Pineapple (Ananas comosus) is an economically important tropical fruit in Hainan Province, China. During September to November 2011, heart rot disese of pineapple was found in Ledong and Wangning of Hainan Province. A survey of 150 ha producing areas of pineapple revealed that the fields were affected at an incidence ranging from 25% to 30%. Infected plants showed water-soaked lesions and soft rot on the base of heart leaves near the soil surface. Heart leaves of infected plants were easily pulled out. As the disease progressed, plants collapsed and died. Diseased tissue fragments (2 × 2 mm) were surface-disinfected for 10 min with 0.3% NaClO, then rinsed three times in sterile water, and plated to 10% V8 juice agar (4). Inoculated dishes were incubated at 26°C in the dark. After 5 days, Phytophthora (identified by the presence of coenocytic hyphae and papillate sporangia) were isolated from the tissue cultures, which has aseptate hyphae. Sporangia were papillate, noncaducous, oval or spherical, and 34.5 to 58.2 μm. Clamydospores, both terminal and intercalary, were also spherical, and were 23.4 to 34.0 μm (2). The ITS region of rDNA was amplified using primers ITS4/ITS5, and the 927-bp product of the ITS showed 99% sequence identity to Phytophthora nicotianae (GenBank Accession No. JF792540), and the sequence was accessed to NCBI (JX978446). Pathogenicity tests were confirmed by irrigating the wounded stem bases of 10 2-month-old pineapple plants with 50 ml of P. nicotionae zoospore solution (15,000 zoospores/ml), and another 10 plants of the same cultivar inoculated with sterile water served as controls. Plants were placed in pots in a greenhouse at 28°C and 90% relative humidity. After 9 days, soft rot was observed clearly on the base of heart leaves of all 10 inoculated plants, while the control plants appeared normal. P. nicotianae was reisolated from the infected pineapple plants, and confirmed to be the same as the inoculated pathogen by conducting a ITS rDNA sequence comparison and morphological characteristics. P. nicotianae was previously reported as the causal agent of heart rot of pineapple in Hawaii, U.S.A. (3) and Guangdong Province of China (1). To our knowledge, this is the first report of P. nicotianae on pineapple in Hainan Province, China.
References: (1) J. Z. Chen et al. J. Yunnan Agric. Univ. 8:134, 2003. (2) H. H. Ho. Mycologia 73:705, 1981.(3) K. W. Howard et al. Plant Dis. Rep. 48:848, 1964. (4) X. B. Zheng. Page 81 in: Phytophthora and its Research Technology. China Agricultural Press, Beijing, 1997.