Seed - derived callus culture for selecting salt - tolerant rices : part I, callus induction plant regeneration, and variations in visible plant traits

Effects of different sodium chloride (NaCl) concentrations in the selection medium on callus growth and plant regeneration were also examined. Varieties differed markedly in their ability to induce callus and to regenerate plants. Callus induction frequencies ranged from 32 to 85% in the absence of yeast and casein extracts, but increased to nearly 100% when these were added. Plant regeneration frequencies ranged from 0% for IR8, IR26, IR28, IR30, IR36, and Koshihikari to 62% for Taichung 65; frequencies decreased as the callus culture period was lengthened. However, 27-week-old callus of Taichung 65 and Nona Bokra retained 30-40% regeneration ability. Even 47-week-old Taichung 65 callus were able to regenerate plants. The addition of NaCl had profound effects on callus growth and plant regeneration. Callus growth was good at concentrations less than 1%. At 1.5% NaCl, callus growth was retarded and at 3% no growth was observed. With 11-week-old callus, plant regeneration frequencies were higher at higher levels of NaCl in all varieties. Variations in visible plant traits were observed in the regenerated plants (R1) and their progeny (R2). In R1 plants of Taichung 65, high sterility (14.6/100 plants), tetraploids (3.4/100 plants), and other abnormal traits, such as stripes, open spikelets, etc., (0.9/100 plants) were observed. In R2 seedlings, the pooled chlorophyll mutation frequency of 1,259 lines was 8.8/100 lines, a value as high as that induced by irradiation but lower than that induced by chemical mutagens. Variations in dwarfism, high sterility, heading date, brown leaf spots, chlorophyll mutations, and various morphological traits were observed on field-grown R2 plants. About 54% of Taichung 65 R2 lines exhibited variations in 1 or more visible plant traits and 17.5% in more than 1 trait. Among trait variations observed, the occurrence of sterility was the most pronounced; occurrence of sterility in R1 and R2 plants did not correlate. (Author abstract, modified).