Number 2 - 2004 - Acta Horticulturae

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Table 4. Seed germination of cucurbitaceous crops as affected by dry heat treatment. Treatment Watermelon Squash Squash Cucumber Bottle gourd Melon ‘Bitna’ ‘Hongtozwa’ ‘Geumsul’ ‘Baeknok’ ‘Partner’ ‘Wonderful’ Early germination % (5 days after sowing) Control 96.7 a 2 95.0 a 96.7 a 98.3 a 73.3 a 98.3 a 35-50-651 98.3 a 96.7 a 95.0 a 85.0 b 66.7 a 100.0 a 35-50-70 100.0 a 100.0 a 96.7 a 86.7 b 66.7 a 100.0 a 35-50-75 95.0 a 95.0 a 98.3 a 86.7 b 43.3 b 95.0 a 35-50-80 95.0 a 76.7 b 88.3 b 78.3 c 30.0 b 93.7 a 35-50-85 91.7 a 41.7 c 86.7 b 51.7 d 5.0 c 90.0 a Final germination % (10 days after sowing) Control 96.7 a 98.3 a 96.7 a 98.3 a 80.0 a 100.0 a 35-50-65 98.3 a 100.0 a 96.7 a 95.0 a 80.0 a 100.0 a 35-50-70 100.0 a 100.0 a 96.7 a 93.3 a 88.3 a 100.0 a 35-50-75 98.3 a 98.3 a 98.3 a 96.7 a 85.0 a 95.0 a 35-50-80 100.0 a 100.0 a 96.7 a 91.7 a 88.3 a 100.0 a 35-50-85 98.3 a 98.3 a 93.3 a 76.7 b 81.7 a 93.3 a (1) Seeds were treated with 35°C for 24 hr followed by 50°C for 24 hr, and finally 65 to 85°C for 72 hr. (2) Mean separation between treatment within a cultivar by DMRT at 5%. Table 5. Effects of DHT on seed germination of various vegetables. Seeds were treated with dry heat at 35°C for 24 hr followed by 50°C for 24 hr and finally at 75°C for 72 hr. Seedling emergence percentage in seeds sown in cell trays in greenhouse (%) Crop and number of cultivars Germination Dry heat treated seeds Control seeds tested in petri dish (%) 7 DAS ( 1 ) 14 DAS 7 DAS 14 DAS Pepper (30) 80.0 96.5 98.0 96.8 98.3 Eggplant (2) 59.5 68.5 80.2 55.7 75.3 Tomato (5) 88.5 80.0 92.3 78.8 95.5 Lettuce (12) 98.0 95.0 97.6 96.7 99.0 Radish (11) 95.9 95.6 98.4 96.0 99.0 (1) DAS = days after sowing The major advantages of DHT, despite the requirements of special equipment and considerable time (Jang, 1998a; Jang, 1998b; Lee et al., 2003), include: 1. Complete inactivation of certain noxious seed-borne viruses, such as tobacco mosaic virus (TMV), cucumber green mottle mosaic virus (CGMMV), lettuce mosaic virus (LMV), and others (Kim and Lee, 2000; Lee et al., 2000 & 2003). 2. Safe and complete inactivation of noxious seed-borne bacterial diseases such as Erwinia, and fungal diseases such and Fusarium, Alternaria, Cladosporium, and others (Table 3). 3. Safe large-scale operations by seed producers. 4. Easy applications of additional seed treatments such as priming after DHT, if needed. 5. Ideal for supplying healthy seeds for organic growers since seeds are not treated with agrochemicals. 6. Specific DHT machines have been developed and are commercially available (Joung et al., 2002). Seeds are routinely treated with maximum temperatures of 70°-75°C for 3-5 days, although the maximum temperature and duration of treatment vary slightly with the crop and seed sources (Table 4). Since seeds are negatively influenced by extreme high temperature, lowering the seed moisture contents is reduced to below 4% before exposing the seeds to the maximum temperature. Gradual increases in temperature from 35° to 75°C (or maximum temperature) are important for successful DHT. For example, seeds are initially treated at 35°C for 24 hours followed by 50°C for 24 hours and finally by 75°C for several days. Gradual decrease in temperature, gradual increases in seed moisture contents up to 6%, and a certain period of post-treatment conditioning of the treated seeds are also important for successful DHT. Continuous airflow in the DHT machine is important for even and fast drying. Even distribution of temperature among the seeds located in the different places within the chamber is the key function of the DHT machine (Joung et al., 2002; Lee et al., 2003). If properly treated, complete inactivation of the target seed-borne virus and some seed-borne fungi such as Fusarium can be obtained with little or no injuries to seed and seedlings (Tables 4 and Table 5). Improper DHT often results in slight to severe incidence of phytotoxicity, i.e., twisting of cotyledons to complete killing of seed. Seedling emergence is considerably delayed by DHT even though final germination percentage is little or not influenced (Fig. 1). However, most of these phytotoxicity symptoms can be minimized by using DHT machines, specifically designed to control the temperature gradually with time changes and moisture control during the DHT (Fig. 2). Seed priming of the dry heat treated seeds greatly promotes early germination thus resulting in even and faster growth as compared to the non-treated seeds (Fig. 3). The presence of seed-borne viruses can be easily detected by ELISA. The seed-borne virus can also be partially inactivated or reduced by other methods but complete inactivation is possible only with DHT. However, even seeds treated with dry heat show positive response to ELISA and bioassays have been the only means of confirming the virus inactivation ISHS • 14
Figure 1. Phytotoxicity symptoms associated with inadequate dry heat treatment of cucurbitaceous crop seeds. Left: Various phytotoxicity symptoms caused by improper treatment of dry heat (A: cotyledon twisting; B: Check; C: Holes in cotyledon; D: Cotyledon tip contraction; E: Chlorotic spot in cotyledon, F: White streaks in cotyledon; Right: emergence of intact bottle gourd seedlings in cell tray (left) and significant delay in seedling emergence in dry heat treated ones (right), respectively. Figure 2. Dry heat treatment machine manufactured by Koregon, Korea. From left: Large, medium, and small machines. Figure 3. Effects of dry heat treatment on ‘Festival’ watermelon seeds and promotion of seed germination by solid matrix priming treatment. From top row to bottom: Germination temperatures in thermogradient table; 24.5, 23.0, 21.5, and 20.0°C, respectively. From left to right: Germination of seeds treated with DHT+Fungicides+SMP, DHT+fungicides, DHT+SMP, DHT only, Check+SMP, and Check only. Figure 4. Seed germination of cucurbits treated with inadequate dry heat treatment. Left: Significant delay in early germination in cucumber (up), bottle gourd (middle), and watermelon (down); Right: Root soft rot caused by Mucor and Rhizopus fungi aggravated by dry heat treatment. CHRONICA HORTICULTURAE •VOL 44 • NUMBER 2 • <strong>2004</strong> • 15
Page 1 and 2: Chronica HORTICULTURAE Volume 44 -
Page 3 and 4: NEWS FROM THE BOARD NEWS FROM THE B
Page 5 and 6: Letter to the Editor Pineapple Wars
Page 7 and 8: Hectares (000) 6,000 5,000 4,000 3,
Page 9 and 10: 150,000 to nearly 500,000 ha under
Page 11 and 12: REFERENCES Gaiani, A., S. Sansavini
Page 13: Table 2. Seed-borne vegetable disea
Page 17 and 18: Figure 6. Pelletizing machine (righ
Page 19 and 20: Table 7. Effects of solid matrix pr
Page 21 and 22: HORTICULTURAL SCIENCE NEWS HORTICUL
Page 23 and 24: protect and genetically certify pla
Page 25 and 26: The third day of the symposium was
Page 27 and 28: Commission Horticultural Engineerin
Page 29 and 30: protected crops may provide good op
Page 31 and 32: there is a less rigid control by pu
Page 33 and 34: the proliferation of pests (white f
Page 35 and 36: Greenhouse Cultivation of Bananas V
Page 37 and 38: tions, while exclusion measures, bi
Page 39 and 40: New Books, Websites The books liste
Page 41 and 42: Courses and Meetings The following
Page 43 and 44: In Memoriam DAVID ROBINSON (1928 -
Page 45 and 46: Turkey. Phone: (90)2244428970, Fax:
Page 47 and 48: ACTA HORTICULTURAE ACTA HORTICULTUR

Number 2 - 2004 - Acta Horticulturae

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