Response of Cassava to Prolonged Water Stress Imposed at Different Stages of Growth

Abstract

A two-year ®eld trial was conducted to study the effects of prolonged water stress on cassava (Manihot esculenta) productivity, and on nutrient uptake and use ef®ciency. Four contrasting cultivars were supplied with adequate fertilization and watering, except when water was excluded by covering the soil with plastic sheets for different periods, depending on treatment: from two to six months, four to eight months, or from six to twelve months after planting (early, mid-season and terminal stress respectively). Sequential harvests were made at 2, 4, 6, 8 and 12 months after planting to determine leaf area index and shoot and root biomass. At ®nal harvest, nitrogen, phosphorus, potassium, calcium and magnesium concentrations in shoots and storage roots were determined.During both early and mid-season stress, leaf area index and shoot and root biomass were signi®cantly smaller than those in the controls across all cultivars. After recovery from stress, leaf area index was greatly enhanced with less dry matter allocated to stems, and root yields approached those in the controls. One cultivar, CMC 40, had greater ®nal root yield under stress treatments. Nutrient concentration in roots and shoots was less in all cultivars with early stress and resulted in higher nutrient use ef®ciency in all elements for root production. The same trend was observed under mid-season stress, except for nitrogen concentration, which remained unchanged.Terminal stress did not affect leaf area index, but reduced the shoot biomass in all cultivars. Final root yields were smaller than those in the controls except for CMC 40 whose ®nal root yield was greater under stress. Nitrogen concentration was greater in root biomass but less in shoot biomass of all cultivars, resulting in lower nitrogen±use ef®ciency for root production. Across cultivars, only potassium-and magnesium-use ef®ciencies were greater than in the controls. CMC 40 was the only cultivar with consistently greater use ef®ciency of nitrogen, phosphorus, potassium, calcium and magnesium for root production under terminal stress. This higher nutrient use ef®ciency was due, mainly, to a greater root production rather than to smaller nutrient concentration. This cultivar is suitable as a gene source for improving cassava in order to maximize root pro-duction per unit nutrient extracted under stressful environmental conditions. introdution Throughout the cassava (Manihot esculenta)-growing areas of South America, the crop is an important staple food used mainly as a source of carbohydrates for

Physiological characteristics of cassava tolerance to prolonged drought in the tropics: implications for breeding cultivars adapted to seasonally dry and semiarid environments

“…Since under stress harvest index increases (see Table 1), reduction in irradiance interception will lead to less crop transpiration rate, and hence, to greater crop water-use efficiency in terms of storage root production. Moreover, when stressed plants recover in wet conditions, they rapidly form new leaf canopy with even higher leaf photosynthetic rates than those in unstressed leaves, thus final yield approaches values obtained in well-watered plants (see Tables 1, 4; El-Sharkawy and El-Sharkawy et al, 1992bEl-Sharkawy, 1993, 2006aCayón et al, 1997;El-Sharkawy and Cadavid, 2002). Under prolonged drought (> 5 months) in semiarid environments with less than 500 mm of effective annual rainfall, cassava survives and produces reasonable yields (3 to 5 t DM ha -1 with improved cultivars) which can be greatly increased (2-3 times) with a second cycle of rainfall(see Tables 6 and 7). during long dry periods.…”

Utility of basic research in plant/crop physiology in relation to crop improvement: a review and a personal account

“…Plant Physiol, 18(4): 2006 practical impact of physiological research on crop breeding for tolerance to drought. Most notably, breeding for various crops under water-limited environments including wheat in Australia, cowpea in India and Africa, sorghum and wheat in Israel, maize in Mexico, and cassava in tropical Africa and Latin America (Fischer and Turner, 1978;Richards and Passioura, 1981a,b;Morgan, 1984;Turner, 1986a;Blum and Sullivan, 1986;Blum, 1988Blum, , 1990Blum, , 1993Cock and El-Sharkawy, 1988;Blum et al, 1989;Blum and Pnuel, 1990;Sedgely and Belford, 1991;Fukuda et al, 1992Fukuda et al, -1993El-Sharkawy et al, 1992b;Hershey and Jennings, 1992;Bolaños and Edmeads, 1993a,b;Bolaños et al, 1993;Whan et al, 1993;El-Sharkawy, 1993Madeley, 1994;de Tafur et al, 1997;Richards, 2000;El-Sharkawy and Cadavid, 2002;Hall, 2004).…”

Environmental regulation and modelling of cassava canopy conductance under drying root‐zone soil water

“…However, for the purpose of precise water applications, it is essential to understand fully cassava's response to water deficit as well as to define water use and its regulations under different field conditions. Several studies reporting the response of cassava to water stress have been carried out on plants grown in large pots in the open , under a controlled environment such as screen or glass house (Alves and Setter, 2000) or under field conditions where water exclusion is artificial by covering the soil with plastic sheets Connor and Palta, 1981;El-Sharkawy and Cock, 1987;El-Sharkawy et al, 1992;El-Sharkawy and Cadavid, 2002). The results of such experiments need confirmation and calibration for the natural environmental conditions under which plants develop .…”