Phytotron and field performance of Taro [Colocasia Esculenta (L.) Schott] landraces from Umbumbulu.

Abstract

The taro landraces that are most preferred by farmers from Umbumbulu, KwaZulu-Natal were identified through focus group discussions with farmers. Farmers ranked taro landraces on the basis of preference as determined by economic value, social significance, ecological importance and food characteristics. Using pairwise ranking, the farmers' preference of taro landraces across all locations was found to be in the following order: Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Dumbe-dumbe was identified as the currently actively cultivated taro whereas Mgingqeni was regarded as a less desirable cultivated taro. Pitshi was regarded as an antiquated landrace and Dumbe-lomfula was generally regarded as a taro type of no economic, social or food value that grew on river banks as a wild species. Glasshouse and field studies were conducted to determine the effects of temperature and growing location [Pietermaritzburg (UKZN) and Umbumbulu] on emergence, plant growth and yield of taro. Starch and mineral composition of taro corms were determined in harvest-mature corms. Effects of three day/night temperature levels (22/12°C, 27/17°C and 33/23°C) were examined on the growth of four taro landraces Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Pitshi-omhlophe, an ecotype of Pitshi for which there was a limited amount of planting material, was also included in the glasshouse studies. The farmers stated that the normal growing season for the economically important landraces, Dumbe-dumbe and Mgingqeni, was six months, but in this study plants were grown in glasshouses for nine months, and in the field, for seven months before the attainment of harvest maturity. Emergence was determined daily for glasshouse experiment until all plants had emerged and it was determined monthly for the field experiment. Leaf number, plant height and leaf area were measured every month to determine growth and development, while number of corms and fresh corm weight were used at harvest to determine yield. For all landraces, time to emergence increased significantly with decrease in temperature from 33/23°C to 27/17°C, but it increased significantly for only Dumbe-dumbe and Mgingqeni from 27/17°C to 22/12°C. Mgingqeni showed the shortest time to emergence, whereas, Pitshi showed the longest delay in emergence. The locations were not significantly different in emergence. Mgingqeni displayed the highest emergence in UKZN (91.4%), whereas, Dumbe-dumbe displayed the highest emergence (95.5%) and Dumbe-lomfula displayed the lowest emergence (55.9%) in Umbumbulu. Leaf number was highest for Pitshi-omhlophe, in glasshouse experiment due to its tendency to produce multiple shoots compared with the other landraces. Plant height increased with increase in temperature for all landraces except for Pitshi, for which height decreased with an increase in temperature. Leaf area was greatest for Dumbe-lomfula at all temperatures and lowest for Pitshi at both 22/12°C and 27/17°C. Leaf number was highest for Mgingqeni and lowest for Dumbe-lomfula at both sites, although it was significantly lower only for Dumbe-lomfula in UKZN. Plant height and leaf area were significantly highest for Dumbe-lomfula at both sites. The highest total number of corms per plant was shown by Pitshi-omhlophe at 22/12°C. Total fresh corm weight was highest for Dumbe-lomfula at 27/17°C and lowest for Pitshi at 22/22°C. The field experiment results showed Pitshi and Dumbe-lomfula with significantly higher total fresh corm weight in UKZN compared with Umbumbulu. Corms were analysed for mineral elements and starch. There were significant differences in starch content between temperatures (P = 0.017) and taro landraces (P = 0.025). There was also a significant interaction of temperatures and landrace (P = 0.002). Starch content increased with temperature for all landraces except for Pitshi-omhlophe and Dumbe-lomfula which showed a decrease at 27/17°C. There were significant differences in corm mineral content between temperatures, locations and landraces (P < 005). It is concluded that the chemical composition of taro corms is influenced by growth temperature and the location (site) where the crop is grown. The results of this study also indicated that taro plant growth is enhanced by high temperatures (33/23°C). High temperatures are, however, associated with short leaf area duration and subsequently low yield. The findings of this study may also be useful in determining taro quality for processing.