Abstract
The objective of this work was to evaluate the effect of drought on genetic parameters and breeding values of cassava. The experiments were carried out in a completely randomized block design with three replicates, under field conditions with (WD) or without (FI) water deficit. Yield of storage roots (RoY), shoot (ShY), and starch (StY), as well as the number of roots (NR), and root dry matter content (DMC) were evaluated in 47 cassava accessions. Significant differences were observed among accessions; according to heritability, these differences had mostly a genetic nature. Heritability estimates for genotypic effects () ranged from 0.25±0.12 (NR) to 0.60±0.18 (DMC), and from 0.51±0.17 (NR) to 0.80±0.21 (RoY and StY) for WD and FI, respectively, as a consequence of greater environmental influence on WD. Selective accuracy was lower in WD, and ranged from 0.71 (NR) to 0.89 (RoY, DMC, and StY). However, genetic gains were quite high and ranged from 24.43% (DMC) to 113.41% (StY), in WD, and from 8.5% (DMC) to 75.70% (StY) in FI. These genetic parameters may be useful for defining which selection strategies, breeding methods, and experimental designs are more suitable to obtain cassava genetic gains for tolerance to drought.
Highlights
Cassava (Manihot esculenta Crantz) is a widely cultivated crop in many tropical countries in Africa, Latin America, and Asia, between 30oN and 30oS, whose coordinates coincide with the boundaries of many developing countries
A reduction of about 42 and 41% was observed for number of roots (NR) and dry matter content (DMC), respectively, when the cassava accessions were subjected to water deficit (WD)
In contrast to the other traits, the CVg was indicative of the presence of high genotypic variability among accessions, whose CVg ranged from 27.78 to 87.47% for shoot yield (ShY) and starch yield (StY), respectively, under water deficit conditions, and 33.60 to 54.64% for NR and StY, respectively, in the absence of water deficit (Table 3)
Summary
Cassava (Manihot esculenta Crantz) is a widely cultivated crop in many tropical countries in Africa, Latin America, and Asia, between 30oN and 30oS, whose coordinates coincide with the boundaries of many developing countries. Cassava is worldwide considered a staple food for over one billion people (The world cassava economy, 2000), so it has great importance for food security. It is a multi‐purpose, highly adaptable crop to different agricultural production systems. Cassava is adaptable to marginal soils with low fertility, and to irregular rainfall conditions, and as it holds a relatively stable productivity and flexibility for the harvesting process, the challenges posed by global climate change (both temperature and drought severity increasing) have caused negative impacts on this crop productivity. In 2012 the average root yield of Northeastern Brazil was about 10 times lower than the crop’s potential, estimated at 90 Mg ha‐1 under experimental conditions (El‐Sharkawy, 2005). The main factors contributing to this low productivity is the use of traditional varieties with low tolerance to drought and the use of marginal soils with low fertility
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