Factors contributing to variation in heading date in spring barley were examined in several studies commencing with a survey of developmental variation in a large collection of genotypes and concluding with the molecular genetic analysis of 7 doubled haploid populations. Genotypes varied considerably in their specific responses to photoperiod and vernalisation, and in the duration of a pre-inductive (or juvenile) phase defined in this paper as a 'basic vegetative period'. The latter includes differential genotype responses to ambient temperature and their interaction with photoperiod. Combinations of these largely independent environmental variables account for variation in heading date associated with differences in growing season conditions, particularly geographic region, sowing dates, and cultivar adaptation. Under extended and natural (short) photoperiods, in both summer and winter field plantings, conventional genetic analysis was characterised by simple Mendelian segregation combined with considerable transgressive segregation within distinct early and late flowering subpopulations. Equivalent transgressive segregation characterised molecular genetic analysis that identified 16 quantitative trait loci (QTLs) with contributions ranging from >50% of the variation recorded to <10%. These were dominated by 2 QTLs located on chromosome 2, one of which on 2HS was associated with response to extended photoperiod and the other, located near the centromere, with variation in the duration of the basic vegetative period. As only one population segregated for response to vernalisation, all analyses were restricted to parents and progeny homozygous for no response. Three other QTLs on 1HL, 3HL, and 5HL were primarily associated with vernalised parents and progeny characterised by prostrate seedling growth habits, which questions any assumption of a pleiotrophic association between genes for vernalisation and growth habit.The potential for exploiting markers for selection is considered to be limited by the considerable transgressive segregation observed in lines homozygous for parental alleles, and the limited understanding of the causes of variation in the phenotypic expression of the QTLs identified. Such markers would be useful in the selection of backcrossed progeny and in developing materials for investigating fundamental mechanisms contributing to developmental variation.

Brassinosteroids (BRs) have been reported to counteract various stresses. We investigated effects of exogenously applied brassinosteroid, 24-epibrassinolide (EBR), and brassinosteroid-mimic compound, 7,8-dihydro-8-20-hydroxyecdysone (DHECD), on the photosynthetic efficiency and yield of rice (Oryza sativa L. cv. Pathum Thani 1) under heat stress. Solutions (1 nM) of EBR and DHECD were separately sprayed onto foliage of individual rice plants during their reproductive stage. Five days after the application, the plants were transferred to the day/night temperature regime of 40/30ºC for 7 days and then allowed to recover at normal temperature for 7 days. We demonstrated that both DHECD and EBR helped maintain the net photosynthetic rate. The DHECD and EBR application enhanced stomatal conductance, stomatal limitation, and water-use efficiency under the high-temperature regime. DHECD-and EBR-treated plants showed an increase in the nonphotochemical quenching that was lower than that in the control plants. Moreover, DHECD and EBR treatments maintained the maximal quantum efficiency of PSII photochemistry and the efficiency of excitation capture of the open PSII center. Furthermore, the treatments with DHECD or EBR resulted in higher chlorophyll content during the heat treatment compared with the control plants. The paddy field application of 1 nM EBR and/or 1 nM DHECD at the reproductive stage during the hot season could increase the rice yield, especially, the number of filled seeds. DHECD and EBR enhanced total soluble sugar and reducing sugar in straw and more starch was accumulated in rice seeds. Consequently, our results confirmed that DHECD showed biological activities mimicking EBR in the improvement of photosynthetic efficiency and in rising the rice yield under heat stress.

The application of brassinosteroids (BRs) has been reported to alleviate heat stress. This study investigated the effect of 7,8-dihydro-8a-20-hydroxyecdysone (DHECD)-a BR mimic-by comparison with 24-epibrassinolide (EBR) on the changes in photosynthetic performance, lipid peroxidation, and rice seed set. The results demonstrated that 10 28 M EBR and 10 27 M DHECD had the best actions to counteract the lethal heat temperature of 47°C for 2 h indicated by a reduction in the number of wilted leaves and an increase in the relative water content and leaf greenness. Moreover, plants treated with EBR or DHECD were exposed to high day/night temperatures of 40/30°C for 7 days. EBR-treated and DHECD-treated plants showed a high shoot fresh weight, leaf area, chlorophyll content, and carotenoid content. High temperature significantly decreased the leaf net CO 2 assimilation rate as well as increased lipid peroxidation. The application of EBR and DHECD maintained the high level of the net CO 2 assimilation rate by increasing the stomatal conductance and photochemical quenching. On the other hand, EBR and DHECD decreased the intracellular CO 2 content and nonphotochemical quenching leading to enhance photosynthesis under heat stress. EBR-treated and DHECD-treated plants significantly reduced their malondialdehyde and hydrogen peroxide contents as well as increasing their total soluble sugar contents. Moreover, BR treatments increased the filled seed of rice. This study confirmed that DHECDa BR mimic-has activities of heat stress alleviation similar to EBR.

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Hemp (Cannabis sativa L.) from a tradiiional Thai variety was used as a source of fiber in this research. The variety has been grown for a long time by the Hmong, a hill tribe, for the purpose of textiles. Hemp was grown in Chiang Mai, in the North of Thailand. Fiber fineness, fiber strength, fiber length, and lignin content of bast fibers from the lop, middle, and bottom part of hemp stems aged 65 and 120 days were measured after chemical separation. The results showed that ihe finest fiber was from the top of the stem. The fiber fineness determined from tbe airflow method varied from 14.2 to 27.0 FBAI200, and according to tbe OFDA melhtid it varied from 14.1 to 19.1 ^m. The highest strength fiber was from the middle part of the stem; fiber strength (Stelomeler ~ collective test) varied from 10.9 to 27.4 cN/tex. Fiber length varied from 22.0 to 28.4 mm. At the early stages Tbitivara Sengloung and Lily Kaveela are affiliated wilb the Senghung, Kaveeta, and MUssig 21 of mule pollinution, male plants had a lower lignin content than female planls. The meusureincnl meliuKl, age of plant. itrnJ part of stem analyzed atïecled fiber properlies. This iradiliunal Thai hemp showed fine fiber and ean he improved lo a eommereial level for the lexlile industry.