The xylem hydraulic conductivity of the panicle neck is considered to be responsible for the maintenance of the panicle water status which is not under the stomatal control in rice. To clarify the hydraulic properties of the panicle neck, the water transport function of the panicle neck and panicle characters were examined in 12 paddy and 8 upland rice genotypes originating from various countries. The hydraulic conductivity (K) under full hydration increased with the increase in the number of spikelets per panicle (N_s), panicle area (A_p, projected area of a whole panicle which was considered to be an indicator of the evaporative surface) and the number of large vascular bundles of the panicle neck (N_b) in paddy rice. A large variation in K was also detected in upland rice, but not in N_s and N_b, and the relationships of K with N_s, A_p and N_b were not significant. On the other hand, there was a significant relationship between the diameter of the large xylem vessels and K in the paddy and upland rice genotypes. A positive relationship was found between K/A_p or K/N_s (ability of the xylem of the panicle neck to supply water per unit evaporative surface or to one spikelet) and the size of the spikelet (A_s, calculated as A_p/N_s) . Since upland rice has large spikelets, the value of K/A_p was higher in upland rice. The xylem became vulnerable as N_s increased in paddy and upland rice genotypes. These results suggested that upland rice was able to cope with dry environments not because of a less vulnerable xylem to dysfunction but due to the higher hydraulic conductivity of the xylem. The relationships found in this study may enable to estimate the hydraulic properties based on the panicle characters.

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A pot experiment was conducted to investigate the presence of heterosis for photosynthetic and morphological characters at the active tillering, heading and dough-ripe stages in five F₁ rice (Oryza sativa L.) hybrids produced by crossing a thermo-sensitive genic male sterile (TGMS) line with indica and japonica cultivars. CO₂ exchange rate (CER) in single leaf and some other photosynthetic characters viz., SPAD reading (a parameter of chlorophyll content) and leaf nitrogen (N) content were lower in most F₁ hybrids than in their respective male parents during the growing season. A positive correlation of CER with SPAD reading and leaf N content was observed in the F₁ hybrids and parent cultivars at all the growth stages. Specific leaf area (SLA) in most F₁ hybrids was higher than that in the parent cultivars, and it was negatively correlated with CER. All the F₁ hybrids showed a significantly positive heterosis over both the male parents and the mid-parents for the number of tillers, leaf area, root dry weight and dry matter accumulation per plant at all the growth stages. It is considered that the positive heterosis for dry matter accumulation was mainly due to the larger number of the tillers and lager leaf area per plant at the early stage of development. The improved development of the root system at the early stages also contributed to heterosis for dry matter production in the F₁ hybrids.

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The ability to maintain water continuity in the xylem under a low water potential (low vulnerability of xylem to dysfunction) is considered to be responsible for adaptation to drought in cashew. The effect of shading on the xylem vulnerability of cashew seedlings was evaluated since the plants are grown under shading at the nursery stage. A strain with a resistant xylem (A3-1) and two strains with a vulnerable xylem (G-85 and Wonogiri-2) were grown in an open field and under shading for four months, and then the xylem vulnerability was determined. In A3-1, the applied pressure that induced a 50% loss of hydraulic conductivity (P₅₀), which was the indicator of xylem vulnerability, was 1.55 MPa in the open field and A3-1 was found to be less vulnerable than G-85 and Wonogiri-2 in which the P₅₀ value was ca. 1.2 MPa. The vulnerability increased under shading in A3-1, whereas it was not affected by shading in G-85 and Wonogiri-2, resulting in the absence of difference in vulnerability among the strains under shading. Stem length/diameter ratio increased in the three strains under shading, indicating the existence of spindly growth. The degree of spindly growth was largest in A3-1 and the vessel diameter increased only in A3-1. It was considered that the fragile vessel wall and the increase in the vessel diameter associated with spindly growth was responsible for the increase in the vulnerability under shading in A3-1. These results suggested that it would be important to grow the seedlings of A3-1 which displayed a resistant xylem under shading without spindly growth.

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Among the 23, 591 native rice varieties preserved at the International Rice Research Institute (IRRI), varieties resistant to bacterial blight consist of four major variety groups: Xa3 (Java14 group), Xa4 (TKM6 group), xa5 (DZ192 group), Xa10 (Cas209 group) based on inoculation tests with Philippine races 1 to 4. Additional inoculation with races 5 and 6 had enabled to further detect the SSSSRS reaction, which corresponds to that of Xa14, and a fifth variety group Xa14 (TN1 group) was identified. However, inoculation tests had not been completed for the varieties from Vietnam, Laos and Myanmar. Therefore, varieties showing the SSSS reaction (races 1 to 4) were inoculated with Japanese isolates I to V to determine the whole spectrum of Asian distribution of Xa14. The results indicated that the RRSSR (Japanese isolates I to V) reaction was associated with the presence of Xa14 which was confirmed in these countries. As a whole in Asia, it was suggested that the presence of the single gene Xa14 was frequent in Malaysia and Vietnam. China was considered to form the eastern margin of the distribution, while the coexistence of Xa14 with other BB resistance genes was frequently observed in Indo-China, particularly with the Xa10 belt, followed by Xa4. Single gene presence was considered to comprise a secondary center, while the coexistence with other genes was considered to involve a primary gene center. It is likely that the primary center is located in the Himalayan foothills of Indo-China.

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In order to estimate cassava productivity in Northeast Thailand, notorious for its low and unstable agricultural production, simple yield models were developed using water use efficiency (WUE) and radiation conversion efficiency (Cs) . In the WUE model, daily dry matter production was estimated by the WUE and transpiration, whereas in the Cs model, by absorbed solar radiation, Cs and LAI. Daily transpiration was estimated by LAI and evapotranspiration, which was estimated from air temperature and solar radiation. The effect of water stress was incorporated through the calculation of actual transpiration in the WUE model, and through a water stress index, i.e. the ratio of actual against potential transpiration in the Cs model. Several experiments, conducted in an experimental farm in Khon Kaen University, located in Northeast Thailand, provided parameters necessary for the models. Validations in the experimental farm and a farmers' field indicated that the models developed were able to estimate the growth and yield of cassava to an acceptable level. Although both models were equally successful, the WUE model seems preferable for application in regional level productivity analysis, because of its simplicity.

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Eight mixed substrates at a ratio of 1: 1 (v/v), namely coconut coir: rice husk (CC: RH), coconut coir: peanut husk charcoal (CC: PHC), rice husk charcoal: rice husk (RHC: RH), rice husk charcoal: peanut husk charcoal (RHC: PHC), bagasse charcoal: rice husk (BGC: RH), bagasse charcoal: peanut husk charcoal (BGC: PHC), peat moss: rice husk (PM: RH) and peat moss: peanut husk charcoal (PM: PHC), were compared with commercial growing media (COM) for their potential for transplant production of lettuce and cabbage. Tha values of shoot length, shoot: root ratio, leaf area, total dry weight and growth analysis parameters of the transplants grown in the substrates containing PHC were higher than those of the transplants grown in the substrates containing RH for lettuce at the last sampling stage. However, the lettuce transplants grew successfully in all the mixed substrates. The cabbage transplants grown in the PM: PHC and CC: PHC mixtures showed higher values for the leaf area and total dry weight than those grown in the other mixed substrates, although the values were lower than those of the transplants grown in COM. Moreover, growth analysis parameters of the transplants grown in the CC: PHC mixture were similar to those of the transplants grown in the PM: PHC mixture. The excessive level of soluble salts in the CC: PHC and BGC: PHC mixtures and high sodium concentration of the substrates containing CC did not affect the transplant growth in either species. The RHC: PHC and CC: PHC mixtures could be recommended for lettuce and cabbage transplant production, respectively, due to their low cost and to their availability in the tropical zone.

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Lao P.D.R. (hereinafter referred to as Laos), the only landlocked country in Southeast Asia, is a multi-ethnic country divided into altitudinal zones inhabited by Tai Group, the rice grower in the lowlands, and non-Tai Groups comprised of farmers engaged in slash-and-burn agriculture. These groups contribute to the formation of a unique composite society from cultural and agricultural aspects, through exchanges of material and culture, with the preservation of the respective production systems. This study aimed at elucidating the characteristics of rice cultivation in Luang Phabang, northern Laos, by analyzing grain and ecological characteristics of cultivated rice varieties.
The predominant grain type of the rice varieties grown in the study area was the b-type, according to MATSUO's classification. Differentiation between glutinous and non-glutinous varieties by farmers corresponded to the results of iodine tests, and the glutinous varieties were predominant in the study area. Non-glutinous varieties tended to belong to the c-type. Phenol test showed the coexistence of positive (+) and negative (-) reactions, and the positive reaction (+) predominated in the lowland varieties. On the other hand, in the glutinous upland varieties of the b-type, the phenol reaction was negative, suggesting that the varieties belonged to the tropical japonica group. Based on cluster analysis of several grain and ecological characteristics, cultivated rice varieties in this area may be classified into clusters A and B. All the b-type varieties in cluster A were glutinous, and grouped into 3 sub-clusters. In the study area, while some ethnic groups preferred to cultivate non-glutinous upland rice varieties, most of the inhabitants planted glutinous upland varieties belonging to Cluster A-2. Tai Group also tended to cultivate lowland varieties belonging to Clusters A 1 and B, which may have the genetic background of the indica type. It will be necessary, in future, to investigate the characteristics of the varieties that on grown under both upland and lowland conditions.

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