by
C.S. Venkatesh
Forest Research Institute, Dehra Dun, India
A systematic interspecies hybridization programme on Eucalyptus began in 1965 at this Institute. The species involved thus far have been E. camaldulensis Dehn. (River red gum), E. tereticornis Sm. (Forest red gum), E. tereticornis Sm. (Forest red gum), E. grandis Hill ex Maiden (Flooded gum) and very recently, E. alba Reinw. ex Bl. (Poplar gum, Khaki gum).
Of the approximately dozen F1 species hybrids produced/isolated and tested so far, those belonging to the 1970 reciprocal crosses FRI-4 (E. tereticornis x E. camaldulensis, northern form) and FRI-5 (E. camaldulensis northern form x E. tereticornis) both displayed a striking and sustained degree of hybrid vigour (heterosis) in height and diameter growth, and hence in volume production, in an experimental field trial (2m × 2m espacement) at Dehra Dun (Latitude 30°N., altitude 640m, rainfall type: summer; total 2000mm). At age 4, which corresponds to only half or one third of the 8 – 12 year rotation cycle currently practised for eucalypts grown in India, these hybrids held four times more standing volume than the parental controls, and more than twice that of the Mysore Gum, which is today the most widely planted eucalypt in this country.
The aforementioned hybrids possessed a better stem form as compared to the Eucalyptus camaldulensis parent. Heterosis was moreover manifested in flowering precocity and higher reproductivity capacity, so much so that the F1 hybrid trees have already started producing substantial quantities (enough to raise a million or more nursery seedlings annually) of viable F2 hybrid seed by natural pollinations. This seed is heavier and showed greater germination energy than those harvested off the P0 and P1 trees of the parental species. It has also produced, in early nursery tests at Dehra Dun, vigorous F2 seedling families which, phenotypically at any rate, were as good and some even better than the comparable F1 hybrids. Open pollinated seed harvested off the selected best individual F1 hybrid trees and bulked varietywise, is now being supplied as pedigreed breeder or nucleus seed, for performance and yield trials under different bioclimatic and edaphic conditions, in various parts of India.
After meeting internal demands, small surplus quantities of the above seed can be supplied to overseas correspondents who may wish to undertake similar trials abroad. Request for seed should be addressed to: Dr. C.S. Venkatesh, Plant Geneticist, Forest Research Institute, Dehra Dun 248006, India.
