Evaluation of agronomic performance of beta-carotene rich ( yellow fleshed ) cassava varieties in Nigeria

Twenty-five yellow fleshed cassava varieties including three checks (two improved and one local) were evaluated in a randomized complete block design with four replications in three locations in Nigeria. Tuber yield, dry matter content, root size, fiber content, harvest index, sprouting and vigor of the varieties evaluated were all significant at 0.05 significant levels across the locations. Taste, color of unexpanded leaves, height at branching, and internode length were not significant. In Ibadan, plant height, vigor and root size were not significant. In Mokwa, plant height was not significant. Traits such as dry matter, mealiness and taste were significant. In Onne, dry matter was not significant. Clones such as 01/1413, 01/1442, 01/1663, 98/2132, 01/1277, and 01/1235 were stable across locations, 94/0330 had the highest dry matter (38%) which was better than the best check 30572 (37%). All clones were resistant to cassava mosaic disease, cassava bacteria blight, cassava green mites and cassava anthracnose disease vector infection and to the spread of the pathogens within the plant and across locations. Clones 01/1115, 011413, 01/1663, and 01/1335 had high beta-carotene content of range 7 on a color chart. Clones 01/1368, 01/1371, 98/2132, 90/01554 and 94/0330 had dry matter values ranging from 30 to 38%; these were acceptable values. In terms of yield, the best clones were 01/1368 (26 t/ha), 98/2132 (25 t/ha) and 01/1663 (24.5 t/ha). For gari yield clone 01/1649 gave 25%; 94/0330 gave 23% and 90/01554 gave 23%. They were better than the best check, with 22% garri yield. Cultivating cassava with yellow pigmented root flesh is a valid strategy to solve the problem of improving the nutritional value of the diet in the region where cassava is a staple food.


INTRODUCTION
Cassava (Manihot esculenta Crantz) is a major staple food in Nigeria, consumed daily by more than 100 million people.The global production of cassava in 2014 was 278.7 million tons with an estimate of 281 million tons for 2015 and 288.4 million tons for 2016 (FAO, 2016).From available records, Nigeria still stands out as the world's largest producer of cassava with a progressive production pattern that increased from 42.5 million metric tons *Corresponding author.E-mail: naadetoro@gmail.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License in 2010 to 54 million metric tons in 2012 with average production output of 12.2 t/ha in 2010 increased to 14.03 t/ha in 2012 (FAOSTAT, 2013).Total area harvested of the crop in 2012 was 3.85 million ha (FAOSTAT, 2013).The diverse uses of cassava largely explain its popularity in the tropics.In Africa, most cassava produced is used for food consumption with 50% in processed form and 38% in the fresh and/or boil form; and 12% is used for animal feed.The diverse uses of cassava largely explain its popularity in the tropics.However, many pathogens and pests reduce cassava yields, especially in Africa including Nigeria.Diseases such as cassava mosaic disease (CMD), transmitted by a whitefly (Bemisia tabaci) vector and spread by infected cuttings, cassava brown streak virus disease (CBSD), cassava bacterial blight (CBB; Xanthomonas axonopodis pv.manihotis), and anthracnose (CA; Colletotrichum gloeosporoides) are among the most important diseases.Pests with a wide African spread are the cassava mealybug (CM; Phenacoccus manihoti), African root and tuber scale (Stictococcus vayssierei), cassava green mite (CGM; Mononychellus tanajoa) and nematodes (particularly Meloidogyne species) (Abaca et al., 2014).
Over-dependence on cassava-based diets may result in poor health, stunted growth, reduced capacity for physical activity, and in extreme cases, a high incidence of anaemia, corneal blindness, and compromised immunity (Saltzman et al., 2013).However, while the commonly available white cassava can provide most of the body's daily energy requirements, it does not provide sufficient proteins, essential micronutrients and vitamin A, required for a healthy and productive life.Vitamin A deficiency can impair the body's immunity to infectious diseases and cause eye defect that can lead to partial or complete blindness.Nearly one in three Nigerian children under five and one-quarter of all pregnant women in the country are vitamin A deficient (FAO, 2014).Billions of people around the world suffer from hunger and 'hidden hunger' or micronutrient malnutrition.Around 805 million people were considered chronically undernourished over the 2012 to 2014 period (FAO, 2014).
Those that do not get enough vitamin A and micronutrients (zinc and iron) from the foods they eat face severe health complications and even death.Micronutrient malnutrition can lower intelligence quotient (IQ), cause stunting and blindness in children, lower resistance to disease in both children and adults, and increase risks for both mothers and infants during childbirth.Malnutrition is the underlying cause of 45% of child deaths under the age of 5 (WHO, 2015).In 2013, an estimated 161 children under the age of 5 were stunted (below median height for age) and another 51 million were wasted (below median weight for height) (Thompson et al., 2013).This is especially true in regions with prolonged dry seasons that limit production and access to alternative sources of micronutrients such as fresh vegetables (Von Grebmer et al., 2014).
Pro-vitamin A varieties that are presently available provide up to 40% of the daily recommended vitamin A intake for children less than 5 years old (De Moura et al., 2015).Nevertheless, new crosses to select varieties with an even higher content of β-carotene varieties are being generated through recurrent selection breeding scheme (Sánchez et al., 2014).This paper reports on the agronomic performance and suitability for quality garri production of adapted beta-carotene rich (Pro-vitamin A) cassava clones in diverse locations (Ibadan, Mokwa, and Onne) in Nigeria.

MATERIALS AND METHODS
The fields were plowed, harrowed and ridged at 1 m apart.Mature stem cuttings (0.25 m long) of 25 genotypes including three checks were planted on plots of four ridges (Table 6).The ridges were about 50 cm high, each 10 m long and spaced 1 m apart.The plot size was 4 m × 10 m (40 m 2 ).The experimental design was a randomized complete block with four replications.Blocking was done according to the topo-sequence of the field.The plots were weeded six times after planting and no fertilizers were applied.The experiment was conducted in three locations (Mokwa, Ibadan, and Onne) in Nigeria for two seasons (Figure 1).Mokwa (Niger State) is located in the southern Guinea savanna zone with latitude 9°18'N and longitude 5°04'E at about 457 m altitude about sea level (masl) and has a unimodal rainfall pattern with an annual total of 1069 mm, falling between June and October.Radiation is about 450 MJ m -2 year -1 .The soil is alfisols and ultisols.The second environment was Ibadan (Oyo State) with latitude 7°31'N and longitude 3°54'E and is located in the forest savanna transition zone at about 150 masl.It is characterized by a bimodal rainfall also averaging 1300 mm annually, most of which falls between May and October.Radiation is about 5285 MJ m -2 year -1 .The soil is slightly acidic alfisols.The third test environment, Onne (Rivers State), latitude 4° 43'N, longitude 7° 01'E, and 10 masl is in the rainforest zone, has a unimodal rainfall pattern with an annual average of 2400 mm falling between February and December.Relative humidity remains high throughout the year, with average values ranging from 78% in February to 89% in July and September.This site receives an average 4 h of direct sunshine daily, reaching 5060 MJ m -2 year -1 .The soil is representative of highly leached acid ultisols.

Data collection
One month after planting, data was collected on Cassava Mosaic Diseases (CMD).Cassava Bacterial Blight (CBB) was scored monthly until 6 months after planting.Cassava anthracnose disease (CAD) was scored for 6 months after planting and monthly till 9 months after planting.Cassava green mite (CGM) was scored for between January and February.That was when it normally appeared and reached its peak period.The scale used for scoring was 1 to 5 (1= zero attack or resistance; 2 = little attack or little resistance; 3 = medium or moderate resistance; 4 = high attack or susceptible; and 5 = very high attack or highly susceptible).
Number of cassava plants sprouted at 1 MAP was counted and scored as number sprouted or germinated over total number planted.The plant growth vigor at one month after planting was rated visually, per plot basis, using 3 for low vigor, 5 for intermediate vigor, and 7 for highly vigor cassava plants.Root size was categorized into small, moderate and large with the scale 3 = Dry matter content of the tuberous root is an important character for the acceptance of cassava roots by consumers who boil or process them.Fresh sample of 100 g were taken from each clone in each replicate and dried at 70°C in oven and they were reweighed after 72 h of drying and have attained constant drying.The dried sample was weighed and root dry matter content percentage was calculated as the ratio between fresh weight (FW) and dry weight (DW), that is, DM (%) = (DW/FW) × 100.
For fresh root yield, all the underground roots per plot were weighed in kilogram (kg) and converted to tones per hectare (t/ha).
Garri yield is the weight of garri (a dried granule gotten from 10 kg of fresh cassava roots of each clone, after being peeled, grated, fermented, dewatered, fried and sieved) measured in kilogram.Harvest index was calculated by (root weight / root weight + shoot weight) × 100.

Statistical analysis
The data collected were subjected to analysis of variance (ANOVA) using General Linear Model (GLM) procedure for randomized complete block design in statistical analysis system (SAS, 1996) to test for the treatment of effect and significant interaction of the variables considered.The results of the different experiments were subjected to combined analysis of variance to examine genotype by environment interaction (G × E) effect and standard errors were calculated for each trait.

Plant height
Plant height was measured and the mean was calculated.The analysis of variance (Table 4) of the plant height indicated significant differences among the clones at probability level of 0.05 in Onne with CV of 17%, while in Ibadan and Mokwa a non-significant difference was observed.

Vigor
The result of vigor in G × E (Table 5) was very significant with CV of 17.90%.In Ibadan, the CV was 10.66% and not significant.In Onne, the CV was 21% and showed significance and in Mokwa it was 18% and significant.This result shows that vigor is a stable trait and not affected by the environment (Table 4).

Fresh tuber yield
This was very significant among the clones.From G × E analysis, the CV (31.28%) from combined analysis (Table 3) indicated a wide spread of the difference in the mean of the yield among the genotypes and across the locations.The yield could be considered stable at Onne with a high yield of about 24 t/ha.While Ibadan and Mokwa had yield of 15 t/ha (Table 4).

Dry matter
Dry matter content is a very important trait for acceptability of the cassava by consumers.It was significant in Ibadan at 0.05 (Table 4), with CV of 11.17%.In Onne, it was not significant.However, in combined analysis it was significant at a probability level of 0.001 with a CV of 12.88% and has a mean ranged from 28 to 35 across the locations (Table 5).This shows high dry matter percentage.Edoh et al. (2018) also reported higher dry matter percentage of 33.5% in one of her findings.
Cultivating cassava with yellow-pigmented root flesh is a valid strategy to solve the problem of how to improve the nutritional value of the diet in the regions where cassava is a staple food.
From the analysis of the 25 accessions, a significant (p=0.01)carotene content was determined within the range of variability for carotene concentration in the roots.A few genotypes were high up to 7 when a color chart that ranges from 1 to 8 was used.Olapeju et al. (2013) also reported higher carotene concentration in some of the varieties.
Locations accounted for most of the G × E interaction significance (p=0.001) which reflects the differences in soil types in which the clones were grown.This suggested that for the evaluation of cassava clones, it might be more appropriate to test genotypes over space rather than over time.This experiment was able to identify stable clones across locations such as 01/1413, 01/1442, 01/1663, 98/2132, 01/1277, and 01/1235.
Tuber yield, dry matter content, root size, fiber content, harvest index, sprouting and vigor of the varieties evaluated were all significant among the clones in the combined analysis (Table 5).Taste color of unexpanded leaves, height at branching, leaf area, and internode length were not significant.Overall, dry matter content showed that clone 94/0330 (yellow root) had the highest dry matter (38%), which was better than the best check 30572 (37%), followed by the clones 90/01554, 01/1335, 01/1368 and 01/1371 with values ranged from 30 to 35% (Table 3).However, in Ibadan (Table 4), plant height, vigor, mealiness and root size were not significant.In Mokwa (Table 4), sprouting and plant height were the only traits that were not significant.In Onne (Table 4), dry matter, sprouting, mealiness and taste were not significant.
In terms of disease resistance, all the clones evaluated were resistant to CMD and CBB vector infection and to the spread of the pathogen within the plant and across the locations (Tables 1 and 2).

Conclusion
The results showed that all clones were resistant to CMD, CGM and CAD vector infection and to the spread of the pathogen within the plant and across the locations.In terms of beta-carotene, clones 01/1115, 01/1413, 01/1663, and 01/1335 had high beta-carotene content, indicating the best genotypes for recommendation.In terms of dry matter content, clone 94/0330 (yellow root, 38%) was better than the best check 30572 (37%), clones 90/01554, 01/1335, 01/1368 and 01/1371 had dry matter values ranged from 30 to 35%, which were acceptable values.In terms of garri yield; yield per 50 kg of fresh root submitted for garri showed that clones 01/1649 (25%), 94/0330 (23%), and 90/01554 (23%) were better than the check 30572 (22%).Most of the clones evaluated were sweet, some were bland and nonwas bitter in terms of taste. In

Figure 1 .
Figure 1.Map of Nigeria showing the three experimental locations.

Table 2 .
Mean performance of (combined analysis) G × E of beta-carotene in cassava genotypes evaluated for multilocation trial at Ibadan, Mokwa and Onne for disease pest effects.

Table 3 .
Mean performance of G × E beta-carotene in cassava genotypes evaluated for multilocational trial at Ibadan, Mokwa and Onne for agronomic traits effect.

Table 5 .
Mean performance of G × E of 25 beta-carotene cassava evaluated for multilocational trail at Ibadan, Mokwa and Onne for agronomic traits effect.