Mycoflora Associated With Pyrethrum Seed and the Integration of Seed Steam Treatment Into Foliar Disease Management Strategies

A complex of foliar diseases can affect pyrethrum in Australia, but those of greatest importance are ray blight, caused by Stagonosporopsis tanaceti, and tan spot, caused primarily by Didymella tanaceti. Isolation of fungi from pyrethrum seed lots produced over 15 years resulted in recovery of six known pathogens: S. tanaceti, D. tanaceti, Alternaria tenuissima, Colletotrichum tanaceti, Stemphylium botryosum, and Botrytis cinerea. The incidence of S. tanaceti and D. tanaceti isolated from seed varied between 0.9 and 19.5% (mean = 7.7%) and 0 and 24.1% (mean = 5.3%) among years, respectively. Commercial heat treatment of pyrethrum seed via steaming reduced the incidence of D. tanaceti from 10.9 to 0.06% and the incidence of S. tanaceti from 24.6% to nondetectable levels (<0.18%). In a second experiment, both species were reduced to nondetectable levels (<0.20%) from their initial incidences of 22.4 and 2.4%, respectively. In a field study in 2013, colonization of pyrethrum foliage by S. tanaceti was reduced from 21.1 to 14.3% in early winter when heat-treated seed was planted. However, isolation frequency of D. tanaceti was not affected significantly by seed treatment in this year. In a related experiment in 2015, the isolation frequency of D. tanaceti in plots planted from heat-treated seed depended on both prior application of an industry-standard fungicide program and proximity to another pyrethrum field in autumn. The fungus was recovered at a similar frequency in fungicide-treated and nontreated plots located near other pyrethrum fields (13.8 versus 16.3%, respectively), whereas recovery of the pathogen was reduced by fungicide applications in geographically remote pyrethrum fields (6.7 versus 1.4%, respectively). However, these differences in isolation frequency of D. tanaceti in autumn did not obviate the need for later fungicide applications to suppress foliar disease intensity in spring or flower yield in summer, independent of the proximity to other pyrethrum fields. This study suggests that steam treatment of seed can delay development of the foliar disease complex on pyrethrum, although an extremely low level of remaining infected seed or exogenous sources of inoculum necessitates the use of foliar fungicide applications in spring.

Pathogenicity of Phoma Chrysanthemicola to Chrysanthemum Plants (Asteraceae Family) and Control of Pathogen by Chemical and Biological Approach

ABSTRACT: The Chrysanthemum also known as mums or chrysenths, are useful in ornamental applications, insecticidal, air pollution reducer, perfume production etc. The Phoma causes infection to Chrysanthemum which results in serious lesion. The present study reports protection of Chrysanthemum against fungal infection. The morphology of Phoma chrysanthemicola was studied in PDA, CZA and MEA medium. The pathogenicity of fungus was examined on different variety of chrysanthemum plants. The control of P. chrysanthemicola was contemplated by utilizing some commercial available fungicides and extract of medicinal plants. The organism causes root rot and ray blight to Chrysanthemum plants. Chrysanthemum sp. 2 was found more sensitive to pathogen took after by Chrysanthemum sp. 1 and 3. Relationship between diseases severity and incubation period of pathogen with various chrysanthemum plant was found R2 0.95, 0.97 and 0.87 for Chrysanthemum sp. 1, 2 and 3. Carbendazim was recorded more effective on P. chrysanthemicola followed by mancozeb and zineb with P value of 0.065 at 0.05 level. Azadirachta indica extract and plant extract from methanolic solvent were found more effective against P. chrysanthemicola. Now it is presumed that fungal pathogen has strong ability to infect chrysanthemum but chemical and biological alternate can control the chrysanthemum against pathogen.

Rapid Changes in the Genetic Composition of Stagonosporopsis tanaceti Population in Australian Pyrethrum Fields

A novel set of microsatellite markers were developed and employed for geographical and temporal population analyses of Stagonosporopsis tanaceti, the cause of ray blight of pyrethrum in Australia. Genotyping of 407 isolates, using 13 markers, suggested an asexual mode of reproduction with significant linkage disequilibrium and high levels of clonality. Low geographical differentiation and widespread distribution of a few multilocus genotypes (MLGs), in the absence of airborne ascospores, suggested the role of human-mediated movement of seed as a major means of long-distance pathogen dispersal. The genetic composition of S. tanaceti was stable for a decade then changed rapidly in only 2 years. Bayesian clustering analyses and minimum spanning networks determined only two major clonal lineages in and prior to 2010. However, in 2012, a previously unobserved cluster of MLGs was detected, which significantly increased in frequency and displaced the historically dominant MLGs by 2013. This rapid change in the genetic composition of S. tanaceti could indicate a second introduction then a selective sweep, or strong selection pressures from recently introduced fungicides or pyrethrum varieties. These results may have serious implications for durability of management strategies for this disease.

Minimizing Crop Damage Through Understanding Relationships Between Pyrethrum Phenology and Ray Blight Disease Severity

The most damaging foliar disease of pyrethrum in Australia is ray blight caused by Stagonosporopsis tanaceti. The probability of growers incurring economic losses caused by this disease has been substantially reduced by the implementation of a prophylactically applied spring fungicide program. This has been traditionally initiated when 50% of the stems have reached between 5 and 10 cm in height. Data collected on the emergence of stems from semidormant plants over late winter from 27 fields across northern Tasmania from 2009 to 2011 were used to develop a degree-day model to assist with initiation of the fungicide program. Temporal changes in cumulative proportion of plants with elongated stems were well described by a logistic growth model (R2 ≥ 0.97 across all fields). These models were used to calculate the number of days until 50% of the sampling units had at least one elongated stem for the calculation of simple degree-days, assuming a nominal biofix date of the austral winter solstice. The median date for 50% stem elongation was estimated as 30 August in these data sets. Mean error and root mean square error of degree-day models were minimized when a base of 0°C was selected. Mixed-model analysis found prediction errors to be significantly affected by geographic region, requiring the use of scalar correction factors for specific production regions. In the Western region, 50% stem emergence was predicted at 590.3 degree-days (mean prediction error = 0.7 days), compared with 644.6 (mean prediction error = 7.7 days) in the Coastal region and 684.7 (mean prediction error = 0.7 days) degree-days in the Inland region. The importance of fungicide timing for initiation of the spring disease management program in minimizing losses (expressed as percent disease control in October) was also quantified. This relationship was best explained by a split-line regression with a significant break-point of 513.8 degree-days, which corresponded to 10.7% of sampling units with elongated stems. Overall, this research indicated that disease management may be improved by applying the first fungicide of the program substantially earlier in phenological development of the stems than currently recommended.

Interactions between waterlogging and ray blight in pyrethrum

The effects of waterlogging, alone and combined with ray blight disease (caused by Stagonosporopsis tanaceti), on pyrethrum (Tanacetum cinerariifolium) plant growth were quantified in glasshouse trials. Six pyrethrum cultivars were initially studied for their response to 6 days of waterlogging and their recovery from waterlogging during 26 days post-waterlogging. Waterlogging caused substantial root death and leaf wilting and accelerated senescence in all cultivars. Root growth was 80% more reduced than shoot growth. Cultivar ‘F’ showed significantly higher root porosity and growth following waterlogging than other cultivars. In contrast, cv. ‘C’ had the greatest growth reduction from waterlogging and poor root-system recovery after waterlogging. Plants of cvv. C and F inoculated with S. tanaceti and then waterlogged were more significantly affected than were those exposed to waterlogging only. For both cultivars, shoot growth under the combined treatment, relative to initial growth, recovered up to 25%, but root growth suffered irreversible damage. The combined treatment decreased the number of stems by 39% compared with waterlogging alone after the post-waterlogging period. In conclusion, pyrethrum cultivars showed differential reactions to waterlogging; but growth in all cultivars was seriously affected by a combination of waterlogging and infection by ray blight.

Lack of Evidence for Recombination or Spatial Structure in Phoma ligulicola var. inoxydabilis Populations from Australian Pyrethrum Fields

Ray blight, caused by Phoma ligulicola var. inoxydabilis, causes substantial annual losses in Australian pyrethrum fields. Fifty-nine P. ligulicola var. inoxydabilis isolates were randomly selected from fields in three distinct geographical regions in Tasmania, Australia. Genetic diversity was characterized using random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP). Based on genetic similarities of less than 99%, 56 distinct genotypes (putative clones) were observed. Mean haploid gene diversity of clone-corrected populations ranged between 0.05 and 0.31, and 0.11 and 0.32, for the RAPD and AFLP data sets, respectively. Cluster analysis indicated two distinct groups of isolates supported by all bootstrap replicates. The first cluster contained all but four isolates with representatives from all three populations. The second cluster contained two isolates from the Western and Central populations, respectively, while the remaining isolates were not able to be grouped with any distinct cluster. Analysis of the population structure suggested no evidence for spatial autocorrelation at the smallest distance classes. The presence of linkage disequilibrium was indicated regardless of population scale. Collectively, these findings provided further evidence for the absence or minor role of the teleomorph in the epidemiology of ray blight in Australian pyrethrum fields.