On indigenous production, genetic diversity and crop ecology of enset (Ensete ventricosum (Welw.) Cheesman)

Abstract

Keywords : Enset, staple, indigenous knowledge, genetic diversity, AFLP, characterisation, conservation, Leaf Appearance Rate, Radiation Use Efficiency, yield potential, transplanting, leaf pruning, fermentation, 'kocho', food security The indigenous enset-farming complex of the south and southwestern highlands of Ethiopia has supported a higher population density than any other farming system. Enset ( Ensete ventricosum (Welw.) Cheesman) has been cultivated as (co-)staple food for about 7-10 million people. Since the last three decades, however, because of population pressure, recurrent drought and diseases there has been degradation of natural resources and, thus, the system failed to sustain the population. In the study, described in this thesis, the indigenous enset production methods, farm-based enset biodiversity and the plant characteristics and environmental factors influencing productivity were analysed to identify yield potentials and constraints in Sidama, Wolaita and Hadiya. The ultimate goal was to develop improved agronomic practices and enhance the use of the existing genetic diversity to reduce the gap between the actual yield and yield potential. Some indigenous cultivation methods vary among regions: initiation of suckers, frequency of transplanting, leaf pruning and planting patterns. Morphologically diverse enset clones were identified in Sidama (52), Wolaita (55) and Hadiya (59). Among 146 clones, a total of 180 AFLP fragments was scored of which 104 (58%) appeared polymorphic. The AFLP-based dendrogram showed more duplication groups than the farmers' characterisation method suggesting that farmers overestimate the genetic diversity. The correlation between the two methods was only weak. Yet, the comparison between the AFLP-based and farmers-based characterisation methods showed that some aspects such as absence of clear regional clusters and clustering of clones with various prefixes to a single group corresponded well. Duplications in the clones identified by both methods may be safely removed from a conservation programme. Variation in farmers' skill in discriminating between clones may suggest that the areas where the people's culture is closely associated with the crop, should receive high priority for collecting clones or serving as sites for in situ conservation. Plant height and LAI of different clones increased faster at Awassa or Areka than at Sidama because of a higher leaf appearance rate associated with temperatures being closer to the optimum. This led to higher early interception of photosynthetically active radiation and higher dry matter production. The mean extinction coefficient was between 0.56-0.91 and radiation use efficiency (RUE) ranged from 1.43-2.67 g MJ -1. Yield potential differences between clones existed, mainly because of differences in RUE. The average ratio actual yield : yield potential (0.24) suggest that much can be done to reduce the yield gap. Transplanting suckers directly into permanent field shortens the period until maturity, provides a reasonable yield soon after removing the suckers from the mother corm and reduces the chance of attack by disease or pests. The partitioning of dry matter to the harvestable parts, the harvest indices at different states of processing and the losses caused by scraping or fermentation, however, became more advantageous as a result of repetitive transplanting. At flowering, harvest indices based on fermented enset products of once, twice and three times transplanted suckers were 0.20, 0.35 and 0.25, respectively. Leaf pruning or the interaction between leaf pruning and transplanting did not significantly affect dry matter partitioning, harvest index or processing losses. The maximum fresh weights of kocho after fermentation from enset plants transplanted once, twice and thrice were respectively 25.9, 54.1 and 37.1 kg plant -1. In terms of weight and energy, enset is the most productive crop in the country, sweet potato is second, taro is third and Irish potato is fourth. The cultivation of enset in densely populated areas under low-input conditions can sustain the population better than that of any other crop. Moreover, enset produces various by-products and the prolonged presence of a closed canopy has an ecological advantage similar to that of forest. This study combines indigenous technical knowledge, agronomic, physiological and molecular studies. It has contributed significantly to the understanding of the production methods and the genetic diversity. It has also investigated some strategies to reduce the gap between the actual yield and yield potential. Furthermore, it has underlined the relevance of physiological studies by generating basic physiological parameters. The information gained in this study also helped to underline future research topics