The root systems of higher plant consist of primary, lateral, and adventitious roots. There is a current hypothesis, named ‘root apical dominance’, that root-derived suppressor negatively regulates the formation of adventitious and lateral roots. According to this theory, we have studied the mechanisms involved in the regulation of adventitious and lateral root formation. trans-zeatin riboside (ZR), one of cytokinin species, was identified in squash root xylem sap as a main suppressor of adventitious root formation in cucumber, suggesting that ZR transported from root via xylem sap acts as an endogenous suppressor of hypocotyl adventitious root formation in planta. Moreover, we isolated Arabidopsis mutant, wooden leg-3 (wol-3), for stimulated adventitious root formation in intact plants. Analyses of wol-3 mutant have revealed that cytokinin receptors are necessary for the primary and lateral root formation via the formation of auxin-transporting vascular tissues in the hypocotyl, but not for adventitious roots. In this mini review, we discuss the relationship between cytokinin and adventitious and lateral root formation.

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The System of Rice Intensification (SRI) was developed in Madagascar in 1983 as a revolutionary paddy cultivation method to achieve very high paddy yields with reduced resources such as irrigation water, fertilizer and chemicals. Recently SRI planting tests have been done in about 20 countries, and SRI planting areas have been expanding in many developing countries. Over the past four years, a Japanese-funded irrigation project in Eastern Indonesia has evaluated the SRI to assess its potential to reduce resources utilization while rewarding farmers with higher production and incomes. This paper reports the results and conclusions from this assessment. In summary, comparison trials managed by 1, 849 farmers on 1, 364ha and supervised by project staff have given an average SRI yield of 7.2t/ha compared to 3.9t/ha with conventional methods, an 84% increase. Water saving has been assessed to be around 40%, with reduction of 50% for utilization of fertilizer and chemicals, and accompanied by in costs of production per hectare of >25%. The economic attractiveness of SRI methods is very great, giving farmers strong incentive to accept increase of burden for water management and weeding. At present, actual practice of SRI such as intermittent irrigation cycle and way of fertilizer application have been determined based on trial and error. Systematic research and analysis on phenomenon of SRI effects are not enough, and this has restricted the smooth extension of SRI. Research and analysis on SRI effects are necessary to strengthen SRI as a real technology and further extension.

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