Genetic diversity and identification of potential cold tolerant ecotypes from the Brazilian Hevea germplasm of international rubber research and development board collection

Hevea brasiliensis is a commercially cultivated species for its natural rubber (NR) latex in Southeast Asian countries and its genetic base is very narrow. India has received a share of the wild Hevea germplasm from the 1981 IRRDB collection of Brazil. To meet the ever-increasing demand, NR cultivation has been extended to non-traditional regions in India. Eighteen wild Hevea accessions along with two modern clones RRII 203 and PB 235 and two check clones RRIM 600 and Haiken 1 were evaluated in RBD at Nagrakata, West Bengal, the sub-Himalayan cold-prone region of India. In Hevea, low temperature causes reduction in plant growth, thereby increasing its uneconomical immaturity period. The genotypes exhibited highly significant clonal differences (P=0.05) for all the growth traits. The highest mean noted for the plant height 19.62 m (RO 2727); bark thickness 5 mm (MT 900); girth of plant in the 14^th year after planting 92.32 cm (MT 915); annual girth increment (cm/year) over seven years 5.61 cm (MT 915); winter girth increment (cm/year) over seven years 1.05 cm (MT 915). The 22 genotypes were grouped into 5 clusters, reflected the presence of considerable genetic diversity in the population. The top 30% of the potential accessions showing high growth vigour under cold stress were identified which could be used in reducing immaturity period in this crop. These ecotypes/selections have high potential value for the development of cold-tolerant clones to mitigate climate change for these regions and also in broadening the genetic base of the present-day cultivated rubber.