Genetic Variation Within Cassava Germplasm in Response to Potassium

Abstract

As cassava is grown mostly by small resource-limited farmers throughout the tropics on lowfertility soils with little fertilization and, due to the large potassium (K) export in harvested roots, genotypes that tolerate low-K soils and respond to K fertilization are warranted. The objective of this study was to evaluate cassava germplasm and identify such genotypes.Fourteen cultivars of cassava (Manihot esculenta) selected from the core germplasm at CIAT were grown under rainfed conditions for ten months over ®ve consecutive seasons in Inceptisols either with no K application or with 50, 100 or 200 kg K ha 71 applied annually together with adequate nitrogen and phosphorus. All cultivars responded to K application both in terms of root and shoot biomass with the highest yields obtained by CM 507-37 and M Ven 25 in the absence of K application and at high K levels. These cultivars had the highest adaptation indices to low K and the highest K use eciency for total biomass production. CM 507-37 had the highest K use eciency for root production at all K levels. Thus, it is desirable to use this material for breeding cassava which is adapted to low-K soils and is able to respond to fertilizer application. However, because of the high hydrocyanic acid (HCN) content in their roots, these cultivars should be crossed with genotypes that are low in HCN, such as HMC-1 and M Cub 74, in order to select lines with both high K use eciency and low HCN for fresh cassava consumption. Root HCN contents were signi®cantly reduced by application of K across all cultivars. Application of K fertilizer to low-K soils is warranted to minimize health hazards when fresh cassava is used for human consumption.

How can calibrated research-based models be improved for use as a tool in identifying genes controlling crop tolerance to environmental stresses in the era of genomics-from an experimentalist's perspective

“…These findings imply that cassava productivity, as a source for food, feed, and energy in the tropics and subtropics, is likely to be enhanced by the expected increases in AC and associated rises in global temperature. Cassava photosynthesis (El-Sharkawy and , 1992a, 1993, Ramanujam 1990, CIAT 1992 and yield and growth (Irikura et al 1979, Connor et al 1981, Keating et al 1982, CIAT 1992-95, El-Sharkawy et al 1990, 1992b, 1993, Ramanujam 1990, ElSharkawy 1993, 2003, Pellet and El-Sharkawy 1993a, 1997, El-Sharkawy and Cadavid 2000, 2002 were greatest in tropical and subtropical environments in wetter soils and with higher temperature, air humidity, and intense sunlight.…”

Understanding cassava yield response to soil and fertilizer nutrient supply in West Africa

“…Thus, CROPSIM assumes that P and K are not limiting cassava growth, and is therefore not suited to assess nutrient limited yields in the nutrient depleted production systems of West Africa. Particularly, K deficiency is important in such low external nutrient use systems since cassava as a root crop has a high K demand (El-Sharkawy and Cadavid 2000;Howeler 2002;Pellet and El-Sharkawy 1997). The QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) model could be a practical tool to assess nutrient requirements in cassava production systems.…”

Comparative photosynthesis, growth, productivity, and nutrient use efficiency among tall- and short-stemmed rain-fed cassava cultivars

“…Introducing mulching with crop and weed residues also improved soil nutrients and water contents, enhanced soil organic carbon, decreased surface soil temperature, and increased cassava productivity, particularly in poor sandy soils (Cadavid et al 1998, Howeler 2002. Working with several cassava cultivars grown in acidic Inceptisols in Colombia, El-Sharkawy (1993b, 1997), ElSharkawy et al (1998a), andCadavid (2000) found genetic diversity in nutrient use efficiency (NUE) in terms of storage root production per unit of nutrient uptake [kg(dry storage root) kg -1 (nutrient)]. In Kerala state, in southern India, Byju and Anand (2009) found that under sufficient rainfall (>1,500 mm in 10 months), the short duration improved cultivar, namely Sree Vijaya (6 months duration) had greater yield and greater NUE in terms of storage root production per unit of nitrogen uptake than the traditional cultivar, namely M-4 (10 month duration).…”

“…Such a situation is further aggravated in hillside ecosystems where cassava is grown on steep marginal lands prone to water erosion that results in significant losses in organic matter and nutrients in absence of adequate cultural practices (Reining 1992, Zöbisch et al 1995, Lal 1997, Ruppenthal et al 1997. To minimize these environmental negative effects, improved technologies were sought for and developed via sound agronomic practices as well as genetic improvements (Leihner 1983, CIAT 1983-1998, Pellet and El-Sharkawy 1993a,b, 1997, Ernst-Schaeben 1994, Tscherning et al 1995, Ruppenthal et al 1997, Cadavid et al 1998, El-Sharkawy et al 1998a, El-Sharkawy and Cadavid 2000, Howeler 2002, El-Sharkawy 2004, Ravi and Mohankumar 2004. Planting grass barriers in hillside cassava-based systems reduced water runoff, soil erosion, and soil organic matter and nutrient losses, while maintaining and/or increasing cassava productivity (Ruppenthal et al 1997, Leihner 2002.…”