carefully to prevent the increase ofC. coccodes inoculum in the soil and that weeds may help maintain viable inoculum ofC. coccodes in the absence of potato. Based on these results we recommend that wheat, barley, maize, or rye be used in rotation with potato in areas whereC. coccodes is present in high levels in the soil.     

Prevalence of fumonisin-producing Fusarium species in Brazilian corn grains

The aims of this study were to perform morphological and molecular characterization of Fusarium species within the Liseola section isolated from corn grains from different geographic regions in Brazil, and to evaluate their potential for fumonisins production. The results showed that Fusarium verticillioides is the predominant species (99%) associated with corn grains, and other toxigenic species, Fusarium proliferatum, was incidental in Brazilian corn. Although there was a high variability in the total fumonisin production among the isolates (0.01–2.39 μg g⁻¹), all fifty isolates analyzed produce fumonisins. The level of total fumonisin production was not correlated with the geographic origin of the isolates.     

Evaluating Incidence of Helminthosporium solani and Colletotrichum coccodes on Asymptomatic Organic Potatoes and Screening Potato Lines for Resistance to Silver Scurf

Silver scurf, caused by Helminthosporium solani, and black dot, caused by Colletotrichum coccodes, cause tuber blemishes on potato (Solanum tuberosum L.) which affect processing and fresh market trade. Tubers from ten cultivars were collected at harvest from three organic farms in Wisconsin and categorized as symptomatic or asymptomatic based on visual symptoms of silver scurf and black dot and/or signs of H. solani and C. coccodes. Tuber incubation and PCR assays were performed on asymptomatic tubers to detect H. solani and C. coccodes. Tuber incubation and PCR assays were in slight to fair agreement (kappa coefficient <0.4) for detecting both pathogens. Most asymptomatic tubers tested were positive by one or both assays for H. solani (75 %) or C. coccodes (94 %). Minituber inoculation assays were also performed to screen potato lines for resistance to silver scurf. Of the 14 lines tested, a diploid interspecific hybrid, C287, had consistently low sporulation, suggesting it has partial resistance to silver scurf. Since the majority of tubers harvested are already infected with one or both pathogens further research should focus on organically acceptable management practices that may inhibit disease development in field and in storage.     

Characterization of fungicide resistant isolates of Phaeoacremonium aleophilum infecting grapevines in Spain

Fungicide resistance in Phaeoacremonium aleophilum, one of the most frequent fungal pathogens associated with grapevine trunk diseases, was investigated and found to exist in some isolates of the pathogen against a commercial formulation, Escudo^®. The effect of this compound and its two active substances, carbendazim and flusilazole, was first evaluated on the mycelial growth of P. aleophilum. Escudo^®-resistant isolates were estimated at a frequency of 24% in Spanish vineyards. Then, the two active substances were used individually to test their effect on mycelia growth of twelve single-spore cultures originating from six Escudo^®-resistant isolates. Flusilazole (DMI-triazole) did not inhibit mycelia growth of any single-spore cultures of P. aleophilum. Carbendazim (benzimidazole) used alone allowed the growth of the same single-spore cultures that were also resistant to Escudo^®. AFLP characterization of sensitive and resistant single-spore cultures showed genetic diversity within P. aleophilum isolates but no AFLP markers were associated with resistance. New primers set (L2/R1) were designed to partially amplify the exon 6 of the beta-tubulin gene of P. aleophilum. Two different point mutations resulted in glycine (GGC) or lysine (AAA) replacing the glutamic acid (GAG) at codon 198 of the beta-tubulin gene in some of the resistant single-spore cultures studied. Resistant single-spore cultures of P. aleophilum were shown to have different aggressiveness levels as sensitive single-spore cultures by inoculation of wood segments of Vitis vinifera in the presence and absence of fungicide.     

Potato Virus Y NTN : A Coat and P1 Protein Sequences Analysis of a Brazilian Isolate

Potato tubers (Solanum tuberosum L. cv. Monalisa) showing superficial necrotic rings typical of Potato virus Y ^NTN (PVY^NTN) infection were collected from commercial potato fields in the State of São Paulo (Brazil). An isolate named IAC-PVY^NTN was characterized by sequencing 822 and 836 nucleotides from the coat protein and P1 protein coding genes, respectively. The IAC-PVY^NTN was observed as a European/North American recombinant isolate closely related to three Eu-PVY^NTN isolates that share an alternative recombination site in the coat protein cistron near position 144. Therefore, the IAC-PVY^NTN isolate may represent a novel recombinant variant between PVY^N N-605 Swiss (European) and PVY O-139 Canadian (North American). Cluster analysis of the P1 sequences found IAC-PVY^NTN in the sub-cluster of Eu-PVY^N/NTN/N:O. This study supports previous evidence of a common origin for PVY^N/NTN in Europe and Brazil.     

Effects of Soil Water Level,Black Dot (Colletotrichum coccodes) Infested Soil and Nutrient Depletion on Potato in a Controlled Environment

The effects of soil water level and soil infested or not infested with Colletotrichum coccodes were quantified and compared on Umatilla Russet potato in repeated greenhouse trials. Nitrogen levels in leaflets and tuber yield differed significantly for effect of water level but there was no effect for soil infestation in both trials. More leaflet N as measured by chlorophyll and less tuber yield occurred in the low than the medium and high soil water treatments. Number of progeny tubers was not affected by C. coccodes but numbers were significantly less for the low water level than the high water level in one trial. Root weight was significantly reduced by C. coccodes in both trials and was significantly less in the high than the low and medium soil water levels in one trial. Incidence of infected progeny tubers was significantly reduced in infested soils for the low soil water compared to the medium or high soil water levels in one trial. The effect of increasing levels of water in infested soils had large and significant increases for percentage of stem area with sclerotia in both trials. Managing soil water by not overwatering in irrigated potato fields in the presence of C. coccodes may reduce black dot severity and quantity of sclerotia that potentially can overwinter and serve as sources of infection for subsequent crops. Analyses demonstrated a potential for significant associations between plant and disease variables not evidence for cause and effect.     

Identification of mating types and metalaxyl resistance in North American populations ofPhytophthora infestans

The A² mating type ofPhytophthora infestans was first reported in the United States in 1990. Concurrently,P. infestans strains resistant to metalaxyl ere found in the Pacific Northwest. Collaborative surveys were undertaken during 1991–1993 to investigate the frequency of occurrence of A² mating types and metalaxyl resistant strains in populations ofP. infestans isolated from outbreaks of late blight in potato and tomato crops in North America.In vitro testing indicated that isolates from the northeastern U.S. and Atlantic Canada were primarily (52/55) metalaxyl sensitive and all were A¹ mating types. Among 85 isolates from late blight epidemics in Florida and Texas, greater than 61% were both metalaxyl resistant and A² mating type. Metalaxyl resistance and A² mating types were identified also in a few tomato isolates from North Carolina. Although the majority of 134 isolates from the Pacific Northwest (British Columbia and Washington) were metalaxyl resistant, only 2 isolates from Washington were A² mating types. Among 111 isolates from 2 sites in central Mexico, 63% and 77% were both metalaxyl resistant and A² mating types. The data indicate also a higher frequency of metalaxyl resistance in A² isolates, than in A¹ isolates, among isolates from Florida and Texas. Highest metalaxyl resistance levels were found, however, in A¹ isolates from California, where no A² isolates were recovered.     

Virulence Complexity and High Levels of Fungicide Resistance Suggest Population Change of Phytophthora infestans in the Heilongjiang Province of China

Samples of Phytophthora infestans were isolated from 12 city and county fields in the main potato production areas of Heilongjiang province of China between 2004 and 2008. A total of 72 isolates were tested for virulence on a potato R gene differential set and 39 of these isolates were also analysed for their resistance to the fungicide metalaxyl. All 11 differential plants were infected by one or more of the isolates collected; the most commonly overcome differentials were R1, R3, R4, R7, R10, and R11. Most (89.7%) of the tested isolates were resistant to metalaxyl and the rest (10.3%) were sensitive. The proportion of metalaxyl-resistant isolates differed between sites (χ ²?=?25.42, df?=?10, p?<?0.005), but not between years (χ ²?=?4.63, df?=?4, p?>?0.05). Taken together and in comparison with earlier pathogen population studies, our findings suggest that the population of P. infestans in Heilongjiang is different from that existing in the province two decades ago and that at various locations within the province, the new population has a high frequency of resistance to metalaxyl.     

Anastomosis Group and Pathogenicity of <Emphasis Type="Italic">Rhizoctonia solani </Emphasis>Associated with Stem Canker and Black Scurf of Potato in Heilongjiang Province of China

From 2012 to 2015, a total of 226 isolates of Rhizoctonia solani were collected from the stem cankers on potato stems and sclerotia on tubers from different potato cultivation areas of Heilongjiang Province, China. These isolates were assigned to the anastomosis group (AG) by performing conventional PCR assays using previously published primers for ITS-rDNA regions, as well as by observing hyphal interactions where appropriate. Most of the isolates were assigned to AG-3PT (58.85 %), and several were assigned to AG-5 (21.68 %), AG-2-1 (7.08 %) and AG-4 (12.39 %). Pathogenicity tests showed that the AG-3 and AG-5 isolates had the highest virulence, and the disease indices were 1.96a and 2.47a for stem and 1.48a and 1.6a for root (P < 0.05) after analyzed by LSD multiple comparisons, respectively. Both two isolates consistently caused large brown lesions with sunken on the potato stems and roots in in vitro and greenhouse experiments. This is the first detailed report on the AG composition, variability and pathogenicity of R. solani isolates associated with stem cankers and black scurf found on potatoes cultivated in Heilongjiang Province.     

Genetic Diversity among Parents of Hybrid Rice Based on Cluster Analysis of Morphological Traits and Simple Sequence Repeat Markers

Heterosis has been successfully exploited on a large scale in rice (Oryza sativa L.), which is a self-pollinated crop. The selection of parental lines plays a vital role in developing ideal combinations. Therefore, it is essential to study the relationshi…     

Therapeutic Potential and Nutraceutical Profiling of North Bornean Seaweeds: A Review

Malaysia has a long coastline surrounded by various islands, including North Borneo, that provide a suitable environment for the growth of diverse species of seaweeds. Some of the important North Bornean seaweed species are Kappaphycus alvarezii, Eucheuma denticulatum, Halymenia durvillaei (Rhodophyta), Caulerpa lentillifera, Caulerpa racemosa (Chlorophyta), Dictyota dichotoma and Sargassum polycystum (Ochrophyta). This review aims to highlight the therapeutic potential of North Bornean seaweeds and their nutraceutical profiling. North Bornean seaweeds have demonstrated anti-inflammatory, antioxidant, antimicrobial, anticancer, cardiovascular protective, neuroprotective, renal protective and hepatic protective potentials. The protective roles of the seaweeds might be due to the presence of a wide variety of nutraceuticals, including phthalic anhydride, 3,4-ethylenedioxythiophene, 2-pentylthiophene, furoic acid (K. alvarezii), eicosapentaenoic acid, palmitoleic acid, fucoxanthin, β-carotene (E. denticulatum), eucalyptol, oleic acid, dodecanal, pentadecane (H. durvillaei), canthaxanthin, oleic acid, pentadecanoic acid, eicosane (C. lentillifera), pseudoephedrine, palmitic acid, monocaprin (C. racemosa), dictyohydroperoxide, squalene, fucosterol, saringosterol (D. dichotoma), and lutein, neophytadiene, cholest-4-en-3-one and cis-vaccenic acid (S. polycystum). Extensive studies on the seaweed isolates are highly recommended to understand their bioactivity and mechanisms of action, while highlighting their commercialization potential.     

Sensitivity and cross-resistance patterns to demethylation-inhibiting fungicides in California populations of Alternaria alternata pathogenic on pistachio

Alternaria late blight (ALB) caused by Alternaria spp. is an annual production concern for pistachio growers in California. In this study, isolates of Alternaria alternata collected from California pistachio orchards between 1998 and 2003 (population A, n = 46) and in 2010 (population B, n = 38) prior to the registration and use of sterol demethylation-inhibiting (DMI) fungicides for ALB control, were tested for their sensitivity to difenoconazole, propiconazole, and tebuconazole using an in vitro mycelial growth assay. The 50% effective dose (EC₅₀) values for isolates in population A to difenoconazole, propiconazole, and tebuconazole, respectively, ranged from 0.02 to 0.82 μg/mL (mean = 0.17), 0.25–5.73 μg/mL (mean = 1.29), and 0.02–2.76 μg/mL (mean = 0.96), and from 0.02 to 0.93 μg/mL (mean = 0.21), 0.13–5.36 μg/mL (mean = 1.25), and 0.17–5.47 μg/mL (mean = 1.03) for those in population B. Among 65 isolates collected in 2012 from orchards with very limited exposure to difenoconazole, propiconazole or metconazole (population C, n = 65), the EC₅₀ values for tebuconazole ranged from 0.02 to 2.99 μg/mL (mean = 0.51), while EC₅₀ values for difenoconazole of 55 of these isolates varied from 0.01 to 0.44 μg/mL (mean = 0.06). The DMI-exposed population C was found to be on average two to four times less sensitive compared with the populations A and B. Pearson correlation analyses of EC₅₀ values for the three fungicides showed significant positive correlations between the sensitivities of tebuconazole and propiconazole (P < 0.01, r = 0.32), tebuconazole and difenoconazole (P < 0.01, r = 0.26), and difenoconazole and propiconazole (P < 0.01, r = 0.40). Results indicate a clear difference in fungicide intrinsic activity, with difenoconazole being more active than the two other DMIs. Although wide variations in sensitivities for tebuconazole and propiconazole were observed in the non- and DMI-exposed Alternaria populations, efficacy of DMI products has been excellent against ALB. The data collected here will be crucial for the rational use of DMIs in fungicide spray programs for ALB management and serve as a reference to detect any shifts in A. alternata sensitivity to these fungicides in subsequent years as they become more frequently used in California pistachios.     

Yield Traits and Associated Marker Segregation in Elite Introgression Lines Derived from O. sativa × O. nivara

Introgression lines(ILs)derived from interspecific crosses are a source of new genetic variability.A total of 55 ILs derived from two crosses Swarna×O.nivara IRGC81848(population A)and Swarna×O.nivara IRGC81832(population B)were characterized for yield and yield-related traits/QTLs.Segregation of 103 simple sequence repeat(SSR)markers associated with yield-related QTLs was studied.Population A showed an average of 12.6%homozygous O.nivara alleles and population B showed 10.6%.Interestingly,three SSR markers,RM223,RM128 and RM517,showed conspicuous pattern of segregation.The distribution of parental alleles at three loci RM223,RM128 and RM517 linked to yield-related traits was unique.These markers flanked to several yield-related QTLs.RM223,flanking to qyld8.3,was heterozygous in almost all the 55 ILs except in IL10-3S and IL131S.RM128 on chromosome 1 and RM517 on chromosome 3 were mutually exclusive in 46 out of 55 ILs.These 46 ILs showed either of the marker allele RM128 or RM517 from O.nivara but not both.IL166S had both RM128and RM517 from O.nivara and the other ILs showed homozygous Swarna allele at RM517 except IL65S.Population structure assigned the 55 ILs to three sub-populations based on their genomic diversity.IL65S,IL166S,IL248S,IL7K and IL250K showed high yields in multi-location trials,and IL248S was released for cultivation as DRRDhan 40.