Significance to Industry: This study demonstrates how the mini-Horhizotron can be util ized in plant pathology, and investigates the disease severity of Pythium u/timum, Pythium aphanidermatum, and Rhizoctonia so/ani on bedding plants grown in peat based substrates containing varying percentages of pine wood chips, and an industry standard potting mix. Horhizotrons, when used in addition to other disease assessment techniques, can help provide a more well-rounded and accurate assessment of root disease severity. The ability to view the rhizosphere and the accuracy with which root length can be measured suggests that the mini-Horhizotron could have broad applications in plant pathology research . The results from these experiments show that disease severity of these pathogens was equal and often less prevalent than in a traditional potting mix, which offers additional evidence of the viability of pine wood chips to be used as a replacement to perlite in substrates for greenhouse crop production .

Genetic variation in resistance to Phytophthora cinnamomi was investigated for two fir species endemic to the Republic of Turkey. Open-pollinated families of seedlings of Trojan fir (Abies equi-trojani) and Turkish fir (Abies bornmuelleriana) were grown from seed in a greenhouse for approximately 15 months, inoculated with rice grains colonized with P. cinnamomi, and subsequent mortality assessed biweekly for 16 weeks. Final seedling mortality was higher in Trojan fir (56.4 %) compared to Turkish fir (32.9 %). Mortality in both species varied by geographic origin, decreasing from west (59.8 %, Open image in new window ) to east (21.4 %, Karabük). As mortality increased following inoculation, both narrow-sense individual-tree \( \left( {h_i^2} \right) \) and family mean \( ( {h_f^2} ) \) heritabilities increased, plateauing at 0.62 ± 0.162 and 0.97 ± 0.011 for Trojan fir and 0.50 ± 0.102 and 0.96 ± 0.01 for Turkish fir, respectively. Terminal and lateral branch bud break assessed under greenhouse conditions were also under strong genetic control. For terminal bud break, individual-tree heritabilities for Trojan and Turkish fir were 0.49 ± 0.146 and 0.45 ± 0.099, respectively, while family mean heritabilities were 0.88 ± 0.035 and 0.88 ± 0.027, respectively. The family mean correlation between bud break and final disease mortality was not significant for lateral buds but positive and significant for terminal buds (r = 0.32) suggesting that selection for resistance would either not alter, or slightly reduce, early bud break. These are encouraging results for ongoing tree improvement efforts in North America and Europe to develop planting stock for the Christmas tree industry.

Root rot and stem canker caused by Oomycete species belonging to the genus Phytophthora often seriously limit culture of true firs (Abies spp.)

Population dynamics of Aphelenchoides fragariae were assessed over three growing seasons and during overwintering for naturally-infected, container-grown lantana (Latana camara) plants in a North Carolina nursery. During the growing season, the foliar nematode population in symptomatic leaves peaked in July each year then remained above 100 nematodes/g fresh weight into late summer. Foliar nematodes were also detected in asymptomatic and abscised leaves. Results suggest that leaves infected with foliar nematodes first develop symptoms at populations of about 10 nematodes/g. Foliar nematodes were detected in symptomatic and asymptomatic plant leaves and in abscised leaves during overwintering in a polyhouse, but the number of infected plants was low. A steep disease gradient was found for infection of lantana plants by A. fragariae on a nursery pad with sprinkler irrigation. When the canopies of initially healthy plants were touching the canopies of an infected plants, 100% of the plants became infected within 11 wk, but only 5 to 10% became infected at a canopy distance of 30 cm. Overwintering of A. fragariae in infected plants and a steep disease gradient during the growing season suggests strict sanitation and an increase in plant spacing are needed to mitigate losses from this nematode pest.

The pathogenicity of Pythium vexans isolates collected from fir samples with typical root rot symptoms in North Carolina was evaluated on Fraser fir seedlings (Abies fraseri). Two replicated pathogenicity trials involving seven treatments were conducted in the lath house and greenhouse. Although the P. vexans isolates examined in these trials were able to colonize Fraser fir root systems, they did not cause mortality or incite root rot symptoms. In comparison, Phytophthora cinnamomi, a known aggressive pathogen of Fraser fir, caused severe root rot symptoms in all plants. These experiments provided no evidence that P. vexans is a pathogen of Fraser fir. Accepted for publication 12 July 2008. Published 6 October 2008.

Three root-colonizing fungi, binucleate Rhizoctonia (BNR) isolates BNR621 and P9023 and Trichoderma hamatum isolate 382 (T382), were studied for suppression of Botrytis blight in geranium by induction of host systemic resistance. Resistance to Botrytis blight was observed in geraniums transplanted into potting mix amended with formulations of P9023 and T382 2 weeks prior to inoculation with Botrytis cinerea when grown under environments either highly or less conducive to disease development. In the less conducive environment, P9023 and T382 provided protection equal to (P<0.0001) the fungicide control. Specific stages in infection by B. cinerea were tested by counting germination of conidia in leaf extracts or by assessing lesion size in detached leaves taken from BNR- and T382-treated geraniums. No differences in conidial germination were observed. Lesion area results depended on time between application of inducing agents and detachment of leaves for inoculation. In geranium leaves detached and inoculated 7 days after topdressing with a Pesta formulation of BNR621 and P9023, AUDPC calculated from lesion area was smaller (P<0.0001) than T382 and the inoculated control. Whereas, leaves detached and inoculated 14 days after topdressing with a formulation of T382 had a smaller (P<0.0001) AUDPC from lesion area than plants treated with BNR621. Restriction of lesion development may play a role in the suppression of Botrytis blight in geranium. Our results may be the first to demonstrate induced systemic resistance by BNR fungi to a foliar pathogen and support additional research into use of T382 in an integrated management program for B. cinerea.

Economic, environmental, and technological influences complicate the task of achieving disease-free products in the ornamentals industry. Integrated pest management (IPM) is a cornerstone of floriculture and nursery crop production: strategies include sanitation, clean stock, host resistance, and control through biological, cultural, environmental, chemical, and regulatory means. Sanitation measures and cultural controls must keep pace with new production technologies. Clean stock programs are used for many crops that are propagated vegetatively. Breeding, selection, and biotechnology provide crops resistant to pathogens. Offshore production for economic competitiveness can introduce pathogens that make regulatory programs necessary. New biocontrol and chemical products continue to improve control while meeting the requirement for minimal environmental impact. Continual introduction of new crops and new production technologies creates new opportunities for pathogens to exploit, such that new disease management tactics must be discovered and old ones rediscovered to achieve optimum health management for ornamentals.

Seventeen-month-old seedlings from three fraser fir ( Abies fraseri [Pursh] Poir.) seed sources (Mount Mitchell, Richland Balsam and Roan Mountain) were inoculated in an outdoor lath house with five genotypes of Phytophthora cinnamomi Rands. After 122 days, overall mortality was 90.5% with significant ( p ≤ 0.07) differences among seed sources. The Mount Mitchell source had lower mortality (83.2%) than the Roan Mountain source (95.8%), while the Richland Balsam source (92.5%) was intermediate. Mortality curves were developed using nonlinear regression (Richards' function). Due to a significant seed source × inoculum genotype interaction ( p ≤ 0.0001), equations were developed for each combination of seed source and inoculum genotype. Results suggest that while the overall frequency of resistance in fraser fir is low, seed sources differ in their frequency of resistance and that more than one resistance gene may be present. Survivors from this or similar inoculations could be cloned via grafting or rooted cuttings for further resistance testing and/or grafted into a Phytophthora- resistant fraser fir seed orchard.

An overview of the history of poinsettia cultivation, and a description of the management strategies used by growers of poinsettia to control and prevent the especially challenging diseases faced by this holiday favorite. Accepted for publication 18 January 2002. Published 12 February 2002.

Isolates BNR621 and P9023 of binucleate Rhizoctonia spp. (BNR) in Pesta and rice flour formulations were evaluated for control of preemergence damping-off of impatiens caused by R. solani. Amendment of a soilless potting mix with the formulations at 0.47% (vol:vol) 3 days prior to seeding and infesting did not improve control compared to amendment 1 day prior to seeding and infesting regardless of whether the moistened amended potting mix was stored in closed plastic bags or in plug trays under a mist system. BNR fungi were no more effective in biocontrol of R. solani in formulations amended at 0.9%. Control of damping-off was comparable but not consistent between formulations of BNR fungi and the fungicide thiophanatemethyl. Damping-off was controlled better with formulations of BNR fungi than with SoilGard based on Trichoderma virens. Shelf life of Pesta and rice flour formulations at 4°C was determined by assessing viability of BNR isolates over time. Viability of the BNR isolates, measured as CFU/g of formulation, declined to approximately 68 to 79% of the original propagule concentration after 6 months in Pesta and rice flour formulations, with the greatest decline in the first 2 months. Shelf life of BNR isolates in formulation significantly affected control of preemergence damping-off but was isolate dependent. Preemergence damping-off was only 5 to 7% with fresh formulations but increased to 30 to 50% with 4-month-old formulations. Controlled atmospheres, maintained with saturated salt solutions, were established to measure the effect of water activity on shelf life of formulations. Water activities (aw) of 0.12 and 0.33 aw enhanced BNR survival in formulations by approximately 2 to 3 months compared with aw of 0.53 and 0.75 aw. Storage of Pesta and rice flour formulations at 4°C significantly improved BNR survival by 4 to 5 months compared with storage at 25°C. These results suggest that improved shelf life of BNR isolates is needed before formulated products can be developed for biocontrol of preemergence damping-off.

This article takes a historical look at the Christmas tree industry and discuss three diseases limiting growers' ability to meet the demand for noble and Fraser fir in North America: Phytophthora root rot and stem canker, current season needle necrosis (CSNN), and interior needle blight. Accepted for publication 14 September 2000. Published 13 October 2000.

Containerized seedlings of Fraser fir [Abies fraseri (Pursh) Poir.], momi fir (A. Firma Sieb. & Zucc.), and Siberian fir (A. siberica Ledeb, var. argentea) were tested for resistance to Phytophthora cinnamomi Rands (two experiments). Fraser fir was very susceptible, with many plants dead after 4 to 5 weeks. Symptoms developed more slowly in Siberian fir, but most plants were dead or dying after 10 weeks. Momi fir appeared somewhat resistant to the pathogen. Though undesirable as a Christmas tree, momi fir might be useful as a rootstock for grafting better quality species in areas affected by root rot.

Genetic engineering approaches offer an alternative method to the citrus canker resistance breeding. The ethylene response factor (ERF) family is a member of families of transcription factors that are particular to plants and contribute significantly to biotic stress response and to plant growth. CsAP2-09 belongs to the citrus AP2/ERF transcription factor family. Initially, we proved the induction of CsAP2-09 in wild-types by Xcc and some hormones involved in pathogen response. We successfully cloned the CsAP2-09 and proved that CsAP2-09 protein is targeted to the nucleus. The CsAP2-09 was functionally characterized with over-expression and RNAi silencing strategy. In the overexpression lines, the diseased lesions and disease index were significantly decreased while in RNAi lines of CsAP2-09 the diseased lesions and disease index were significantly enhanced. Thus, the over-expression conferred Xcc resistance to transgenic citrus while silencing of CsAP2-09 in sweet orange leads to Xcc susceptibility. When the transcriptomes of WT and overexpression transcriptomes were compared, they revealed that some genes involved in phenylpropanoid biosynthesis, pathogen responses, transcript regulation etc. were modified. Our results provide a possibility for improving citrus canker disease resistance by over-expression of CsAP2s. Furthermore, various functions of CsAP2-09 provide significant information about the role of AP2/ERFs in plant disease resistance and stress tolerance.

Nitrogen (N) footprints quantify the anthropogenic release of reactive nitrogen (Nr) from resource consumption, but do not connect to the resulting environmental impacts. Australia has the largest measured N footprint, but is generally perceived as a “green and clean” country. To explore this discrepancy, we developed an indicator, Nr spatial intensity (NrSI) that estimates the intensity of the Nr loss on a per area basis. The system boundary of the N footprint is any resource consumption by an entity, regardless of where the Nr is released. In contrast, the NrSI framework maps the geographical locations of anthropogenic Nr losses. We found that the pattern of NrSI among nations was very different from that of their N footprint. Factors that affect the comparison include land area, population density, and the import and export of food. Australia had the lowest NrSI (6 kg N ha−1 yr−1) while the Netherlands had the highest NrSI (217 kg N ha−1 yr−1) of the seven nations studied. In concert with the N footprint, the NrSI could be used as a benchmark for assessing the environmental pressure from Nr in a nation and for setting priorities of mitigating Nr pollution to help achieve the Sustainable Development Goals by 2030.

Epidemiology and management of root diseases , Epidemiology and management of root diseases , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی