PUMPKIN (Cucurbita pepo)

Pumpkin Germplasm Evaluation and Screening for Resistance to Powdery Mildew, Downy Mildew, Angular Leaf Spot, Anthracnose and White Speck (Microdochium Blight), 2010

Bob Precheur, Jim Jasinski, Mac Riedel, Landon Rhodes and Marie Buerlson

Dept. of Horticulture and Crop Science, Southwest Extension IPM, Department of Plant Pathology, The Ohio State University, Columbus, OH 43210.

Introduction

Pumpkins are the third largest fresh market vegetable in OH with nearly 7,000 acres in production. Pumpkins account for 10 to 40 % of annual gross income for some vegetable producers. It is important for our producers to use cultivars that consistently produce high yields of quality fruit. Of equal importance is to incorporate new cultivars into the program that provide good disease tolerance in order to reduce pesticide input and production costs while maintaining high quality. This project was supported in part by a research grant from the Ohio Vegetable and Small Fruit Research and Development Program.

Objectives:

1. To evaluate pumpkin cultivars for horticultural characters such as: size, shape, yield, color, and handle quality.

2. To evaluate pumpkin germplasm for useful resistance to Powdery Mildew, Downy Mildew, Angular Leaf Spot, Bacterial Spot, Anthracnose, White Speck (Microdochium or Plectosporium Blight) and watermelon mosaic virus (WMV).

Plots were established 8 Jun on a Crosby silt loam soil and Brookston silty clay loam (pH 6.1, OM <2%) at the Western Branch Research Station, The Ohio State University, South Charleston, OH (Clark Co.). Plots consisted of single 30-ft rows of pumpkins direct seeded 2.5 ft apart in rows 15 ft apart. Transplants were used to fill in bare spots between 10 and 14 days after seeding. Each variety (15 standard, 5 small fruited types) was replicated four times in a randomized complete block design. Fertilizer (100 lb/A N, P2O5, K20) was broadcast over the field on 7 Jun. At seeding, or one day prior to transplanting, the insecticide Admire Pro 4.6 F (7 oz/treated A) was applied for cucumber beetle. Strategy 2.1 SC at (5 pt/A) + Dual Magnum II, (1.3 pt/A) + Roundup Weathermax 4.5 EC (32 oz/A) was applied post planting preemergence for weed control on 8 Jun. During the season weeds were controlled by cultivation and hand weeding. For control of cucumber beetle feeding on fruit rind, Sevin XLR (1 qt/A) was applied to all plots at on 16 Aug. One third of each plot was left unsprayed for disease control to evaluate disease resistance to powdery mildew. Fungicide applications for the remaining two thirds of each plot consisted of Bravo Weather Stik 6F (3pt/A) + Procure 50 WS (6 oz/A) on 26 Jul, 9, 23, 30 Aug and 7 Sep and Quintec 2.08SC (6 oz/A) + Bravo Weather Stik 6F (3pt/A) on 20 Jul, 2, 16, 30 Aug and 14 Sep to control powdery mildew and fruit rots. Fungicides and insecticides were applied at 55 psi and 50 gal/A with a tractor-mounted, PTO driven sprayer with a 12 ft boom carrying 7 Teejet TXVS-18 cone jet nozzle tips spaced 20 in apart. On 10 Sep, six leaves were chosen at random in the unsprayed section of the plot to determine the percentage of leaf coverage of powdery mildew on the upper and lower surface of the leaves. Pumpkins were harvested on 16, 17 Sep and graded into marketable orange fruit. All plots were trickle irrigated to maintain 1 in. of water per week. Rainfall for Jun, Jul, Aug, and Sep was 4.34, 5.36, 1.42, and 0.58 in., respectively.

Results

Powdery mildew development on the foliage was first observed the last week of Jul. Magic Wand had only 3% powdery mildew on the upper leaf surface and significantly less than all standard varieties except Gladiator, Moonshine, Phatso Jr, HMX 9699 and Phatso II. All other varieties had 28% infection or higher. In the small varieties HMX5684 and Munchkin had significantly less powdery mildew on the upper leaf than Lil Orangemen. There was no other significant difference among the other small varieties but % infection was four times higher on the upper surface than HMX5684 and Munchkin. On the lower leaf surface, Magic Wand had significantly less powdery mildew than all standard varieties except Gladiator, Phatso II, Mustang PMR and Corvette PMR. Varieties with % severity on the lower leaf less than 50% were Mustang PMR, Corvette PMR, Gladiator, Phatso II, HSC186 (superfreak type), Phatso Jr , HMX 9699 and ranged from 24 % to 45% infection. The other varieties had % infection coverage on the lower leaf surface of 60% or higher. Magic wand had the best powdery mildew resistance among the standard varieties and HMX 5684 and Munchkin of the small varieties.

Presence or absence of powdery mildew on handles was not significantly different among varieties. Foliar virus symptoms were seen a small number of plots but had little or no effect on yield and marketability. Angular leaf spot was present and unusually high in all plots and decreased yield. Fruit quality was good but yield and average fruit size was depressed 50% from previous years due to very hot weather in the summer and dry weather near the end of the season despite the application of irrigation water. Differences in average fruit size are influenced by variety.

Some color pictures of the varieties plus comparison views among varieties are below and a complete set is available at the VegNet website: http://vegnet.osu.edu

Table 1. Evaluation of powdery mildew resistance and yield characteristics of pumpkin cultivars.

		Powdery Mildew Severity (% of leaf coverage)^z		Marketable Yield^y
	Variety Standard Types	Upper leaf surface	Lower leaf surface	Total fruit no/A	Total yield (t/A)	Avg wt/fruit (lb)
18	Magic Wand^{v……………………….}	3 g^x	2 i	1597 bc	10.4 a	12.7 ab
17	Gladiator^{v……………………………}	28 efg	32 efhgi	1379 bc	7.1 a	9.8 abc
1	Moonshine^{t…………………………..}	32 defg	63 abcdef	1815 bc	5.5 a	7.1 cd
5	Phatso Jr^{r……………………………...}	34 cdefg	45 cdefgh	1379 bc	8.1 a	11.3 abc
12	HMX 9699 (Apollo)^{v…………...}	37 bcdefg	44 defgh	1742 bc	7.5 a	8.4 bc
6	Phatso II^{r……………………………...}	38 abcdefg	35 defghi	1561 bc	10.2 a	12.8 a
16	Aladdin^{v………………….....................}	47 abcdef	52 bcdef	1415 bc	6.8 a	11.4 abc
4	Mustang PMR^{u…………………….}	50 abcdef	24 ghi	1960 bc	10.1 a	10.3 abc
2	HSC 186^{t……………………………...}	58 abcde	42 defgh	1820 bc	6.3 a	8.2 c
3	Corvette PMR^{u…………………….}	59 abcde	32 efghi	2287 b	9.5 a	8.5 abc
9	SSX 5024^{s……………………………}	67 abcde	70 abcd	1997 bc	8.1 a	8.4 bc
7	Diablo^{u…………………………………}	70 abcd	80 abc	1525 bc	6.8 a	10.2 abc
10	Charmed (ACX7301)^{w………...}	73 abc	85 ab	1379 bc	5.3 a	7.6 cd
8	Fall Splendor^{s……………………...}	75 ab	67 ab	3484 a	5.8 a	3.5 d
11	Magical (ACX7302)^{w…………..}	78 a	95 a	1016 c	5.2 a	10.9 abc
	LSD 0.05%	40	36	1060	5	4
	Small Fruited Types
14	HMX 5684^{v…………………………}	11 fg	13 hi	3267 d	4.2bc	2.5 b
20	Munchkin^{v……………………………}	13 fg	27 fghi	13322 a	2.3 c	0.4 d
19	Cannonball^{v………………………..}	48 abcdef	46 cdefgh	4247 cd	7.0 a	3.3 a
13	HMX 8698^{v………………………….}	48 abcdef	80 abc	8204 bc	2.2 c	0.5 d
15	Lil Orangemon^{v…………………..}	56 abcde	61 abcdef	11761 ab	6.2 ab	1.1 c

	LSD 0.05%	40	36	4134	2.2	0.2

z Powdery Mildew Severity is the average percentage of leaf area on the upper or lower leaf surface with symptoms of powdery mildew as determined by rating 6 randomly selected leaves per plot by 2 different raters.

y Marketable Yield includes only good orange fruit of proper size, shape and free of defects.

x Column numbers followed by the same letter are not significantly different at P=0.05 determined by Fisher’s protected LSD.

w Obtained from Abbott & Cobb Seed Company .

v Obtained from Harris Moran Seed Company.

u Obtained from Hollar Seed Company.

t Obtained from New Zealand Hybrid Seed Company.

s Obtained from Sakata Seed Company.

r Obtained from Siegers Seed Company.

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