scholarly journals A Detached Cucumber Fruit Method to Screen for Resistance to Phytophthora capsici and Effect of Fruit Age on Susceptibility to Infection

Plant Disease ◽  
2006 ◽  
Vol 90 (10) ◽  
pp. 1276-1282 ◽  
Author(s):  
A. J. Gevens ◽  
K. Ando ◽  
K. H. Lamour ◽  
R. Grumet ◽  
M. K. Hausbeck
Keyword(s):  
Management Strategy ◽  
Phytophthora Capsici ◽  
Fruit Rot ◽  
Michigan State University ◽  
State University ◽  
Plant Introductions ◽  
Susceptibility To Infection ◽  
Cucumber Fruit ◽  
History Of ◽  
Standard Practices

Identification and utilization of resistance to Phytophthora capsici could provide the basis for a viable management strategy against cucumber fruit rot, a persistent threat in cucumber (Cucumis sativus) production. Our objectives were to develop a method for testing detached, nonwounded, cucumber fruit for resistance to P. capsici, and to screen cucumber cultivars and plant introductions (collectively referred to as cultigens) for resistance. Four P. capsici isolates (differing in their sensitivity to the fungicide mefenoxam and compatibility type) were compared for their fruit infection capability in 1999 and 2000. No significant differences were found among isolates, and a single isolate was used for all subsequent screens. From 1999 to 2004, 480 cucumber cultigens were grown according to standard practices at Michigan State University research farms in four fields with no history of P. capsici. Commercially mature fruit were harvested, inoculated with P. capsici, and rated for lesion diameter, pathogen sporulation diameter, and density of pathogen sporulation. Although no fruit exhibited complete resistance to P. capsici, some cultigens exhibited limited pathogen sporulation. In the process of screening, it was observed that younger, smaller fruit were comparatively more susceptible than older, larger fruit. Replicated trials with hand-pollinated fruit showed that the transition from susceptible to more resistant appeared to coincide with the transition from the period of rapid fruit elongation to the period of increased fruit diameter. This is the first report using a nonwounded fruit screen to analyze cucumber resistance to P. capsici.

scholarly journals Developmental Changes in Cucumber Fruit Susceptibility to Infection by Phytophthoracapsici

HortScience ◽  
2005 ◽  
Vol 40 (4) ◽  
pp. 1117D-1118
Author(s):  
Kaori Ando ◽  
Rebecca Grumet
Keyword(s):  
Fruit Rot ◽  
Limiting Factor ◽  
Screening Methods ◽  
Plant Introductions ◽  
Susceptibility To Infection ◽  
Pickling Cucumber ◽  
Cucumber Fruit ◽  
Age Dependent ◽  
Oomycete Pathogen ◽  
Resistant Genotypes

Phytophthoracapsici, a soil-borne oomycete pathogen causing fruit rot in cucumber, has become a limiting factor for cucumber production in the Midwest. In the process of screening plant introductions (PIs) for resistance to P. capsici, it appeared that degree of susceptibility might decrease as fruits develop. To examine this more carefully, detached, greenhouse-grown, hand-pollinated `Vlaspik' fruits aged 2–18 days post-pollination (dpp) were inoculated with P. capsici mycelium and evaluated for symptoms. There was a reproducible decrease in susceptibility with increasing fruit age. The fruits that sporulated were usually younger and smaller (2–9 dpp), 10-3 dpp fruit tended to develop water-soaked symptoms, while the fruits that remained symptom-free were usually older (>14 dpp) and oversized for pickling cucumber. The transition from susceptible to more resistant appeared to occur at the end of the period of rapid fruit elongation. Detached field-grown `Straight Eight' fruits showed similar size-related trends. Candidate resistant genotypes identified from the PI screening were re-screened using 7 and 14 dpp fruits. Again an age-dependent difference in response was observed, indicating that the increase in resistance is not genotype-specific. Furthermore, field observations suggest a gradation of susceptibility within the fruits as the blossom end was most frequently infected. Preliminary tests of detached greenhouse-grown, hand-pollinated fruits suggested that as the fruits grew older, the blossom end remained susceptible longer than the stem end. These findings could have implications for appropriate screening methods, the stage of fruit likely to become infected in the field, and appropriate spray practices.

scholarly journals Evaluation of a Diverse, Worldwide Collection of Wild, Cultivated, and Landrace Pepper (Capsicum annuum) for Resistance to Phytophthora Fruit Rot, Genetic Diversity, and Population Structure

2015 ◽  
Vol 105 (1) ◽  
pp. 110-118 ◽  
Author(s):  
R. P. Naegele ◽  
A. J. Tomlinson ◽  
M. K. Hausbeck
Keyword(s):  
Genetic Diversity ◽  
Population Structure ◽  
Phytophthora Capsici ◽  
The United States ◽  
Fruit Rot ◽  
Sources Of Resistance ◽  
Plant Introductions ◽  
Genetic Clusters ◽  
Commercial Breeding ◽  
Moderately Resistant

Pepper is the third most important solanaceous crop in the United States and fourth most important worldwide. To identify sources of resistance for commercial breeding, 170 pepper genotypes from five continents and 45 countries were evaluated for Phytophthora fruit rot resistance using two isolates of Phytophthora capsici. Genetic diversity and population structure were assessed on a subset of 157 genotypes using 23 polymorphic simple sequence repeats. Partial resistance and isolate-specific interactions were identified in the population at both 3 and 5 days postinoculation (dpi). Plant introductions (PIs) 640833 and 566811 were the most resistant lines evaluated at 5 dpi to isolates 12889 and OP97, with mean lesion areas less than Criollo de Morelos. Genetic diversity was moderate (0.44) in the population. The program STRUCTURE inferred four genetic clusters with moderate to very great differentiation among clusters. Most lines evaluated were susceptible or moderately susceptible at 5 dpi, and no lines evaluated were completely resistant to Phytophthora fruit rot. Significant population structure was detected when pepper varieties were grouped by predefined categories of disease resistance, continent, and country of origin. Moderately resistant or resistant PIs to both isolates of P. capsici at 5 dpi were in genetic clusters one and two.

scholarly journals Greenhouse Whitefly Control of Salvia, 1997

1998 ◽  
Vol 23 (1) ◽  
pp. 356-357
Author(s):  
D. R. Smitley ◽  
T. W. Davis ◽  
M. M. Williams
Keyword(s):  
Irrigation System ◽  
Michigan State University ◽  
State University ◽  
Greenhouse Whitefly ◽  
Large Numbers ◽  
Untreated Check ◽  
History Of ◽  
Pre Treatment ◽  
Eggs And Larvae ◽  
Clay Pots

Abstract Salvia plants were started from seeds in 25" X 14" tubs at the Pesticide Research Center greenhouses at Michigan State University on 7 May. These 3 tubs were surrounded by fully grown zinnia plants that had large numbers of white-fly. The larger Zinnia plants had previously been placed in a research greenhouse with a long history of whitefly problems. After the Salvia from the tubs grew to approximately 1 to 2 inches, they were replanted into individual 6" clay pots. The plants were irrigated with 120 mL of water daily, with a drip irrigation system. Plants were also fertilized with Peters 20-20-20 at 1000 ppm biweekly. Pre-treatment counts were made on 19 Jun by taking five leaves per plant and counting the number of eggs and larvae on the bottom of the leaves using a dissecting scope. Treatments were blocked by using an adjusted precount. The adjusted precounts represented 33% of the eggs added to the total number of larvae. Each treatment was replicated 6 times. Due to the number of treatments, the test was arranged in several blocks, each with an untreated check. Single application granular treatments were all applied on 25 Jun and spray applications were applied on 25 Jun, 2 Jul, and 9 Jul. A hand-held R&D CO2 sprayer with an 8003 nozzle at 50 psi was used. Whitefiles were counted by collecting leaves on 2 Jul, 17 Jul, 22 Jul and examining in the same manner as for the precounts.

scholarly journals 487 Assessment of Chemical Induction of Acquired Resistance to Phytophthora Fruit Rot in Field-grown Pickling Cucumber

HortScience ◽  
1999 ◽  
Vol 34 (3) ◽  
pp. 529A-529
Author(s):  
Priscilla M. Hockin ◽  
Irvin E. Widders
Keyword(s):  
Systemic Acquired Resistance ◽  
Phytophthora Capsici ◽  
Acquired Resistance ◽  
Lesion Size ◽  
Plant Diseases ◽  
Fruit Rot ◽  
Chemical Induction ◽  
Resistance Response ◽  
Chemical Inducers ◽  
Cucumber Fruit

Systemic acquired resistance (SAR) is a physiological defense response in plants conferring broad spectrum resistance to pathogens. SAR is inducible through infection by necrotizing pathogens or chemical inducers and involves the systemic activation of defense related genes. Our objectives were to evaluate resistance expression to phytophthora soft rot fruit in cucumber in response to increasing concentrations of 2,6 dichloroisonicotinic acid (INA) and benzo (1,2,3)thiadiazole-7-carbothioc acid S-methyl ester (BTH) by foliar applications. Excised leaves exhibited a resistance response to foliar applications of all concentrations of INA and BTH tested when challenge inoculated with Colletotrichum lagenarium. There was increasing benefit with increasing concentration of each chemical applied. Harvested cucumber fruit, 3.4 to 4.5 cm in diameter, were challenge inoculated with Phytophthora capsici; there were no significant chemical and rate interactions in terms of internal lesion measurements. Overall, INA consistently reduced lesion size in cucumber fruit. A bioassay conducted on fruit of different maturity levels, as defined by fruit diameter, revealed that larger sized fruit (4 to 5 cm) were more resistant to fruit rot. Fruit with diameters of 3 to 4 cm from plots treated with BTH showed little resistance as compared to the control and fruit from the same treatment with diameters of 2 to 3 cm. Fruit from plots treated with INA had at least 50% reduction in lesion size than the control. It is unclear if these differences were attributable to changes in physiological or anatomical factors. The true importance of these results should be interpreted with caution. Yield studies have not been conducted, and thus, with the experienced stunting, treatment with 100 ppm INA would be expected to lower yield and perhaps fruit quality. Determination of the optimal application regime and other cultural factors will provide broad control of plant diseases.

scholarly journals First Report of Mefenoxam-Resistant Isolates of Phytophthora capsici from Lima Bean Pods in the Mid-Atlantic Region

Plant Disease ◽  
2008 ◽  
Vol 92 (4) ◽  
pp. 656-656 ◽  
Author(s):  
J. F. Davey ◽  
N. F. Gregory ◽  
R. P. Mulrooney ◽  
T. A. Evans ◽  
R. B. Carroll
Keyword(s):  
Foliar Application ◽  
Phytophthora Capsici ◽  
Crop Protection ◽  
Lima Bean ◽  
Fruit Rot ◽  
Resistant Isolate ◽  
Phaseolus Lunatus ◽  
Atlantic Region ◽  
History Of ◽  
Lima Beans

Phytophthora capsici Leonian, the causal agent of lima bean pod rot, was first identified as a pathogen of lima bean in 2002 (1) and poses a new threat to lima bean (Phaseolus lunatus L.) production in the Mid-Atlantic Region. The phenylamide fungicide mefenoxam (Ridomil Gold; Syngenta Crop Protection) is widely used in the region for controlling foliar and soilborne diseases caused by Oomycetes. Isolates of P. capsici were collected from lima bean pods from production fields in Delaware, Maryland, and New Jersey from 1998 to 2004. These isolates originated from survey samples of lima bean fields for another pathogen, P. phaseoli, in 1999 and 2000 and diagnostic samples were submitted to the Plant Disease Clinic. Isolates were from lima bean, except for one from pepper (basal stem). Identification was made on the basis of morphometric characteristics. No known sensitive or insensitive isolates were included in the evaluation. Single zoospore cultures were evaluated for mefenoxam sensitivity on V8 agar plates amended with 100 ppm of mefenoxam, a previously tested concentration (2). Seven-millimeter-diameter agar plugs of each isolate were cut from the edge of actively expanding cultures of P. capsici with a cork borer and transferred to three V8 agar plates amended with mefenoxam and three unamended V8 plates. The plates were arranged in a completely randomized design and incubated at 25°C in the dark for 3 days. After incubation, colony growth was measured in millimeters and averaged for the three replicate plates of each isolate and percent growth relative to the unamended control was calculated. Mefenoxam sensitivity was assigned according to methods of Lamour et al. (2). The experiment was repeated once, and also run with a treatment of 200 ppm of mefenoxam. Of sixteen isolates screened, nine were rated as sensitive, four were intermediately resistant, and three were resistant. There was no difference between the 100 and 200 ppm results, except for a slight increase in sensitivity for one isolate. A subsequent experiment tested five isolates at concentrations of 1, 10, 100, and 1,000 ppm. Results were consistent with previous tests, with resistant isolates exhibiting some growth at the highest concentration of mefenoxam. One resistant isolate was from a field in Delaware previously cropped to slicing cucumbers with a history of mefenoxam applications. The second was from Caroline County, MD, which is heavily cropped to pickling cucumbers and likely to have been exposed to mefanoxam applications for the control of fruit rot; the origin of the third insensitive isolate from lima bean is unknown. Mefanoxam usage on lima bean is usually limited to one foliar application of mefenoxam+copper hydroxide to control downy mildew in the fall crop in wet seasons. This study indicates that mefenoxam resistance is present in populations of P. capsici in lima bean fields in the Mid-Atlantic Region, presumably as a result of mefenoxam applications to other vegetable crops, principally cucurbits, which are planted in rotation with lima beans or from nearby cucurbit fields. Implementing strategies to minimize fungicide resistance in other vegetables is important to slow resistance development associated with this emerging pathogen on lima beans. Lima bean pod rot continues to be seen sporadically each year in fields with a history of P. capsici and abundant rainfall or excessive irrigation. References: (1) C. R. Davidson et al. Plant Dis. 86:1049, 2002. (2) K. H. Lamour et al. Phytopathology 90:396, 2000.

scholarly journals Screening the Cucumber Plant Introduction Collection for Young Fruit Resistance to Phytophthora capsici

HortScience ◽  
2014 ◽  
Vol 49 (3) ◽  
pp. 244-249 ◽  
Author(s):  
Marivi Colle ◽  
Elizabeth N. Straley ◽  
Stephanie B. Makela ◽  
Sue A. Hammar ◽  
Rebecca Grumet
Keyword(s):  
High Throughput Screening ◽  
Phytophthora Capsici ◽  
Plant Introduction ◽  
Fruit Rot ◽  
Cucumber Plant ◽  
Post Inoculation ◽  
Sources Of Resistance ◽  
Major Constraint ◽  
Cucumber Fruit ◽  
Symptom Rating

Fruit rot caused by Phytophthora capsici is a major constraint in cucumber (Cucumis sativus) production. In an effort to identify a source of resistance, we developed a more streamlined detached fruit method for high-throughput screening and tested the U.S. cucumber PI collection for fruit rot resistance. A total of 1076 PI collections, from 54 geographic locations around the world, along with the susceptible commercial cultivar, Vlaspik, were grown in the field and tested for resistance to P. capsici. Using the knowledge gained from our prior studies regarding greater susceptibility of young fruits compared with older fruits, very young fruits (≈3 to 4 days post-pollination) were collected and inoculated with zoospore suspensions of P. capsici isolate OP97. From the screens performed in 2011 and 2012, 99% of the tested PIs were rated as moderately or highly susceptible based on symptom development and pathogen growth at 5 days post-inoculation. The cv. Vlaspik control showed consistent high susceptibility to P. capsici with a mean symptom rating of 8.0 on a 9-point scale. A set of 28 PIs was chosen for further testing in the greenhouse or field in 2013. The disease ratings of PIs rescreened in 2013 were much lower compared with that of the full collection of PIs. Three accessions, PI109483, PI178884, and PI214049, showed consistent low mean disease ratings and may be considered as possible sources of resistance to young cucumber fruit infection by P. capsici. Evaluation of the S1 progeny of PI109483 suggests that the resistance is heritable and should allow for development of useful breeding materials that can be used for developing P. capsici-resistant cucumber cultivars.

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