Cross-transmission of bunchy top virus from and to banana (Musa sp.) cv. Lakatan and abacá (Musa textilis Nee) cv. Tinawagan Pula was achieved. Bunchy top virus (BTV) from abacá showed a 10% rate three months post-inoculation when aphid-inoculated to banana, whereas a 30% infection rate was obtained when BTV from banana was transmitted to abacá in the same manner. We also confirmed plant species outside the Musaceae family, namely Alpinia zerumbet (shell ginger), known as “gettou” in Japanese, Colocasia esculenta (satoimo) and Canna indica, were alternate hosts of Banana bunchy top virus (BBTV) isolates from banana in Japan and the Philippines. C. indica was found to be a host of BBTV isolates from Japan and the Philippines in which the latter inoculum source could induce severe bunchy top symptoms at a high incidence (100%). Interestingly, A. zerumbet served for the first time as a silent host of Japanese BBTV isolates with a low detection frequency (2/8) yet was conducive for aphid, Pentalonia nigronervosa, multiplication at a rate comparative to varieties of C. esculenta (satoimo, gabi and taimo). Moreover, C. esculenta (satoimo) was found to be an alternate host of Japanese BBTV isolates (11%) for the first time. These findings partly explain the naturally occurring specificity of BBTV isolates towards cultivated and wild plant species as a component of plant-aphid-virus etiology.

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The rapid economic growth of Thailand has resulted in a rapid increase in the demand for agricultural production which has in turn led to the increased use of pesticides and chemical fertilizers. Recent increases in pesticide application may cause environmental pollution problems in the Bangkok metropolitan area and the surrounding provinces. This study was conducted to investigate if environmental problems could be caused by the pesticide residues. We collected information about pesticides used in Thailand from a pesticide company in Bangkok and from farmers in suburban agricultural fields. Based on this information, soil samples were collected in the Nakhon Pathom province, a vegetable production area on the west side of Bangkok, and pesticide residues in these samples were analyzed. Pesticide residue analyses were carried out at the Central Laboratory (Thailand) Co., Ltd. in Bangkok by the in-house method based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method or a standard method. We focused on insecticides because of their relatively higher toxicity than that of herbicides and fungicides. In most sampling sites except in a sweet potato field, no or only a small amount of pesticides were detected. In the sweet potato field, significant amount of pesticides was detected, but analysis after 5 months showed that pesticide residue concentrations were much lower than those of previous residues. The results of this study show that, as of yet, pesticide residues are not persistent in this area.

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We examined the quality of rice seeds, including both seed-companies’ seeds sampled randomly from agricultural input suppliers and farmers’ seeds sampled randomly from farmers, in terms of three indicators: pure seed rate, germination rate of pure seeds and germination rate of seeds including off-types. Results obtained showed: the quality of farmers’ seeds was significantly better than that of companies’ seeds, particularly with respect to the germination rates, the ability of farmers to maintain and improve the quality of their own seeds was high, and training for farmers including lectures and practices about how to improve seed quality was an efficient means to enhance farmers’ ability to control the quality of their rice seeds. These findings indicate that building capacity of farmers by training on seed production, selecting and rouging of off-types is important to improve and maintain rice quality over a long period of time starting from the initial small quantity of pure seed. This is particularly relevant to the smallholder setting in sub-Saharan Africa where rice growing farmers mostly handle small quantities of seeds for small acreages.

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The growth of vine cuttings in water yam was influenced by the time when the cuttings were collected. Since it was considered that endogenous plant hormones affect the growth, we analyzed the fluctuations of the concentrations of endogenous plant hormones in the mother plants and compared them with the growth of vine cuttings. Endogenous plant hormones, GA₁, GA₄, IAA, ABA, JA, JA-Ile, SA, tZ, DHZ and iP were identified and quantified in water yam leaves and/or leaf axils to observe the fluctuations of their concentrations in the leaves and leaf axils during the plant growth. Moreover, the rate of mini-tuber formation and root development of vine cuttings exhibited a high correlation with the level of GA₄ and IAA, respectively. Therefore, it was revealed that the changes in the growth of vine cuttings was affected by the fluctuations of the concentrations of endogenous plant hormones. To our knowledge, this is the first report in which a comparison between the concentrations of endogenous plant hormones and the growth of vine cuttings in water yam was carried out.

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To analyze the growth and yield response to salinity of soybean genotypes with differences in salt tolerance at the vegetative stage, eleven genotypes which were classified into 4 groups, namely AGS313, G00209, G00028 and G00283 in the tolerant group, PK416, AGS399 and G00138 in the moderately tolerant group, BARI soybean 5 (BARI-S-5) and Shohag in the moderately susceptible group, and Bangladesh soybean 4 (BD-S-4) and G00046 in the susceptible group were grown in pots filled with soil at the Department of Agronomy of Bangabandhu Sheikh Mujibur Rahman Agricultural University in Bangladesh. The salt solutions (0, 50 and 100 mM NaCl) were applied from the appearance of the 1^st trifoliate leaf stage till maturity. Though the onset of flowering in most of the soybean genotypes was not affected by the NaCl salinity, except for three genotypes that flowered late, pod maturity in all the eleven genotypes was enhanced substantially. The relative grain yield (% value to the control treatment) of the genotypes displayed a positive correlation with the relative total dry weight, relative pod number plant, relative seed number per pod, and 100-seed weight. The relative reduction in the leaf dry weight, total dry weight, grain yield and yield-contributing characters due to salinity was lower in the genotypes of the tolerant group than in those of the susceptible group. The genotype AGS313 displayed the highest values of the relative leaf dry weight, root dry weight, total dry weight and grain yield at both 50 and 100 mM NaCl, followed by G00209. The highest relative grain yield of the genotype AGS313 was attributed mostly to the combined effect of the high value of the relative 100-grain weight and pod number per plant. Therefore, the high relative yield of AGS313 indicated its high genetic potential for the improvement of salinity tolerance in soybean.

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Our previous studies indicated that soybean genotypes displayed wide genotypic variations in their salt tolerance. The present experiment was initiated to analyze the pattern of changes in accumulation of different mineral ions and water relation traits associated with salinity in two soybean genotypes, differing considerably in their relative salt tolerance. AGS 313 (salt-tolerant) and Shohag (moderately susceptible) were grown in pots filled with soil and treated with 0, 50 and 100 mM NaCl solutions till maturity. Grain yield and yield associated characters, accumulation of mineral ions, such as Na⁺, K⁺ and Ca²⁺ in different plant parts and water relation traits, such as relative water content (RWC), water retention capacity (WRC), leaf water potential and exudation rate (ER) at 15, 30, 45, 60 days after treatment imposition and at harvest were measured. NaCl salinity affected markedly the grain yield and yield associated characters of the two soybean genotypes. However, Shohag was more affected by the salinity than AGS 313. The grain yield of the genotype AGS 313 was 56% and 32 %, whereas that of Shohag was only 22% and 13% at 50 mM and 100 mM NaCl, respectively. The grain yield reduction by salinity was attributed to the reduction in the number of pods per plant, number of seeds per pod and 100-grain weight. However, the number of pods per plant was most affected compared to the other characters. Salinity increased the content of Na⁺ while it decreased that of K⁺ and Ca²⁺ in all the plant parts. The increase in Na⁺ content and decrease in the accumulation of the other mineral ions due to salinity became larger with the plant age. Except for roots, Na⁺ accumulation in different plant parts of Shohag was much higher than that of AGS 313 in all the measurements. However, K⁺ and Ca²⁺ accumulation in different plant parts of AGS 313 was substantially higher than that in Shohag. Moreover, under saline conditions, in AGS 313, the values of RWC, WRC, leaf water potential and ER were higher at all the levels of salinity and plant age than Shohag. It was concluded that the relatively high salt tolerance of AGS 313 was associated with the limited accumulation of sodium and high accumulation of different mineral ions in different plant parts, as well as the maintenance of better water relations under salinity than in the case of Shohag.

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