Breeding for disease resistance in Hevea spp. - status, potential threats, and possible strategies.
| Authors: | Chaendaekattu Narayanan, Kavitha K. Mydin |
| Year: | 2012 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | In: Sniezko, Richard A.; Yanchuk, Alvin D.; Kliejunas, John T.; Palmieri, Katharine M.; Alexander, Janice M.; Frankel, Susan J., tech. coords. Proceedings of the fourth international workshop on the genetics of host-parasite interactions in forestry: Disease and insect resistance in forest trees. Gen. Tech. Rep. PSW-GTR-240. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp. 240-251 |
Abstract
Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg., a forest tree native to the tropical rain forests of Central and South America, has only been recently domesticated outside its natural range of distribution. Almost all of the commercially cultivated clones of H. brasiliensis represent a very narrow genetic base since they originated through hybridization or selection from a few seedlings of so called Wickham germplasm. Hence, the commercial rubber cultivation, due to their genetic vulnerability, is under a constant threat of attack by native as well as exotic diseases and insects. Climate change, which is clearly felt in the traditional rubber growing regions of India, may possibly alter the host-pathogen interactions leading to epidemics of otherwise minor diseases.
Pathogenic fungal diseases including Phytophthora-caused abnormal leaf fall (ALF) and shoot rot, pink disease caused by Corticium salmonicolor, Corynespora-caused leaf disease, and powdery-mildew (Oidium sp.) are challenging diseases posing epidemic threats to rubber cultivation. South American leaf blight (SALB) is a devastating disease caused by Microcyclus ulei (=Dothidella uleif) which has prevented large-scale planting of rubber in Brazil due to epidemic outbreaks. The SALB is a looming threat to other rubber growing areas. Hence, it is essential that a global SALB resistance breeding program be implemented to tackle such future threats of epidemics. Hevea clones clearly exhibit variable levels of susceptibility to pathogenic diseases. Hevea clones have been tested for their capacity to produce phytoalexins; a strong correlation was observed between phytoalexin accumulation and clone resistance. More lignin accumulation was also often associated with clone resistance. Attempts have been made to identify possible disease resistance gene analogues in rubber. The role of M13-1bn marker (a putative quantitative trait locus) in screening for resistance to SALB had been investigated through genome mapping, but needs further validation. Earlier selection and breeding of Hevea clones resistant to M. ulei and Phytophthora sp. in Brazil led to screening of resistant clones. Most of the resistant material had been derived from H. benthamiana "F4542." Few other attempts for inter-specific hybridization have been made, particularly for SALB resistance (H. camargoana x FX 4098), but they did not follow large-scale evaluations for field resistance.
Many man hours of labor and enormous quantities of fungicidal chemicals are required every year for management of above diseases in vast areas of rubber plantations in India and other rubber growing countries. The cost of fungicides and their long-term effect on environment justify the need for breeding disease resistant trees. There are several theories for genetic basis for disease resistance (horizontal/vertical) in Hevea. Nevertheless, there is every possibility for breakdown of resistance due to ever-evolving pathogenic races coupled with climate change, which is exemplified by evolving SALB races. A multidisciplinary breeding program for development of disease resistant clones would have to continuously utilize Wickham resource as well as wild germplasm, in addition to other Hevea spp., in order to have sustainable rubber production.