Powdery Mildew-resistant Melon Variety Evaluation, New York 2012 Margaret T. McGrath, Cornell University, Riverhead, New York Karen LaMarsh, Cornell University, Riverhead, New York Sandra Menasha, Cornell Cooperative Extension-Suffolk County, New York Powdery mildew is a very common disease that can reduce yield (fruit quantity and/or size) and market quality (flavor, color, storability, etc.) in melons. Successful control of powdery mildew in melon is critical to ensure leaves remain healthy until fruit mature and obtain high sugar content, which results in good flavor. The only control measures are fungicides and resistant varieties. The pathogen, Podosphaera xanthii, produces an abundance of easily wind-dispersed spores and infects under a wide range of environmental conditions; therefore, rotation and other practices to avoid the pathogen are not effective options, nor are drip irrigation or other methods to reduce leaf wetness commonly used for other fungal diseases. Many varieties of melon currently marketed have resistance to powdery mildew. Races of the powdery mildew pathogen have been differentiated on cantaloupe. Most varieties have resistance to Races 1 and 2, which have been thought to be the dominant races in the United States. Varieties with this resistance generally have provided a very high degree of suppression against these races in previous variety evaluations conducted on Long Island, New York. However, all varieties with resistance to both races do not perform similarly because the sources of genetic resistance, in particular regarding presence of modifier genes, differ among these resistant varieties. There is concern that the pathogen will again evolve a new race able to overcome the current resistance genes. In 2008, a new race (designated S ) was confirmed in Georgia. Resistant melon varieties did not suppress powdery mildew in 2010 as effectively as in previous years in the variety evaluations conducted on Long Island. Fortunately in 2011, the melon varieties evaluated again provided very good suppression. The goals of this experiment, were (1) to continue to monitor adaptation in the pathogen that has been reducing the effectiveness of powdery mildew resistance in cucurbit crops, (2) to determine whether varieties with resistance to Races 1 and 2 more effectively suppress powdery mildew than varieties with resistance to only Race 1, and (3) to evaluate the resistance, fruit quality, and yield of new varieties. This is part of a multi-year project. Materials and Methods A field experiment was conducted at the Long Island Horticultural Research and Extension Center in Riverhead on Haven loam soil. Controlled-release fertilizer (N-P-K, 19-10-9) at 525 lb./a (100 lb./a of N) was broadcast over the bed area and incorporated on June 8. Beds were formed with drip tape and covered with black plastic mulch on June 11. A waterwheel transplanter was used to make planting holes and apply starter fertilizer plus insecticide on June 11. Seeds were sown on May 23 in the greenhouse. Seedlings were transplanted by hand into the planting holes on June 15. During the season, water was provided as needed via drip irrigation lines. Weeds were managed by mowing and hand weeding. Cucumber beetles were managed with Admire Pro (2.8 fl. oz./1000 ft.) applied in the transplant water on June 11.
No fungicides were applied to manage powdery mildew. The following fungicides were applied preventively for downy mildew (Pseudoperonospora cubensis) and/or Phytophthora blight (Phytophthora capsici): ProPhyt (2 qts./a) on July 18; Presidio (4 fl. Oz./A) on July 31; Curzate 60 DF (5 oz./a) on July 31; and Ranman 400 SC (2.75 fl. Oz./A) on July 31 and August 24. Plots were three adjacent rows each with four plants spaced 24 inches apart. Rows were spaced 68 inches apart. To separate plots and provide a source of inoculum, two plants of a powdery mildew-susceptible squash cultivar were planted between each plot in each row. A combination of three cultivars were used: Daisy and Fortune (summer squash), and Spineless Beauty (zucchini). A randomized complete block design with four replications was used. Upper and lower leaf surfaces were assessed for powdery mildew on July 25 and on August 1, 6, and 16. Powdery mildew colonies were counted; severity was estimated when colonies had coalesced or were too numerous to count. Colony counts were converted to severity values using the conversion factor of 30 colonies/leaf=1% severity. Average severity for the entire canopy was calculated from the individual leaf assessments. Area Under Disease Progress Curve (AUDPC) values were calculated from July 25 through August 16. Ripe fruit were harvested on August 6, 10, and 17. Average monthly high and low temperatures ( F) were 78/61 in June, 85/68 in July, and 83/67 in August. Rainfall (inches) was 5.44, 4.35, and 3.24 for these months, respectively. Results and Discussion Powdery mildew developed naturally. Symptoms were first seen on July 23. Early in disease development, while severity was low (July 25 assessment), no significant differences were detected among any of the cultivars (data not shown). Powdery mildew on Superstar, the susceptible standard cantaloupe cultivar with no known genes for resistance included for comparison in this experiment, had become significantly more severe than all resistant cultivars by the next assessment on August 1. The resistant cultivars provided a high level of suppression, indicating only race 2 and/or race 1 of Podosphaera xanthii were present (Table 1). Degree of control relative to Superstar based on AUDPC values on upper and lower leaf surfaces was 99% and 100%, respectively, for Samoa, a Harper-type melon, 98% and 100% for Visa Premium, a galia-type melon, and 99% and 99% for Cleopatra, a standard cantaloupe. Control for the other resistant cultivars ranged from 86% to 98% on upper lower leaf surfaces and 83% and 96% on lower surfaces. Eclipse, which has major-gene resistance only to race 1 of Podosphaera xanthii, was not significantly more severely affected by powdery mildew than all the cultivars with resistance to races 1 and 2, suggesting that race 1 was the dominant race present. The two powdery mildew-resistant honeydew-type melons, Dream Dew and Summer Dew, were numerically but not significantly less severely diseased than Honeydew Green Flesh, a comparable susceptible cultivar. Dream Dew, with resistance only to race 1, was numerically more severely affected than Summer Dew, which is resistant to races 1 and 2. Powdery mildew was more severe on resistant cultivars in a similar experiment in 2010. The other melons evaluated in 2012 produce Tuscan type fruit (Orange Sherbert and Napoli) or standard or personal-size cantaloupe-type fruit. The highest yielding varieties were Visa Premium, Cleopatra, and Lilliput and Sugar Cube (both personal-sized cantaloupe) (Table 2).
Table 1. Severity of powdery mildew on leaves of melon varieties compared on Long Island, New York, in 2012. Varieties are listed based on fruit type. Variety (resistance) x z Powdery Mildew Severity (%) Seed Source w Upper Leaf Surface y Lower Leaf Surface y Aug 6 Aug 16 AUDPC v Aug 6 Aug 16 AUDPC v Superstar (S) H 14.0 a 62.1 488.4 a 8.5 a 60.4 a 378.3 a Eclipse (R1) SI 0.1 b 10.4 40.3 bc 0.0 b 30.1 ab 59.3 bc Avatar (R) SI 1.0 b 7.8 23.0 c 0.5 b 17.6 b 19.6 bc Cleopatra (R) H 0.0 b 2.3 5.4 c 0.0 b 13.3 b 4.5 bc Lilliput (R) SW 0.0 b 1.3 7.4 c 0.0 b 10.4 b 11.4 bc Pixie (R) SW 0.2 b 12.6 58.5 bc 0.0 b 10.2 b 40.3 bc Sugar Cube (R) H 0.0 b 36.4 20.3 c 0.0 b 9.6 b 17.4 bc Orange Sherbert (R) SI 0.7 b 53.5 69.3 bc 0.6 b 6.0 b 27.3 bc Napoli (R) SW 0.0 b 6.9 14.1 c 0.0 b 5.5 b 20.5 bc Samoa (R) SW 0.0 b 1.6 4.6 c 0.0 b 5.1 b 0.3 c Visa Premium (R) SW 0.0 b 0.9 7.8 c 0.0 b 3.3 b 1.3 c Honeydew Green Flesh (S) H 1.4 b 90.0 171.0 b 0.0 b 2.7 b 139.2 ab Dream Dew (R1) H 0.2 b 11.9 59.3 bc 0.1 b 0.3 b 62.8 bc Summer Dew (R) H 0.0 b 6.7 25.8 bc 0.0 b 0.1 b 16.2 bc P-value (treatment) <0.0001 0.2202 <0.0001 0.0003 <0.0001 <0.0001 z Exact colony counts were made when possible and severity was estimated using the conversion factor of 30 colonies/leaf = 1%. y Numbers in each column followed by the same letter or no letter are not significantly different from each other (Tukey s HSD, P=0.05). x S indicates susceptibility to Podosphaera xanthii. R1 indicates resistance to Race 1. R indicates resistance to Races 1 and 2. w H=Harris, SI=Siegers, SW=Seedway. v UDPC values were square root transformed before analysis. Table contains detransformed values.
Table 2. Yield of melon varieties compared on Long Island, New York, in 2012. Yield (number of fruit/plant) z Variety (fruit type) x Marketable Total y Aug 6 All w Aug 6 Aug 17 All v Superstar (C) 0.52 bcd 1.54 bcd 0.52 b 0.10 c 1.85 bcde Eclipse (C) 0.23 d 0.65 cde 0.23 b 0.29 c 0.71 e Avatar (C) 0.81 bc 1.69 bc 0.81 b 0.19 c 1.75 cde Cleopatra (C) 1.77 a 2.54 ab 2.48 a 0.00 c 3.31 abc Lilliput (PC) 0.27 cd 3.33 a 0.31 b 1.44 a 3.50 ab Pixie (PC) 0.10 d 1.33 bcde 0.15 b 0.67 abc 1.52 de Sugar Cube (PC) 0.42 cd 2.31 ab 0.46 b 1.13 ab 2.44 abcd Orange Sherbert (T) 0.25 cd 1.02 cde 0.25 b 0.44 bc 1.08 de Napoli (T) 0.42 cd 1.27 bcde 0.46 b 0.27 c 1.35 de Samoa (H) 0.13 d 0.69 cde 0.13 b 0.52 bc 0.71 e Visa Premium (G) 1.02 b 2.46 ab 2.31 a 0.00 c 4.00 a Honeydew Green Flesh (HD) 0.00 d 0.27 de 0.04 b 0.23 c 0.33 e Dream Dew (HD) 0.13 d 0.69 cde 0.25 b 0.33 bc 0.83 de Summer Dew (HD) 0.00 d 0.23 e 0.13 b 0.10 c 0.52 e P-value (treatment) <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 z Numbers in each column followed by the same letter are not significantly different from each other (Tukey s HSD, P=0.05). y Total includes fruit that were marketable and unmarketable, which were mostly over-ripe or had rotted. x C=cantaloupe, PC=personal-size cantaloupe, G=galia, H=harper, HD=honeydew, T=Tuscan. w Includes yield from all harvest dates which were August 6, 10, and 17. Some fruit did not ripen by the last date.
Table 3. Fruit characteristics of melon varieties compared on Long Island, New York, in 2012. Varieties are listed based on taste with best first. Variety Length (in) Width (in) Fruit Quality Assessments z Cavity y Color x Brix (% sucrose) Taste Rib w Net v Lilliput 4.0 g 4.4 e 7.0 a 9.0 a 10.3 ab 7.3 2.3 cd 8.8 a Sugar Cube 4.5 fg 4.6 e 6.5 ab 8.8 a 12.3 ab 7.1 2.0 cd 9.0 a Eclipse 5.6 ef 6.3 abc 4.6 ab 7.9 a 8.9 ab 6.4 2.3 cd 9.0 a Samoa 7.0 a-d 5.9 abc 5.8 ab 3.8 bc 7.7 b 6.2 1.6 cd 9.0 a Napoli 6.2 c-e 5.3 cde 6.3 ab 7.5 a 9.5 ab 6.0 4.5 b 8.8 a Visa Premium 5.8 d-f 5.3 cde 6.4 ab 3.5 bc 10.0 ab 6.0 1.0 d 9.0 a Cleopatra 6.8 b-e 5.7 bcd 6.5 ab 8.8 a 9.3 ab 5.6 1.8 cd 8.4 ab Superstar 6.3 c-e 6.2 abc 4.5 b 6.9 ab 8.0 b 5.5 7.8 a 8.5 a Orange Sherbert 8.1 a 6.1 abc 5.8 ab 7.0 ab 8.5 ab 5.1 5.8 b 7.1 Avatar 6.5 c-e 6.3 ab 5.8 ab 7.4 a 8.8 ab 5.1 3.0 cd 9.0 a Pixie 4.6 fg 4.8 de 6.5 ab 8.6 a 13.3 a 5.1 1.0 d 7.8 ab Dream Dew 7.2 a-c 6.2 abc 5.8 ab 2.8 c 9.4 ab 4.8 1.0 d 1.0 c Honeydew Green Flesh 7.9 ab 6.8 a 5.0 ab 2.8 c 9.3 ab 4.3 1.0 d 1.0 c Summer Dew F1 6.2 c-e 7.0 a 6.0 ab 2.7 bc 9.6 ab 3.1 1.0 d 1.1 b P-value <0.0001 <0.0001 0.0152 <0.0001 0.0288 0.1193 <0.0001 <0.0001 z Numbers in each column followed by the same letter or no letter are not significantly different from each other (Tukey s HSD, P=0.05). y (Seed) Cavity: 1-9 rating. 1=large and little flesh, 9=closed. x (Flesh) Color: 1-9 rating. 1=pale, 9=deep. w Rib: 1-9 rating. 1=none, 9=heavy. v Net: 1-9 rating. 1=little, 9=excellent (resembling western shipper type).
Acknowledgments This project was funded by the Friends of Long Island Horticulture Grant Program. Seed were donated by companies listed in Table 1. Pesticides were donated by DuPont Crop Protection, FMC Corporation, Gowan Company, Helena Chemical Company, and Valent USA Corporation.