Substitution mapping and characterization of brown planthopper resistance genes from indica rice variety, ‘PTB33’ (Oryza sativa L.)

Rice (Oryza sativa L.) yield is severely reduced by the brown planthopper (BPH), Nilaparvata lugens Stål, in Asian countries. Increasing resistance in rice against BPH can mitigate yield loss. Previous reports indicated the presence of three BPH resistance genes, BPH2, BPH17-ptb, and BPH32, in durable resistant indica rice cultivar ‘PTB33’. However, several important questions remain unclear; the genetic locations of BPH resistance genes on rice chromosomes and how these genes confer resistance, especially with relationship to three major categories of resistance mechanisms; antibiosis, antixenosis or tolerance. In this study, locations of BPH2, BPH17-ptb, and BPH32 were delimited using chromosome segment substitution lines derived from crosses between ‘Taichung 65’ and near-isogenic lines for BPH2 (BPH2-NIL), BPH17-ptb (BPH17-ptb-NIL), and BPH32 (BPH32-NIL). BPH2 was delimited as approximately 247.5 kbp between RM28449 and ID-161-2 on chromosome 12. BPH17-ptb and BPH32 were located between RM1305 and RM6156 on chromosome 4 and RM508 and RM19341 on chromosome 6, respectively. The antibiosis, antixenosis, and tolerance were estimated by several tests using BPH2-NIL, BPH17-ptb-NIL, and BPH32-NIL. BPH2 and BPH17-ptb showed resistance to antibiosis and antixenosis, while BPH17-ptb and BPH32 showed tolerance. These results contribute to the development of durable BPH resistance lines using three resistance genes from ‘PTB33’.     

Effects of Environmental Temperature on Structure and Gelatinization Properties of Wheat Starch

The effects of environmental temperature on gelatinization properties and amylopectin structures of wheat endosperm starch were examined by isolating starches from four wheat cultivars matured in growth chambers at daytime temperatures of 15, 20, 25, or 30°C. Kernel weight and starch content per kernel were reduced by high maturation temperature. Amylose content showed no significant change at high maturation temperature in some cultivars; in other cultivars, there was a slight increase. Principal component analysis of data on relative peak areas of debranched amylopectin showed that amylopectin from wheat grown at a lower temperature had a greater proportion of shorter chains. Amylopectin branch chains were classified into three groups based on the correlation coefficients between the data of branch chain length distribution and principal component scores, degree of polymerization (DP) of 6–12, DP 13–34, and DP ≥ 35. The gelatinization temperature of starches increased markedly at a higher maturation temperature, with increases exceeding 10°C at high maturation temperatures. Gelatinization properties correlated significantly with amylopectin chain length distribution.     

Study of Internal Structure of Waxy Wheat Starch Granules by KI/I2 Solution

Wheat starch granules were separated from waxy wheat flour by the acetic acid (pH 3.5) fractionation technique. Waxy wheat starch samples were stained red‐brown using KI/I₂ solution. Subsequently, the concentration of the KI/I₂ solution was increased to >2.5% KI and 1.0% I₂. Then the appearance of the waxy wheat starch granules quickly became ghostlike. The internal structure of the ghost could be observed. This structure consisted of two parts with different colors: a red‐brown central part and a slightly pinkish surrounding part. Sonication of the ghost at 20 kHz for 20 sec separated the central part from the surrounding part. Each of the separated parts were subjected to gel‐filtration chromatography, and their chromatography profiles indicated only amylopectin and no amylose. The central and surrounding parts had molecular weights of 54.3 × 10⁵ and 23.8 × 10⁶ from Berry plots, respectively.