Juvenile growth, rubber yield and putative tolerance to foliar diseases in interspecific hybrids and half-sibs of Para rubber tree (Hevea spp.)

Introgressive hybridization was initiated using different Hevea spp. and wild germplasm accessions. High yielding H. brasiliensis clones but susceptible to foliar diseases (RRII 105, RRII 414 and RRII 430) were hybridized with other Hevea spp. (H. spruceana and H. camargoana) and wild accessions (RO 380 and RO 2871) which are putatively tolerant to important foliar diseases. In addition, half-sibs were collected from a disease tolerant interspecific hybrid clone, Fx 516. The F1 hybrids and half-sibs were evaluated for growth and yield at the age of three years. Regarding family-wise growth in terms of girth, RRII 430 x RO 380 (mean, 28.6 cm) and RRII 430 x Hevea spruceana (mean, 23.0 cm) had more girth. In contrast, RRII 105 x H. camargoana and RRII 430 x H. spruceana had progenies with low girth. With reference to family mean yields, RRII 414 x RO 380 gave a mean yield of 64.8 g/t/10t followed by RRII 430 x RO 380 (mean yield, 15.3 g/t/10t) and RRII 430 x H. camargoana (mean yield, 15.2 g/t/10t). Remaining cross-combinations produced progenies with low yield ranging from 7.1-8.5 g/t/10t. The highest yielding individual of the family RRII 414 x RO 380 gave a yield of 190.8 g/t/10t. Half-sibs of Fx 516 had a mean yield of 17 g/t/10t with maximum individual yield of 56 g/t/10t. Progenies were variably affected by powdery mildew disease caused by Oidium. After confirming segregation of disease resistance trait among progenies through detailed field evaluation in hot spots, the F1 population will be continuously used in back crossing programme to ensure introgression of disease resistance traits.