There was significant difference among the cassava genotypes for all the variables except fresh and dry root yield while seasonal effect was significant for only harvest index (Table 2). Significant genotype x season interaction was observed for only percentage of survival plants. The mean and other descriptive statistical parameters of the evaluated traits are summarised in Table 3. The evaluated cassava had plant architecture and root quality that ranged from 2 (UIC-17-2040) to 5 (TMS07/0593, UIC-17-108 and UIC-17-2174) and from 2 (TMS07/0593 and UIC-17-2031) to 4 (UIC-17-2040, UIC-17-627, UIC-17-208, and UIC-17-58), respectively. Meanwhile, the severity of CMD ranged from score of 1 (UIC-17-2428) to 5 (TMS30572). Varieties TMS07/0593 and TMS30572 had CMD scores of 2 and 5, respectively. Genotype UIC-17-2600 and variety TMS07/0593 produced the least number of roots (5) per plant
while genotype UIC-17-2031 had the highest number (11). Genotypes TMS07/0593 and UIC-17-58 had the least (58%) and highest (100%) rate of survival, respectively. The fresh and dry storage root yields range between 21 t/ha (TMS30572) and 39 t/ha (UIC-17-2031) and 4.9 t/ha (UIC-17-583) and 10.5 t/ha (UIC-17-2031), respectively. The mean harvest index (HI) across seasons ranged from 0.41 (UIC-17-2174) to 0.63 (UIC-17-2031). The mean root DMC ranged from 22.8–37.2% with an average of 29.0%. Genotype UIC-17-58 had the highest DMC (37.2%) while UIC-17-583 had the lowest DMC (22.8%). The results from the pairwise correlation among traits is presented in Table 4. The most strongly correlated traits were fresh (FRY) and dry root yield (DRY) (r = 0.87; P < 0.001). Root quality (Rootqlt) and DMC at harvesting had a significant positive moderate correlation (r = 0.50; P < 0.001). The FRY and DRY had negative correlation with CMD.
Table 2
Combined analysis of variance for survival rate, response to cassava mosaic disease, plant architecture, yield and yield components among some cassava genotypes at advanced breeding stage
Source of variation | DF | Arch | Rootqlt | DMC(%) | CMDSS | %Surv | FRY(kg/ha) | HI | DRY(kg/ha) | Roots/plt |
Genotypes (G) | 17 | 2.85*** | 1.54*** | 71.96*** | 5.80*** | 475.30*** | 91.88 | 0.01*** | 9.89NS | 9.27** |
Season (S) | 1 | 0.89 | 0.22 | 0 | 0.013 | 21.31 | 165.42 | 0.49*** | 15.27 | 13.84* |
GxS | 17 | 0.27 | 0.28 | 0 | 0.10 | 71.55** | 100.24 | 0.005 | 8.76 | 3.78 |
Residual | 35 | 0.34 | 0.40 | 20.49 | 0.09 | 23.43 | 76.06 | 0.004 | 7.103 | 2.92 |
*, **, *** significant at probability < 0.05, 0.01 and 0.001 levels, respectively; Arch = Plant architecture; Rootqlt = Root quality; DMC (%) = Dry matter content; CMDSS = Cassava Mosaic Disease Severity Score; %Surv = Percent survival rate; FRY = Fresh Root Yield; HI = Harvest Index; DRY = Dry Root Yield; Roots/plt = Number of roots per plant.
Table 3
Mean performance of traits of the 18 cassava genotypes evaluated in two seasons in Ibadan
Genotype | Arch | Rootqlt | DMC(%) | CMDSS | %Surv | FRY(kg/ha) | HI | DRY(kg/ha) | Roots/plt |
TMS07/0593 | 5 | 2 | 26.1 | 2 | 58 | 24.1 | 0.43 | 6.3 | 5 |
TMS30572 | 4 | 3 | 26.5 | 5 | 99 | 21.0 | 0.53 | 5.6 | 7 |
UIC-17-108 | 5 | 3 | 23.0 | 1 | 91 | 27.8 | 0.48 | 6.3 | 7 |
UIC-17-110 | 3 | 3 | 30.6 | 1 | 100 | 25.9 | 0.51 | 7.9 | 8 |
UIC-17-2009 | 4 | 3 | 29.3 | 1 | 100 | 31.4 | 0.49 | 9.3 | 7 |
UIC-17-2031 | 3 | 2 | 27.1 | 1 | 99 | 39.0 | 0.63 | 10.5 | 11 |
UIC-17-2040 | 2 | 4 | 27.7 | 1 | 100 | 25.9 | 0.49 | 6.8 | 9 |
UIC-17-2081 | 3 | 4 | 34.4 | 1 | 99 | 23.0 | 0.52 | 7.9 | 8 |
UIC-17-2174 | 5 | 3 | 33.2 | 1 | 100 | 26.4 | 0.41 | 8.7 | 10 |
UIC-17-2428 | 4 | 3 | 31.6 | 5 | 98 | 21.9 | 0.43 | 6.7 | 7 |
UIC-17-2576 | 4 | 3 | 26.8 | 1 | 76 | 27.6 | 0.53 | 7.8 | 7 |
UIC-17-2600 | 5 | 2 | 25.1 | 1 | 99 | 24.0 | 0.49 | 6.1 | 5 |
UIC-17-375 | 5 | 2 | 27.3 | 1 | 91 | 34.5 | 0.58 | 9.2 | 7 |
UIC-17-46 | 3 | 3 | 36.4 | 1 | 99 | 21.3 | 0.58 | 7.8 | 8 |
UIC-17-58 | 4 | 4 | 37.2 | 1 | 100 | 27.8 | 0.56 | 10.4 | 8 |
UIC-17-583 | 3 | 3 | 22.8 | 1 | 98 | 21.4 | 0.50 | 4.9 | 6 |
UIC-17-627 | 4 | 4 | 30.9 | 1 | 99 | 25.0 | 0.44 | 7.7 | 9 |
UIC-17-833 | 3 | 3 | 26.6 | 1 | 99 | 29.5 | 0.50 | 7.8 | 9 |
Mean | 4 | 3 | 29.0 | 1 | 95 | 26.5 | 0.50 | 7.6 | 8 |
CV (%) | | 0.27 | 0.18 | 1.21 | 0.13 | 0.35 | 0.23 | 0.38 | 0.27 |
Arch = Plant architecture (1–5 scoring); Rootqlt = Root quality; DMC (%) = Dry matter content; CMDSS = Cassava Mosaic Disease Severity Score; %Surv = Percentage of survival rate; FRY = Fresh Root Yield; HI = Harvest Index; DRY = Dry Root Yield; Roots/plt = Number of roots per plant; CV (%) = Coefficient of Variation.
Table 3
Correlation coefficients among traits of eighteen cassava genotypes evaluated in Ibadan in two seasons
| Arch | CMDSS | DMC | DRY | FRY | HI |
CMDSS | 0.14 | | | | | |
DM_% | -0.13 | -0.03 | | | | |
DRY | -0.02 | -0.22 | 0.36** | | | |
FRY | 0.03 | -0.22 | -0.12 | 0.87*** | | |
HI | -0.25* | -0.12 | 0.006 | 0.07 | 0.08 | |
Rootqlt | -0.17 | -0.06 | 0.50*** | 0.01 | 0.24* | -0.09 |
Arch = Plant architecture; Rootqlt = Root quality; DMC = Dry matter content; CMDSS = Cassava Mosaic Disease Severity Score; FRY = Fresh Root Yield; HI = Harvest Index; DRY = Dry Root Yield.