Inheritance of resistance to the root-knot nematode Meloidogyne javanica in lettuce

Wilson Roberto Maluf, Sebastião Márcio Azevedo, Luiz Antonio Augusto Gomes and Ana Cláudia Barneche de Oliveira

Departamento de Agricultura, Universidade Federal de Lavras (UFLA), C.P. 37, 37200-000 Lavras, MG, Brazil

Corresponding author: W.R. Maluf

E-mail: [email protected]

Genet. Mol. Res. 1 (1): 64-71 (2002)

Received February 20, 2002

Published March 19, 2002

ABSTRACT. Resistance to the root-knot nematodes Meloidogyne spp. would be a valuable attribute of lettuce Lactuca sativa L. cultivars grown in tropical regions. The looseleaf lettuce ‘Grand Rapids’ is resistant to both M. incognita and M. javanica. Resistance to M. incognita has a high heritability, under the control of a single gene locus, in which the ‘Grand Rapids’ allele, responsible for resistance (Me), has predominantly additive gene action, and has incomplete penetrance and variable expressivity. We studied the inheritance of the resistance of ‘Grand Rapids’ (P2) to M. javanica in a cross with a standard nematode-susceptible cultivar Regina-71 (P1). F1 (Regina-71 x Grand Rapids) and F2 seed were obtained, and the F2 inoculated, along with the parental cultivars, with a known isolate of M. javanica to evaluate nematode resistance. A high broad sense heritability estimate (0.798) was obtained for gall indices. Class distributions of gall indices for generations P1, P2, and F2 were in agreement with theoretical distributions based on a monogenic inheritance model for the range of assumed degrees of dominance between approximately -0.20 and 0.20. M. javanica resistance appears to be under control of a single gene locus, with predominantly additive gene action. Whether or not the Grand Rapids allele imparting resistance to M. javanica is the same Me allele imparting resistance to M. incognita remains to be determined.

Key words: Lactuca sativa L., Lettuce, Resistance, Meloidogyne javanica, Nematode