ANALYSIS OF MOLECULAR MARKERS LINKED TO CORYNESPORA LEAF FALL DISEASE RESISTANCE IN RUBBER PLANTS

Abstract

Rubber cultivation in Indonesia and other major natural rubber producing countries faced the constraint of the Corynespora leaf fall (CLF) disease attack that significantly reduced the production of latex.  The use of resistant rubber clones as a planting material is one of the effective and economic solutions in CLF disease control. The rubber breeding program to obtain superior clones resistant to CLF disease is constrained by the length of time required for the selection process. The progress of the molecular biology provides a chance to solve this problem. To identify moleculer markers linked with resistance to CLF disease a series of experiments that consisted of genetic analysis of C. cassiicola isolates, evaluation of the CLF disease resistance level of the rubber germplasm accessions and identification of the QTL  linkage to CLF disease on the rubber tree were carried out. The rDNA-ITS sequences and virulence analysis of 23 C. cassiicola isolates showed that there were 5 haplotypes of isolates and  that differences were present in the virulence level of isolates to the rubber clones tested. Three isolates collected from rubber clones PR 303, RRIM 600 and Tjir 1 have a very high virulence level. Resistance test of 56 rubber germplasm accessions with four of C. cassiicola isolates showed that 12 accessions could be classified as very resistant, 13 as  resistant, 23 as susceptible and 8 as very susceptible. Three accessions of the IRRDB 1981 population namely PN 451, PN 494 and PN 604 have better resistance levels compared to Wickham population. The resistant (BPM 1) and susceptible (RRIM 600) rubber clones were selected as a parent clones to obtain a mapping population for QTL analysis that produced 30 F1 plants and 74 embryonic F1. Linkage analysis by using 30 selected SSR primers showthat there were four linkage groups on the LOD 3 with total 8 loci, while LOD 2 had two linkage groups with total 11 linked loci. QTLs linked to CLF disease have not been identified on the linkage map, but based on the single marker analysis, four loci (EHB70, EHB081, EHBp18 and SSRH548) associated with two isolates used (CC-06 and CC-22) were found. The informations obtained in this study are the first step for the development of Marker Assisted Selection (MAS) of rubber resistant to CLF disease.

Keywords: Corynespora  cassiicola, genetic linked map, Hevea brasiliensis, QTL, rDNA-ITS