4.3. Results
4.3.1 Germplasm reaction to GRD under high disease pressure
(primary branches on the main stem), number of pods (total number of pods per plant) and number of kernels (average number of kernels contained in 10 pods per plot). Data on yield and related traits were recorded on per plot basis as follows; pods per plot which were harvested and sun dried to approximately 8-10% moisture content and then weighed to determine pod yield. Thereafter, the pods were shelled to determine kernel yield). Later, 100 seed mass weight which is the weight of 100 kernels from pods randomly drawn from each plot was weighed and shelling percentage was determined which is a 100g pod sample from each plot which was shelled and weighed. The formula for shelling % = (seed weight ÷ pod weight before shelling) x 100.
4.2.5 Data analysis
Disease incidence data were transformed by arcsine before analysis in order to stabilize the error variance (Gomez and Gomez, 1984). Data on GRD, yield and yield components were analysed in REML using Genstat 12th Edition statistical package (Payne et al., 2009).
Genotypes were considered fixed effects, while year, genotype x year interaction, replication and blocks were fitted as random effects. The model for REML analysis was as follows;
Yijkl = µ + Gi + Sj + GSij + Rk + Bl + ɛijkl
Where: µ is the general mean, G are the genotype effects, S are the year effects, GS are the interaction effects of genotype and year, R are replication effects, B are the block effects and ɛ is the random term.
Correlations were done using Pearson’s correlation procedure to determine the relationship between GRD incidence and agronomic performance. Analysis of variance was performed on aphid data counts following the standard procedure for analysing RCBD.
Table 4.2. There were highly significant (P≤0.001) differences between genotypes for all traits. Highly significant (P≤0.001) differences due to seasons were also observed for all traits except for plant height and number of primary branches.
Mean values of PDI, yield and other traits combined over the two seasons is presented in Table 4.3 and Appendix 4.1. PDI values ranged from 0% to 82.7% with a mean of 50%. Five genotypes were highly resistant, 6 resistant, 26 moderately resistant and 63 susceptible. The highly resistant genotypes included ICG 14705, ICG 9449, ICGV-SM 05701, MW 2694 and MW 2672. They showed no symptoms of GRD up to the end both the seasons. Farmer preferred genotypes namely Chalimbana, CG 7, and Tchayilosi were all moderately resistant having PDIs of 46.5%, 48.8% and 49.8% respectively while Kalisele was susceptible with a PDI of 64%. The resistant checks (ICGV-SM 90704 and ICG 12991) and the susceptible check (JL 24) were moderately resistant with PDIs of 32.7%, 35.8% and 46.2% respectively.
Most of the susceptible materials dried before the end of the season especially in 2010/11 season due to the severity of the disease infection.
The mean values for pod yield over the seasons was 289.1 kg/ha with genotypes varying from 57.4 kg ha-1 (ICG 1142) to 969.4 kg ha-1 (ICG 14705). The susceptible check JL 24 had yields up to 33% and 73% higher than the resistant checks, ICGV-SM 90704 and ICG 12991, respectively. Three of the highly resistant genotypes, (ICG14705, ICGV-SM 05701 and MW 2672) were the top yielding genotypes producing 969.4 kg ha-1, 736.1 kg ha-1 and 727.8 kg ha-1 respectively while ICG 9449 produced (166.7 kg ha-1) 42% lower than the mean. Among the farmer preferred genotypes, Chalimbana produced (417.4 kg ha-1) 44.3%
higher than the overall mean compared to Kalisele which produced (174.1 kg ha-1) 39.7%
lower than the overall mean. The other traits with variations among genotypes included plant height (from 100 to 378 mm), number of primary branches (from 4 to 10 branches), number of pods per plant (from 2 to 18.8 pods), pod length (from 17.0 to 37.0 mm), number of kernels per pod (2 to 3 kernels), 100 seed mass weight (9.1 to 50.6g), shelling % (7.7 to 76.7%), and kernel yield (from 5.91 to 682.8 kg ha-1).
Correlations among traits recorded for genotypes grown under high disease pressure are presented in Table 4.4. PDI was negatively correlated with pod yield (r = -0.4, P˂0.001), kernel yield (r = -0.3, P˂0.001), and number of pods per plant (r = -0.4, P˂0.001). The correlation between PDI and number of seeds per pod was positive and significant (r = 0.20, P˂0.001). However, no significant correlation between PDI and plant height was observed.
Table 4.2: Wald statistic for percent disease incidence (PDI), yield and other traits of 100 groundnut genotypes evaluated for 2 seasons under high disease pressure
Wald statistic
Source df
PDI Height (mm)
Number of primary branches
Number of pods per
plant
Pod length (mm)
Number of seeds per
pod
100 seed mass
weight (g) Shelling %
Yield (kg ha-1)
Kernel yield (kg ha-1) Replication
Genotype
1
99 402.8*** 400.5*** 527.3*** 529.3*** 527.4*** 1009.7*** 344.1*** 395.9*** 344.3*** 289.5***
Year 1 930.1*** 0 0 380.4*** 67.5*** 42.5*** 11.3*** 36.2*** 10.0 3.1
Genotype x
Year 99 163.2*** 0.7 2.2 252.6*** 205.9*** 315.6*** 107.8 117.1*** 109.3 90.5
Error 198
Note: *** Significant at P˂0.001, df = degrees of freedom
88
Note: HR = highly resistant, R= resistant, MR = moderately resistant and S = susceptible.
Genotypes presented in this table comprise of all those found to be highly resistant to GRD, all the farmer preferred varieties, the checks and other 3 randomly selected genotypes which were either resistant or susceptible.
Table 4.3: Genotypic means for percent disease incidence (PDI), yield and other traits over 2 seasons under high disease pressure Traits
Genotype
PDI
% Inference
Height (mm)
Number of primary branches
Number of pods per plant
Pod length
(mm)
Number of seeds per
pod
100 seed mass weight (g)
Shelling
%
Pod yield ( kg ha-1)
Kernel yield (kg ha-1)
ICG 14705 1.7 HR 254 7.9 12.8 24.4 2.0 41.1 68.4 969.4 682.8
ICG 9449 0.0 HR 195 5.3 8.9 22.7 2.0 21.9 48.7 166.7 98.6
ICGV-SM 05701 0.0 HR 170 7.6 16.5 26.7 2.0 39.7 59.6 736.1 462.9
MW 2672 0.0 HR 178 5.8 11.6 27.0 2.0 40.1 55.9 727.8 414.1
MW 2694 0.0 HR 157 7.7 15.8 30.2 2.1 43.4 55.7 549.3 313.2
MW 2684 22.7 R 346 4.7 12.0 27.0 2.0 35.4 68.1 586.8 413.5
MW 618 24.2 R 238 5.0 13.2 23.1 2.0 27.5 68.4 500.7 343.4
CG7 48.8 MR 201 8.1 9.2 30.8 2.0 43.3 58.7 342.4 204.1
CHALIMBANA 46.5 MR 228 7.7 7.2 30.8 2.1 43.4 57.0 417.4 242.7
Tchayilosi 49.3 MR 196 5.8 8.8 28.3 2.2 31.9 56.8 409.0 248.6
Kalisele 64.7 S 162 7.1 6.3 23.4 2.0 32.9 33.0 174.1 56.0
MGV5 57.6 S 182 6.7 8.7 25.2 2.0 40.2 42.0 181.9 106.8
Checks Resistant
ICG 12991 35.8 MR 300 5.9 11.6 22.0 2.0 26.1 67.2 348.6 236.4
ICGV-SM 90704 32.7 MR 209 6.7 13.9 27.2 2.0 32.9 49.9 409.7 246.9
Susceptible
JL 24 46.2 MR 239 4.6 13.6 28.9 2.1 35.2 65.0 611.1 410.7
Mean 50.0 196 6.4 8.5 26.2 2.1 30.2 48.4 289.1 181.6
s.e.d. avg 11.5 41 1.0 2.1 2.5 0.1 5.4 9.0 138.2 102.5
s.e.d max. 11.8 50 1.2 2.8 3.2 0.2 6.5 10.8 176.9 122.0
s.e.d min 11.1 41 1.0 2.0 2.3 0.1 4.7 8.2 130.8 96.0
Table 4.4: Correlations for percent disease incidence (PDI), yield and other traits among 100 groundnut genotypes evaluated over 2 seasons under high disease pressure
100 seed
mass PDI Height
Kernel yield
Number of pods per
plant
Number of primary
branches
Number of seeds per pod
Pod
length Pod yield
Shelling
% 100 seed mass -
PDI -0.08 -
Height 0.06 0.03 -
Kernel yield 0.44*** -0.33*** 0.41*** - Number of pods per
plant 0.14 -0.45*** 0.11 0.36*** -
Number of primary
branches 0.19 -0.05 -0.28*** -0.16** -0.01 -
Number of seeds
per pod -0.11 0.21*** 0.06 -0.04 -0.17** -0.13 -
Pod length 0.15 -0.04 -0.26*** -0.19** -0.23*** 0.17 0.23*** -
Pod yield 0.47*** -0.40*** 0.37*** 0.98*** 0.38*** -0.13 -0.04 -0.12 -
Shelling % 0.52*** -0.09 0.34*** 0.72*** 0.25*** -0.19*** -0.00 -0.28*** 0.65*** - Note: **, *** Significant at P≤0.01 and P≤0.001, respectively