Interspecific mapping of the Ascochyta gene(s) of lentil (Lens culinaris Medikus) using RAPD technology

Abstract

Ascochyta blight caused by Aseochyta fabae f. sp. lentis is a destructive disease of lentil affecting the host-plants with serious consequences on yield. The aim of this study was to map the gene(s) for resistance using morphological and RAPD markers in an interspecific cross Lens culinaris ssp. culinaris cv. Titore and L.c. ssp. orientalis, W6 3261. As a part of this study a protocol was developed for improved clonal propagation of lentil. Clonally propagating F₂ progeny is useful for assessing relationship between marker-genotype with resistance phenotype, as they are genetically uniform. While attempting to clonally propagate lentils in a previously reported water-agar medium, we encountered shoot-tip necrosis in almost 100 per cent in vitro grown seedlings. The use of twice as much calcium in the MS salts + sucrose was demonstrated to overcome the problem entirely.

The genetics of host-resistance was studied in F₃ families of the interspecific cross Titore x W6 3261. The F₃ segregation ratio (1 homozygous resistant: 2 heterozygote: 1 homozygous susceptible) indicated that resistance against ascochyta blight may be controlled by a single dominant gene. We, however, observed a poor fit to the expected 3 dominant: 1 recessive ratio in the heterozygote F₃- families.

The inheritance study indicated simple Mendelian segregation of the three morphological characters studied, epicotyl colour, flower colour and flowers per inflorescence and the RAPD marker OPB-8. No linkage was detected between morphological characters, however, epicotyl colour was found to be loosely linked to ascochyta resistance. Though this linkage is loose it indicates that markers known to be on linkage group 1 (as previously reported for epicotyl colour) in lentils should be examined first as possible markers for this particular ascochyta resistance gene/region. The study did not indicate any linkage relationship of the RAPD marker OPB-8 with any of the characters studied including ascochyta blight. However, simple Mendelian inheritance of the RAPD marker OPB-8 within a segregating population of 48 F₂ progeny indicated that the cross could be successful for mapping gene(s) underlying ascochyta resistance and linkage mapping in lentil.