Inhibition of Botrytis cinerea Growth and Suppression of Gray Mold on Petunia Leaves Using Chitosan.

Exogenous application of chitosan has been shown to reduce plant disease severity in food crops; however, less is known about the potential use of chitosan in floriculture. The objective of this study was to investigate the effectiveness of chitosan to suppress gray mold on petunia leaves caused by Botrytis cinerea using in vitro and in planta approaches. We also aimed to determine if chitosan molecular weight influences efficacy. Medium and high molecular weight reagent grade chitosan reduced growth of B. cinerea in vitro at chitosan concentrations ranging from 1.25 to 2% (v/v), while low molecular weight reagent grade chitosan only reduced growth at 2.0% (v/v). In detached leaf assays, all reagent grade chitosan treatments reduced Botrytis lesion size on petunia leaves up to 65% compared to the water control. The commercial product Tidal Grow reduced in vitro growth of Botrytis, starting at 0.5%, and reduced disease severity at 0.75% on petunia leaves. The commercial product ARMOUR-Zen 15 reduced Botrytis growth in vitro at 3.75% and higher and reduced disease severity at 0.3 and 1.0% on petunia leaves. Under greenhouse conditions, low, medium, and high molecular weight reagent grade chitosan and ARMOUR-Zen 15 at 0.4% chitosan reduced Botrytis lesion size on petunia leaves up to 60% compared to the water control. Suppression in vitro suggests that chitosan may have direct phytotoxic effects on fungal growth, however our in planta and greenhouse trials suggest that additional modes of action may also play a role in the observed suppressive effects.

Evaluation of Disease Severity and Molecular Relationships Between Peronospora variabilis Isolates on Chenopodium Species in New Hampshire.

Quinoa is a potential new crop for New England; however, its susceptibility to downy mildew, caused by Peronospora variabilis, is a key obstacle for cultivation. The objectives of this study were to evaluate differential resistance within the Chenopodium genus, identify novel sources of resistance for use in future genetic studies or breeding programs, and investigate phylogenetic relationships of P. variabilis isolates from different Chenopodium hosts. The long-term goal of this research is to develop a resistant variety of quinoa to be grown in New England. Field trials conducted at the University of New Hampshire evaluated downy mildew disease severity on 10 Chenopodium accessions representing four species. Disease severity for each treatment was compared and significant differences in disease severity were observed between accessions. C. berlandieri var. macrocalycium ecotypes collected from Rye Beach, New Hampshire and Appledore Island, Maine exhibited the lowest disease severity over the growing season. P. variabilis was isolated from each accession, and COX2 sequences were compared. Phylogenetic analyses suggest no effect of host species on P. variabilis sequence similarity; however, isolates are shown to cluster by geographic location. This research provides the first step in identifying potential New England native sources of resistance to downy mildew within the genus Chenopodium and provides preliminary information needed to further investigate resistance at the genomic level in Chenopodium spp.

Evaluation of Endospore-Forming Bacteria for Suppression of Postharvest Decay of Apple Fruit.

The use of microbial biocontrol agents for control of postharvest disease has been the subject of intensive research over the past three decades resulting in commercialization of several biocontrol products. The objective of this research was to test endospore-forming bacteria collected from apple leaves for suppression of bitter rot and blue mold on apple. Bacteria were collected from abandoned, low-input, organic, and conventionally managed orchards in Pennsylvania and were screened for their ability to produce endospores, hydrolyze chitin, reduce pathogen growth in vitro, and suppress postharvest disease in vivo. Several isolates reduced bitter rot lesion size on 'Rome Beauty' from 40-89% compared to untreated controls. Bacillus megaterium isolates, A3-6 and Ae-1, resulted in the greatest suppression of bitter rot lesion size. One isolate, A3-2, suppressed blue mold lesion size. Scanning electron microscopy of inoculated apple wounds suggests parasitism as a mode of action explains the suppression of bitter rot lesion size by isolate A3-6. Of the top seventeen isolates exhibiting biocontrol potential, 70% were collected from abandoned or unmanaged locations. This research demonstrates abandoned apple orchards can be a source of new biocontrol agents for control of postharvest diseases of apple.

Risk of Spreading Soft Rot Through Cutting Dips Against Whiteflies in Greenhouse-Grown Poinsettia.

Dipping is a quick and cost-effective technique to reduce pest infestations on unrooted cuttings of greenhouse ornamental crops. Large numbers of cuttings are immersed in an insecticidal treatment, e.g., biopesticides and/or insecticidal soap, before they are stuck in the growing medium and rooted. This research investigated the risk of cross-contamination of poinsettia cuttings with Pectobacterium carotovorum subsp. carotovorum, a potentially devastating pathogen causing soft rot, through the dipping process. Sampling at four commercial greenhouses showed that P. carotovorum subsp. carotovorum was present in all dip suspensions during and after processing poinsettia cuttings; concentrations up to 1 × 105 CFU/ml were detected. A laboratory experiment determined that P. carotovorum subsp. carotovorum-infected cuttings could contaminate clean dip suspensions to similar levels. These results indicated that there is potential for disease transfer during dipping. The potential for cross-contamination of healthy cuttings was evaluated by immersing poinsettia cuttings in dip suspensions artificially inoculated with P. carotovorum subsp. carotovorum (from 1 × 103 to 1 × 107 CFU/ml). Disease incidence increased as P. carotovorum subsp. carotovorum concentrations in the dip suspension increased and the variety 'Prestige Red' was more susceptible than 'Freedom White.' However, even at the highest P. carotovorum subsp. carotovorum concentration of 1 × 107 CFU/ml, the proportion of diseased cuttings was low at 6% for var. 'Freedom White,' but higher at 21% for var. 'Prestige Red.' We conclude that P. carotovorum subsp. carotovorum transfer among unrooted poinsettia cuttings through the dipping process is relatively low although some varieties are sensitive to high levels of inoculum. Even so, strict sanitation practices are still important to prevent build-up of inoculum in the dip treatment.

Finding the Gaps: An Assessment of Concepts, Skills, and Employer Expectations for Plant Pathology Foundational Courses.

Foundational plant pathology courses, taught at the undergraduate level, serve students from a wide array of disciplines, and for most will be the only plant pathology course taken. This work examined the content, skills, and delivery modes of undergraduate plant pathology courses at a national scale, and assessed employer expectations for these courses and for students entering the workforce with degrees in plant science-related disciplines. While content knowledge coverage among plant pathology courses was generally consistent and aligned well with employers' knowledge expectations, delivery modes and skill development components were more variable and less aligned. Significant gaps were found between skills expected by employers and those emphasized by instructors, particularly in the areas of general laboratory skills (e.g., media preparation, molecular techniques, microscopy, and competence with other lab equipment) and recognition of plant problems that are not caused by pathogens. Employers also emphasized the value of (and frequent lack of) critical soft skills, such as teamwork, adaptability, communication, writing, and critical thinking. Results of this study will provide a foundation for course and curriculum development and evaluations. Recommendations are also discussed for enhanced interactions among educators and employers outside of academia.

Assessment of Application Timing of Bacillus spp. to Suppress Pre- and Postharvest Diseases of Apple.

Four isolates of Bacillus spp. were tested in a 2-year field study for biological control of pre- and postharvest diseases of apple. For the preharvest test, bacteria were applied to 'Golden Delicious' and 'Rome Beauty' trees in May or May and June. Foliar apple scab severity was assessed weekly. After harvest, fruit were wounded and then either left untreated or given a postharvest application of the bacteria. Wounded fruit were then inoculated with the bitter rot pathogen and lesion size was measured over 8 days. Bacillus megaterium isolate A3-6, B. mycoides isolate A1-1, and B. cereus isolate FLS-5 applied in May or May and June significantly reduced fruit and foliar apple scab severity in both years. A postharvest application of the bacteria (alone or in combination with a preharvest application) resulted in the greatest suppression of bitter rot on both cultivars (P < 0.04). The May + June + postharvest application of isolate A3-6 resulted in the greatest suppression of bitter rot, with an average of 45 and 95% reduction in lesion size compared with nontreated controls on 'Golden Delicious' and 'Rome Beauty' fruit, respectively. Results from this study indicate that preharvest applications of the bacteria were able to reduce foliar and fruit scab and an additional postharvest application was effective in reducing bitter rot severity.