Genetic dissection of root growth in rice (Oryza sativa L) .1. a hydrophonic screen

Root growth is an important component of the adaptation of rice to drought-prone environments. A hydroponic screen was used to study root growth of 28 rice varieties. Both maximum root length and adventitious root thickness varied widely between varieties. In general, japonica varieties had larger root systems than indica varieties. Two F-2 populations involving the thick-and long-rooted upland japonica variety 'Azucena' and two poor-rooting varieties, namely the upland indica 'Bala' and the Italian japonica 'Maratelli', were made and screened in hydroponics. Generation means analysis revealed significant additive and dominance main effects for the root length traits with a prevalence of dominance gene effects in both crosses. The dominance x dominance type of nonallelic interactions were important for maximum root length from day 7 to day 28, root volume, root thickness and root cell length in the cross 'Bala'x'Azucena'. The heritability (broad-sense) estimates varied from low to high for the traits and displayed differences between populations. This suggested that recombinant lines with improved root traits can be developed from the two crosses with selection methods that involve some form of progeny evaluation, In a companion paper, we report the mapping of quantitative trait loci (QTLs) for root growth traits in the 'Bala' x 'Azucena' population using restriction fragment length polymorphisms (RFLPs).