Identification and Distribution of Races of Fusarium oxysporum f. sp. niveum on Watermelon in Korea

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Cucurbit Genetics Cooperative Report 21:33-36 (article 12) 1998

Young-Seok Kwon and Young-Hyun Om
Alpine Agricultural Experiment Station, Pyongchang, 232-950, Rep. of Korea

Hoe-Tae Kim
Pusan Horticultural Experiment Station, Pusan, 618-300- Rep. of Korea

Introduction. Fusarium wilt in watermelon, caused by Fusarium oxysporum f. sp. niveum (E.F.Sm.) Snyd. & Hans., which occurs throughout the world, is one of the most serious production problems confronting watermelon growers. The disease has been found wherever the crop has been grown in Korea. All commercial cultivars have been found to be susceptible to Fusarium wilt. Disease control in Korea has been accomplished by grafting watermelon on squash, but grafting is accompanied by high labor costs and reduced fruit quality.

Three pathogenic races (0, 1 and 2) of Fusarium oxysporum f. sp. niveum have been identified based on pathogenicity to a set of different cultivars (2,6). The races may also be distinguished by vegetative compatibility tests. Races 0 and 1 were first classified in 1972 by Citrulli, while race 2 was first described in Israel by Netzer (8). Many commercial cultivars have resistance to races 0 and 1, while race 2 was first described in Israel by Netzer(8). Many commercial cultivars have resistance to races 0 and 1, while race 2 is more aggressive and overcomes all currently available wilt resistant watermelon cultivars, except PI296341-FR (3,5,7). Race 2 is now established in Texas, Oklahoma and Florida (1,4) and is becoming more common in Mississippi. This research was carried out to identify race distribution in Korea as part of a watermelon Fusarium disease resistance breeding program.

Materials and Methods. Single spore isolates of F. oxysporum f. sp. niveum were obtained in 1994 from stem sections of naturally infected plants cultured on Potato Dextrose Agar (PDA) medium. Insolates were tested for pathogenicity on a susceptible watermelon cultivar and stored on PDA. Inoculum of each isolate was prepared by growing the isolate for one week at 25 C in Potato Dextrose broth (200g potato, 20g dextrose per liter) under continuous fluorescent light. Cultures were filtered through four layers of sterile cheese cloth, and suspensions were adjusted 1 x 105 micro conidia/ml. Sterilized seeds of the following indicator plants ‘Sugar Baby’, ‘Charleston Grey’, and ‘Calhoun Grey’ (Table 1), were planted in flats containing a 1:1:1 (v/v) mixture of vermiculite, perlite and peat. Three-week-old seedlings were root-dip inoculated for 5 minutes in isolate suspensions adjusted to a x 105 microconidia/ml and transplanted into larger pots (12 cm diameter) containing the described potting mix. Seven to 12 plants were used per indicator cultivar and the experimental design was a random arrangement. Control plants were root-dip inoculated with distilled water. Wilt symptoms were recorded after 3 weeks. The following index was used: resistance 20% wilt; susceptibility, 80% wilt.

Results and Discussion. A total of 55 isolates of F oxysporum f. sp. niveum were collected from 22 commercial watermelon fields in the South and Central areas of South Korea from March to october 1994 (see Figure 1). All commercial cultivars were susceptible to the disease. Pathogenicity tests conducted on ‘Sugar Baby’ indicated that 22 isolates were pathogenic, while 33 isolates were nonpathogenic. Three pathogenic races could be identified (Figure 1 and Table 2): race 0 at 2 locations; race 1 at 8 locations; and race 2 in 11 fields. However, only one isolate (race 2) was recovered per location.

This study documents the existence and distribution of three races of F. oxysporum f. sp. niveum in south Korea and the need to develop resistance in commercial cultivars to the three races.

Table 1. Watermelon differentials used to separate the three races of Fusarium oxysporum f. sp. niveum.

Race z

Host differential
0
1
2
Sugar Baby S S S
Charleston Grey R S S
Calhoun Grey R R S

z R = Resistant; S = Susceptible

Figure 1. Distribution of races of Fusarium oxysporum f. sp. niveum on watermelon in Korea.

figure 1

 

Table 2. Pathogenicity and race identification of isolates on Fusarium oxysporum f. sp. niveum collected in watermelon fields in S. Korea.

Identification of racesz

Isolate

number

Date (1994)

Pathogenicityy

Sugar

Baby

Charleston

Grey

Calhoun

Grey

Race
Fon-1 March 15 S S S S 2
2 March 15 S S S R 1
3 June 29 S S S R 1
4 June 29 S S S R 1
5 June 29 S S S S 2
6 June 30 S S S S 2
7 June 30 S S S R 1
8 June 30 W S R R 0
9 June 30 S S S R 1
10 May 14 M S S R 1
11 August 17 M S S R 1
12 August 17 S S S R 1
13 August 17 M S R S 2
14 August 18 S S S R 0
15 August 18 W S S S 2
16 Sept. 14 S S S S 2
17 Sept. 14 S S S S 2
18 October 4 S S S S 2
19 October 4 M S S S 2
20 October 4 S S S S 2
21 October 4 S S S S 2
22 October 14 M S R R 0

y S = Strong, M = Medium, W = Weak
z R = Resistant, S = Susceptible

Literature Cited

  1. Biles, C.L. and R.D. Martyn. 1989. Local and systemic resistance induced in watermelons by formae specials of Fusarium oxysporum. Phytopathology 79:856-860.
  2. Henderson, W.R., S.F. Jenkins, Jr. and J.O. Rawlings. 1970. The inheritance of Fusarium wilt resistance in watermelon, Citrullus lanatus (Thund.) Mansf. J. Amer. Soc. Hort Sci. 95:276-282.
  3. Martyn, R.D. and D. Netzer. 1991. Resistance to races 0, 1, 2 of Fusarium wilt of watermelon in Citrullus sp. PI 296341-FR. HortScience 26:429-432.
  4. Smarty, R. D. and B. D. Brut on. 1989. An initial survey of the United States for races of Fusarium oxysporum f. sp. niveum. HortScience 24:696-698.
  5. Martyn, R.D. 1987. Fusarium oxysporum f. sp. niveum race 2: A highly aggressive race new to the United States. Plant Disease 71L: 233-236.
  6. Martyn, R.D. and R.J. McLaughlin. 1983. Effects of inoculum concentration of the apparent resistance of watermelon to Fusarium oxysporum f. sp. niveum. Plant Disease 67:493-495.
  7. Netzer, D. and R.D. Martyn. 1989. PI 296341, a source of resistance in watermelon to race 2 of Fusarium oxysporum f. sp. niveum. Plant Disease 73:518.
  8. Netzer, D. 1976. Physiological races and soil population level of Fusarium wilt of watermelon. Phytoparasitica 4:131-136.