The aim of this study was to investigate the effect of waterlogging on morphological and physiological traits of sorghum (Sorghum bicolor L. Moench) cultivars. Four sorghum cultivars, cv. Wray, Keller, Bailey (sweet cultivar) and cv. SP1 (forage cultivar) at five expanded leaf stage were subjected to 20 days of waterlogging and drained pots were kept as the control. Twenty days of waterlogging did not cause a significant difference in shoot and root biomass among cultivars. Flooding reduced leaf area (69%), plant height (30%) and youngest leaf expansion rate of all cultivars but severely reduced in SP1 (35-80%). Flooding promoted leaf senescence of all cultivars and biomass allocation to shoot (increase in shoot/root) in Wray, Keller and Bailey, but increased biomass partitioning to root in SP1. The initiation of new nodal root was noted in SP1, whereas the ability to maintain root surface area by increase in longest root length and nodal root development near soil surface was found in Wray. Photosynthetic rate, stomatal conductance and transpiration rate were severely reduced under waterlogging conditions of sweet cultivars (65-78%), but enhanced over the control in forage cultivar (56%). The ability to conserve root surface area, allocate more biomass to shoot during waterlogging and develop root near soil surface may support new growth in Wray, whereas the ability to maintain leaf gas exchange parameters in SP1 was due to the active nodal root growth. Nevertheless, there was no relationship between photosynthetic rate and shoot growth of sorghum under anaerobic conditions.

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A declining farm labor force and increasing water scarcity worldwide are forcing rice farmers to adopt directseeding rice production. Under this production system, speed of germination, field emergence, and crop yield depend prominently on rice seed vigor. We hypothesized that seed priming can enhance rice seed vigor and agronomic performance. The objective of this study was to evaluate the effect of GA 3 and wood vinegar seed priming on seed vigor, seedling performance, and grain yield in farmer's fields. The experimental design was a split-split plot with four replications and planted in Thailand between April to December 2013 and 2014. Two rice cultivars (KDML 105 and RD6) were main plots; two planting methods (broadcast and row) were sub-plots, and three seed priming treatments (GA 3 , wood vinegar, and untreated control) were sub-sub-plots. Seed priming enhanced speed of germination and final germination percentage under both laboratory and field condition. However, soil moisture availability during flowering and seed formation significantly affected agronomic performance. Wood vinegar-primed seeds had greater shoot growth and plant population at maturity, while GA 3-primed seed had more rapid germination. Yieldrelated agronomic performance characteristics of tillers plant −1 and yield in ton ha −1 were significantly higher for primed seed, and weed biomass was significantly reduced in 2013. Here, we show for the first time that wood vinegar is a sustainable alternative to chemicals for seed priming. Also, when water is available during flowering and seed development, wood vinegar priming increases grain yield and reduces weed pressure.

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Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/sagb20 A flood-free period combined with early planting is required to sustain yield of pre-rice sweet sorghum (Sorghum bicolor L. Moench) AbstractUnderstanding the responses of sweet sorghum to flooding and the characters associated with flooding tolerance may be a useful strategy for pre-rice production and help meet demand for biofuel feedstock. Three sweet sorghum genotypes (Bailey, Keller and Wray) and five flooding treatments including non-flooding control, continuous flooding extended from 30, 45, 60 and 75 days after emergence to harvest were conducted under greenhouse conditions. Flooding decreased leaf dry weight (22Á60%), leaf area (10Á70%), number of node per stalk (1Á5%), shoot dry weight (5Á20%) and stalk yield (2Á22%) with highest reduction in 30 days after emergence flooding treatment. Flooding later than 30 days after emergence did not significantly affect shoot growth, yield and yield components. Brix value, sucrose content and total sugar content were not significantly affected. All studied cultivars had similar shoot growth response. Flooding induced development of roots in water; root length, root dry weight, nodal root and lateral root number and interconnection of aerenchyma spaces from roots in flooded soil to stalk base above water level but suppressed root growth in flooded soil. The acclimation traits were highest in Keller, flooding from 30 days after emergence but there was a lack of root development in 75 days after emergence flooding treatments. These findings indicate the effect of waterlogging on sweet sorghum growth and yield strongly depends on the growth stage at which it occurs. There were genetic variations in root morphological and anatomical responses to flooding of sweet sorghum. The development of nodal and lateral roots and aerenchyma formation from flooded plant parts to stalk bases above water level may distribute to flooding tolerance in sweet sorghum. Based on the results, a flood-free period of at least 30 days after emergence is required to sustain yield of pre-rice sweet sorghum and early planting is highly recommended.

Following the high rubber prices in the second half of the 2010s, rubber plantations expanded greatly especially in Southeast Asia. Smallholders were important actors of the recent rubber boom. However, large landholdings and foreign investments were also very present in some Southeast Asian rubber producing countries leading some researchers to ask whether we are witnessing resurgence of plantations in tropical Asia. Looking at entrepreneurial rubber farms in Thailand, the first producer of natural rubber in the world, where very little information is available on this type of farms, is one way to contribute to the debate. After identifying large rubber holdings using secondary data completed by some field explorations, we conducted a survey on a limited number (13) of large rubber holdings. Qualitative analysis revealed that the recent development of large plantations in the rubber sector was actually limited in Thailand, and that this (limited) expansion of large rubber plantations mainly involved family business farms. Together with family farms, these family business farms largely contributed to the recent expansion of rubber plantations rather than entrepreneurial farms. In addition, these large landholdings shared several similar technical and organizational patterns with smaller family farms. Finally, Thailand represents a specific pattern of change in farm structure in which family farms have always persisted over enterprise farms. Family business farms are a type of farm structure that now appears to be expanding. In addition to continuing to support small and medium family farms, government policies should consider such changes in farm structure and provide support to improve the technical management of these developing forms of production. In parallel, support should be provided to help maintain the smallholdings thereby limiting land concentration when it is not wanted by the owners.

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