Breeding improved rice cultivars for temperate regions: a case study

Abstract

An accelerated rice-breeding program was initiated in 1969 at the California Rice Experiment Station. The program is broad in scope, developing cultivars in all US market classes (long, medium, and short grains) and special purpose types (waxy and aromatics). This grower-funded rice-breeding program has released 27 new cultivars as well as improved germplasm lines. Statewide paddy rice yields have risen from 6.2 to 9.3 t/ha since 1978. The incorporation of semi-dwarfing genes, earlier maturity, and increased yield potential have contributed significantly to increases in grain yield. High experimental yields (>I1 t/ha) are routine and achieving increased increments of yield will become more difficult. After the initial shift to semi-dwarf cultivars, increasing efforts were directed toward improving adaptation to environmental stresses and grain quality. Screening and selection for cold tolerance in the form of seedling vigour for water seeding and resistance to cool temperature induced sterility at the reproductive stage are integral parts of the rice-breeding program. Progress is being made on incorporation into California rice cultivars of resistance to stem rot (Sclerotiurn oryzae Cattaneo) and aggregate sheath spot [Rhizoctonia oryzae-sativae (Swada) Mordue] from wild species and tolerance to rice water weevil (Lissorhoptus oryzophilus Kuschel). New restrictions and regulations of agronomic management practices may negatively impact rice production, creating problems in stand establishment, soil fertility, and weed, disease, and insect control. Breeding efforts to help minimise the adverse effect of these restrictions on yield and quality will increase in the future. Increased emphasis is being placed on improving milling yield and cooking and processing characteristics, and new laboratory methods are being explored to aid in evaluation and selection for grain quality.