Abstract:

The number of secondary laticifer rows in the trunk of Hevea brasiliensis has a significantly positive correlation with the latex yield, and the differentiation of the secondary laticifer can be induced by tapping wound in mature tree trunk. In the study, the secondary laticifer differentiation of different Wickham germplasm mature trees induced by pre-tapping were studied, which would provide a basis for the identification and evaluation of germplasm resources, and the prediction of the differentiation ability of secondary laticifer of mature trees after tapping. Fresh bark samples were dyed by iodine-bromine reagent and embedded in paraffin. The differentiation of the secondary laticifers were observed with an optical microscope and the number of secondary laticifer rows were recorded for statistical analysis. There was a significant difference of secondary laticifer differentiation among the 110 different accessions of Wickham germplasms induced by pre-tapping. According to the number of secondary laticifer rows after pre-tapping, the differentiation ability of secondary laticifer from low to high was roughly classified into 4 grades:1, 2, 3 and 4 grades. Based on these criteria, there were 32, 49, 24 and 5 accessions corresponding to grade 1, 2, 3 and 4, with the percentage of 29%, 45%, 22% and 4% among 110 accessions respectively. Therefore, the secondary laticifer differentiation ability most of the Wickham germplasms was relatively low level of grade 2. Further, there was also obvious difference in the differentiation ability of secondary laticifer between the germplasms introduced directly from abroad and those selected from domestic germplasms. Among 58 germplasms introduced from abroad, the percentage of accessions corresponding to grade 1, 2, 3, and 4 was 29.31%, 44.83%, 22.41%, and 3.45%, respectively. Among 52 germplasm selected from China, the percentage of accessions corresponding to the grade 1, 2, 3, and 4 was 28.85%, 44.23%, 21.15%, and 5.77% respectively. So, the domestic germplasms generally were superior to the abroad ones, in which especially the proportion of germplasms with 4-grade was significantly higher than that of foreign germplasms. In different breeding series, the PB, RRIM and RRIC series from abroad and the Daling, Haiken, and Dafeng series from domestic germplasms showed a better differentiation effect. To analyze the progenies of two hybrid combinations, the results showed that generations of PB86 × PR107 had strong differentiation ability, in which 3 accessions were grade 3 and 1 accession was grade 4. In comparison, the generations of RRIM600 × PR107 showed lower differentiation ability with 2 accessions from grade 1 to grade 3 respectively. PB86 and PR107 progenies showed strong double transgressive phenomenon in the aspect of laticifer differentiation and could be chose as superior breeding parents. The ability of secondary laticifer differentiation induced by pre-tapping could be used as an effective indicator for early prediction of high-yield and peak yielding period, and the results also provided the basis for identification and evaluation of the germplasm resources for rubber tree.

Key words: Hevea brasiliensis, Wickham germplasm, pre-tapping, secondary laticifer differentiation, early prediction