Inheritance of Tolerance to Chilling Stress in Rice during Germination and Plumule Greening

Rice cultivars ( Oryza sativa L.) that are adapted to high altitude areas of the sub‐tropics, such as Nepal, have to germinate and rapidly synthesize chlorophyll in the emerging plumule at chilling temperatures. This study was conducted to determine, at the chilling temperature of 17°C, the heritabilities of four traits: germination, the rate of germination (RG) index, plumule greening, and plumule vigor. Estimates were made in the F 3 generation of two crosses between two Nepalese chilling‐tolerant cultivars and a chilling‐susceptible Nepalese cultivar. Most traits were significantly heritable. Heritability estimates ranged from 0.7 to 0.9 for germination and the rate of germination, and was 0.7 for plumule vigor and for plumule greening at chilling temperature. Four methods of estimating germination rate were examined. Of these, an index that took into account final percentage germination, unlike the index usually used for rate of germination at optimal temperatures, gave the highest heritability. Predicted genetic advances due to selection were highest for germination rate and greening ability. All of the traits were significantly correlated ( P ≤ 0.05) with early seedling vigor in the field. We conclude that it would be useful in a breeding program for improved chilling tolerance to screen for germination rate with an index and to select for plumule greening ability because these traits are highly heritable, easily measured, and correlate well with field performance at high altitudes.