Genotype × Environment Interaction and Stability Analysis for Selected Agronomic Traits in Cassava (Manihot esculenta)

Cassava (Manihot esculenta Crantz) is an important starchy root crop utilized for human consumption, animal feed and various industrial applications [1]. The starchy storage roots of cassava are important source of dietary energy in sub-Saharan Africa (SSA) as they provide more returns per unit of input than any other staple crop [2–4]. Cassava serves as food security and income generation crop for resource poor farmers due to its tolerance to climate changes such as erratic rainfall and poor soil fertility. In Sierra Leone, cassava is the second most important staple crop after rice. The cassava root production in the country has increased from 82,500 tons in 1970 to 4.59 million tons in 2019 growing at an average annual rate of 12.08% [5]. However, on-farm cassava yields are significantly lower than the potential yields of improved varieties estimated at > 25 t ha-1 [6]. For instance, in 2019, 59,660 ha were cultivated to cassava by 101,021 households, producing 817,342 MT [6]. A wide yield variability ranging from 6.5 MT ha-1 to 33.9 MT ha-1 exists among genotypes, with an average yield (14.5 MT ha-1) below 50% relative to yields obtained under good agronomic practices [6]. Cassava is cultivated in all regions of Sierra Leone due to its easy propagation, value of cultivation and utilization.

Despite its enormous significance, increased cassava productivity is limited by a number of biotic and abiotic factors [7]. For instance, cassava green mite attack can cause about 15 and 73% yield losses in resistant and susceptible genotypes of cassava, respectively Bellotti [8], whereas about 88% yield loss can be due to cassava mealybug infestation insusceptible genotypes [9]. Low crop yields are also caused by low yielding varieties, environmental variability and poor environmental management or use of elite agronomic packages.

The performance of any character is a combined result of the genotype (G), the environment (E) and the interaction between genotype and environment (GE) [10]. The GEinteraction (GEI) exists when the responses of two genotypes to different levels of environmental stress are inconsistent. The GEI and yield-stability analyses have become increasingly important for measuring cultivar stability and suitability for cultivation across seasons and ecological zones [11]. Multi-environment trials (METs) have been found to be important in plant breeding for studying cultivar stability and predicting yield performance of cultivars across environments [12].

Several authors have noted the effects of GEI in cassava. Tumuhimbise et al. [13] reported a non-significant GEE effect for early fresh storage root yield (FSRY). Moreover, the effect of GEI on dry matter content (DMC) has been well noted [14,15]. In Sierra Leone, there is dearth of information of the GEI effects and stability performance of putative cassava genotypes developed for key agronomic traits (yield, disease resistance, root dry matter content, starch content and harvest index). A good understanding of GEI effects is useful to plant breeders for selection of suitable genotypes for specific environments. The determination of stability performance of genotypes across varying test sites requires use of specific tools and methods [10]. The univariate, bivariate and multivariate techniques are the common methods often utilized for stability analysis [16]. The additive main effects and multiplicative interaction (AMMI) multivariate analytical technique is the most widely used method for GEI assessment [10]. The AMMI method effectively captures a large portion of the GEI sum of squares [17]. The identification of yield-contributing traits and knowledge of GEI and associated yield stability are important considerations inbreeding new cultivars with improved adaptation to the environmental constraints that prevail in target environments [18]. Thus, the objective of this study was to determine the magnitude of Genotype × Environment Interaction and stability performance of genotypes for its effective utilization to improve key agronomic traits in cassava.