Previously it was detemined that cv. 'Licatol' exhibits root-knot-nematode horizontal resistance which causes reduction both in root knot and egg-mass number after inoculation. Genetic analysis of resistance was done following Mather and jinks and Cavali Methods (Mather and Jinks, 1971), evaluating the F1 and F2 populations and the backcrosses to both parents from a cross between "Rutgers' (susceptible parent) and 'Licatol' (resistant parent). Additionally, an estimation of the reciprocal effects was done in another cross between 'Tropic' and 'Licato.' The obtained results for both variables (i.e. root knot and egg-mass number) after inoculation with 2000 nematode eggs/plant were similar. Root knot number (Table 1) of population means for the several generations and the genetic analysis results suggest partial dominance of susceptibility and that an additive-dominance model with epistatic interactions of an additive x dominant type could explain the observed variability for both variables. This would imply that the observed resistance is conditioned by at least 2 genes with non-allelic interactions. It is possible that the two evaluated variables are controlled by a group of genes with pleiotropic effects. The reciprocal effects that were found (Table 2) suggest that besides the nuclear genes for resistance there may be a cytoplasmic factor in 'Licatol' conditioning resistance.
Literature cited:
Mather, K. and L. Jinks. Components of means: additive and dominance effects. In: Biometrical Genetics. Cornell Univ. Press., Ithaca, NY, 1971.
Table 1. Expected and observed values for root-knots number by plant after inoculation with the root-knot-nematode (dosage 2000 eggs/plant) to different generations of a cross between 'Rutgers' (P1) and 'Licato' (P2).
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Number Root-knots number/plant (Four
of parameter model) (1)
Generation plants ______________________________
Observed Expected
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P1 30 25.65 +/-3.39 27.49 +/- 2.33
P2 30 8.33 +/-0.77 8.43 +/- 2.33
F1 30 23.43 +/-3.75 26.98 +/- 3.89
BC 53 22.83 +/-2.28 22.47 +/- 3.35
F2 59 27.23 +/-3.47 21.29 +/- 3.35
F2 140 22.73 +/-2.25 23.64 +/- 2.89
X^2^ 2.74
p^2^ 0.5 - 0.25
Scaling Test
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A 3.41 +/- 6.81 n.s.
B 22.68 +/- 7.92*
c 10.08 +/- 12.23 n.s.
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(1) m: (average effect) 17.96 +/- 1.64**
d: (additive effect): 9.53 +/- 1.65**
h: (dominance effect): 9.01 +/- 3.53
j: (additive x dominance interaction):23.80 +/- 8.71*
*Significant (95% confidence);
**Highly significant (99% confidence)
Table 2. Reciprocal effects for root-knot and egg-mass number for a cross
between 'Tropic' and 'Licato' after inoculation with 2000 root-knot nematode
eggs by plant.
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Genotype (1)
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Variable 'Tropic' X 'Licato' 'Licato X Tropic'
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Root-knots number 34.45 +/- 6.93 A 14.10 +/- 2.24 B
Egg-mass number 15.25 +/- 3.14 A 7.55 +/- 1.32 B
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(1) Averages with different letter in each row are different
(Student test with 95% of confidence).