Performance and stability of a bi-parental sweet potato population for storage root yield, dry matter, starch and sugar content

Abstract

Sweetpotato production and utilization has taken a new trend, as farmers look more into value addition for an increased income. This means that root quality traits such as starch and sugar content that received less attention for decades must be of focus to meet particular end-user needs. This study assessed the performance and stability of USA bi-parental sweetpotato progenies for storage root yield, dry matter, starch and sugar content. The aim was to identify and select clones with outstanding performance and stable across locations for studied traits. Also, the study determined the heritability of dry matter, starch, amylose, amylopectin, sucrose, and glucose and fructose contents in the studied population. Fifty six bi-parental clones were evaluated along four local checks in replicated trials at three locations; Rwebitaba, Bulindi and Abi Zonal Agricultural and Development Institutes (ZARDIs). Significant differences (p ≤ 0.001) were observed among genotypes for all studied traits. Also, genotypes interacted significantly (p ≤ 0.001) with environment for all studied traits. This meant that there was an influence of environment on expression of studied traits and selection of outstanding clones was done per environment. Across locations, means for storage root yield, dry matter, starch, amylose, amylopectin, sucrose, glucose and fructose contents were 17.84 t/ha, 25.61%, 62.28%, 16.94%, 83.07%, 11.89 g/100g DW, 8.08 g/100g DW and 2.44 g/100g DW, respectively. Mean root yield and DM ranged from 1.67-43.70 t/ha and 14.10-32.20%, respectively. The highest mean root yield (38.16 t/ha) and DM (30.76%) were observed from clone 17 at Rwebitaba ZARDI and clone 51 at Abi ZARDI, respectively. Mean starch content ranged from 55.00-71.28% and clone 49 at Abi ZARDI had the highest mean starch content (70.27%). Mean amylose and amylopectin contents across locations ranged from 8.40-22.54% and 72.88-94.01%, respectively. The highest mean amylose (27.12%) and amylopectin (91.60%) contents were observed at Rwebitaba ZARDI from clones 5 and 17, respectively. The mean ranges for sucrose, glucose and fructose contents across locations were 2.70-20.75 g/100g DW, 2.50-15.25 g/100g DW and 0.55-5.57 g/100g DW, respectively. The highest sucrose, glucose and fructose contents were 34.15 g/100g DW (clone 78, 12 Abi ZARDI), 26.29 g/100g DW (clone 79, Abi ZARDI) and 12.32 g/100g DW (clone 65, Bulindi ZARDI), respectively. Dry matter, glucose, sucrose and fructose contents had 33.89%, 47.78%, 37.22%, and 35.55% of transgressive segregants to the high parents, respectively. The Additive Main effect and Multiplicative Interaction (AMMI) model assessed the stability of best performing clones across environments. AMMI discriminated Rwebitaba ZARDI (IPCA score = 4.90) and Abi ZARDI (IPCA score = -1.92) as the highest and least yielding environments, respectively. Based on AMMI stability values, the most stable clones for storage root yield, dry matter, starch, glucose, sucrose, fructose, amylose and amylopectin contents were 71 (ASV = 0.15), 56 (ASV = 0.03), 43 (ASV = 0.08), 3 (ASV = 0.04), 60 (ASV = 0.002), 66 (ASV = 0.15), 17 (ASV = 0.03) and 49 (ASV = 0.01), respectively. These genotypes additionally had exceptional performance for respective traits and are recommended for use as parents for breeding for these traits. Sweetpotato storage root starch was positively correlated with dry matter content (p<0.05; r2 = 0.08) and negatively correlated with all sugars (sucrose, r = -0.68; glucose, r = -0.21 and fructose, r = -0.26). Glucose content had a strong and negative correlation (p<0.01; r2 = 0.61) with sucrose content. Glucose and fructose contents were positively correlated (r2 = 0.18). These results implied that starch and dry matter, glucose and fructose contents could be effectively improved together. These combinations are good for production of high quality sweetpotato flour and puree as ingredients for bakeries and baby food processing industries. Broad sense heritability estimates (H2) for starch, dry matter, amylose, amylopectin, fructose, glucose, sucrose were 0.56, 0.59, 0.91, 0.91, 0.20, 0.19 and 0.08, respectively. This result meant that amylose and amylopectin, starch and dry matter and then the sugars; were highly, moderately and low heritable traits, respectively. This implied that except for sugar contents, where a large germplasm base may be needed to improve the heritability values, it is possible to breed for starch, dry matter, amylose and amylopectin contents in sweetpotato