Evaluation of selected genotypes from the 1995 RRIM Hevea germplasm collection for resistance to Corynespora cassiicola.

Hevea brasiliensis, or the Para rubber tree, is a major commercial source of natural rubber (NR). The rubber tree is susceptible to various fungal attacks, which affect NR production and Corynespora cassiicola is one of the major pathogens affecting young and mature rubber trees. Corynespora leaf fall disease (CLFD) outbreaks often cause serious loss in latex productivity by adversely affecting tree health. Since fungicidal chemical control is uneconomical and unsustainable, improving host resistance is the most effective strategy for the long-term management of this disease. In this context, 78 Hevea genotypes were screened against two virulent isolates of two races of C. cassiicola (Race 1 and Race 2). The level of host resistance was determined in vitro using detached leaf bioassay and those genotypes that were found to be highly resistant were subjected to further evaluation under greenhouse conditions. Seven genotypes were classified as highly resistant against both races of C. cassicola in vitro, with less than 20% disease intensity. Subsequent assessment under greenhouse conditions identified three genotypes with less than 40% disease severity and corresponding rAUDPC value of less than 0.4 when challenged with both races of C. cassiicola. These resistant genotypes are suitable candidates to be included in breeding programmes aimed at the development of superior clones with durable resistance against Corynespora leaf fall disease. [ABSTRACT FROM AUTHOR]