Rice Genetics IV - IRRI books - International Rice Research Institute

In temperate regions, breeders have used naturally occurring early varieties assources of early maturity or relied upon transgressive segregation for earliness incrosses. Early maturity mutants have often been induced in otherwise well-adaptedvarieties (Carnahan et al 1989, Rutger et al 1987). The ease with which earliness isacquired is an indication that early maturity usually is rather simply inherited. Forexample, in California, an early maturity mutant was found to be controlled by asingle partially dominant gene (McKenzie et al 1978).Glabrous hullThe recessive gene for glabrous hull (gl) has been very important for the U.S. riceindustry. Initially, the glabrous hull characteristic, which also confers glabrous leaves,became valued for hand harvesting and threshing of rice in the humid southern U.S.environment. Less itching occurred because the glabrous varieties lacked the small leafbarbs (trichomes) of pubescent varieties. Subsequently, it was observed that the bulkdensity of paddy rice of the glabrous varieties was greater because the glabrous kernelspacked closer together. Also, less dust was created in the dehulling of paddy rice atmills, which are often in urban areas and are subject to clean-air acts. The first glabroushullvarieties in the U.S. were Rexoro, selected in Louisiana in 1926 from the varietyMarong-paroc introduced in 1911 from the Philippines, and Nira, selected in Louisianain 1928 from an unnamed variety introduced in 1916 from the Philippines (Jones et al1941). By the 1950s, most southern U.S. varieties were glabrous, having descendedfrom either Rexoro or Nira. Glabrous varieties were developed in California at laterdates. The first was CS-M3, which received its glabrous gene from Smooth No. 4 ofunrecorded origin (Mastenbroek and Adair 1970). The second was CS-S4, which receivedits glabrous gene from Smooth No. 3, also of unrecorded origin (Adair et al1972). Virtually all U.S. varieties today are glabrous, as are many Australian varietiesthat share U.S. parentage. To date, the glabrous gene has been “neutral” with no selectiveadvantage or disadvantage. Most of the world’s rice varieties are pubescent, exceptfor tropical japonica varieties including upland and bulu types, which are characteristicallyglabrous.Gold hullGold hull (gh) color was previously popular in U.S. varieties, beginning with the landmarkvariety Carolina Gold, which apparently arrived as a mixture in Carolina White, aline introduced into South Carolina in 1694 from Madagascar (Jones 1936). These twovarieties became famous in the clean-rice markets of Europe and were grown in theU.S. for nearly two centuries (Jones 1936). Later varieties, including Rexoro and Delitus,also had gold hulls (Jones et al 1941). Rexoro was the gold-hull source for severalvarieties released in the southern U.S. between 1930 and 1965. The last widely growngold-hull variety was Bluebelle (Bollich et al 1968). By the mid-1970s, the gold-hullvarieties lost their popularity because of the increased use of parboiling, in which penetrationof the gold color into milled rice produced undesired off-color rice. Allelicrelationships of gold hull color in Carolina Gold and the Rexoro source have not beendetermined. It is well known that the gold hull color from the Rexoro source is con-Application of Mendelian genetics in rice breeding 29