Incidence Of Infected Plants Research Articles

Evaluation of Rice Resistance to Southern Rice Black-Streaked Dwarf Virus and Rice Ragged Stunt Virus through Combined Field Tests, Quantitative Real-Time PCR, and Proteome Analysis.

Diseases caused by southern rice black-streaked dwarf virus (SRBSDV) and rice ragged stunt virus (RRSV) considerably decrease grain yield. Therefore, determining rice cultivars with high resistance to SRBSDV and RRSV is necessary. In this study, rice cultivars with high resistance to SRBSDV and RRSV were evaluated through field trials in Shidian and Mangshi county, Yunnan province, China. SYBR Green I-based quantitative real-time polymerase chain reaction (qRT-PCR) analysis was used to quantitatively detect virus gene expression levels in different rice varieties. The following parameters were applied to evaluate rice resistance: acre yield (A.Y.), incidence of infected plants (I.I.P.), virus load (V.L.), disease index (D.I.), and insect quantity (I.Q.) per 100 clusters. Zhongzheyou1 (Z1) and Liangyou2186 (L2186) were considered the most suitable varieties with integrated higher A.Y., lower I.I.P., V.L., D.I. and I.Q. features. In order to investigate the mechanism of rice resistance, comparative label-free shotgun liquid chromatography tandem-mass spectrometry (LC-MS/MS) proteomic approaches were applied to comprehensively describe the proteomics of rice varieties’ SRBSDV tolerance. Systemic acquired resistance (SAR)-related proteins in Z1 and L2186 may result in the superior resistance of these varieties compared with Fengyouxiangzhan (FYXZ).

Assessment of the effect of surface drip irrigation on Verticillium dahliae propagules differing in persistence in soil and on verticillium wilt of olive

For efficient integrated management of verticillium wilt in olive (VWO), it is important to establish whether irrigation treatments (with Verticillium dahliae‐free water) that mitigate the disease in V. dahliae‐infested soil, also reduce the levels of more and less persistent propagules of the pathogen in the soil. Effects of irrigation on VWO and V. dahliae propagules were evaluated under natural environmental conditions. Potted plants were irrigated (pathogen‐free water) to two ranges of soil water content (RWC; high and low) at three surface drip‐irrigation frequencies (daily, weekly, and daily during some periods and otherwise weekly). VWO and total inoculum density (ID), density of less persistent micropropagules (MpD) and more persistent sclerotia in wet soil (SwD), and sclerotia density for air‐dried soil (SdD) were monitored. A logistic model (multiple sigmoid) of disease incidence revealed the lowest parameter values in treatments irrigated daily. Daily frequency of irrigation showed significantly lower disease incidence (39.2%) and disease intensity index (43.9%) and MpD (88.0%) values as areas compared with other frequencies, regardless of the RWC. High RWC significantly reduced (70.8–84.9%) ID, SwD and SdD as areas, but significantly increased (18.0%) the incidence of infected plants (IIP), regardless of the irrigation frequency. The disease incidence was not correlated with temperature. Daily irrigation to low RWC mitigated the VWO and the IIP, kept soil to the lowest MpD and resulted in the lowest SdD level at the end of the trial. Results suggested that less persistent propagules could have played a part in the disease development.

First Report on the Association of a 16SrII-A Phytoplasma with Sesame (Sesamum indicum) Exhibiting Abnormal Stem Curling and Phyllody in Taiwan.

Sesame (Sesamum indicum L.), an annual plant, is grown as an oilseed crop and the seeds are used in bakery products in Taiwan. In June 2013, plants exhibiting symptoms including phyllody and abnormal stem curling were observed in sesame fields in Pitou Township, Changhua County, Taiwan. Incidence of infected plants was estimated to be greater than 90% within a single field. Phytoplasmas associated with sesame exhibiting phyllody, witches'-broom, or virescence have been classified as strains of 16SrI-B in Myanmar (GenBank Accession No. AB558132), 16SrII-A in Thailand (JN006075), 16SrII-D in Oman (EU072505) and India (KF429486), 16SrIV-C in Iran (JF508515), and 16SrVI-A (KF156894) and 16SrIX (KC139791) in Turkey (1). Three symptomatic and four asymptomatic plants were uprooted and transplanted in a greenhouse for further study. Transmission electron microscopy (TEM) revealed clusters of phytoplasma cells ranging from 300 to 800 nm in diameter only in phloem sieve elements of stems of three symptomatic and two asymptomatic plants. Comparable tissues from two other symptomless plants were devoid of phytoplasma cells. Total DNA was extracted with a modified CTAB method (2) from plant tissues (100 mg each) including stem, leaf, petiole, and root from the same plants used for TEM work. Analyses by a nested PCR using universal primer pairs P1/P7 (5'-AAGAGTTTGATCCTGGCTCAGGATT/5'-CGTCCTTCATCGGCTCTT) followed by R16F2n/R16R2 (5'-GAAACGACTGCTAAGACTGG/5'-TGACGGGCGGTGTGTACAAACCCCG) were performed to detect putative phytoplasma DNA (3). Each primer pair amplified a single PCR product of either 1.8 or 1.2 kb, respectively, only from the three symptomatic and two asymptomatic plant tissues that had phytoplasma cells in their sieve elements. It is likely that these two asymptomatic plants were in the early stage of infection before symptoms became noticeable. The nested PCR products (1.2 kb) amplified from the symptomatic plants were cloned separately and sequenced (GenBank Accession Nos. KF923391, KF923392, and KF923393). BLAST analysis of the sequences revealed that they shared 99.2% sequence identity with strains reported from India and Thailand (KF429486 and JN006075), which were classified to the 16SrII-D and 16SrII-A subgroups, respectively. Moreover, iPhyClassifier software (4) was used to perform sequence comparison and generate a virtual restriction fragment length polymorphism (RFLP) profile. The 16S rDNA sequences shared 99.4% identity with that of the 'Candidatus Phytoplasma australasiae' (Y10097) and the RFLP patterns were identical to that of the 16SrII-A subgroup, indicating the Taiwanese strain is a 'Ca. P. australasiae'-related strain. To our knowledge, this is the first report of a 16SrII-A subgroup phytoplasma causing phyllody and abnormal stem curling on sesame in Taiwan. The occurrence of phytoplasma on sesame could have direct implications for the cultivation of this economically important oilseed plant and the bakery industry in Taiwan.

First Report of a 16SrII-A Subgroup Phytoplasma Associated with Purple Coneflower (Echinacea purpurea) Witches'-Broom Disease in Taiwan.

Purple coneflower (Echinacea purpurea), widely grown as an ornamental and medicinal plant, is a perennial flowering plant that is native to eastern North America. In July 2011, symptoms indicative of phytoplasma disease, including floral virescence, phyllody, and witches'-broom (WB), were observed to be affecting plants in coneflower fields in Wufeng, Taichung City, Taiwan. Incidence of infected plants was estimated to be greater than 90% within a single field. Phytoplasmas previously associated with purple coneflower WB disease have all been classified as aster yellows group (16SrI) strains (GenBank Accession Nos. EU333395, AY394856, EU416172, and EF546778) except for pale purple coneflower (Echinacea pallida) WB in Australia, which was identified as a subgroup 16SrII-D member (2). Three diseased plants were uprooted and transplanted in a greenhouse for further study. Transmission electron microscopy revealed clusters of phytoplasma cells ranging from 170 to 490 nm in diameter in phloem sieve elements of virescent and phylloid flowers and stems from diseased plants. Comparable tissues from symptomless plants were devoid of phytoplasma. Total DNA was extracted from plant tissue samples (50 to 100 mg each) including stems, leaves, and flowers by a modified CTAB method (1) from three symptomatic plants as well as from three asymptomatic coneflower plants seedlings. Analyses by a nested PCR using universal primer pairs P1/P7 followed by R16F2n/R16R2 were performed to detect putative phytoplasma (2). Each primer pair amplified a single PCR product of either 1.8 or 1.2 kb, respectively, from diseased plant tissues only. The nested PCR products (1.2 kb) amplified from phylloid flowers of the three diseased plants were cloned separately and sequenced (GenBank Accession Nos. JN885460, JN885461, and JN885462). Blast analysis of the sequences revealed a 99.7 to 99.8% sequence identity with those of Echinacea WB phytoplasma strain EWB5 and EWB6 (GenBank Accession Nos. JF340076 and JF340080), which reportedly belonged to the 16SrII-D subgroup (2). Moreover, iPhyClassifier software (3) was used to perform sequence comparison and generate the virtual restriction fragment length polymorphism (RFLP) profile. The 16S rDNA sequences share a 99.4 to 99.5% similarity with that of the 'Candidatus Phytoplasma australasiae' reference strain (Y10097) and the RFLP patterns are identical to that of the 16SrII-A subgroup. Taken together, these results indicated that the phytoplasma infecting purple coneflower in Taiwan is a 'Ca. Phytoplasma australasiae'-related strain and belongs to the 16SrII-A subgroup. To our knowledge, this is the first report of a 16SrII-A subgroup phytoplasma causing WB disease on purple coneflower in Taiwan. The occurrence of phytoplasma on purple coneflower could have direct implication for the economically important ornamental, medicinal plant, and floral industry in Taiwan, especially to the growers and breeders that eagerly promote the purple coneflower industry.

Efficiency of Adaptive Cluster Sampling for Estimating Plant Disease Incidence

Conventional sampling designs such as simple random sampling (SRS) tend to be inefficient when assessing rare and highly clustered populations because most of the time is spent evaluating empty quadrats, leading to high error variances and high cost. In previous studies with rare plant and animal populations, adaptive cluster sampling, where sampling occurs preferentially in the neighborhood of quadrats in which the species of interest is detected during the sampling bout, has been shown to estimate population parameters with greater precision at an effort comparable to SRS. Here, we use computer simulations to evaluate the efficiency of adaptive cluster sampling for estimating low levels of disease incidence (0.1, 0.5, 1.0, and 5.0%) at various levels of aggregation of infected plants having variance-to-mean ratios (V/M) of approximately 1, 3, 5, and 10. For each simulation, an initial sample size of 50, 100, and 150 quadrats was evaluated, and the condition to adapt neighborhood sampling (CA), i.e., the minimum number of infected plants per quadrat that triggers a switch from random sampling to sampling in neighboring quadrats, was varied from 1 to 4 (corresponding to 7.7 to 30.8% incidence of infected plants per quadrat). The simulations showed that cluster sampling was consistently more precise than SRS at a field-level disease incidence of 0.1 and 0.5%, especially when diseased plants were highly aggregated (V/M = 5 or 10) and when the most liberal condition to adapt (CA = 1) was used. One drawback of adaptive cluster sampling is that the final sample size is unknown at the beginning of the sampling bout because it depends on how often neighborhood sampling is triggered. In our simulations, the final sample size was close to the initial sample size for disease incidence up to 1.0%, especially when a more conservative condition to adapt (CA > 1) was used. For these conditions, the effect of disease aggregation was minor. In summary, both precision and the sample size required with adaptive cluster sampling responded similarly to disease incidence and aggregation, i.e., both were most favorable at the lowest disease incidence with the highest levels of clustering. However, whereas relative precision was optimized with the most liberal condition to adapt, the ratio of final to initial sample size was best for more conservative CA values, indicating a tradeoff. In our simulations, precision and final sample size were both simultaneously favorable for disease incidence of up to 1.0%, but only when infected plants were most aggregated (V/M = 10).

A newly described plant disease complex involving two distinct viruses in a native Alaskan lily,Streptopus amplexifolius

The etiology of a previously unknown disease of Streptopus amplexifolius (L.) DC. (twisted stalk) that occurred in south central Alaska was elucidated. Symptomatic plants with yellow-green dashes and streaks on their leaves contained distinct viruses belonging to the family Potyviridae and (or) tentatively to the family Flexiviridae genus Carlavirus . Each virus’ identity was confirmed by a combination of morphology, serology (ELISA and (or) Western analysis), and sequences obtained from reverse transcriptase – polymerase chain reaction products previously generated by potyvirus- or carlavirus-specific primers. The mechanical transmission of particles (purified from twisted stalk as a mixture of both viruses or as a single preparation of each virus) to S. amplexifolius, Chenopodium amaranticolor Coste et Reyn, and Chenopodium quinoa Willd., fulfilled Koch’s postulates. The relatively high incidence of infected plants and associated severe symptoms in populations from several sites in south central Alaska gave evidence that native plants are susceptible to, and are adversely affected by viral diseases. Even though Streptopus species grow throughout the temperate regions of the world, this is the first report of a pathogen(s) infecting plants in the genus Streptopus.

Effect of Endophyte Incidence in Perennial Ryegrass on Distribution, Host-Choice, and Performance of the Hairy Chinch Bug (Hemiptera: Lygaeidae)

Finding toxic, fungal endophyte-infected, grass cultivars that are not avoided by phytophagous insects could be an advantageous strategy when mixing Kentucky bluegrass, Poa pratensis L., and endophyte-infected grasses to control turfgrass pests. Field observations revealed that nymphs of the hairy chinch bug, Blissus leucopterus hirstus Montandon, are found mainly in thatch rather than on plants, regardless of time of day. We therefore developed laboratory bioassays incorporating thatch as a component of the hairy chinch bug habitat as a 1st step toward searching for advantageous grass-endophyte associations for chinch bug management in northeastern America. In nonchoice tests, a high incidence of endophyte ( Neotyphodium ) infection in tillers of the perennial ryegrass ‘Prelude II’, Lolium perenne L., induced high mortality of 3rd instars, whereas Prelude II with lower incidence of infected tillers or the Kentucky bluegrass ‘Merit’ were significantly more suitable. Incidence of infected plants affected nymph habitat selection, because all individuals in the presence of Prelude II with elevated percentage of infected tillers were found in thatch, whereas a significantly higher proportion of plants was colonized by nymphs confined with Prelude II with a lower incidence of endophyte infection or with Merit. In choice tests, Merit was strongly preferred over Prelude II, regardless of endophyte status of the ryegrass. Moreover, nymph mortality was not affected by the presence of endophyte-infected Prelude II when Merit was also available. These results suggest that highly mobile 3rd-instar hairy chinch bugs have the capacity to avoid toxic endophyte-infected grass cultivars. Such behavior could limit the value of mixing endophyteinfected grasses with Kentucky bluegrass for lawn protection, unless toxic cultivars that are not avoided by the hairy chinch bug can be found.

Effect of rotation with barley and oats on crown rot of wheat in the northern wheat belt of New South Wales

We investigated the incidence of Fusarium graminearum Group 1 (infection, stem colonisation) and crown rot in 3-year crop sequences of 1 or 2 years of barley, oats, or mown oats followed by wheat, compared with 3 years of wheat. Seed was sown into the stubble of the previous crop. Stubble production was estimated for each cereal treatment. Plants of each cereal were infected by the crown rot pathogen. Oats were susceptible to infection but did not express symptoms of crown rot in 2 years of the trial. Oats can, therefore, be considered a symptomless host that may contribute to the maintenance of inoculum. The overall mean incidence of infected plants increased from 12% in 1987 to 81% in 1989. The various treatments did not significantly reduce the incidence of infected wheat plants in November of the final year. The incidence of crown rot of wheat in 1989 was greatest after 2 prior wheat crops and lowest after 1 or 2 years of mown oats. The 3 species produced a similar amount of straw by weight; however, mown oats produced significantly less. Oat straw decomposed more rapidly than that of other cereals in controlled conditions.

Reaction of Australian cultivars of oats and barley to infection by Fusarium graminearum Group 1

The incidence of infection by Fusarium graminearum Group 1 and the incidence of crown rot were compared for various cultivars of oats, wheat and barley in glasshouse and field experiments. In glasshouse studies, the incidence of infected plants was lower in oats than in wheat or barley at 6 weeks after sowing. Crown rot symptoms were not observed in oats of any cultivar. The incidence and severity of crown rot in barley was similar to that in wheat cv. Banks. Between 17 and 29 genotypes of oats, wheat and barley were assessed in field trials over 3 years. Stem browning, a symptom of crown rot, was common in wheat and barley but was not observed in any cultivar of oats. Among plants of wheat and barley, the effect of cultivar on incidence of crown rot was significant (P = 0.05) in 3 of 4 trials. Results suggest that oats are a symptomless host. This should be considered when growing oats in rotation to reduce crown rot inoculum. The barley cultivars assessed all developed moderate-severe crown rot symptoms and thus may incur yield limitations where crown rot is prevalent.

Yield losses to maize streak disease andBusseola fusca(Lepidoptera: Noctuidae), and economic benefits of streak‐resistant maize to small farmers in Zaïre

Abstract Results of two seasons of on‐farm trials are reported. In 1986/87 yield losses to maize streak disease were 6.5–8.9 kg/ha for each additional 1% increase in incidence of infected plants. In fertilized plots losses to borers ranged from 9.1 to 13.6 kg of maize/ha for each 1% increase in incidence of borer‐attacked plants; in unfertilized plots losses were insignificant. When different parameters of yield loss to streak disease were compared, incidence × symptom severity was more highly correlated with loss than either incidence or severity alone, but the difference was slight, and data on incidence were more easily collected. Sampling of young plants ( 8 weeks old). Increases in disease incidence and severity and in borer infestation rates were characterized. In 1987/88 the streak‐resistant variety Babungo‐3 generally out‐yielded the local variety and showed lower streak incidence and symptom severity. The average farm family must apply ...

The incidence of crown rot in wheat, barley and triticale when sown on two dates

Thirteen bread wheat cultivars, a durum wheat, a barley and a triticale cultivar were assessed in the field for their reaction to crown rot (Fusarium graminearum Group 1), based on the incidence of basal browning. Plots were sown in May and again in July at 2 sites i n northern New South Wales where the incidence of crown rot was high in the previous year. The incidence of infected plants and the incidence of plants with basal browning tended to be higher in all cultivars when sown in May. There was a mean loss in potential yield at 1 site of 35% and 18% at the other site. However, the mean loss in potential yield was unaffected by sowing date.

Susceptibility of zinc-deficient wheat plants to colonization byFusarium graminearum Schw. Group 1

Wheat plants were grown at three levels of zinc nutrition in potted soil under controlled conditions. The surface soil in half of the pots was inoculated with a thin layer of milled chaff colonized byFusarium graminearum Group 1. Forty days after sowing, the plants were assessed for dry matter production and the extent of colonization by the pathogen. The concentration of zinc in the plant tissues was also determined. The zinc status of the plants ranged from severe deficiency through subclinical deficiency to sufficiency. The extent of colonization above the point of infection was decreased significantly by increasing the level of zinc supply. However, colonization of the seminal or secondary roots was not affected by zinc supply, nor was the incidence of infected plants. The unidirectional effect on resistance suggests that zinc has modified the contribution of the xylem flux to the upward spread of the pathogen.