Phytohormones play critical roles in regulating plant responses to stress. Here, we investigated the effects of salt stress and stress recovery by applying jasmonate to the two different rice (Oryza sativa L.) cultivars Dongjinchalbyeo (DJC, salt-tolerant) and Dongjinbyeo (DJ, salt-sensitive). Salt stress remarkably decreased the root length of plants even at low NaCl concentration (20 mm). Salt stress led to a sharp increase in the concentrations of abscisic acid (ABA) in 20 and 40 mm NaCl, when compared with the control values. The concentrations of ABA in the salt-tolerant cultivar DJC plants progressively increased with increasing NaCl levels, whereas in the salt-sensitive cultivar DJ, they sharply decreased in all three parts of rice plants at 80 mm NaCl treatment. The decrease of jasmonic acid (JA) concentrations in salt-tolerant cultivar DJC was lesser than in the saltsensitive cultivar DJ plants in the shoot. Post-application in the stressed plants with 30 lm JA at 24 and 48 h after NaCl treatment, recovered salt inhibition on dry mass production more effectively than application of JA at 48 and 24 h before salt stress, and during salt stress simultaneously. The uptake of Na decreased especially in the salt-sensitive cultivar DJ plants, whereas there was an increase in Ca and Mg levels and slight increase of K by JA application. Leaf water potential, leaf photosynthetic rate, and maximum quantum yield of photosystem II (PSII) also remarkably recovered when 30 lm JA was applied 24 h after the salt stress compared with the 40 mm NaCl-treated plants. These results clearly indicate that post-application with exogenous JA can ameliorate salt-stressed rice seedlings, especially the salt-sensitive cultivar rather than the salt-tolerant cultivar. This may change the balance of other endogenous plant hormones.Key words: abscisic acid -ion uptake -jasmonic acid -leaf photosynthesis -leaf water potential -maximum quantum yield of PSII (Fv/Fm)

High resistance to zucchini yellow mosaic virus-China strain (ZYMV-CH) and moderate resistance to watermelon mosaic virus (WMV) were found in a selection of PI 595203 (Citrullus lanatus var. lanatus), an Egusi type originally collected in Nigeria. Mixed inoculations showed primarily that these two viruses have no cross-protection. This fact may explain the high frequency of mixed infection often observed in commercial fields. When plants were inoculated with a mixture of the two viruses, the frequency of plants resistant to ZYMV was lower than expected, indicating that WMV infection may reduce the ability of a plant to resist ZYMV. We studied inheritance of resistance to ZYMV-CH and WMV, using crosses between a single-plant selection of PI 595203 and the ZYMV-susceptible watermelon inbreds 9811 and 98R. According to virus ratings of the susceptible parents, the resistant parent, and the F1, F2, and BC1 generations, resistance to ZYMV-CH was conferred by a single recessive gene, for which the symbol zym-CH is suggested. The high tolerance to WMV was controlled by at least two recessive genes.

We identified Broad bean wilt virus 2 (BBWV-2) in yams based on particle morphology, test plant symptoms, protein features, aphid transmission, and molecular classification using nucleotide sequences of coat protein genes. Key words Broad bean wilt virus 2 · Dioscorea opposita · Mosaic diseaseA spherical virus was detected in 1985 in Chinese yam (Dioscorea opposita Thunb.) plants in Ojima, Gunma Prefecture, Japan (Ishikawa et al. 1985b). The virions measured 28 nm in diameter and included two proteins of 23 kDa and 46 kDa, respectively. The virus caused local lesions and mosaic symptoms on Chenopodium amaranticolor and vein-clearing and ring spots in Petunia ¥ hybrida after concentrated sap inoculation. Ishikawa et al. (1985a) identified the virus as broad bean wilt virus (BBWV); however, the symptoms of BBWV on Chinese yam were unknown. Isolates of BBWV from other plants were categorized into two serotypes, I and II, by double immunodiffusion tests (Uyemoto and Provvidenti 1974) and were subsequently classified as distinct species, Broad bean wilt virus 1 (BBWV-1) and Broad bean wilt virus 2 (BBWV-2), in the genus Fabavirus in the family Comoviridae (Goldbach et al. 1995). Kobayashi et al. (1999) demonstrated that sequence analysis of coat proteins was useful for identification of BBWV-1 and BBWV-2. To characterize BBWV in yams accurately, we isolated BBWV from Chinese yam and investigated its biological and molecular properties.We used the reverse transcription-polymerase chain reaction (RT-PCR) to detect BBWV in yams. Total RNA was extracted from fresh leaf samples using SepaGene RV-R (Sanko Junyaku, Tokyo, Japan). RT-PCR was performed using Ready-To-Go RT-PCR beads (Amersham Biosciences, Buckinghamshire, UK). Because nucleotide sequences of both BBWV-1 and BBWV-2 had already been described, we designed two degenerate primers [BBWVVSSP (5¢-GTBTCDAGTGCTYTDGAAGG-3¢, B = C, G, or T; D = A, G, or T; Y = C or T) and BBWVKMRM (5¢-TDGWDCCATCVAGICKCATTTT-3¢, W = A or T; V = A, C, or G; I = Inosine; K = G or T)] to detect BBWV-1 and BBWV-2. With this primer pair, RT-PCR products were predicted to be 322 bp in length, covering a region from the C-terminal of the large coat protein (LCP) to the N-terminal of the small coat protein (SCP). RT-PCR was carried out as follows: 1 cycle at 42°C for 15 min for RT and then 95°C for 5 min, 35 cycles at 95°C for 1 min, 51°C for 1 min, and 72°C for 1 min for PCR. Yam samples were collected from Aomori, Akita, Nagano, Saitama, and Yamaguchi prefectures. Of 75 samples, 24 were BBWVpositive. BBWV was detected alone or in complex with Chinese yam necrotic mosaic virus, Japanese yam mosaic virus, or Yam mild mosaic virus in Chinese yam (cv. Nagaimo, Ichoimo, and Yamatoimo) and Japanese yam (D. japonica) by RT-PCR. Dioscorea opposita Thunb. cv. Nagaimo plants in which BBWV was detected alone had mosaic symptoms, vein-clearing, rugosity, and malformation of the leaves (Fig. 1). Spherical virus particles 25 nm in diameter were identified in the Nagaimo plants using electron microscopy with ...