Sudden wilt of passion fruit trees (Passiflora sp.) was observed on Okinawa Island, Okinawa, and Hachijo Island, Tokyo. The disease occurred on two or three-year-old stock of passion fruit trees. From the collar-rot lesions, reddish perithecia and white mycelia were observed and identified as Haematonectria ipomoeae (Halst.) Samuels & Nirenberg and Fusarium striatum Sherb., respectively. From the monoascospore and monoconidium isolation, the former was confirmed to be the teleomorph of the latter. Typical collar-rot lesions were incited after artificial inoculations using monoascospore and monoconidium isolates. Inoculation of Passiflora species revealed that P. caerulea was especially susceptible. The pathogen was recovered from apparently symptomless cuttings of scion tissue. It is possible that cuttings taken from latently infected cutting plant scions may perpetuate the disease.
Secondary transmission of Acidovorax avenae subsp. citrulli (Aac) from infested watermelon seedlings to healthy nursery plants at the nursery was studied. Infested watermelon seeds were sowed in four single 3-cm square plastic cells at the center of 80-cell trays that had been sowed with healthy seed and irrigated overhead 3 times/day. Aac from infested seedlings and from diseased seedlings spread to healthy seedlings around the point source of Aac, and a numerous seedlings became infested by Aac. When scions were cut from healthy watermelon seedlings with knives that were infested from cutting diseased seedlings or from sap of watermelon seedlings inoculated with cultured Aac (106cfu/ml), all grafted nursery plants became diseased. When scions were prepared with knives used to cut infested seedlings without primary symptoms, 67.5% of grafted nursery plants became diseased. Aac was also transmitted from infested scions to healthy ones from wet newspapers and tap water used to maintain humidity around scion. Secondary transmissions thus occur through overhead irrigation and grafting techniques. Symptomless Aac carrier nursery plants were produced from a small amount of infested watermelon seeds.
The immunological agglutitation method, using either latex particles or Staphylococcus aureus conjugated with anti-Aac-IgG, was tested for diagnosing bacterial fruit blotch of watermelon caused by Acidovorax avenae subsp. citrulli (Aac). In either case, when the suspensions of various plant pathogenic bacteria were tested, only Aac yielded a strong positive reaction. When sap prepared from sections including lesions was tested, both methods produced positive reactions with all sections from artificially inoculated watermelon plants. Moreover, positive reactions were observed with lesions older than 28 days. These methods are very simple, and only about 5min/sample is needed to reach a diagnosis.