1. Fungicide resistance and host susceptibility of
Colletotrichum orbiculare infecting cucurbit
crops in North Carolina
Nicholas Noël and Lina M. Quesada-Ocampo, PhD
Department of Plant Pathology, North Carolina State University, Raleigh, NC
Introduction
1. Evaluate commercially available watermelon cultivars for their
agronomic traits and disease resistance in the field and
greenhouse.
1. Characterize C. orbiculare populations infecting cucurbit crops
in NC for fungicide resistance and virulence.
Results
Results
Objectives
Conclusions and Future
Directions
Acknowledgements
Methods
In vitro FungicidesIn North Carolina, watermelon (Citrullus lanatus) production for
the 2015 growing season was valued in excess of $32.3 million1.
The eastern and northeastern parts of the state are ideal for
production, where the Coastal Plain provides rich and diverse
soil for agriculture. As of 2015 North Carolina produces 6% of
the US’s watermelons, place the state 6th in total value of US
production2.
Cucurbit anthracnose, caused by the ascomycete Colletotrichum
orbiculare syn. lagenarium, is a widespread fruit and foliar
disease that results in yield losses across the United States. In
North Carolina, favorable environmental conditions, host
availability, and long growing seasons offer ample opportunity for
disease development, resulting in significant economic losses.
Application of effective fungicides and planting of resistant
cultivars, along with appropriate cultural practices, have proven
effective in reducing anthracnose.
Isolates of C. orbiculare were obtained from collaborators in
South Carolina, Indiana, Maryland, and Florida or through
submissions to the NCSU PDIC. All isolates were grown on
PDA, placed into long-term storage and revived on PDA.
Agar plugs (7 mm in diameter) were cut from the edge of actively
growing cultures grown on PDA for 10 days. Plugs were placed
onto fungicide-amended media and were incubated at 24 ± 1°C
under a 16-hour photoperiod. After 7 days of growth, two
perpendicular colony diameters per plate were measured and
averaged. The diameter of the agar plug was subtracted from
the colony diameters before calculating means3.
C. orbiculare isolates were obtained from infected leaves, stems,
and fruit on watermelon samples submitted to the Plant Disease
and Insect Clinic at NC State University.
36 cultivars were selected on the basis of their diseases
resistance and their popularity among growers in NC. Plots
were designed to optimize disease pressure equally across all
cultivars and plots were replicated 4 times at Cherry Research
Farm in Goldsboro, NC.
1. 23 lines showed less than 10% disease severity and
incidence indicating that anthracnose resistance is available
in commercial cultivars.
2. Initial fungicide resistance evaluations indicate sensitivity to
Pyraclostrobin, but insensitivity to Chlorothalonil was
observed in 1 isolate.
3. Field and greenhouse evaluations will be replicated next year
and fungicide resistance evaluation will be expanded to 100
diverse US isolates.
We thank all members of the Quesada Lab, Shawn Butler from
the NCSU PDIC, the Cherry Farm, Extension Agents, and
grower cooperators. We also thank Anthony Keinath (Clemson),
Dan Egel (Purdue), Fanny Iriarte (Florida), Kathryne Everts
(Maryland), Bhabesh Dutta (Georgia), and the ATCC for
providing isolates. Funding for this work was provided by USDA-
SCRI CucCAP.
Variety Trial
Methods
Greenhouse seeding occurred on 4/19/16 and transplanted on
5/20/16. Isolates were grown on V8 agar at 24 ± 1°C under a
16-hour photoperiod. Conidia were harvested, filtered through
cheese cloth, and concentrated to a final application rate of
50,000 spores/ plot. Inoculations occurred on 6/14, 6/30, 7/5,
7/28 via Solo backpack sprayer. Disease ratings were taken on
7/9, 7/16, and 7/24. Fruit was harvested and graded on 7/26.
A
References
1. USDA-NASS, 2016; State Agriculture Overview: North Carolina
2. USDA-NASS, 2016; Vegetable 2015 Summary
3. Keinath, AP. 2015. Baseline Sensitivity of Didymella bryoniae to Cyprodinil and
Fludioxonil and Field Efficacy of these Fungicides Against Isolates Resistant to
Pyraclostrobin and Boscalid. Plant Dis. 99:-822
Figure 2: A, Congo, a resistant cultivar,
shows low disease incidence and severity; B,
AU Producer, tolerant to Race 1 and Race 2,
shows medium disease incidence and
severity; C, Moon & Stars, a susceptible
cultivar, shows high disease incidence and
severity; D, Sorbet F1, with intermediate
resistance to anthracnose, shows the highest
disease incidence and severity.
Table 1: Selected cultivars for field and
greenhouse trials.
Figure 3: A, Average disease ratings over
three rating periods across four replicates; B,
Average fruit yield and weight across four
replicates; C, Sensitivity of South Carolina
isolates to recommended fungicides.
Figure 1: A, Anthracnose symptoms on watermelon, depicting characteristic lesions; B,
Colletotrichum orbiculare on PDA after 7 days incubation at 24 ± 1°C under a 16-hour
photoperiod; C, Conidia harvested from V-8 agar via Tween-20/water solution.
SCCO12 (Race 1) SCCO14 (Race 2) SCCO15 (Race 2B) SCCO17 (Race 2B) SCCO18 (Race 2B)
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Disease(%)
Cultivar Number (Table 1)
Figure 3: Disease ratings
Table 1: Selected Cultivars for Field Trial
Plot Variety Seeded Resistance Race
#1 Congo Seeded Resistant Anth
#2 Black Diamond Seeded N/A N/A
#3 Vista Seeded Tolerant Anth
#4 Bold Ruler Seedless N/A N/A
#5 SSX 8585 Seeded High Resistance Anth1
#6 Carolina Cross Seeded N/A N/A
#7 Estrella Seeded Intermediate R Anth1
#8 Dixie Queen Seeded N/A N/A
#9 Mardis Gras Seeded Intermediate R Anth1
#10 Florida Giant Seeded N/A N/A
#11 Top Gun Seeded Intermediate R Anth1
#12 Jubilee Seeded N/A N/A
#13 Jubilee II Seeded N/A N/A
#14 Au Producer Seeded Tolerant Anth1, Anth2
#15 Mickylee Seeded N/A N/A
#16 SV0241WA Seedless High Resistance Anthracnose
#17 Moon & Stars Seeded N/A N/A
#18 Sorbet F1 Seedless Intermediate R Anthracnose
#19 Provider Seedless N/A N/A
#20 Travaler F1 Seedless Intermediate R Co
#21 Tri-X 313 Seedless N/A N/A
#22 Troubadour F1 Seedless Intermediate R Co
#23 Unbridled Seedless N/A N/A
#24 Royal Sweet Seeded High Resistance Co1
#25 Starbrite Seeded High Resistance Co1
#26 Yellow Buttercup Seedless N/A N/A
#27 720 Seeded Intermediate R Co1
#28 Solitaire Seedless N/A N/A
#29 7387 Seedless Intermediate R Co1
#30 Tendersweet Orange Seeded N/A N/A
#31 Fantasy Seeded Intermediate R Co1
#32 Sangria Seeded Intermediate R Co1
#33 Melody Seedless Intermediate R Co1
#34 Secretariat Seedless N/A N/A
#35 Ruby Seedless Intermediate R Co1,3
#36 Sweet Delight Seedless N/A N/A
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Weight(lbs)
Cultivar Number (Table 1)
Figure 3: Average Fruit Count and Weight
Total Fruit
Average Fruit Weight (lbs)
100 ppm10 ppm1 ppm0.1 ppm0.01 ppm0.001 ppm 100 ppm10 ppm1 ppm0.1 ppm0.01 ppm0.001 ppm 100 ppm10 ppm1 ppm0.1 ppm0.01 ppm0.001 ppm 100 ppm10 ppm1 ppm0.1 ppm0.01 ppm0.001 ppm 100 ppm10 ppm1 ppm0.1 ppm0.01 ppm0.001 ppm
PDA Control 10.3 9.13 13.5 11.7 10.9
Pyraclostrobin 2.43 9.56 9.67 10.7 10.2 9.47 3.48 9.54 10.5 9.65 9.11 9.65 3.19 13.6 15.2 14.9 12.4 12.4 2.76 11.9 13.1 11.2 11.7 11.7 3.26 11.4 12.7 11.0 10.0 7.75
Chlorothalonil 7.11 8.10 6.52 8.23 6.93 8.30 5.97 7.89 7.86 7.00 8.12 8.41 9.91 10.8 11.3 10.4 11.7 12.1 8.49 8.83 11.5 9.50 9.37 10.8 11.9 9.95 11.1 10.1 9.68 10.4
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Areaof
Growth,sq.cm.
Figure 3: Fungicide sensitivity of Colletotrichum orbiculare