Nursery Performance of Full and Half-sib Progenies and Juvenile Screening for Selection in Rubber (Hevea brasiliensis Muell Arg.) Breeding

摘要

In order to report growth and yield performance of progenies of 2002-hand pollination programme and to discuss the observations vis-a-vis juvenile screening in Hevea breeding, test tapping at three years was carried out. Latex volume, instead of dry rubber, was collected as yield from each tapping. Dry rubber content (DRC) of top selections was determined for calculation of rubber yield. Distribution of seedlings in different girth, yield and DRC classes were studied. Mean range in latex yield noted in the full-sib progenies of Wickham X Wild accessions was 0.1 to 4.5 mL t~(-1) t~(-1) (mL per tree per tapping) while in Wickham X Wickham progenies it was 0.1 to 19.6 mL t~(-1) t~(-1). In the clonal half-sibs (HS), mean yield was low in HS progenies of RRII 105 and PB 330 while in RRII414 and RRII429 it was higher. Maximum latex yield noted from a tapping was 33.0 mL t~(-1) t~(-1). Dry rubber yield in the top 20% selections showed a range of 0. 7 to 4.1 g t~(-1) t~(-1) (grams per tree per tapping). Mean yield from 10 tappings ranged from 7 to 41 g t~(-1) 10t~(-1) (grams per tree per 10 tappings). DRC among the top 20% selections varied from 14.3% to 38%. In the low girth class only one was included in the top 20% of selections. Moderate and average girth classes each contributed 41 and 38 seedlings that included most of the top 20% of selections. It was concluded that test-tapping at age three, rather than at two, was more useful. Measurement of yield in terms of latex volume as opposed to that of dry rubber yield, can result in more accurate yield recording. Latex can be used for determining rubber content and biochemical and physiological determinants of yield that can further boost the probability of potential selections. For maximum genetic gain in juvenile selection, seedlings of moderate to high girth class and average yield seemed more promising.