New approach to increasing rice lodging resistance and biomass yield through the use of high gibberellin producing varieties

Abstract

Traditional breeding for high-yielding rice has been dependent on the widespread use of fertilizers and the cultivation of gibberellin (GA)-deficient semi-dwarf varieties. The use of semi-dwarf plants facilitates high grain yield since these varieties possess high levels of lodging resistance, and thus could support the high grain weight. Although this approach has been successful in increasing grain yield, it is desirable to further improve grain production and also to breed for high biomass. In this study, we re-examined the effect of GA on rice lodging resistance and biomass yield using several GA-deficient mutants (e.g. having defects in the biosynthesis or perception of GA), and high-GA producing line or mutant. GA-deficient mutants displayed improved bending-type lodging resistance due to their short stature; however they showed reduced breaking-type lodging resistance and reduced total biomass. In plants producing high amounts of GA, the bending-type lodging resistance was inferior to the original cultivars. The breaking-type lodging resistance was improved due to increased lignin accumulation and/or larger culm diameters. Further, these lines had an increase in total biomass weight. These results show that the use of rice cultivars producing high levels of GA would be a novel approach to create higher lodging resistance and biomass.

Figure 1. Gross morphology of plants used in this study.

(A) to (D) Photographs show GA-related mutant lines 40 days after heading and are compared with original lines (Norin 29, Ginbozu, T65, and Nipponbare) at far left of each panel.

Figure 2. Culm length of rice lines used in this study.

(A) Diagram of plant height and internode length. (B) Elongation pattern of the culms. The length of the upper four internodes were averaged in each plant line, and the relative length against the total internode length is shown (n = 5). Original lines are shown at the left of each group. Mutant lines defective in GA signaling, and plants with elevated GA levels are classified into a single group. Error bars indicate the standard error. Asterisks indicate statistically significant differences with respect to original cultivars (P<0.01; Dunnett [33]).

Figure 3. Bending-type lodging resistance of plant lines enhanced or suppressed for GA signaling.

Mutants suppressed for GA signaling show improved cLr values, whereas GA-enhanced plants show reduced cLr values (n = 5). The asterisks indicate statistically significant differences in comparison to the original line (P<0.01; Dunnett [33]).

Figure 4. Enhancement and suppression of GA signaling leads to increased and reduced culm diameter, respectively.

Culm diameters of uppermost to the fourth internode were measured (n = 5). The asterisks indicate statistically significant differences with respect to the original line (*P<0.05, **P<0.01; Dunnett [33]).

Figure 5. Lignin content of plants used in this study.

Lignin was measured by thioglycolic acid method at the uppermost internode (Suzuki et al., 2009) and divided by the total dry weight of the sample (n = 3). The asterisks indicate statistically significant differences with respect to the original cultivar (*P<0.05, **P<0.01; Dunnett [33]).

Figure 6. Phloroglucinol staining of transverse sections at the second internode of various rice cultivars and mutants.

Compared to the original lines, gid1-8 and Slr1-d1 show weak staining and SD-1^K shows stronger staining, especially in the sclerenchyma layer. The arrow and arrowhead show sclerenchyma and a vascular bundle, respectively. Bar  = 100 µM.

Figure 7. Expression of rice lignin biosynthesis genes.

The uppermost internode of each plant at 13 days after flowering was used for analysis (n< = 3). Expression was analyzed by the quantitative reverse transcription PCR. (A) Expression of Os4CL3 gene. (B) expression of OsCAD2 gene. (C) Expression of OsCOMT gene. Asterisks indicate statistically significant differences relative to the original lines (*P<0.05, **P<0.01; Dunnett [33]).

Figure 8. Bending moment at breaking lodging.

The region apical to the fourth internode of each plant was used for analysis (n = 5). Asterisks indicate statistically significant differences relative to the original lines (*P<0.05, **P<0.01; Dunnett [33]).

Figure 9. Tiller numbers (n = 5) in cultivars and mutants used in this study.

Asterisks indicate statistically significant differences relative to the original cultivar (P<0.01; Dunnett [33]).

Figure 10. Accumulation of GA leads to increased total biomass in rice.

Rice was sampled 40 days after heading, air-dried for 2 weeks, and sampled foliage for dry weight by measuring the foliage. (A) Total dry weight per plant (n = 30), and (B) total dry weight per tiller (n = 10). Asterisks indicate statistically significant differences relative to original cultivars (P<0.01; Dunnett [33]).