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In Mozambique, sweetpotato plays a significant role in rural areas, where the farmers use it to feed their families and as an income. In this study, we aimed to investigate the performance of different sweetpotato varieties in Niassa, Mozambique. The trial was set up in Malulu, Sanga district, located 60 km away from Lichinga, capital of Niassa, Mozambique. In Sanga, the rainy and hot season occurs from December to March, and the dry and cold season is from May to October. In this trial, the treatments correspond to sweetpotato varieties. We used the randomized block design with 12 sweetpotato varieties and 3 replications. The evaluated traits were as follows: weevil damage, roots commercial yield, roots non-commercial yield, total yield, and vine yield. Regarding statistical analysis, the results per trait were submitted to the Bartlett test of homogeneity of variances and Shapiro-Wilk normality test, and then the analysis of variance and means comparison using the Scott-Knott test when necessary was performed. All the statistical analysis was conducted at 5% on the R programming language. For commercial and total yield, the varieties Local, Sumaia, Olga, and Alisha presented the best results. Esther and Irene were the varieties most attacked by weevils.

Introduction

In Mozambique, agriculture is the main population’s economic activity, several crops are grown in the rural areas, with special attention to maize, cassava, rice, beans, and sweetpotato (Ipomoea batatas [L.] Lam). Farmers from rural areas prefer growing sweetpotato because it is a rustic, easy to maintain, and drought-tolerant crop with a relatively low production cost, minimum investments, and high returns per unit area [1]. Sweetpotato is among the world’s most important, versatile, and under-exploited food crops, with over 90 million tons in annual production, contributed mostly by Asian and African countries [2]. This crop is positioned as the sixth most major food crop in the world and the fifth most essential food crop on a fresh weight basis in developing countries after rice, wheat, maize, and cassava [3]. In Mozambique, sweet potato is mainly grown in Zambézia province, with a production of about 146.476 tons, followed by Tete, with a total production of 85.955 tons [4].

Sweetpotato is grown in numerous tropical and subtropical countries for the consumption of its edible leaves, vines, and roots with huge special nutritional and health-promoting properties for human diet and animal feed, such as carotenoids, flavonoids, anthocyanins, minerals, carbohydrates, phenolic acids, and fibers [5], [6]. Sweetpotato is not only grown for food and fodder purposes but is also processed into indispensable raw materials for the production of starch, alcohol, and natural pigments [6], [7]. Several different health benefits, such as antioxidant, cardioprotective, anti-inflammatory, anti-cancer, anti-diabetic, antimicrobial, and anti-obesity. In addition, consumption of the sweetpotato varieties containing beta carotene contributes to a reduction in vitamin A deficiency, especially among children under five and pregnant women [8].

The color of sweetpotato skin ranges from white, cream, yellow, orange, pink, and red to purple, while flesh colors may be white or various shades of cream, yellow, orange, or even purple [9], [10]. In Mozambique, over the past years, a lot of research related to sweetpotato breeding has been conducted. The aim of the sweetpotato breeding program in Mozambique is to release varieties that are drought tolerant, have high root yield, have high dry matter content, have high nutritional content, and are more resistant to pests.

The purpose of the current study was to investigate the performance of different sweetpotato varieties released jointly by the International Potato Center and the Institute of Agronomic Research of Mozambique from a breeding program under the agro-ecological conditions of Niassa province.

Materials and Methods

Site Characterization

The trial was set up in Malulu, Sanga district, located 60 km away from Lichinga, capital of Niassa, Mozambique. In Sanga, the rainy and hot season occurs from December to March, and the dry and cold season is from May to October. The average annual precipitation is between 1000 to 1200 mm; Sanga’s soils are mostly clayey, red, deep, and well-drained, associated with humid and subhumid climates [11]. Figs. 1 and 2 show the average monthly precipitation and temperature during the trial period.

Fig. 1. Average monthly precipitation during the trial period.

Fig. 2. Temperature during the trial period.

Soil tillage and harrowing were performed in the beginning of October 2022. Soil fertilization was not performed in order to mimic local farmers’ production conditions.

Sweetpotato planting was performed in the second half of October. Sweetpotato planting material (sweetpotato vines) was cut in pieces of 30 cm length and planted on top of ridges with a planting spacing of 90 cm between ridges and 30 cm between plants within the same ridge. Irrigation was only performed for three weeks in the beginning of the trial to guarantee adequate plant establishment. Afterwards, the plants were maintained under rainfed system until harvest period. Figs. 1 and 2 show the average monthly precipitation and temperature during the trial period.

Treatments

In this trial, the treatments were sweetpotato varieties whose characteristics are summarised in Table I. We used the randomized block design with 12 sweetpotato varieties and 3 replications. Each variety was planted in plots with 5 lines (ridges), each line with a 4.5 m length.

Varieties Type of plant Predominant color in the branches Color of the mature leaves Predominant shell color Main pulp color
Irene Semi-erect (75–150 cm) Totally purple Green Red Light orange
Sumaia Semi-erect Green Green with young purplish leaves Cream Deep orange
Delvia Semi-erect Green Green Purple Orange with yellow
Gloria Prostrate Unknown Unknown Unknown Orange/yellow
Esther Semi-erect Light green Light green Purple Intermediate orange
Alisha Scattered Green Green Intermediate orange Orange pulp
Caelan Scattered (151–250 cm) Green Green Red Purple-white pigmentation
Ken Semi-erect (75–150 cm) Green Green Red Intermediate orange
Palmira Semi-erect (75–150 cm) Green Green Orange Intense Orange
Olga Scattered (151–250 cm) Moderately dark purple Green with purple edges Orange chestnut Strong purple pigmentation
Super-Margarete Semi-erect (75–150 cm) Totally purple and dark Green with purple veins on the top page Red Strong purple pigmentation
Local Unknown Green Green Cream White/cream pulp
Table I. Morphological Features of the Sweetpotato Varieties

Measured Traits

Weevil Damage

Weevil damage was determined through scoring using a scoring mechanism/system developed by CIP (2019). The scores range from 9 to 1, where 9 to 8 severe damage (>60% of the roots are affected); 7 to 6 severe (30%–60% of the roots are affected); 5 to 4 moderate (10%–30% of the roots are affected); 3 to 2 weak (few roots affected) and 1 no roots affected [14].

Roots Commercial Yield

Commercial root yield was determined by selecting and weighing roots with over 100 g weight, free from any kind of damage. This trait was computed in tons/hectare.

Roots Non-Commercial Yield

Non-commercial root yield was determined by weighing roots below 100 g weight, and those affected by pest and disease damage. This weight was computed in tons/hectare.

Total Yield

To compute the total root yield, we summed the commercial and non-commercial roots yield, computed in tons/hectare.

Vine Yield

We also computed the vine yield, the vine yield corresponds to the weight of the plants shoots, computed in tons/hectare.

Statistical Analysis

The results per each measured trait were submitted to the Bartlett test of homogeneity of variances and Shapiro-Wilk normality test, and then the analysis of variance and means comparison using the Scott-Knott test when necessary was performed. The advantage of the Scott-Knott test is that it doesn’t allow the same treatment to belong to two or more different groups at the same time, reducing the ambiguity in the treatment comparison. All the statistical analysis was conducted at 5% in the R programming language [15].

Results and Discussion

Correlations among the measured traits are presented in Fig. 3. A significant and high correlation was only observed between commercial roots yield and total roots yield.

Fig. 3. Correlations among the traits.

For the weevils attack, the results are presented in the boxplot in Fig. 4. Esther and Irene were the varieties most attacked, followed by the varieties Local and Palmira; for the other varieties, the levels of attack were similar, being classified in a level 1 of attack, i.e., no roots affected.

Fig. 4. Weevil's level of attack.

Different results were observed by [16] in a study about 9 sweet potato varieties in Mozambique, where the varieties Alisha and Super-Margarete had a weevils level of attack of 4 on a scale from 1 to 9. This study was conducted in a rainy season (Fig. 1), weevils attack is more abundant and cause more damage in the dry season than in the rainy season, as in the dry season, the soil forms some cracks which facilitate the roots attack by the weevils [17]. It’s important to highlight that weevil control is important for market-oriented producers to enhance the percentage of marketable roots [18].

Results about commercial, non-commercial, and total yield are presented in Table II. Regarding commercial yield, the highest yields were observed for the varieties.

Varieties Vine yield Non-commercial yield Commercial yield Total yield
Irene 20.78 c 4.70 WD 13.77 b 18.47 b
Sumaia 37.64 b 3.67 29.24 a 32.92 a
Delvia 28.22 c 2.48 16.74 b 19.23 b
Gloria 33.20 b 4.96 16.42 b 21.39 b
Esther 24.48 c 4.47 15.13 b 19.61 b
Alisha 22.03 c 4.05 24.59 a 28.64 a
Caelan 49.39 a 4.22 6.95 c 11.17 c
Ken 45.53 a 5.85 11.80 b 17.66 b
Palmira 10.47 c 3.10 9.00 c 12.10 c
Olga 37.57 b 5.25 19.08 a 24.34 a
Super-Margarete 19.68 c 4.43 6.96 c 11.39 c
Local 36.40 b 3.86 26.81 a 30.67 a
Table II. Commercial, Non-Commercial, and Total Yield

Sumaia, Local, Alisha, and Olga, and no significant differences were observed for these varieties; however, numerically, Sumaia presented the highest yield (29.24 tons/hectare). The lowest yields were observed in the varieties Super-Margarete, Caelan, and Palmira.

No significant differences were found for non-commercial yield, but it’s important to highlight that the highest value was observed in the variety Ken and the lowest in the variety Delvia. As for the total yield trait, Sumaia variety presented the highest value (32.92 tons/hectare), no significant differences were observed among Sumaia, Alisha, Olga, and Local varieties. Lowest values for total yield were observed for the varieties Super-Margarete and Caelan and Palmira. Total yield followed the same trend as the commercial yield of both traits, which are positively correlated (Fig. 3). Similar results were observed by [16] in a study about a proposal to release 9 sweetpotato varieties, where Alisha variety reached 25.28 tons/hectare of total yield in Chókwe. In a study conducted in Lichinga, in 2022, Irene variety surpassed (23.07 tons/hectare) Esther variety (5.79 tons/hectare) [19]. However, variety Esther in the previous study presented a much lower total yield (5.79 tons/hectare) when compared to its yield in the current study (19.6 tons/hectare); these differences may be explained by differences in the soil properties and climate conditions as our study was conducted in Sanga district.

In the current study, the varieties Sumaia, Delvia, Gloria, Alisha, Olga, and Local surpassed 15.57 tons/hectare for commercial yield.

It’s important to note that different authors use different criteria to distinguish commercial roots from non-commercial roots. According to Filgueira [20], the sweetpotato is considered commercial when it presents roots with average mass ranging from 200 g to 400 g, this a classification different from the one used in our study.

The differences in commercial root yield could be attributed to the genetic variations among the sweetpotato varieties in partitioning photosynthesis [21]. In our study, we did not conduct soil analysis to gain information on the soil’s nutritional condition; according to Pedrosa et al. [22], the total productivity of roots is dependent on the genotype, soil and climate conditions, and cycle duration.

For vine yield, no significant differences were observed between Caelan and Ken varieties being the varieties with the highest values were observed by the Caelan and Ken varieties. The lowest values were observed for Palmira variety (10.47 tons/hectare). However, Palmira presented a vine yield of 50.47 tons/hectare in a study in Chókwe [12].

Conclusion

For farmers with similar agroecological conditions as that of Sanga district, in Niassa, the varieties Olga, Sumaia, Alisha are the recommended improved sweetpotato varieties.

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