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 dro ught-prone environments. A hydroponic screen was used to study root gr owth of 28 rice varieties. Both maximum root length and adventitious r oot thickness varied widely between varieties. In general, japonica va rieties had larger root systems than indica varieties. Two F-2 populat ions involving the thick-and long-rooted upland japonica variety 'Azuc ena' and two poor-rooting varieties, namely the upland indica 'Bala' a nd the Italian japonica 'Maratelli', were made and screened in hydropo nics. Generation means analysis revealed significant additive and domi nance main effects for the root length traits with a prevalence of dom inance gene effects in both crosses. The dominance x dominance type of nonallelic interactions were important for maximum root length from d ay 7 to day 28, root volume, root thickness and root cell length in th e cross 'Bala'x'Azucena'. The heritability (broad-sense) estimates var ied 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 th at involve some form of progeny evaluation, In a companion paper, we r eport the mapping of quantitative trait loci (QTLs) for root growth tr aits in the 'Bala' x 'Azucena' population using restriction fragment l ength polymorphisms (RFLPs).