Abstract:

“Teqing”, both an elite conventional cultivar with high yields and a male parent for two-line indica hybrid rice production, had a great contribution to rice production at the end of last century in China. However, the amylose content (AC) in the endosperm of Teqing seeds is high, resulting in poor cooking and eating quality of the milled rice. The amylose in rice endosperm is synthesized by the granule-bound starch synthase (GBSS), which is encoded by the waxy (Wx) gene. Our previous researches showed that AC was correlated with the ability of excising intron 1 from the leader sequence of the Wx transcript, and a single nucleotide polymorphism (G or T) located at the first nucleotide of splice donor site of Wx intron 1 might be the key factor responding for the alterative splicing. Thus, a CAPS (Cleaved amplified polymorphic sequence) molecular marker, named as PCR-AccI, was subsequently developed to identify whether the nucleotide in this site is G or T, which preferred to easily infer the AC in a genetic or breeding material (Fig.1). In this study, by using the developed molecular marker and its assisted selection, the AC in Teqing was successfully down-regulated for improving its cooking and eating quality by introgressing the Wx locus from an indica rice line (Wx-TT genotype) with intermediate AC and good quality. Three elite improved Teqing lines, Teqing-TT-1, Teqing-TT-2 and Teqing-TT-3, were selected after four backcrosses and two selfinges (Table 1); in each generation the molecular marker-assisted selection was applied to select the individuals carrying Wx locus with GT or TT genotype (Fig.1). In the selected lines, the AC in endosperm was reduced to a relative low level of about 15% from 28.5% of their original (Table 3). Consequently, the two-line hybrids derived from the selected lines and Pei’ai 64S also showed a reduced amylose level (Table 3). The northern blot analysis showed that the reduction of amylose synthesis in selected lines and their hybrids resulted from the lower expression of the introduced Wx gene compared with in the originals (Fig.2). In the field trials, the agronomic performance in the improved lines and their hybrids was examined to be comparable as the originals except for a negative impact on grain weight (Table 1 and Table 2). Simultaneously, the other key factor involved in rice cooking and eating quality, gel consistency (GC), was also improved by the effect of reduced AC in the selected lines and their hybrids (Table 3), but the gelatinization temperature (GT) showed a little increase in the selected lines by comparison with the original one. The selected Teqing lines would have a great potential for the production of both conventional and hybrid indica rice with high quality and yielding.

Key words: Indica rice, Amylose content, Molecular marker-assisted selection, Cooking and eating quality, Two-line hybrid rice