Common bean accessions were evaluated to identify white- or light-seeded beans with resistance to Pythium ultimum Trow. In total, 568 common bean (Phaseolus vulgaris L.) accessions were inoculated with a hyphal suspension of P. ultimum under greenhouse conditions. The bean accessions included represented the Andean-Middle American core collections (406 accessions) and 162 additional white- or cream-seeded accessions. The accessions were categorized into 12 groups according to seedcoat color. Accessions with light seedcoats exhibited higher levels of disease symptoms, with white-seeded bean accessions being the most susceptible class. No symptomless white-seeded accessions were identified. The most resistant white-seeded accessions were PI 430207, PI 527803, PI 290996, PI 299021, PI 194574, and PI 304110. Cream-seeded beans exhibited higher levels of resistance, with nine accessions rated as symptomless out of 188 cream and white accessions tested. Of 568 accessions, 48 tested were symptomless, whereas disease ratings of the other accessions ranged from resistant to highly susceptible.
Abstract
Selected seed-propagated hybrid geranium (Pelargonium × hortorum Bailey) cultivars were evaluated for resistance to crown and root rot caused by Pythium ultimum Trow in the presence or absence of foliarly applied STS, a petal-shattering preventative that has been demonstrated to increase plant death due to P. ultimum. Plants were evaluated for resistance to plant death, plant stunting, and flower delay by comparing plant growth in P. ultimum-infested medium with plant growth in a noninfested medium. Although immunity to P. ultimum was not identified in the 42 cultivars screened, resistance appeared to be present and may provide a valuable source of germplasm for further screening and subsequent hybridization for resistance.
The U.S. Clean Air Act bans the use of methyl bromide after 2005. Consequently, the development of alternative methods for control of soilborne pathogens is imperative. One alternative is to exploit the pesticidal properties of Brassica L. species. Macerated leaves (10 g) from `Premium Crop' broccoli [B. oleracea L. (Botrytis Group)], `Charmant' cabbage [B. oleracea L. (Capitata Group)], `Michihili Jade Pagoda' Chinese cabbage [B. rapa L. (Pekinensis Group)], `Blue Scotch Curled' kale [B. oleracea L. (Acephala Group)], Indian mustard [B. juncea (L.) Czerniak, unknown cultivar] or `Florida Broadleaf' mustard [B. juncea (L.) Czerniak] were placed in 500-mL glass jars. Petri dishes with either Pythium ultimum Trow or Rhizoctonia solani Kühn plugs on potato-dextrose agar were placed over the jar mouths. Radial growth of both fungi was suppressed most by Indian mustard. Volatiles were collected by solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry. Allyl isothiocyanate (AITC) comprised >90% of the volatiles measured from `Florida Broadleaf' mustard and Indian mustard whereas (Z)-3-hexenyl acetate was the predominant compound emitted by the other species. Isothiocyanates were not detected by SPME from `Premium Crop' broccoli and `Blue Scotch Curled' kale although glucosinolates were found in freeze-dried leaves of all species. When exposed to AITC standard, P. ultimum growth was partially suppressed by 1.1 μmol·L-1 (μmol AITC/headspace volume) and completely suppressed by 2.2 μmol·L-1 R. solani was partially suppressed by 1.1, 2.2, and 3.3 μmol·L-1 AITC. Use of Brassica species for control of fungal pathogens is promising; the presence of AITC in both lines of B. juncea suppressed P. ultimum and R. solani but some Brassicas were inhibitory even when isothiocyanates were not detected.
Shrunken-2 supersweet (sh2) sweet corn is susceptible to preemergence damping-off caused by Pythium ultimum, especially when planted into cold soil. Bio-priming, a seed treatment which combines the establishment of a bioprotectant on the seed with preplant seed hydration, was developed to protect seeds from damping-off.
In a series of field experiments conducted in Montana's Bitterroot and Gallatin Valleys, bio-priming or seed bacterization with Pseudomonas fluorescens AB254 protected sweet corn from P. ultimum damping-off. Bio-priming corn seed with P. fluorescens AB254 was comparable to treatment with the fungicide metalaxyl in increasing seedling emergence. Seedlings from bio-primed seeds emerged from the soil more rapidly than from nontreated seeds and were larger at three weeks postplanting. Seeds of sh 2 and sugary enhancer (se) sweet corn, as well as that of several sh 2 cultivars, were protected from damping-off by bio-priming.
Rooted cuttings of 22 different Euphorbia pulcherrima Willd. ex Klotzsch cultivars were grown in root substrate inoculated with 0, 5000,15,000, and 30,000 oospores of Pyuthium ultimum Trow per 10-cm containers. The root substrate was a mixture of 50% peat, 30% perlite, and 20% soil, adjusted to a pH 5.5. Plants were grown in a greenhouse with a temperature range of 15-32 °C, and were fertilized daily with 200 ppm N (Excel 15-5-15, Scotts Co. Marietta, Ga). After 8 weeks, roots were rated for disease incidence and root fresh and dry weights were determined. The data were analyzed using ANOVA with six blocks in a 22 × 4 factorial design, linear regression, and cluster analysis. Significant differences among the responses of the cultivars were found. The slopes of the regression equations, using the log10 of the inoculum level for the X axis, were more positive for disease incidence and more negative for fresh and dry root weights in the more susceptble cultivars. The cultivars were separated, by the cluster analysis, into three groups, less susceptible, moderately susceptible, and highly susceptible. Cultivars Marblestar and Galaxy Red were representative of less susceptible, `Pepride' and `Jolly Red' were representative of moderately susceptible, and `Snowcap' and `Success' were representative of highly susceptible cultivars.
incidence of Pythium spp. in floriculture crops was reported in Pennsylvania in 2002 ( Moorman et al., 2002 ): P. irregulare and P. aphanidermatum were the most common species. In Michigan, it was found that P. irregulare , P. ultimum , and P
Mandelbaum, 1986 ; Lumsden et al., 1983 ; Zhang et al., 1996 ). Considering that geranium plants are susceptible to root diseases caused by a multitude of pathogens, including numerous Pythium species such as P. splendens ( Griffin, 1972 ), P. ultimum
, Salmonella sp.) with varying but significant degrees of efficiency ( Kadlec and Wallace, 2009 ). For example, Gruyer et al. (2011) showed that AWs were effective in reducing Pythium ultimum and Fusarium oxysporum populations. Previous studies also
; however, P. ultimum , P. aphanidermatum , and P. irregulare are isolated frequently from symptomatic plants in commercial production ( Del Castillo Múnera and Hausbeck, 2016 ; Moorman et al., 2002 ). Pythium species are ubiquitous in natural
, Phytophthora cactorum , Phytophthora erythroseptica , Pythium ultimum , and Phytophthora cinnamomi were maintained and analyzed on Corn Meal Agar (CMA) (Becton, Dickinson & Co.). Before inoculation, fungal and oomycetes isolates were subcultured onto these