Screening of Rubber Rootstock by the Assessment of Root Growth and Genetic Background

Abstract

Rubber seedlings from two early-introduced clones (EIRpsu 1 and EIRpsu 2) in southern Thailand were evaluated for root growth performance under field conditions. The two clones had been screened for white root disease tolerance. Genetic analysis of EIRpsu 1 and EIRpsu 2 was compared to RRIM 600 (the major cultivated variety of Hevea rubber in Thailand) using random amplified polymorphic DNA markers with 10 primers. Results from cluster analysis indicated that EIRpsu 2 was closer to RRIM 600 than EIRpsu 1 with similarity coefficients of 0.850, 0.860 and 0.890, respectively. Root growth of EIRpsu1 and EIRpsu2 was monitored at a rubber plantation in Langsuan district, Chumphon province during 2012–2013. Six-month-old seedlings of each clone were transplanted into a rhizobox. The experiment was designed as a randomized complete block design with four replications, with one plant per rhizobox. Shoot growth and root proliferation of the seedlings were recorded at two-monthly intervals from October 2012 to March 2013. The shoot growth was monitored by measuring plant height, trunk diameter and the number of compound leaves. It was found that RRIM 600 exhibited the highest shoot growth under field conditions, and it was significantly different from the other two clones. The root length density was measured by scanning the root systems of each seedling from a panel in the rhizobox. Results showed that the seedlings of EIRpsu 1 and EIRpsu 2 had better root growth than RRIM 600. The spatial distribution of roots indicated a rather deeper root system for the two selected clones.