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Carlos E. Bogran, H. Brent Pemberton, Thomas Isakeit, and William R. Roberson

A strain of Rhizoctonia solani was isolated from wax begonia (Begonia Semperflorens-Cultorum hybrids) plants in garden evaluation trial plots. This strain was then used to test for disease tolerance in a controlled environment experiment. Inoculated plants of 12 cultivars were evaluated for disease development and the area under the disease progress curve was calculated. No plants were disease free, but `Stara White', `Stara Pink', and three colors from the Party series exhibited greater disease tolerance than `Ambassador Coral', `Ambassador Deep Rose', and two experimental varieties. `Stara White', `Party Pink Bronze Leaf', and `Party White Bronze Leaf' were more tolerant than `Cocktail Vodka', an industry standard. When the same cultivars were grown in field garden evaluation plots, `Cocktail Vodka', four colors from the Stara series, and three colors from the Party series exhibited superior garden performance and flowering ratings to `Ambassador Coral' and an experimental `Rose' cultivar. For most cultivars, garden performance was correlated to disease tolerance. However, `Cocktail Vodka' exhibited good garden performance despite having a high level of disease in the inoculation experiment, indicating that other factors may be involved in determining garden performance.

Open access

Mando A. Shehata, D.W. Davis, and F.L. Pfleger

Abstract

A modified Environmental Shift Technique based on use of a disease index (scoring) gave consistent separation between susceptible and moderately resistant pea (Pisum sativum L.) genotypes to Aphanomyces euteiches Drech. root rot in 3 tests. A moderately high association (r = −0.63 to −0.83) between disease index and percentage of plant survival was found in segregating populations. Minnesota 108, moderately resistant to A. euteiches, produced adventitious roots readily at an early stage. Root rot resistance and number of adventitious roots were inherited independently. Broad sense heritability (BSH) ranging between 0.45 and 0.57 for resistance to A. euteiches root rot, and between 0.39 and 0.44 for resistance to Rhizoctonia solani Kuehn stem rot, varied by parental combination, experiment, and method of estimation. However, heritability based on gain by selection in the F3 ranged from 0.28 to 0.46 and from 0.21 to 0.44 for resistance to A. euteiches and R. solani, respectively. Frequency distribution of resistant and susceptible plants suggested quantitative inheritance of resistance to both diseases. Recurrent selection, in which each cycle includes one intermating, selfing, and testing generation, is suggested to improve and transfer resistance.

Open access

A. R. Moody, P. S. Benepal, B. Berkley, and E. J. Koch

Abstract

Seven-day-old hypocotyls of 149 bean cultivars were inoculated with Rhizoctonia solani and incubated in a growth chamber for 72 hours at 30°C. Based on the mean size of the largest lesion, and 10 most resistant cultivars were: ‘Dwarf Horticultural Long Pod’, ‘Yellow Eye’, ‘White Kidney’, ‘Romano Pole’, ‘French Horticultural’, ‘Red Kidney’, ‘Manitou’, ‘Sutter Pink’, ‘Wren’s Egg’, and ‘Red Mexican UI 37’. The mean largest lesion for ‘Dwarf Horticultural Long Pod’ (the most resistant) was 3.0 mm2 while that for the Bush Blue Lake 274 (susceptible) was 64.4 mm2. These 10 cultivars were further tested using 5 different isolates of R. solani. ‘Yellow Eye’ was the most resistant to all 5 isolates with a mean largest lesion size of 10.0 mm2 while ‘Bush Blue Lake’ had a mean lesion size of 90.9 mm2. The root rot ratings were highly correlated with the areas of the largest lesion, and the number of lesions. ‘White Kidney’ was the only white-seeded resistant cultivar.

Free access

Mark W. Farnham and Anthony P. Keinath

Wirestem, caused by Rhizoctonia solani, is a destructive disease of B. oleracea cole crops and is distributed worldwide. Effective means of wirestem control include soil fumigation and soil treatment with pentachloronitrobenzene, which are increasingly expensive and environmentally undesirable. As a consequence, alternative methods of wirestem control are needed. Thus, we conducted controlled-environment and field experiments to develop methodology to study host-plant resistance and possibly biocontrol agents as potential wirestem control alternatives. Seedlings of 12 cultivars (three each of cauliflower, broccoli, cabbage, and collard) at the four- to five-leaf stage were transplanted to trays in a growth room or into field plots and covered with soil infested with R. solani AG-4 sclerotia. Disease progression (percent of plants healthy, diseased, and dead) was observed every 3 days for 2 weeks in the controlled environments and for 3 weeks in field trials. At the end of two studies, plants were dug with roots intact and rated for disease using a 1 to 10 scale. In all trials, percent healthy plants stabilized at about 2 weeks after inoculation. Incidence of wirestem disease varied among experiments ranging from 70% to 100% diseased, dead plants in controlled environments, and from 51% to 88% and 33% 65% in the two respective field studies. Disease rating was always negatively and significantly correlated with percent healthy plants. Although a genotype × environment interaction was observed, some cultivars (i.e., `Snowcone' and `Snowcrown' cauliflowers) were always severely diseased, while others (i.e., `Viking' broccoli and `Blue Max' collard) were consistently among the least diseased.

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Craig S. Charron and Carl E. Sams

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.

Open access

George H. Silva and Richard W. Hartmann

Abstract

F3 progeny tests were used to confirm individual F2 plant Rhizoctonia resistance classifications determined from greenhouse inoculations of bean seedlings. F2 segregations within individual disease classes mostly agreed with the hypothesis that genetic control of resistance to Rhizoctonia is controlled by 3 pairs of genes acting equally and additively. Partially resistant families postulated to be homozygous for 2 pairs of genes for resistance were recovered in the segregating generations in the frequencies expected.

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D.E. Green II, J.D. Fry, J.C. Pair, and N.A. Tisserat

Mowing heights from 1.2 to 5.1 cm, five N sources with two application rates (74 and 148 kg N/ha per year), and seven preemergence herbicides were evaluated in field studies in Manhattan and Wichita, Kan., for their effect on large patch disease, caused by Rhizoctonia solani Kuhn AG 2-2, in zoysiagrass (Zoysia spp.). Turf mowed at 1.2 and 2.5 cm was more severely blighted than turf mowed at 4.5 or 5.1 cm. At all mowing heights, turf recovered by August or September. Disease severity was not influenced by N source, N rate, or preemergence herbicides.

Free access

Michael S. Uchneat and Todd C. Wehner

Belly rot, caused by the fungal pathogen Rhizoctonia solani Kühn., is a severe disease in many regions that produce cucumber (Cucumis sativus L.). Annual crop loss to belly rot is commonly 5% to 10%, but losses as high as 80% can occur in individual fields. There are no resistant cultivars, so fungicides are used to provide partial control. Genetic resistance in an acceptable cultivar would be more desirable and economical. Studies were conducted in Summers 1991 and 1992 to screen promising germplasm for belly rot resistance using field and detached-fruit screening methods. In 1991, 105 cultigens (cultivars, breeding lines, and plant introduction accessions) were evaluated for belly rot resistance. The tests were repeated in 1992 with 63 cultigens, including the most resistant cultigens identified in 1991 and appropriate controls. Several cultigens were identified as potential sources of resistance genes. Pickling cucumbers showing resistance included PI 197085, PI 271328, and an F4 selection of PI 197087 × PI 280096. Slicing cucumbers with resistance included `Marketmore 76' and the F1 of Gy 14 × PI 197087. Belly rot resistance was not correlated with other horticultural traits measured, including fruit type, skin type, spine color, and firmness. The resistant cultigens identified should be useful for developing cucumber cultivars with enhanced resistance to Rhizoctonia solani.

Free access

Michael A. Fidanza and Peter H. Dernoeden

A field investigation was conducted during 1991 and 1992 to determine the effectiveness of enzyme-linked immunosorbent assay (ELISA) to predict brown patch (Rhizoctonia solani Kühn) infection events in `Caravelle' perennial ryegrass (Lolium perenne L.). Turfgrass samples were collected either between 7:00 and 8:00 am or 4:00 and 5:00 pm, and from plots mowed to a height of either 1.7 or 4.5 cm. Pathogen detection levels were generally higher in am-sampled turf and in plots mowed to a height of 4.5 cm. During 2 years, only 7 of 15 infection events were predicted from samples collected from high-cut turf and only three from samples collected from low-cut turf. While this technology is useful for confirming the presence of R. solani, it was unreliable for predicting infection events.

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J.H. Dunn, D.D. Minner, B.F. Fresenburg, and S.S. Bughrara

We evaluated the effect of fertilization treatments in combination with clippings disposal on perennial ryegrass (Lolium perenne L.) in two adjacent locations. Clippings left on turf during mowing decreased dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in both locations during three summers compared with clippings removed in mower baskets. However, brown patch (Rhizoctonia solani Kuhn) increased during July and Aug. 1995 when clippings were left on turf. Dollar spot was more severe with N (kg·ha–1·year–1) at 120 compared to 240; brown patch was more severe at 240. While clippings disposal had significant effects on disease incidence, implementation may not be practical because of the contrary responses of the observed diseases to this management approach.