Longevity of Plant Pathogens in Dry Agricultural Seeds During 30 Years of Storage

Plant diseases may survive and be spread by infected seeds. In this study we monitored the longevity of 14 seed-borne pathogens in 9 crop species commonly grown in the Nordic countries, in addition to a sample of sclerotia of Sclerotinia sclerotiorum. The data from the first 30 years of a 100-year seed storage experiment located in a natural −3.5 °C environment (permafrost) in Svalbard, Norway, are presented. To date, the pathogens, tested by traditional seed health testing methods (freezing blotter, agar plates, growing on tests), have survived. Linear regression analyses showed that the seed infection percentages of Drechslera dictyoides in meadow fescue, Drechslera phlei in timothy, and Septoria nodorum in wheat were significantly reduced compared to the percentages at the start of the experiment (from 63% to 34%, from 70% to 65%, and from 15% to 1%, respectively), and that Phoma betae in beet had increased significantly (from 43% to 56%). No trends in the infection percentage were observed over the years in Drechslera spp. in barley (fluctuating between 30% and 64%) or in Alternaria brassicicola in cabbage (fluctuating between 82% and 99%), nor in pathogens with low seed infection percentages at the start of the experiment. A major part of the stored sclerotia was viable after 30 years. To avoid the spread of seed-borne diseases, it is recommended that gene banks implement routines that avoid the use of infected seeds.

Detection of Cercospora beticola and Phoma betae on Table Beet Seed using Quantitative PCR

Cercospora beticola and Phoma betae are important pathogens of table beet, sugar beet, and Swiss chard (Beta vulgaris subsp. vulgaris), causing Cercospora leaf spot (CLS) and Phoma leaf spot, root rot, and damping-off, respectively. Both pathogens may be seedborne; however, limited evidence is available for seed infestation by C. beticola. Due to the limitations of culture-based seed assessment methods, detection of these pathogens was investigated using PCR. A P. betae-specific quantitative PCR assay was developed and used in conjunction with a C. beticola-specific assay to assess the presence of pathogen DNA in 12 table beet seed lots. DNA of C. beticola and P. betae was detected in four and eight seed lots, respectively. Plate tests and BIO-PCR confirmed the viability of each pathogen; however, competitive growth of other microbes and low incidence limited the frequency and sensitivity of detection in some seed lots. The results for P. betae support previously described infestation of seed. Further investigation of C. beticola-infested seed lots indicated the ability of seedborne C. beticola to cause CLS on plants grown from infested seed. Detection of viable C. beticola on table beet seed demonstrates the potential for pathogen dispersal and disease initiation via infested seed, and provides valuable insight into the epidemiology of CLS. Surveys of commercial table beet seed are required to determine the frequency and source of C. beticola seed infestation and its role as primary inoculum for epidemics, and to evaluate the effectiveness of seed treatments.

Pathogenicity of Phoma betae isolates from red beet (Beta vulgaris) at seed farms in Canterbury, New Zealand

Phoma betae is an economically important pathogen of red beet causing preemergence seedling damping, leaf spot and root rot. However, the pathogenicity of P. betae is unknown in New Zealand despite the economic importance of this pathogen. Twenty-five isolates were collected from a survey of red beet seed farms in Canterbury, New Zealand during 2016/2017 and three of these PB101 (from seeds), PB103 (from roots) and PB106 (from leaves) were used for pathogenicity testing of two red-beet cultivars. Isolate PB106 was further used to investigate its effects on spinach and fodder beet as well as red beet under greenhouse conditions. All three P. betae isolates were pathogenic on both red-beet cultivars tested, causing leaf-spot symptoms. Isolates PB101 and PB106 produced significantly larger leaf-spot lesions (P<0.001) compared with PB103. Phoma betae isolate PB106 was pathogenic to both red-beet cultivars, spinach and fodder beet but fodder beet was less susceptible than the other species tested. Regardless of cultivar, <i>P. betae </i>is an important pathogen of beets and is capable of causing leaf spots.

Genome Resource forNeocamarosporium betae(syn.Pleospora betae), the Cause of Phoma Leaf Spot and Root Rot onBeta vulgaris

Neocamarosporium betae (syn. Phoma betae, Pleospora betae) is the cause of Phoma leaf spot and root decay on Beta vulgaris worldwide. Despite the economic importance of the pathogen, many aspects of its life cycle and population biology remain unknown. The first genome assembly of N. betae was constructed to facilitate identification of mating-type loci and development of microsatellite markers for population genetics studies. The de novo assembled genome is provided as a resource for future genetic studies to understand the genetic mechanisms underlying disease development and host-pathogen interactions.

Phoma Leaf Spot Susceptibility and Horticultural Characteristics of Table Beet Cultivars in New York

Phoma leaf spot (PLS), caused by Phoma betae (syn. Neocamarosporium betae), is an important fungal disease affecting table beet (Beta vulgaris L. subsp. vulgaris) production in New York. PLS lesions on the foliage can lead to rejection in fresh market sales and can reduce leaf integrity, which can disrupt mechanized harvesting. Eight popular table beet cultivars were assessed for susceptibility to PLS using P. betae isolates representative of the New York population in two small-plot, replicated field trials in Geneva and Freeville, NY. There were significant differences in PLS incidence, severity, and epidemic progress (as measured by area under the disease progress stairs) and horticultural characteristics among cultivars. Non-red table beet cultivars (Avalanche, Boldor, and Chioggia Guardsmark) were less susceptible to PLS than red cultivars (Falcon, Merlin, Rhonda, Red Ace, and Ruby Queen). Significant differences in fresh weight of roots and dry weight of foliage were detected between cultivars at harvest (86 days after planting [DAP] in Freeville and 91 DAP in Geneva). Falcon had significantly higher root weight than Boldor, and Ruby Queen produced significantly more foliage than Boldor. Information on the performance of these cultivars provides locally valuable information for cultivar selection in a broad range of markets.

Fungi associated with leaves of Sonneratia apetala Buch. Ham and Sonneratia caseolaris (L.) Engler from Rangabali coastal zone of Bangladesh

A total of six species and one genus of fungi associated with black leaf spot of Sonneratia apetala Buch. Ham (Kewra); and anthracnose and small leaf spot of S. caseolaris (L.) Engler (Choila) were isolated following “Tissue planting” method. The fungi associated with black spot of S. apetala were Aspergillus fumigatus Fresenius, Colletotrichum lindemuthianum (Sacc. & Magn.) Br. & Cav., Pestalotiopsis guepinii (Desm.) Stey. and Phoma betae Frank. Anthracnose of S. caseolaris showed the association of A. fumigatus and P. guepinii. The fungi associated with leaf spot of S. caseolaris were Curvularia fallax Boedijn, Fusarium Link, Penicillium digitatum (Pers.) Sacc. and P. betae. Frequency percentage of association of P. guepinii was highest (74.10) in black spot of S. apetala whereas the same fungus showed highest frequency percentage (85.70) in case of anthracnose of S. caseolaris. Phoma betae showed highest frequency percentage (60.00) in leaf spot of S. caseolaris. Phoma betae is first time recorded from Bangladesh. Dhaka Univ. J. Biol. Sci. 27(2): 155-162, 2018 (July)

Influence of Harvest Timing, Fungicides, and Beet necrotic yellow vein virus on Sugar Beet Storage

Root rots in sugar beet storage can lead to multimillion dollar losses because of reduced sucrose recovery. Thus, studies were conducted to establish additional fungicide treatments for sugar beet storage and a greater understanding of the fungi involved in the sugar beet storage rot complex in Idaho. A water control treatment and three fungicides (Mertect [product at 0.065 ml/kg of roots; 42.3% thiabendazole {vol/vol}], Propulse [product at 0.049 ml/kg of roots; 17.4% fluopyram and 17.4% prothioconazole {vol/vol}], and Stadium [product at 0.13 ml/kg of roots; 12.51% azoxystrobin, 12.51% fludioxonil, and 9.76% difenoconozole {vol/vol}]) were investigated for the ability to control fungal rots of sugar beet roots held up to 148 days in storage during the 2012 and 2013 storage seasons. At the end of September into October, roots were harvested weekly for 5 weeks from each of two sugar beet fields in Idaho, treated with the appropriate fungicide, and placed on top of a commercial indoor sugar beet storage pile until early February. Differences (P < 0.0001 to 0.0150) among fungicide treatments were evident. Propulse- and Stadium-treated roots had 84 to 100% less fungal growth versus the control roots, whereas fungal growth on Mertect-treated roots was not different from the control roots in 7 of 12 comparisons for roots harvested each of the first 3 weeks in both years of this study. The Propulse- and Stadium-treated roots also reduced (P < 0.0001 to 0.0146; based on weeks 1, 3, and 4 in 2012 and weeks 1, 3, 4, and 5 in 2013) sucrose loss by 14 to 46% versus the control roots, whereas roots treated with Mertect did not change sucrose loss compared with the control roots in 7 of 10 evaluations. The predominant fungi isolated from symptomatic roots were an Athelia-like sp., Botrytis cinerea, Penicillium spp., and Phoma betae. If Propulse and Stadium are labeled for use on sugar beet in storage, these fungicides should be considered for root rot control in commercial sugar beet storage and on roots held for vernalization for seed production of this biennial plant species.