Combining ability effects of clonal rootstocks and scions in rubber trees (Hevea)
Paulo de Souza Gonçalves and Antonio Lucio Mello Martins
Rootstocks and scions combinations of five rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell-Arg.] clones were evaluated for rubber yield and growth vigor to detect the rootstock with the best general combining ability (GCA) and the best specific combining ability (SCA), using the method 1, suggested by Griffing. The clones (scions) involved were: IAN 873, RRIM 600, RRIM 701, PB 235 and GT 1 grafted in five different rootstocks from illegitimate seeds of the same clones. The ANOVA mean squares for GCA and SCA reciprocal effects were highly significant for both characters. The general GCA: SCA ratios were 24:1 and 4:1 for rubber yield and growth vigour, respectively. The rootstock of the RRIM 600 clone was the best general combiner for rubber yield (gi = 8.25), followed by the PB 235 (gi = 5.20).Although negative, the rootstock of the RRIM 600 clone showed the best GCA (gi = -0.0354) for growth vigour, followed by rootstock of the GT 1 clone which presented a gi = -0.5194 value. The maximum SCA effects for rubber yield (sij = 5.55) was obtained by IAN 873 rootstocks combined with the RRIM 600 clone as scion, followed by the PB 235 (rootstock) combined with the RRIM 600 scions (sij = 3.06). For growth vigour, the best specific combining ability effect of sij = -1.64 was obtained by the IAN 873 clone in combination with the RRIM 701 clone, with their respective rootstock and scion. As for rubber yield, the RRIM 600 rootstocks were classified as the best general combination. In addition, the IAN 873 rootstocks combined with the RRIM 600 scion showed the best specific combining ability.