Dr Ramli Othman Head, Crop Protection & Microbiology Unit Malaysian Rubber Board RRIM Experiment Station 47000, Sg. Buloh Selangor D.E. MALAYSIA Tel: 603-61576751 Fax: 603-61576745 E-mail: rambo@lgm.gov.my

There is a need for the early exchange of germplasm to overcome government reservations on the exchange of clones. The main cost of breeding is in the selection. Intellectual property rights may need to be considered. Breeding is very expensive and duplication should be avoided. There is a need for a Joint Breeding Programme.

The Group Liaison Officer should schedule a symposium (to be separate from the Annual Meeting) on this activity. Breeding is a very important activity and there is the problem and frustration of costly duplication of effort.

The question of the Germplasm Collections should also be considered.

This very important issue should be the subject of a meeting of the Plant Breeding Group to decide at what stage materials are exchanged; the development of IRRDB clones; breeding for disease resistance and breeding to reduce the presence of allergenic proteins.

Report of the IRRDB Plant Breeding Group for previous year

The plant breeders from the rubber producing countries have not met for quite some time to discuss and exchange information about developments in rubber breeding which are relevance to their profession and the NR industry. The IRRDB Liaison Officer Plant Breeding Group would like to suggest that a meeting seminar of all rubber plant breeders from various rubber research institutes be held in 1999. The venue can be in any member countries. The theme for the meeting would be: 'Breeding Strategies For The Development of Resistant Hevea Clones against Corynespora Leaf Fall'.

Rubber is affected by several leaf disease of which Corynespora leaf fall caused by Corynespora cassicolla is becoming of economic importance to the rubber producing countries such as Malaysia, Indonesia, Sri Lanka, Thailand and India. This disease was first recorded in India in 1958, Malaysia in 1960, Indonesia in 1980 and both Sri Lanka and Thailand in 1985. The disease came to prominence (epidemic proportion) in the 1980s mainly in Indonesia, Sri Lanka and Malaysia. Many clones were reported susceptible to Corynespora and some of them are RRIC 103, RRIC 104, RRIM 600, Tjir 1, RRIM 725, IAN 873, FX 25, RRIC 110, RRIC 131, RRIC 132, RRIC 133, KRS 21, PPN 2058, PPN 2444, PPN 2447, BPM 1, GT 1, PR 261, RRIM 610, RRIM 622, RRIC 52, PB 311, KRS 232 KRS 233, KRS 225, RRIC 121, KRS 218, BPM 24, KRS 205, PB 235 and PR 305.

In Malaysia Corynespora leaf fall came to prominence when it was observed attacking RRIM 725 (derived from illegitimate seedling of South American clone FX 25) and two other foreign clones, RRIC 103 and KRS 21, introduced through multilateral exchange clones. Chee (1988) reported a total of 75 clones which were highly resistant (no infection) out of 138 locally bred-clones and 1981Germplasm screened for clonal susceptibility in both laboratory and field conditions. Only two clones were found to be highly susceptible (severe infection) and the rest were with either light or moderate infections. This screening inferred that most of the clones were resistant or partially resistant.

The recent screening carried out by Tan et al. (1992) on 44 clonal materials also showed the same pattern of clonal susceptibility of which 10 of the clones were resistant (no infection) and three were highly susceptible (severe infection). The rest were either lightly or moderately infected. Among these, nine clones viz. PB 235, PB 260, PB 28/59, PB 280, PB 330, PM 10, RRIM 701, RRIM 908 and RRIM 926, which were initially reported by Chee (1988) to be resistant showed light to moderate infection. Moreover, RRIM 600 which was initially reported to be moderately infected had became severely infected. In Sri Lanka, the clone RRIC 110 which was widely planted and earlier reported to be resistant, is now found to be susceptible. The apparent sudden susceptibility of these clones raised the question as to whether resistance had failed due to the presence of other virulent pathotypes, or other factors. Will the other resistant clones succumb to the same fate?

Breeding for resistance has been practiced consciously and unconsciously starting with the selection of resistant parents for crossings to siting trials in disease prone areas and by making casual observations on disease incidence. Of late, potential high yielding clones were screened for resistance in both laboratory and field conditions prior to recommendation to the industry.

The information on disease resistance to Corynespora has been very limited for any effective breeding programme to be carried out. Although previous screenings carried out showed that the present clonal materials had a wide spectrum of susceptibility ranging from no infection to severe infection, implying the high possibility of polygenic and/or monogenic inheritance. Tan and Tan (1995) reported that the major genetic variation of the Corynespora disease resistance could be attributed to additive gene control as well as non-additive gene control from a study using five-parent diallel cross. However, the large number of clones initially screened as resistant clones and became susceptible at later stage is of great concern. Quite interestingly, a number of present resistant clones such as RRIM 712, RRIM 902, RRIM 903, RRIM 904, RRIM 915, RRIM 937 etc had susceptible parents. Therefore, more studies should be carried out to ascertain the genetics of resistance to Corynespora leaf fall and the variation of the physiological races of the disease if the disease resistant trait is to be sustained.

Further Hevea improvement for resistance to Corynespora leaf fall through plant breeding is possible and necessary to sustain the well being of the natural rubber industry.

Updated: 2006-8-14