Powdery Mildew Resistant Zucchini Squash Variety Evaluation, New York, 2009

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1 Powdery Mildew Resistant Zucchini Squash Variety Evaluation, New York, 2009 Margaret T. McGrath, Cornell University, Riverhead, NY George M. Fox, Cornell University, Riverhead, NY Sandra Menasha, Cornell Cooperative Extension-Suffolk County, NY Powdery mildew is an annual production problem for growers of cucurbit crops throughout the United States, reducing yield potential and fruit quality when not controlled. Effective control with fungicides alone has been challenged by development of fungicide resistance to key chemistries. Several squash varieties are now available on the commercial market advertised as having resistance to powdery mildew. The goal of this experiment, which is part of a multi-year variety evaluation project, was to determine whether squash varieties with homozygous resistance (e.g., two copies of the main powdery mildew resistance gene PMRR) are better protected against powdery mildew than varieties with heterozygous resistance (PMR). This was the case in variety evaluations conducted in 2007 and 2008, but not in Most commercial resistant squash varieties have PMR. Ability of the varieties evaluated in 2009 to resist powdery mildew as well as their yielding ability was determined relative to Spineless Beauty, a standard variety lacking powdery mildew resistance. Materials and Methods A field experiment was conducted at the Long Island Horticultural Research and Extension Center in Riverhead on Haven loam soil. The field was plowed on April 30 and conventionally tilled on May 14 and June 1. A blend of controlled release fertilizer (containing 65% of N as ESN, a controlled release formulation) plus muriate of potash (0-0-60) at 100 lb/acre was spread on June 10, and then incorporated by disking. Black plastic mulch and drip tape were laid on June 15. Seeds were sown on May 26 in the greenhouse. Seedlings were transplanted into the plastic-covered beds on June 16. Water was provided as needed through drip irrigation lines located beneath the mulch. Weeds were controlled between plastic mulch strips by applying Strategy (3 pt/acre) and Sandea (0.5 oz/acre) on June 17 with a shielded herbicide sprayer and by hand weeding. Cucumber beetles were managed with Admire 2F ( fl oz/plant) applied after transplanting as a soil drench around transplants on June 29 and with Asana XL (9.6 oz/acre) applied to foliage on June 24 and July 1. No fungicides were applied to control powdery mildew. Ridomil Gold EC (1 pt/acre) + SprayHandler (8 fl oz/acre) were applied to soil on June 8 and incorporated by disking for Phytophthora blight (Phytophthora capsici). The following foliar fungicides were applied preventively for downy mildew (Pseudoperonospora cubensis) and Phytophthora blight: ProPhyt (4 pts/acre) on June 24; Forum 4.16SC (6 oz/acre) on July 27, August 8, August 27, September 13, and September 24; and Ranman 400SC (2.75 fl oz/acre) on July 17, August 1, August 16, September 4, September 18, October 1. Plots were three adjacent rows each with three plants spaced 24 inches apart. Rows were spaced 68 inches apart. Within each of the three rows between each plot a plant of Gentry summer squash, a susceptible variety, was planted to separate plots and provide a source of inoculum. A randomized complete block design with four replications was used.

2 Upper and lower leaf surfaces of 10 to 30 leaves in each plot were assessed for powdery mildew on July 13, 20, and 31; and on August 4 and 14. Initially, the examined leaves were selected from the oldest third of the foliage based on leaf appearance and position in the canopy. As disease progressed, mid-aged and young leaves also were examined. Powdery mildew colonies (spots) 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%. Powdery mildew severity was also assessed on stems and leaf petioles. Squash fruit were harvested and weighed on July 28 and 31; and on August 3, 6, 10, 14, 18, and 25. Fruit were separated into marketable and unmarketable grades based on length, then weighed. There were no unmarketable fruit with blemishes due to disease or insect feeding. Fruit characteristics were also evaluated and overall appearance was rated on a scale of 1 to 9 with 1=poor and 9=best. Average monthly high and low temperatures ( F) were 73/58 in June, 80/64 in July, and 83/68 in August. Rainfall (inches) was 6.43, 4.82, and 2.01 for these months, respectively. Results and Discussion Symptoms of powdery mildew were found on July 13 at a low level (1.6% of older leaves examined). Symptoms were found in most plots on July 20 and all plots on July 31, three days after the first harvest. No significant differences were detected among varieties in powdery mildew severity (Table 1). This is partly due to the fact that plots were assessed in only three replications on August 4 and two on August 14 due to poor growth of plants in the other replications. Powdery mildew severity was substantially lower on Zucchini #8517, which has resistance genes from both parents (PMRR), than all the other resistant varieties tested, which have only one parent with resistance to powdery mildew (PMR). This experimental variety, developed by Outstanding Seeds, had significantly less severe powdery mildew than Envy and Payroll in a similar experiment in Based on these results, homozygous resistance is needed to effectively control powdery mildew in zucchini. All varieties had marketable fruit at the first harvest. There were few significant differences in yield (Table 2). The highest yielding variety was Golden Glory, a golden zucchini fruit type. Marketable fruit weight was low for Amatista because it is a grey zucchini fruit type, which are harvested small. All varieties produced fruit with acceptable characteristics, which were rated at least 7 out of 9 by project investigator and average of at least 3 out of 5 by volunteer evaluators. Zucchini Variety Fruit Descriptions and Assessments Spineless Beauty (standard susceptible variety) Semi-glossy, larger, heavy fruit. Good ridging. Medium green color with many light green speckles. Large peduncle and rounded blossom end. Uniform. 8.5 out of 9 rating for overall appearance. Amatista Green fruit with many, large white speckles giving an almost white appearance. Medium, green peduncle with a rounded, bulbous blossom end. Pear shape fruit, small in size. Semi-glossy. 7.5 out of 9 for overall appearance.

3 Envy Dark green, glossy fruit small to medium in size. Medium size peduncle and a slightly pointed blossom end. Slight ridging on fruit. Very uniform. Good yields. 8.5 appearance rating. Golden Glory Golden yellow fruit with a semi-gloss appearance. Green peduncle. Narrows towards stem end and a slightly pointed blossom end. Medium length fruit. Very slight ridging. 7.5 out of 9. Payroll Medium to light green fruit with many small light green speckles. Longer, more narrow fruit shape with a matte appearance. Medium peduncle and rounded blossom end. Nice shape and uniform. 8 out of 9 for appearance. Reward Medium to dark green, semi-glossy fruit with few, small light green speckles. Longer, more narrow fruit. Medium size, green peduncle. Nice, uniform fruit. 8.5 rating out of 9. SSXP4033 Dark green fruit with very few light green speckles. Matte appearance. Light green peduncle. Bulbous blossom end and then uniform up to the stem end. Slight ridging. Very rounded and smooth blossom end. Fairly uniform. 8.5 out of 9. Zucchini 8517 Medium to dark green, semi-glossy fruit. Medium in length with a narrow, light green peduncle and a slightly pointed blossom end. Very few light green speckles. Slight ridging. Uniform. 8.5 out of 9.

4 Table 1. Suppression of powdery mildew for zucchini varieties compared on Long Island, NY, Amatista is a grey zucchini. Golden Glory is a yellow type. The rest are conventional green fruit types. Varieties are listed in order of disease control based on severity on both leaf surfaces on August 14. Powdery Mildew Severity (%) 3 Variety (resistance) 1 Seed Source 2 Upper Leaf Surface Lower Leaf Surface Aug. 4 Aug. 14 Aug. 4 Aug. 14 Zucchini #8517 (PMRR) OUT Golden Glory (PMR) SI SSXP4033 (PMR) HM Reward (PMR) SW Payroll (PMR) SI Envy (PMR) SI Amatista (PMR) SY Spineless Beauty (S) SI P-value (treatment) PMRR indicates homozygous resistance, PMR=heterozygous resistance, S=susceptible. 2 HM=Harris Moran Seed Company, OUT=Outstanding Seeds, SI=Siegers, SW=Seedway, SY=Syngenta. 3 Exact colony counts were made when possible and severity was estimated using the conversion factor of 30 colonies/leaf = 1%. Data were transformed from percentages by a square root transformation when needed to obtain normality of variance before analysis of variance was performed. The table has de-transformed means. Severity on August 4 is for older leaves where powdery mildew was primarily occurring at that time; younger leaves were also assessed on August 14. Table 2. Yield and fruit quality for zucchini varieties compared on Long Island, NY, Quality was evaluated on a 1-5 scale with 5=best by consumers and growers. Variety (resistance) 1 #/Plant lb/plant Marketable Fruit Total Fruit Fruit Evaluations #/ Plant Lb/ Plant Market -ability Color Shape Appear -ance Zucchini #8517 (PMRR) 5.78 ab ab Golden Glory (PMR) 8.74 a 5.28 a SSXP4033 (PMR) 4.78 b 3.77 abc Reward (PMR) 6.61 ab 4.66 ab Payroll (PMR) 4.72 b 2.89 abc Envy (PMR) 4.04 b 2.92 abc Amatista (PMR) 4.60 b 1.69 c Spineless Beauty (S) 4.26 b 2.57 bc P-value (treatment) Numbers in each column with a letter in common are not significantly different from each other (Tukey s HSD, P=0.05). 2 PMRR=homozygous resistance, PMR=heterozygous resistance, S=susceptible.

5 Acknowledgments This project was funded by the Friends of Long Island Horticulture Grant Program. Seed were donated by the companies listed in Table 1. Pesticides were donated by BASF Corporation, Bayer CropScience, DuPont Crop Protection, Gowan Company, FMC Corporation, Helena Chemical Company, and Syngenta Crop Protection.