Bacterial Rind Necrosis of Watermelon in North Carolina

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Cucurbit Genetics Cooperative Report 5:36-37 (article 18) 1982

Warren R. Henderson and S. F. Jenkins, Jr.
North Carolina State University, Raleigh, NC 27650

Bacterial rind necrosis (BRN) has been reported in Florida (2), Texas (4), and Hawaii (3). Fruits infected with BRN were also observed in research plots in North Carolina in the late 1960’s and have occurred sporadically since that time. The symptoms of BRN in watermelon are a corky, brownish discoloration of the fruit rind. Although surface roughening may occur in the are external to the diseased area, accurate identification of uncut fruits as diseased is usually difficult. Consequently, the consumer may purchase an otherwise acceptable fruit and find upon slicing an unattractive, diseased interior.

Based upon preliminary cultivar evaluations for BRN resistance, ‘Charleston Gray’ ‘Grayhoma’ and ‘Blue Ribbon’ were initially selected for further study. Tests reported herein were conducted for BRN resistance in test 1 based on the percent fruits infested. The cultivars fell into three classes ‘Charleston Gray’ resistant, ‘Grayhoma’ intermediate, and ‘Blue Ribbon’ susceptible (Table 1). Since fruits classed as diseased could have the entire rind infested or contain only a small lesion, a disease index was used in tests 2 and 3 to evaluate for the severity of BRN infestation. A rating of 5 indicated that the fruits were free of BRN, a rating of 4 – rind area equivalent to 1 locule infested with BRN, rating of 3 – area equal to 2 locules infested, and rating of 2 – all 3 locules infested. A rating of 1 would indicate that the fruit rind was completely infested with some entry into the flesh and some breakdown of the rind tissue itself. ‘Sweet Princess’ and ‘Crimson Sweet’ were added in tests 2 and 3. ‘Charleston Gray’, ‘Sweet Princess’, ‘Grayhoma’, and ‘Crimson Sweet’ were classed as resistant whereas ‘Blue Ribbon’ was susceptible – a significance difference in test 3 but not test 2 (Table 2). Thus, in further tests for BRN the cultivars ‘Charleston Gray’, ‘Sweet Princess’. ‘Grayhoma’, and ‘Crimson Sweet’ could serve as resistant checks and ‘Blue Ribbon’ would be satisfactory as a susceptible cultivar.

Elmstrom and Hopkins showed that ‘Sweet Princess’, ‘Charleston Gray’ and ‘Crimson Sweet’ had a similar level of resistance whereas ‘Blue Ribbon’ was less resistant than ‘Sweet Princess’ and ‘Crimson Sweet’ but not different from ‘Charleston Gray’ based on percent fruits diseased (1).

To determine the effect of BRN infestation on soluble solids, the fruits of each variety were classed diseased of one or more locules contained BRN symptoms and disease free if no symptoms occurred. A statistical analysis was not conducted in test 1 because of insufficient number of fruits in certain plots, for example Princess’ were in short supply. There appeared to be no reduction in soluble solids content between the diseased free and diseased fruits of either ‘Charleston Gray’ or ‘Grayhoma’ in test 1. A slight reduction occurred in the diseased fruits of ‘Blue Ribbon’, probably because the infestation was likely much greater than with the other two cultivars.

Although BRN has not become a severe annual problem in North Carolina, it is important because it does show up sporadically and particularly because fruits cannot be identified readily as being infested before cutting.

Table 1. Percent bacterial rind necrosis and soluble solids content of fruits of ‘Charleston Gray’, ‘Grayhoma’ and ‘Blue Ribbon’, Clinton, N.C.

% Soluble Solids

Cultivar

% (arcsin) Fruits Diseased

Fruits Not Diseased

Fruits Diseased
Charleston Gray 15.8 11.4 11.4
Grayhoma 41.2 10.1 10.3
Blue Ribbon 88.7 12.6 11.7
LSD (5%) 16.5
LSD (1%) 35.2

Table 2. Bacterial rind necrosis (BRN) in several watermelon cultivars (disease index)z, Clinton, N.C.

Disease Index y

 

Cultivar
Test 2
Test 3
Charleston Gray 5.0a 5.0a
Sweet Princess 5.0a 5.0a
Grayhoma 4.9a ___
Crimson Sweet —- 4.8a
Blue Ribbon 4.4a 4.1a

y Treatment means followed by the same letter are not significantly different from each other.
z 5.0 = free of BRN; 1.0 = complete infestation of rind.

Literature Cited

  1. Elmstrom, G.W. and D.L. Hopkins. 1973. Variable susceptibility to bacterial rind necrosis in watermelon. Hortscience 8:32.
  2. Hopkins, D.L. 1972. Association of bacteria with rind necrosis of watermelon in Florida. Phytopathology (Abstr.) 62:804.
  3. Ishii, M. and M. Aragaki. 1960. Bacterial rind necrosis of watermelon. Plant Dis. Rpt. 44:761-763.
  4. Thomas, C.E. 1968. Bacterial rind necrosis of watermelon in south Texas. Plant Dis. Rpt. 52:375-377.