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The presence of exotic plants both in Africa and in Asia has long attracted the attention of scholars who have attempted to understand the human activities linked to them. Archaeological and ethnographic evidence for the reconstruction of these activities is often very limited, but indirect methods such as the study of DNA have become useful tools in building models of early human dispersal. Among the plants that were carried across the Indian Ocean, sometimes known as the “tropical food kit”, the staple crop taro (Colocasia esculenta (L.) Schott) has continued to be the subject of ongoing research. The use of this crop in antiquity is well documented by discoveries of ancient taro starch granules found on archaeological artefacts from sites in Southeast Asia and the Pacific islands, making it one of the oldest plants consumed by people. However, less is known about the use of taro in Africa and the Mediterranean region, where it is found both in the wild and under cultivation - often representing a staple crop in Sub-Saharan Africa. In this doctoral thesis, genetic analysis was performed on modern samples of taro collected from Africa and other regions of the Indian Ocean, using four molecular markers. Two main clusters have been identified, and within this main sub-division four populations of taro have been detected in Africa. By integrating the genetic results with historical and linguistic research, and extensive ethnobotanical fieldwork in Africa, two of these populations are proposed to represent early translocations, with modern distribution patterns suggesting diverse dispersal routes at different times. These results open up a new scenario in which the “tropical food kit” is finally unpacked, with important historical implications for each of the crops contained within it.

Taro, Colocasia esculenta, is a unique root crop that serves as an important dietary component in the Pacific islands and in parts of Asia and Africa. Cultivation of taro as a food crop might have ancient origin as is evident from variety of ritualistic use of taro in different parts of the world. Even though it has been postulated that taro was domesticated in the old world, the widespread cultivation of taro calls for a discussion regarding its origin. Wild varieties of C. esculenta are known from regions of Eastern India, Sri Lanka, Sumatra, and the Malay Peninsula. Other wild varieties have been reported from the Indo-Pacific region and China. The two prominent chromosome number series are 2n=28 and 2n=42. But, chromosome number series 2n= 28, 42, 36, and 48 have been reported from India indicating the centre of highest diversity. A certain amount of controversy exists over classification and nomenclature of this polymorphic species. Primary products of the plants are the corms and cormels. Taro is also used in traditional medicine. It has been known to be nutritionally superior to other starchy crops like potato. This document reviews previous works done on classification and nomenclature of taro, morphology, origin of taro, production and agronomy, and finally ethnobotany of taro across the major taro producing countries.

This thesis provides an analysis of the genitive subject in Japanese. The genitive Case marker no can optionally replace the nominative Case marker ga in relative clauses. This is the so-called ga/no conversion. I argue that this phenomenon is not peculiar to Japanese, but is governed by universal principles. I employ the notions "argument/adjunct" and the Unaccusative Hypothesis. In combination with the Subjacency Condition, these universal notions help us to predict which genitive subjects are grammatical .

Field and greenhouse studies were conducted to determine the effects of management practices on taro. Three irrigation methods, three land preparation methods and three population combinations were studied. Factorial combinations of water treatments, age, and nutrients were used to study individual plant response in pots. A cost analysis based on yield from the irrigation experiment and data from puddled flooded soil condition (population, 27 X 103 plants per hectare) was presented. Corm yields were 25, 35 and 26 metric tons/ha at 7, 10 and 13 months under sprinkler irrigation; 27, 41 and 62 tons/ha under furrow and 33, 48 and 64 tons/ha for flooded soil at the same ages respectively. Flooding gave significantly higher total yields over sprinkler at all ages whereas significantly higher yield over furrow was obtained only at 10 months. The yield from furrow irrigation was 82% of yield from flooded plot and that from sprinkler was 75% at 7 months. Corresponding percent yields at 10 and 13 months from the sprinkler and furrow irrigated plots were 75 and 85; and 41 and 97. Corm yield per hectare increased with increasing population. Yield per plant increased as population decreased. The contribution of sucker corms to total yield per plant increased as plant population decreased, while sucker yield per hectare increased as population increased. Suckering was not enough to compensate for increases in yields due to increasing population per hectare. Both greenhouse and field experiments showed that sucker yield was highest in flooded soil and decreased with decreasing water level. Effect of ridging ranged from 94% to 101% of yields obtained from non-ridged plots. Puddling of soil was not essential in taro growth. Yield from unpuddled flooded soil ranged from 92 to 106% of yield from puddled, flooded soil. Corresponding yields from unpuddled furrow and sprinkler irrigated plots were 88 and 92%; and 65 and 58%, respectively. Leaf area of taro can be accurately evaluated by linear dimensions. Both plant height and leaf growth approached a maximum between 4 and 5 months irrespective of irrigation and land preparation methods. Leaf area increased as follows: flood> furrow> sprinkler. The best linear relationship of leaf area with yield was obtained at 3 months (r = 0.83**) and not at 5 and 10 months (r = 0.56**). Leaf production at 5 months in excess of amounts required for optimum corm yield was demonstrated. Maximum leaf area indices (LAI) obtained at 5 months were 6.9, 6.2 and 4.7 respectively for flooded, furrow and sprinkler irrigation. Regression of corm yield and LAI showed that LAI approached 3.0 for optimum corm yield. A distinct optimum was established at this value in the sprinkler treatment while a plasticity in LAI and yield was observed in the furrow and was extreme in the flooded culture. Compared with returns from puddled flooded culture, relative incomes at 27 X 103 plants per hectare were as follows: Sprinkler 52 - 68%, furrow 72 - 87%, flooded unpuddled 70 - 96%. Owing to higher rate of senescence of leaf growth, the N, P, Ca, Mg, Fe and Mn concentrations of taro petiole at 6 months were higher under the sprinkler and furrow irrigation than in flooded samples. There were no differences at 3 months. The N, K, Fe and Mn concentrations at 3 and 6 months were significantly higher under ridged culture in contrast with non-ridged culture. Based on 2-month vegetative growth in a pot study, increases in yield due to application of N and P at 800 and 1200 kg/ha under non-flooded culture was not enough to offset the difference in growth due to flooding. Restricted root growth and penetration were among factors limiting taro growth under non-flooded culture in the pot study. The data presented showed that the difficulty of heavy machinery use in taro culture could be minimized with no significant difference in yield by improved crop management practices. Cultural adjustments suggested include saturated soil by furrow irrigation of non-puddled soil with 60 cm ridge or row spacing and 30 cm (or less) plant spacing. Where machinery specifications make it impracticable for 60 cm ridge or row spacing to be used, a 90 cm spacing could be substituted with no loss in yield. Pot study showed that N and P rates in excess of 800 and 1200 kg/ha, respectively, might be required.